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Basic research on ionic-covalent materials for nuclear applications

Ionic-covalent (non-metallic) solids play an important role in numerous industrial applications, due to their unique thermal, electrical, magnetic and optical properties. Refractory materials find applications at very high temperatures, where metallic materials already melt. Among the extreme environments where such materials are used is the nuclear industry, with impressive diversity of applications for ionic-covalent solids, ranging from nuclear fuel (UO ) to inert matrix materials for actinide transmutation, to host materials for 2 nuclear waste disposal. Research is needed for future nuclear applications, especially high-temperature Gen IV fission reactors as well as fusion reactors, to develop new structural materials and nuclear fuels that can withstand  extreme environment associated with these reactors. Given the different temperature and irradiation conditions in these various applications, it is imperative to better understand basic degradation processes and perform material tests employing a science-based approach. Improved knowledge on underlying principles of materials behaviour in extreme environments will help us to develop materials suitable for nuclear waste forms as well as for the next generation of nuclear power plants.


The previous three symposia on “Basic Research on Ionic-Covalent Materials for Nuclear Applications” at the E-MRS in 2011, 2013 and 2015, successfully inspired a broad community of researchers about the need for addressing the basic mechanisms of radiation damage induced by energetic particles, such as point and extended defect formation, precipitation/dissolution, dislocation formation/dissolution etc., in different ionic- covalent solids, regardless of the particular applications (nuclear industry, microelectronics, materials science). Our program is clearly cross-disciplinary on a wide range of materials (from insulators to semiconductors and even some metal/insulator composite systems), and a broad range of irradiation conditions with charged particles (from keV to GeV), experimental techniques and theoretical computations.  Evidence of the similarity of phenomena occurring in semiconductors and transition-metal or actinide oxides was highlighted in a number of invited and contributed presentations in previous symposia. However, many important questions were left open showing that this field still needs further detailed research  The utmost importance of the electronic excitation effects in radiation damage was also recognized. In this respect, the knowledge of phenomena occurring under irradiation with laser beams is instrumental for advancing the understanding of electronic excitation effects induced by charged particles. On the experimental standpoint, the use of laser-based optical spectroscopies (possibly coupled to ion beams) could be used to probe short time scales and obtain time-resolved data with pulsed beams (or particle bursts), which would be useful for confirming calculations with relevant atomic-scale theoretical models.  In all these atomic-scale processes, charged point defects are known to be produced in ionic-covalent solids under these conditions of electronic excitations. The importance of charged point defects was once again highlighted in our symposium G in 2015 for understanding the behavior of these materials under radiation fields. The complex behavior of UO as regards point-defect properties (e.g. charge states, electronic 2 energy levels, positron lifetimes, formation and migration energies) as well as extended defects (such as dislocation core energies) was highlighted. Moreover, there is a need for improved understanding of the electronic excitation mechanism and the intermediate electronic/nuclear collision regime of radiation damage.  It is necessary to obtain experimental data and develop models of the stability and migration of excited defects on the basis of time-resolved experiments and related computer simulations. Such phenomena are known to take place in particle or photon detectors (scintillators) used for medical applications, high-energy physics, and nuclear security, as well as in irradiated electronic systems used in space applications that have to be improved, to work in high radiation environment of space. It has also been recognized that (non-standard) specific tailored samples could also be instrumental in devising new experiments, as is commonly done in the semiconductor research community. Engineered multi-layered samples (super-lattices) could be prepared by selected deposition techniques (sputtering, MBE, CVD, etc.) and used for test irradiations and round-robin measurements. In this case, the use of specific built-in atomic probes (isotopic markers) could be contemplated, for instance for atomic diffusion or point-defect studies, either with on-line or off-line measurements. We propose a new symposium at the E-MRS 2017 Fall Meeting following these prospects to develop researches and new collaborations in these fields. Some key topics to be addressed in this symposium include: i) synergy of electron and laser beam irradiations, ii) calculation of stopping power from first principles, iii) use of local probes like NMR-active ion species in actinide-bearing oxides and glasses, iv) short-time scale optical spectroscopies, v) high-resolution TEM (HAADF/ABF) of defected ionic-covalent solids, and vi) dislocations and stress fields in ionic-covalent materials. The balance between basic research and applications, and between experimental results and theoretical modeling, was also considered as an important feature of this symposium that should be maintained in the future meetings.

Hot topics to be covered by the symposium:

The symposium will address solid-state processes induced by irradiating particles (electrons, neutrons, or ions) over wide ranges of energy, fluence, flux, temperature, pressure, etc., including:

  • Interaction processes of energetic particles in solids
  • Amorphization and phase transformations under irradiation
  • Role of electronic excitations: track effects, enhanced diffusion…
  • Formation of point defects, extended defects, and defect clustering
  • Mesoscale architectures for improved radiation resistance
  • Dynamic defect recovery, flux effects and radiation-enhanced diffusion
  • Recrystallization and nanophase formation
  • Dissolution of clusters and precipitates, segregation
  • Modifications of physical properties (thermal conductivity, mechanical properties etc.)
  • Degradation mechanisms (creep, embrittlement, swelling, corrosion, etc.)
  • Multiscale modeling and simulation of radiation effects

Tentative list of invited speakers:

  • Kazuhiro YASUDA (Kyushu University, Japan): “STEM STUDIES OF IRRADIATED OXIDES”
  • Karl WHITTLE (University of Liverpool, UK): “RADIATION DAMAGE IN OXIDE MATRICES”
  • David SIMEONE (CEA-Saclay, France) : “PHASE FIELD MODELLING”

Tentative list of scientific committee members:

  • A. CLAVERIE (CEMES, Toulouse, France)
  • F. DJURABEKOVA (Helsinki University, Finland)
  • P. GARCIA (CEA/Cadarache, France)
  • W. J. WEBER (ORNL, Univ. Tennessee, USA)
  • S. ZINKLE (University of Tennessee, USA)
  • R. EWING (Stanford University, USA)
  • A. IWASE (Osaka Prefecture University, Japan)


Papers will be peer-reviewed and published in a Virtual Special Issue of the NIM-B journal.

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09:15 Welcome address: J. M. Costantini    
Urania and Nuclear Materials-1 : E. Kotomin
Authors : David Andersson
Affiliations : Los Alamos National Laboratory

Resume : There are a large number of uranium oxides with a range of different stoichiometries and crystal structures from UO2 to UO3. Several of these phases also exhibit significant non-stoichiometry, including UO2x and U3O8-y. This complex chemistry is driven by uranium ions being able to take U3+, U4+, U5+ and U6+ valences. The uranium oxides are semiconductors with predominantly ionic bonding, but in many cases, there is a significant covalent contribution as well. Uranium dioxide is a common nuclear fuel used in light water reactors and it is the most important of the uranium oxides from an application standpoint. DFT modeling of uranium oxides is complicated by the strongly-correlated uranium 5f electrons. In order to capture the semi-conducting properties of UO2, calculations must go beyond the standard LDA and GGA methods. There are several options, such as hybrid functionals, DMFT and DFT+U, of which the latter is computationally the least expensive. Many properties important for nuclear fuel performance involve lattice defects, which is particularly the case for diffusion properties that are key to fission gas release and swelling. All of these calculations require large supercells and for this reason we have restricted ourselves to the DFT+U methodology. One challenge with this approach is the prevalence of metastable electronic solutions, which can cause unwanted uncertainty for defect properties. There are a few different ways of addressing this issue, including orbital occupation matrix control and so-called U ramping. In this talk the application of the DFT+U methodology to study defects and diffusion in UO2 will be discussed, with specific focus on the behavior of fission gas and fission products, as well as the properties of higher oxides (UO2+x, U4O9, U3O8, etc.). Results for modeling advanced fuels such as doped UO2 and U3Si2 will also be presented.

Authors : L. Casillas-Trujillo, G. Baldinozzi, M.K. Patel, H. Xu, K.E. Sickafus
Affiliations : University of Tennessee, Department of Materials Science and Engineering, Knoxville, TN 37996 USA; Laboratoire Structures, Propriétés et Modélisation des Solides, CNRS, Centralesupélec, 2295 Châtenay-Malabry, France and CEA, DMN, SRMA, 91191 Gif-sur-Yvette, France; University of Liverpool, Department of Mechanical, Materials and Aerospace Engineering, Liverpool, UK; University of Tennessee, Department of Materials Science and Engineering, Knoxville, TN 37996 USA; University of Tennessee, Department of Materials Science and Engineering, Knoxville, TN 37996 USA

Resume : This study examines the effect of local atomic environments on the electron charge density in -UO3, -UO3 and La6UO12. In particular, this study reveals differences in the uranium local atomic environments in these model oxide compounds. To examine the differences in a quantitative way, atoms-in-molecule (AIM) and Bader analysis methods were used to interrogate the electron charge density. The electron charge density of each of the compounds was obtained by density functional theory (DFT). The AIM/Bader analyses provided estimates for the so-called Bader charges on individual lattice atoms, as well as the locations of the bond critical points (BCPs) between bonding atoms and the charge densites at the BCPs. Calculation results revealed a quantitative inverse correlation between the charge density at the BCP and the U-O bond length. In addition, this inverse correlation was found to be surprisingly similar to a well-established crystal chemical relationship between bond strength and bond length.

10:30 Coffee Break    
Urania and Nuclear Materials-2 : C. Trautmann
Authors : Sergey Starikov, Alexey Kuksin, Daria Smirnova, Maria Korneva, Artem Lunev
Affiliations : Joint Institute for High Temperatures of RAS

Resume : Defects and diffusion are key concepts at description of nuclear fuels behavior at thermal and radiation impacts. In this work, we perform the complex study of point defects behavior for two nuclear fuels: uranium dioxide and uranium nitride. We use combination of several methods: ab initio calculations; molecular dynamics simulations with a new interatomic potential; thermodynamic model. The results of atomistic simulation and thermodynamic modeling allow to estimate diffusivity and concentrations of point defects for uranium dioxide and uranium nitride (including compositions different from the stoichiometric). The developed model allows us to evaluate several characteristics important for nuclear fuel description: (1) the diffusivities of xenon atom; (2) the change in thermal capacity; (3) the dependence of partial pressure (nitrogen pressure for UN or oxygen pressure for UO2) on composition and temperature. In addition, the role of defects diffusion in sintering and decomposition processes are discussed.

Authors : Artem Lunev, Sergei Starikov, Alexei Kuksin, Vasily Tseplyaev
Affiliations : - Joint Institute for High Temperatures of the Russian Academy of Sciences, 13 bld. 2, Izhorskaya st., 125412, Moscow, Russia 2 - Moscow Institute of Physics and Technology, 9 Institutsky lane, 141701, Dolgoprudny, Moscow Region, Russia

Resume : Dislocation plasticity in uranium dioxide is an important deformation mechanism at elevated temperatures. To study deformation using computer simulation, many research groups use such simulation methods as molecular dynamics (MD) and dislocation dynamics (DD). However, the results of DD simulation depend on the input parameter and to make the simulations meaningful, the properties of isolated dislocations and their interaction with individual defects such as pores or precipitates must be studied in great detail. Atomistic simulations prove very useful in this regard. We would like to present our latest results of such simulations for uranium dioxide. These include the assessment of mobility functions of edge and screw dislocations in UO2 and the interaction of dislocations with isolated voids. All simulations are performed using LAMMPS software on MVS-100K, MVS-10P supercomputers of the Russian Academy of Sciences and Lomonosov-1 Supercomputer of the Moscow State University.

Authors : Philippe Garcia, Audrey Miard, Yue Ma, Jean-Baptiste Parise, Thomas Helfer, Antonin Aguilar, Mariem Ben Saada, Xavière Iltis
Affiliations : CEA, DEN, DEC, Centre de Cadarache

Resume : Controlling and predicting the high temperature mechanical behaviour of nuclear oxide fuels is essential to guaranteeing the integrity of fuel rods during normal or incidental operating conditions. Although in the past many studies have been devoted to the creep behaviour of uranium dioxide, few have focussed in detail upon the effect of non stoichiometry. In those which have dealt with this issue, strain rate was usually considered as a function of deviation from stoichiometry although the true thermodynamic parameter is the chemical potential of oxygen. In this work we describe very recent developments involving a high temperature compression creep furnace which has been equipped with a system enabling the control and measurement of the oxygen activity in the gas phase. This guarantees the oxygen activity in the solid in equilibrium with it. We report the first creep experiments carried out under these controlled conditions. We also discuss the development of a material model and associated kinematic hardening behaviour law capable of reproducing the near constant strain rate experiments carried out. Although we show that the data may be interpreted in terms of uniaxial loading, due consideration is given to multi-dimensional effects. The physical significance of the material behaviour law parameters is presented, particularly when the parameter is sensitive to oxygen activity. Our ultimate aim is to relate internal variables of the model to the local microstructure. Post test Electron BackScatter Diffraction is shown to be a prospective technique for providing this information and based on it, parallels can be drawn between the mechanisms via which the material accommodates mechanically induced strain and its response to radiation damage.

Authors : Gianguido Baldinozzi, David Andersson, Lionel Desgranges
Affiliations : Centralesupelec, SPMS, LRC Carmen, Gif-sur-Yvette, France; LANL MST-8, Los Alamos, NM, USA; CEA Cadarache, DEC, Saint-Paul-les-Durance, France

Resume : Using density functional theory (DFT) calculations and Rietveld simulations and refinements, the structure of the low temperature α phase of U4O9−y was studied in reference to a neutron powder diffraction pattern measured at 1.5K.

12:30 Lunch Break    
Urania and Nuclear Materials-3 : G. Baldinozzi
Authors : Maulik Patel (1), Luis Casillas-Trujillo (2), Jeffery Aguiar (3), Sven Vogel (4), Guido Baldinozzi (5) and Kurt Sickafus (2)
Affiliations : (1) University of Liverpool, Department of Mechanical, Materials and Aerospace Engineering, Liverpool, UK. (2) University of Tennessee, Department of Materials Science and Engineering, Knoxville, Tennessee, USA. (3) Idaho National Laboratory, Fuel Design and Development Department, 2525 Fremont Ave., Mail Stop 3870, Idaho Falls, Idaho, USA. (4) Los Alamos National Laboratory, Los Alamos, New Mexico, USA. (5) Laboratoire Structures, Propriétés et Modélisation des Solides, CNRS, Centralesupélec, 92295 Châtenay-Malabry, France and CEA, DMN, SRMA, 91191 Gif-sur-Yvette, France.

Resume : Crystal structure stability of several fluorite derivative oxides is often governed by the type of anion defects and defect complexes. Upon relaxation, these oxides then result in structures whose order varies from very long range to short range ordering. It has been seen that small changes in the stoichiometry thus results in tailoring these defect complexes, thus resulting in the modification of physical properties. Among the fluorite derivative oxides, pyrochlores and perovskite type structures are very well studied. Thus, the presentation will discuss some unique crystallographic features and defect complexes in several other fluorite derivative oxides. The discussion will include inferences drawn from the analysis of selected area electron diffraction, X-ray diffraction and neutron diffraction data to present, (1) how non-stoichiometry in some Re2O3:CeO2 compounds results in stabilizing ordered micro domains that can then influence the radiation stability. (2) Crystallographic trends in the delta-A4B3O12 phase (A=Ln and B=Zr, Hf or Ti) family of compounds to understand the role of A and B site cations in stabilizing the ordering of these structures. (3) Structural ordering differences between delta-(A4B3O12), gamma-(A2B5O13) and beta-(A2B7O17) family of compounds (A=Sc and B=Zr & Hf). (4) Correct description for a beta-phase in the Sc2O3:BO2 (B=Zr or Hf) and the influence of non-stoichiometry on structure. In the end, an effort will be made to generalize some trends observed during these studies and how they might influence physical properties of these materials.

Authors : Estevenon P. (1), Welcomme E. (1), Szenknect S. (2), Mesbah A. (2), Moisy P. (3), Poinssot C. (3), Dacheux N. (2)
Affiliations : (1) CEA/DEN/DMRC/SFMA/LPCA, CEA Marcoule – Bat 399, BP 17171, 30207 Bagnols-sur-Cèze cedex, France ; (2) ICSM, UMR 5257 CEA/CNRS/UM/ENSCM, Site de Marcoule – Bat 426, BP 17171, 30207 Bagnols-sur-Cèze cedex, France ; (3) CEA/DEN/DMRC/DIR, CEA Marcoule – Bat 400, BP 17171, 30207 Bagnols-sur-Cèze cedex, France

Resume : Thorite, ThSiO4, and coffinite, USiO4, are two naturally occurring phases which were extensively studied because of their abundance in the environment [1]. The supposed formation mechanism of natural coffinite implies the alteration of oxide phases in reductive and silica rich media. It rose important questions about the actinides’ behaviour consequently to the alteration of spent nuclear fuel under geologic repository conditions [2]. Indeed, silicate compounds’ formation has been suspected for Pu-containing precipitates observed in basic media and for plutonium borosilicate glasses altered by vapour hydration. However, even if PuSiO4 has already been hydrothermally synthesized once [3], the favourable conditions for the formation of this phase and its stability domain are not well constrained. To provide more data on the Pu system and to determine suitable synthesis conditions, three surrogates, CeSiO4, ThSiO4 and USiO4, which crystallize in the same zircon type-structure (space group I41/amd) [3,4] than PuSiO4, were investigated. Optimized conditions of synthesis were determined for these three silicate-based systems by varying several experimental parameters so that they could be transposed to the plutonium system. [1] A. Mesbah et al., Inorganic Chemistry, 54, 6687-6696, 2015 [2] J. Janeczek, R. Ewing, Materials Research Society, Symposium Proceedings, 257, 497-504, 1992 [3] C. Keller, Nukleonik, 5, 41-48, 1963 [4] J. Skakle et al., Powder Diffraction, 15, 234-238, 2000

Authors : T. Cordara, S. Szenknect, L. Claparède, C. Lavalette, A. Mesbah, R. Podor, N. Dacheux
Affiliations : T. Cordara ICSM – UMR 5257 CNRS/CEA/UM2/ENSCM, Site de Marcoule - Bât. 426, BP 17171, 30207 Bagnols/Cèze ; S. Szenknect ICSM – UMR 5257 CNRS/CEA/UM2/ENSCM, Site de Marcoule - Bât. 426, BP 17171, 30207 Bagnols/Cèze ; L. Claparède ICSM – UMR 5257 CNRS/CEA/UM2/ENSCM, Site de Marcoule - Bât. 426, BP 17171, 30207 Bagnols/Cèze ; C. Lavalette AREVA NC/BG aval/DO recyclage/RDP, Direction AREVA - 1 place Jean Millier 92084 Paris La Défense ; A. Mesbah ICSM – UMR 5257 CNRS/CEA/UM2/ENSCM, Site de Marcoule - Bât. 426, BP 17171, 30207 Bagnols/Cèze ; R. Podor ICSM – UMR 5257 CNRS/CEA/UM2/ENSCM, Site de Marcoule - Bât. 426, BP 17171, 30207 Bagnols/Cèze ; N. Dacheux ICSM – UMR 5257 CNRS/CEA/UM2/ENSCM, Site de Marcoule - Bât. 426, BP 17171, 30207 Bagnols/Cèze

Resume : The dissolution of the spent nuclear fuel (SNF) in nitric acid solution is a key step in the reprocessing process. The SNF contains a wide variety of fission products either incorporated in the UO2 matrix, or in various separated phases. However, the impact of the fission products on the normalized dissolution rate of the SNF has not been investigated yet. In order to evidence the influence of selected fission products on the kinetics of dissolution of UO2, several model compounds containing the selected fission products were synthesized from oxalic and hydroxide precursors [1]. Then, the starting precursors were converted into oxides, pelletized and sintered. The prepared samples were characterized from a chemical and a microstructural point of view. Uranium dioxide based compounds incorporating 1 to 20 mol.% of lanthanides elements (ln (III)) were obtained (with 13 % La ; 7.4 % Y ; 25.6 % Ce ; 12 % Pr ; 42 % Nd). Samples of uranium dioxide containing 0.6 to 3 mol.% of particles of platinoid elements (PGM’s) (with 55 % Ru ; 9.6 % Rh ; 35.4 % Pd) were also prepared. The pellets were then used to perform a multiparametric study of the dissolution kinetics. The dissolution experiments were achieved in various nitric acid solutions (from 0.1 to 4 M) and temperatures (from 25 °C to 90 °C). The normalized dissolution rates determined for the samples incorporating the fission products were compared to those obtained under the same conditions for pure UO2 in order to quantify the impact of the selected fission products on the chemical durability. Normalized dissolution rates were found to increase according to the sequence: RL,0 (U) < RL,0 (Ln (III)) << RL,0 (PGM’s). This impact is strengthened at low acidities (CHNO3 < 1M) and remains less important for (CHNO3 > 1M). References 1. Kleykamp, H. 1985, J. Nucl. Mater, Vol. 131, pp. 221-246.

Authors : Christoph Lechner, Philippe Baranek, Holger Vach
Affiliations : Christoph Lechner, EDF R&D - Department Materials and Mechanics of Components (MMC) EDF Lab Les Renardières, Avenue des Renardières, F-77818 Moret-sur-Loing Cedex, France +33160576508,; Philippe Baranek, EDF R&D, Department Economic and Technical Analysis of Energy Systems (EFESE), EDF Lab Chatou, 6 Quai Wattier, F-78400 Chatou Cedex, France; Holger Vach, CNRS-LPICM, Ecole Polytechnique, F-91128 Palaiseau Cedex, France

Resume : In order to optimize the waste management of nuclear graphite used in power plants, it is important to understand the properties of the activated impurities it contains, such as tritium and chlorine 36. A multiscale approach was therefore applied in order to study the local interaction of the radionuclides with the graphite matrix as well as diffusion and trapping mechanisms that occur on the nm-μm length scale. First, we studied the interaction of tritium and chlorine 36 with defects in graphite with density functional theory (DFT). While the bonding of hydrogen is mostly covalent for chemisorption and van der Waals for physisorption, the behavior of chlorine is much more complex. Depending on the defect site, both, dominantly covalent and dominantly charge transfer bonding, is observed. Following that, we used ab initio results to create a bond order potential to model the interaction of chlorine and the graphite matrix, which attributes for both, short and long range interactions. For the tritium-graphite interactions, the bond order potential AIREBO/M was used. These potentials were combined with the bond order potential LCBOP, which describes the C-C interactions. Since irradiated nuclear graphite is a complex system with crystalline, amorphous as well as porous zones, several different model structures were created to account for this diversity. The insertion and diffusion in these model structures was then studied for both radionuclides to evaluate the temperature dependence of these properties.

15:40 Coffee break    
Poster Session-1 : JM Costantini-E. Kotomin-G. Baldinozzi-C. Trautmann
Authors : V.N. Kuzovkov, E.A. Kotomin, A.I. Popov
Affiliations : Institute of Solid State Physics, University of Latvia, Riga, Latvia

Resume : Primary radiation defects in ionic solids consist of Frenkel defects—pairs of anion vacancies with trapped electrons (F-type centers) and interstitial ions. Upon temperature increase after irradiation, the electronic F-type centers are annealed due to recombination with mobile interstitials. Analysis of the recombination (annealing) kinetics allows us to obtain important information on the interstitial migration (e.g. in corundum [1] and alkali halides [2]). At high radiation doses more complex dimer F2-type centers are observed in several charge states, which are well distinguished spectroscopically [3]. In this paper, we analyzed available experimental kinetics of the F2-type center annealing in a wide temperature range (300-1000 K) in three different neutron-irradiated ionic solids: MgO, MgF2 and Al2O3 (corundum) [4]. The phenomenological theory takes into account the interstitial ion diffusion and recombination with the F2-centers as well as mutual sequential transformation with temperature growth of three types of experimentally observed dimer centers: F2 (1); F2 (2), F2 (3) (which differ tentatively by charges with respect to the host crystalline sites : 0. +1, +2). As the result, the relative initial concentrations of three types of electronic defects before annealing are obtained, along with energy barriers between their ground states and the relaxation energies [4]. Surprisingly, these parameters are similar in three different types of materials. The results are compared with available experimental data and theoretical calculations. [1] V.N. Kuzovkov, E.A. Kotomin, A.I. Popov, R.Villa, Nucl. Inst. Meth. B 374, 107 (2016). [2] V.N. Kuzovkov, A.I. Popov, E.A. Kotomin et al, Low Temp. Phys., 42, 748 (2016). [3] E.A. Kotomin A.I. Popov, Nucl. Instr. Meth. B 141, 1 (1998) [4] V.N. Kuzovkov, A.I. Popov, E.A. Kotomin, in preparation

Authors : Yu.A. Mastrikov (1), P.V. Vladimirov (2), V.A. Borodin (3), S. Koch (2), A.Gopejenko (1), Yu.F. Zhukovskii (1), E. A. Kotomin (1), A. Möslang (2)
Affiliations : 1) Institute of Solid State Physics, University of Latvia, Riga, LV-1063 Latvia 2) Karlsruhe Institute of Technology, Institute for Applied Materials-Applied Materials Physics,D-76344 Eggenstein-Leopoldshafen, Germany 3) National Research Centre “Kurchatov Institute”, 123182 Moscow, Russia

Resume : Oxide Dispersed Strengthened (ODS) steels are known for their high stability under irradiation conditions, which makes them a promising construction material for nuclear reactors. High irradiation damage resistance of ODS steels is a critical property for the future fusion reactors. Yttrium oxide is the most common dopant for the ODS steel production, introduced into the host material by mechanical alloying, followed by powder consolidation (e.g., by hot isostatic pressing). ODS particles of various size, shape and spatial distribution were observed experimentally. However, only a few theoretical studies discussed formation process of yttria nanoparticles. Atomic Tomography Probe experiments have shown presence of Y and O in the Fe lattice in a form of solutes. Our atomistic investigation is focused on the comprehensive large-scale calculations of pair-wise interactions between Y and O solutes as well as vacancies in the host bcc and fcc iron matrices. We present the results of ab initio modelling of Y, O and VFe defect complexes in both types of cubic Fe lattice. Calculations were performed with the computer code VASP 5.3 in the 4a0×4a0×4a0 supercell. We demonstrated that vacancies play an essential role in Y stabilization and migration in iron lattices. We investigated vacancy cluster growth, as well as interaction of different size vacancy clusters with Y solute. Single Y solute migration in iron matrix was modelled in details. Pair-wise interactions of singe Y, O and VFe at many different relative distances were calculated. Various structural configurations for the complexes Y/O, Y/2O and 2Y/O were tested. Character of the Y-O chemical bonds in these complexes was analyzed. These results will be used in kinetic Monte Carlo simulations of the yttria nanoparticle growth.

Authors : A. I. Popov (1), I. Kudryavtseva (2), E. Feldbach (2), J. Zimmermann (3), E. Aleksanyan (4), J. Purans (1) and A. Lushchik (2)
Affiliations : (1) Institute of Solid State Physics, University of Latvia, 8 Kengaraga, LV-1063 Riga, Latvia; (2) Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu, Estonia; (3) Fraunhofer-Institut für Silicatforschung, Brentanostr. 2, 63755 Alzenau, Germany; (4) A.I. Alikhanyan National Science Laboratory, 2 Br. Alikhanyan Str., 0036 Yerevan, Armenia

Resume : ScF3 has a simple cubic perovskite ReO3 type structure down to at least 10 K and exhibits a rare property of isotropic negative thermal expansion (NTE) over a large temperature range. In order to reveal the possible manifestations of the NTE effect in optical spectra, we have performed the following investigations: (a) cathodoluminescence analysis of ScF3 single crystals, (b) VUV-luminescence excitation using synchrotron radiation at MAX-Laboratory in Lund, (b) Thermally stimulated luminescence (TSL) study between 80 and 350 K, excited by an electron-beam (10 keV) or VUV radiation. From the TSL data analysis and the comparison with other metal fluorites, we can conclude that in ScF3 there is the effective self-trapping of holes in the form of Vk centres and their thermal destruction occurs at about 100 K. From the creation (excitation) spectra of several TSL peaks as well as the VUV-luminescence excitation spectra, we can conclude that the value of band gap energy in ScF3 exceeds 11 eV.

Authors : A. Dauletbekova1, N. Kirilkin2, R. Zabels3, I. Manika3, J. Maniks3, A.Akilbekov1, M. Baizhumanov4, M. Zdorovets5,6
Affiliations : 1L.N. Gumilyov Eurasian National University, 5 Munaitpassov Str., 010008 Astana, Kazakhstan, 2Joint Institute for Nuclear Research, 6 Joliot-Curie str., 141980, Dubna, Russia 3Institute of Solid State Physics, University of Latvia, 8 Kengaraga str., LV-1063 Riga, Latvia 4Shakarim University, 20a Galkina str., 071412, Semey, Kazakhstan 5Institute of Nuclear Physics, 1 Ibragimov Str., 050032 Almaty, Kazakhstan 6Ural Federal University, 19 Mira street, 620002, Ekaterinburg, Russia

Resume : Depth profiles of photoluminescence of F2 and F3+ centers as well as nanohardness which characterizes the accumulation of dislocations and other extended defects along the ion path in LiF crystals irradiated with light ions (56 MeV 40Ar, 23 MeV 14N and 12 MeV 12C) at cyclotron DC-60, Astana, Kazakhstan have been investigated. Detectable luminescence of F2 and F3+ centers for 12С ions appears at fluences above 3х1010 ions/cm2. Its variation along the ion trajectory follows the depth profile of the electronic energy loss. However, at high irradiation fluences (above 3×1013 ions/cm2) at to the end of the ion range where the contribution of nuclear stopping mechanism becomes dominant the luminescence intensity of F2 and F3+ centers displays a maximum. A similar depth dependence is observed for the ion-induced hardening which also displays two maximums for investigated ions - one at the position of the Bragg’s maximum of electronic energy loss and the second at the maximum of nuclear stopping near the end of the ion range. The results allow us to conclude that the intense formation af anion and cation vacancies by impact mechanism is favourable for the development of aggregation processes via formation of compex F2 and F3+ color centers responsible for the photoluminescence and extended defects (dislocations, defect clusters etc.) responsible for the hardening.

Authors : Roberts I. Eglitis and A. I. Popov
Affiliations : Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga LV1063, Latvia

Resume : The results of ab initio calculations of polar YAlO3 (001) surfaces by means of a hybrid B3LYP exchange-correlation functional as it is implemented in the CRYSTAL computer code are presented. Both polar YO and AlO2-terminations of the cubic YAlO3 (001) surface were considered. We performed relaxation of atoms on the upper three layers of both YO and AlO2-terminated YAlO3 (001) surfaces using slabs containing 22 and 23 atoms and 9 layers, respectively. The Al-O chemical bond covalency change near the AlO2-terminated YAlO3 (001) surface relative to the YAlO3 bulk is discussed. YO and AlO2-terminated YAlO3 (001) polar surface energies are calculated and compared with ABO3 perovskite (001) surface energies [1,2]. Our B3LYP calculated electronic band gaps of the YO and AlO2-terminated YAlO3 (001) surfaces are compared with the YAlO3 bulk band gap. References: 1. E. Heifets, R.I. Eglitis, E.A. Kotomin, J. Maier and G. Borstel, Phys. Rev. B 64, 235417 (2001). 2. R.I. Eglitis and A.I. Popov, J. Saudi Chem. Soc. (2017), submitted.

Authors : E.A. Kotomin*, A.I. Popov*, V.N. Kuzovkov*, E. Shablonin**, A. Lushchik**
Affiliations : *Institute of Solid State Physics, University of Latvia, 8 Kengaraga, Riga, LV-1063 Latvia; **Institute of Physics, University of Tartu, W. Ostwald Str. 1, 50411 Tartu, Estonia

Resume : Radiation-resistant Al2O3 is a promising material for optical windows in fusion reactors. It is important to predict/simulate the kinetics of diffusion-controlled defect accumulation under neutron-irradiation, as well as a long-term defect structure evolution, incl. thermal defect annealing. We developed the advanced approach, based on the correlation function formalism describing spatial distribution of similar (F-F centers) or dissimilar defects (Frenkel pair: F center - interstitial Oi ion), which suits for the study of defect kinetics/aggregation much better than the rate equations. Based on our calculations, the migration energy of F and Oi, their interaction energy and metal colloid size upon annealing were estimated. The kinetics of F,F annealing after ~GeV-ion- or n-irradiation was treated as the bimolecular one with equal amount of complementary F and Oi. It is controlled by Oi mobility, which is much higher than that of F centers. The F center annealing starts at 500-600 K due to the recombination with mobile Oi, while F-type centers are immobile. Note that the F-annealing curve shape is determined by two parameters: Ea and effective pre-exponential factor. The Oi migration energy, extracted from F-center annealing kinetics, varies considerably for different experiments: from 0.8 down to 0.2 eV. The difference is very likely caused by a rarely discussed radiation dose effect. The results obtained are compared with the re-cent ab initio calculations of Oi migration.

Authors : A. Platonenko, Denis Gryaznov, Yu. F. Zhukovskii, E. A. Kotomin
Affiliations : University of Latvia Institute of Solid State Physics, Kengaraga 8, Riga LV-1063; Max Planck Institute for Solid State Research Heisenbergstr. 1 70569 Stuttgart Germany

Resume : Due to high radiation resistance and wide band gap, Al2O3 (sapphire, corundum) has many potential applications, including optical elements in fusion reactors. Radiation-induced changes in the structural and optical properties of corundum are mainly associated with formation of primary Frenkel defects: neutral and charged interstitial oxygen atoms Oi, as well as oxygen vacancies VO (F-type color centers). Unlike the electron centers, properties of interstitial oxygen atoms are experimentally very poorly studied, due to lack of magnetic properties and optical absorption in a suitable energy range. Such a study is very important since in most binary oxides the oxygen interstitials are more mobile than complementary vacancies, and their diffusion-controlled recombination determines stable defect concentrations at moderate and high temperatures. We present the results of ab initio simulations on basic properties and mobility of the neutral and charged oxygen interstitials using the CRYSTAL14 computer code combined with a periodic (supercell) defect model. It has been found that both, neutral and charged, interstitials form O-O species (split interstitials or dumbbells) with regular oxygen atoms, with mutual distances of 1.44 Å for neutral and 1.87 Å for charged interstitials. Migration barriers were estimated using minimal-energy path approach, they were found to be 1.3 eV for neutral and 0.7-1.0 eV for charged defect respectively. Vibrational stretching frequencies in the O-O pairs were compared with those for super- and peroxides in other oxide materials.

Authors : G. Zvejnieks, A. Anspoks, E.A. Kotomin, V.N. Kuzovkov
Affiliations : Institute of Solid State Physics, University of Latvia, Kengaraga Str. 8, LV-1063 Riga, Latvia

Resume : As known, Y2O3 nanoparticles considerably increase radiation resistance of reactor construction materials. To model kinetics of this process, we performed kinetic Monte Carlo (KMC) simulations. We extended the KMC simulated results to the experimentally relevant time limit using autoregressive integrated moving average forecasting. To test the simplest nucleation model, we have studied different attractive interaction energies and particle concentrations, and compared the simulations with experimental results. We have observed the standard Lifshitz-Slyozov-Wagner (LSW) theory, predicting the average cluster radius growth as (time)** (1/3) in the long-time limit, for weak (0.1 eV) and medium (0.3 eV) mutual particle attractions. However, the respective cluster growth rates are here overestimated in KMC simulations compared to the experiments. The best agreement with experiment is obtained for a strong (0.5 eV) attraction, when nano-particle formation occurs already at intermediate asympototic time scale, without reaching actually the LSW long-time limit. An increase of particle attraction from medium to strong interaction in KMC simulations at 1100 C slows down the cluster growth rate thus leading to a better agreement with experimental value. The growth rate is reduced due to a longer time needed to dismantle small clusters in the Ostwald ripening stage. Such a stronger interaction leads also to a more compact 110--faceted nano-clusters. At the same time, the cluster density becomes slightly overestimated. Further modification of a KMC model is discussed.

Authors : A. Useinov (1), D. Gryaznov (2), F. Abuova(1), A. Akilbekov(1), A. Dauletbekova (1), A. I. Popov (2)
Affiliations : (1) L.N. Gumilyov Eurasian National University, 2 Satpaeva Str., Astana, Kazakhstan (2) Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga LV1063, Latvia

Resume : Owing to its high chemical stability, large band-gap energy (>12 eV) and high radiation resistance, MgF2 with a rutile structure is important material with numerous optical applications. In particular, MgF2 doped with cobalt-ions is used in laser applications. In this study, we present and discuss the results of ab initio calculations of the atomic, electronic and optical properties of Co impurities in MgF2, using the LCAO method and hybrid DFT functional as implemented in CRYSTAL14 code [1]. We demonstrate importance of accurate treatment of bulk properties. Therefore, the role of amount of exact exchange on the properties of MgF2 is discussed in detail. The effective atomic charge on Co atom, its magnetic moment, distances between cobalt and nearest fluorine atom as well as density of states and band structure were calculated. The energetic preference between high and low spin states was analyzed, and that with inclusion of symmetry reduction effects. The density of states for ideal MgF2 and MgF2:Co were carefully compared with available experimental data. [1] R. Dovesi, B. Civalleri, R. Orlando, et al., Rev. Comput. Chem. 21 (2005).

Authors : N. Mironova-Ulmane (1), V. Churmanov (2), D. Ivanov (2), V. Ivanov (2), A.I. Popov (1), V. Skvortsova (1), J. Purans (1)
Affiliations : (1) Institute of Solid State Physics, University of Latvia, 8 Kengaraga, LV1063 Riga, Latvia (2) Ural Federal University , Mira str.19, 620002 Yekaterinburg, Russia

Resume : Due to a high radiation resistance to radiation damage, MgAl2O4 was proposed as a very promising material for RF windows in a fusion reactor. On the other hand, it is well known that dopants play a key role in different radiation sensitivity of solid materials. The present work summarizes our experimental studies of fast neutron-irradiation of pure and doped (Mn , Cr etc) MgAl2O4 single crystals. In particular, it was found: 1.Fast neutron irradiation of MgAl2O4 leads to the decrease of the lattice parameter. 2.In stoichiometric MgAl2O4:Mn single crystals, fast neutron irradiation leads to occupancy change of Mn ions from tetrahedral to octahedral coordination position in the crystal lattice. 3. Fast neutron irradiation also leads to F (oxygen vacancy with one trapped electron) lattice defect creation. Using the pulse EPR technique of hyperfine sub-level correlation spectroscopy indicates that an electron from an F centre reveals hyperfine interaction only with neighbouring octahedral coordinated 27Al nuclei. 4.Fast neutron irradiation leads also to the significant broadening of R- and N-luminescence lines of Cr impurity ions in both stoichiometric and non-stoichiometric MgAl2O4. Furthermore, at low fluences (~e16 /cm2) an increase in the intensity ratio of N- to R-lines by 5–20% was clearly observed, while at higher fluences ( ~e20 /cm2 ), the fine structure of R and N zero-phonon lines is not anymore resolved and the total yield of Cr luminescence is decreased.

Authors : V. Lisitsyn1, Zh. Karipbayev2, L. Lisitsyna3, A. Dauletbekova1, M. Golkovskii4, D. Musakhanov2, A. Akilbekov2, A. Kozlovskii5
Affiliations : 1National Research Tomsk Polytechnic University Tomsk, Russia 2L.N. Gumilyov Eurasian National University, Astana, Kazakhstan 3Tomsk State University of Architecture and Civil Engineering, Tomsk, Russia 4Budker Institute of Nuclear Physics, Siberian Branch of RAS, Novosibirsk 5Institute of Nuclear Physics AB, Astana, Kazakhstan

Resume : The mixture consists of MgF2 powder with the WO2 and LiOH with concentrations (0.05 - 0.3)%. The crucible with the mixture were heated during 1 s. by the electron beam with the electron energy of 1.4 MeV and power density of 18 kW/cm2 by the accelerator ELV-6. .After the interaction, the mixture hardened into the ceramic sample with the impurities ratio given in the mixture. SEM research showed that the surface has a complicated form, typical for the hardened melt. The injected impurities of wolfram and oxygen were nonuniformly distributed on the surface. The ratio of oxygen and wolfram ions changes significantly by 32 and 81% during the surface scanning. At the same time the ratio of magnesium and fluorine changed not more than by 7 %. Therefore, during the synthesis process the dissociation of the metal oxide happens and the entrance of activators into the matrix without the bound with the oxygen takes place. The luminescence spectrum of all samples showed the intensive line with the maximum at 480 nm. The intensity of the lines is higher in the crystals with the high concentration of the activator. Thus, the synthesis of MgF2 samples activated by polyvalent ions with luminescent properties is possible by powerful electron beam.

Authors : L. Lisitsyna1, A. Dauletbekova2, Zh. Karipbayev2, A. Markhabayeva3, G. Denisov4, V. Lisitsyn5, A. Akilbekov2
Affiliations : 1Tomsk State University of Architecture and Building, Tomsk, Russia 2L.N. Gumilyov Eurasian National University, Astana, Kazakhstan 3al-Farabi Kazakh National University, Almaty, Kazakhstan 4Kyrgyz Russian State University named aftirst President of Russia B.N. Yeltsin, Bishkek Kyrgyz Republic 5National Research Tomsk Polytechnic University, Tomsk Russia

Resume : The luminescence and excitation spectra, IR spectra (4000-20000 cm-1), optical absorption spectra (195 – 1200 nm) were measured using spectrofluorimeter Agilent Carry Eclipse, IR spectrometer Jasco FT/IP-4700, and spectrometer SPECORD 250 PLU, respectively. Pulsed cathodeluminescence and kinetics after excitation by ns electron pulses were measured. Introduction of the uranium and the OH- impurities show the occurrence of additional absorption in the range of 260-320nm. The IR spectrum in crystals containing OH- has distinguished characteristics absorption band at 3725 cm-1.In crystal doped with uranium the bands 3550-3580 cm-1 are observed, which are responsible for OH- ions. The doped crystals with co-dopant contain an additional band at 3342 cm-1. The luminescence is observed in the 470-500nm spectral range excited by ionizing and UV radiation. Introduction of OH- as a co-dopant into the synthesized LiF crystal with uranium results in a nanodefect in the crystal containing OH- as a structural element.

Authors : L. Luneville (a), J.-C. Sublet (b), D. Simeone (c)
Affiliations : (a) DEN-Service d’Etudes et de Recherche en Mathematiques Appliquees, LRC CARMEN CEA-CNRS-ECP/SPMS, Universite Paris-Saclay, F-91191, Gif-sur-Yvette, France (b) UK Atomic Energy Authority/Culham Science Centre, Abingdon OX14 3DB, United Kingdom. (c) DEN-Service de Recherches Metallurgiques Appliquees, LRC CARMEN CEA-CNRS-ECP/SPMS, Universite Paris-Saclay, F-91191, Gif-sur-Yvette, France

Resume : Numerous oxides extensively used as fuel (UO2, (U,Pu)O2) or nuclear waste matrix (pyrochlores) exhibit numerous sub lattices leading to the used of NRT formula obsolete to compute not only the displacement cross sections estimating he level of damage but also the primary and recoils spectra allowing comparison between different irradiations. To overcome this difficulty, the Lindhard formalism based on the Binary collision Approximation was applied to estimate radiation damage in the DART code. As this code is based on radiation damage induced by isotopes (and not only the chemical composition), it become possible to follow the impact of the burn-up and the burn-in of different isotopes on the damage production rate as well in different spectra.

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Defects in Oxides : J. M. Costantini
Authors : Aleksandr Lushchik
Affiliations : Institute of Physics, University of Tartu, W. Ostwald Str. 1, 50411 Tartu, Estonia

Resume : Radiation-induced structural defects strongly affect the functionality of wide gap materials, incl. those considered as promising materials for optical (diagnostics) windows in future fusion reactors. A comparative study of radiation damage caused by ~MeV fission neutrons, ~GeV swift heavy ions and 100-keV protons in MgAl2O4, Lu3Al5O12 and Lu/Gd mixed oxyorthosilicates has been performed. The damage was analyzed using the methods of induced optical absorption (region of 1.4-9 eV), cathodo- and photo-luminescence and thermoactivation spectroscopy. The thermal annealing (up to 1000 K) of F-type center absorption, measured in a stepwise regime, was compared to that of the EPR signal for new paramagnetic hole centers in a neutron-irradiated spinel crystals (3e18 n/cm2). The possible inversion of spinel lattice is considered to be responsible for high tolerance of MgAl2O4 to heavy irradiation. Optical characteristics of antisite defects, revealed earlier in YAG and LuAG crystals, were tentatively determined for spinel ceramics in optical absorption and luminescence excitation spectra. The accumulation of proton-induced radiation damage (a fluence varies from 1e15 to 5e17 p/cm2) was analyzed for spinel ceramics by means of optical absorption and cathodoluminescence. The joint contribution of universal knock-on mechanism and several nonimpact mechanisms (related to the decay of electronic excitations) to radiation damage of wide gap materials is considered.

Authors : Alexander Shluger, Al-Moatasem El-Sayed, Jack Strand, Moloud Kaviani, Oliver Dicks, David Z. Gao
Affiliations : Department of Physics and Astronomy, University College London, UK; WPI-AIMR, Tohoku University, Sendai, Japan

Resume : Electron and hole localization in solids is fundamental for our understanding of the mechanisms of radiation damage. However, strong localization in complex 3D systems is material specific and difficult to elucidate. We will discuss the results of recent theoretical and experimental studies of intrinsic electron and hole trapping in crystalline and amorphous SiO2, HfO2 and Al2O3. These materials in a bulk crystalline phase exhibit polarons with trapping energies of about 0.2 eV. Recent experimental evidence suggests that both negative and positive charging can occur in amorphous oxides in much deeper states. To investigate whether such charging can be caused by intrinsic electron and hole trapping, we modelled the behaviour of extra electrons and holes in stoichiometric amorphous SiO2, HfO2 and Al2O3 structures using classical simulations and Density Functional Theory. The results demonstrate that single- and bi-polaron electron and hole states can form in a-SiO2 and a-HfO2, where the effect of local disorder is amplified by polaronic relaxation of amorphous network. Only hole trapping is found in a-Al2O3. Both electron and hole bi-polarons can facilitate the formation of Frenkel pairs of oxygen vacancies and interstitial oxygen ions. These results broaden the concept of intrinsic polaron trapping to disordered oxides. We will discuss challenges in predicting polaron trapping and comparing the predicted properties with experiment.

10:30 Coffee Break    
Modeling of Damage : J. Kotomin
Authors : 1D. Simeone, 1J. Ribis, 2L. Luneville, 3V. Pontikis
Affiliations : 1 DEN/Service de Recheche Mettalurgiques Appliquées, CEA, université Paris-Saclay, F-91191, CentraleSupelec-CNRS/SPMS/UMR-8085/LRC CARMEN, F-92291. 2 DEN/Service d'Etude et de Recherche en Mathématique Appliquées, CEA, université Paris-Saclay, F-91191, CentraleSupelec-CNRS/SPMS/UMR-8085/LRC CARMEN, F-92291. 3/DRF/IRAMIS/LSI, CEA, université Paris-Saclay, F-91191, CentraleSupelec-CNRS/SPMS/UMR-8085/LRC CARMEN, F-92291.

Resume : In solid materials, micro-structural patterns resulting from self-organization are responsible for phase transitions and properties changes. Understanding the origin and the selection of possible spatio-temporal patterns far from thermal equilibrium is a major theme of research opening doors to many technological applications ranging from plasmonics to meta-materials. Almost forty years after Turing’s celebrate paper on patterning, progress on modeling instabilities leading to pattern formation has been achieved. The initial concept of dissipative structure is now clearly understood within the Phase-Field framework. Features of spatio-temporal pattern formation are now described in this framework. So far, such an approach obtained promising results in various aspects of materials research from pattern formation during solidification to defect dynamics. In this presentation, we will try to develop an unified presentation of tools, concepts and methods in view to discussing experimental results observed during aging of solids under irradiation. The approach followed in this presentation is comprehensive and not specialized in specific aspects of the Phase-Field modelling (mechanics, mathematics, or numerical methods) at the expense of a holistic picture. Although specialized treatments of this topic are available, this presentation is focused on applications of this appoach to materials submitted to radiation damage.

Authors : Claudia Pecoraro, Santiago Cuesta-López
Affiliations : 1.International Research Centre in Critical Raw Materials-ICCRAM, University of Burgos, Plaza Misael Banuelos s/n, 09001 Burgos, Spain 2.Advanced Materials, Nuclear Technology and Applied Bio/Nanotechnology. Consolidated Research Unit UIC-154. Castilla y Leon. Spain.University of Burgos. Hospital del Rey s/n, 09001 Burgos, Spain.; 1.International Research Centre in Critical Raw Materials-ICCRAM, University of Burgos, Plaza Misael Banuelos s/n, 09001 Burgos, Spain 2.Advanced Materials, Nuclear Technology and Applied Bio/Nanotechnology. Consolidated Research Unit UIC-154. Castilla y Leon. Spain.University of Burgos. Hospital del Rey s/n, 09001 Burgos, Spain.

Resume : Refractory metals are widely used in nuclear engineering and aerospace industry, due to their high resistance to extreme conditions, such as high temperatures, and wear. When used in this context, these materials are subjected to a flux of high-energy radiations that change their microscopic structure by means of the generation of a high number of defects. The production of defects can reach a dramatic amount, thus affecting the macroscopic properties of the material. It is crucial to understand the microscopic changes that occur in these materials, in order to enhance their performances and endurance. Damage production and displacement cascade occur rapidly are impossible to be studied directly. Molecular Dynamics, operating in the nanometer scale and covering a timescale that spans from tenths of femtoseconds up to nanoseconds, can provide a deep insight into the microstructure of the materials in the first moments after the impact. Our study focuses on the analysis of the response of different refractory metals towards radiation damage, by means of studying their behavior after the impact with a high-energy debris. The goal of this analysis is to compute some target properties of the materials, classify them, and state their efficiency as shielding components in aerospace and nuclear industry. Our aim is to compare niobium, for which we already have satisfactory results, to tungsten and tantalum, and to study the same structures with and without a grain boundary interface.

12:30 Lunch Break    
Tracks in Oxides : C. Trautmann
Authors : Kazuhiro Yasuda
Affiliations : Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, JAPAN

Resume : Oxide ceramics, such as ceria, yttria-stabilized zirconia, magnesium-aluminate spinel, are of importance for nuclear applications because of their superior resistance to amorphization. Radiation damage induced by fission fragments (FFs) is the most crucial issue for fuel and target materials, in which high-density electronic excitation is induced to form continuous ion tracks. This paper reports the structure of ion tracks in those oxides throurgh a variety of transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) techniques, to discuss the atomic structure of ion tracks and microstructure evolution at high dose. Atomic resolution STEM observations showed that core damage regions of ion tracks for oxides, CeO2, yttria-stabilized ZrO2 and MgAl2O4, maintain their own crystal structure. The atomic density in core region of ion tracks is, however, depressed and oxygen sublattice is preferentially disordered in fluorite oxides (CeO2, yttria-stabilized ZrO2). Modelling of the accumulation of ion tracks against ion fluence succeeded in evaluation of ion tracks size, size of recovery region, and track formation efficiency. Those values were discussed as a function of electronic stopping power among the oxides. References [1] S. Takaki et al., Nucl. Instrum. Meth. B, 326 (2014) 140. [2] K. Yasuda et al., Int. J. Mater. Res., 102 (2011) 9. [3] K. Yasuda et al., Nucl. Instrum. Meth. B, 314 (2013) 185. [4] S. Takaki et al. Prog. Nucl. Energy 92 (2016) 306. [5] AKM S.I. Bhuian et al. Trans Mat. Res. Soc.-J. 41 (2016) 319.

Authors : M. Saifulin (1,2), A. Janse van Vuuren (3), J. O’Connell (3), V. A.Skuratov (1,2,4), A. Ibraeva (5), M. Zdorovets (5,6)
Affiliations : 1. FLNR, Joint Institute for Nuclear Research, Dubna, Russia, 2. National Research Nuclear University MEPhI, Moscow, Russia; 3. CHRTEM, Nelson Mandela Metropolitan University, Port-Elizabeth, South Africa; 3. CHRTEM, Nelson Mandela Metropolitan University, Port-Elizabeth, South Africa; 1. FLNR, Joint Institute for Nuclear Research, Dubna, Russia, 2. National Research Nuclear University MEPhI, Moscow, Russia, 4. Dubna State University, Dubna, Russia; 5. Institute of Nuclear Physics, Astana, Kazakhstan; 5. Institute of Nuclear Physics, Astana, Kazakhstan, 6. Ural Federal University, Yekaterinburg, Russia;

Resume : The “velocity effect” (VE) in latent track formation has been observed for a variety of materials irradiated with swift heavy ions. The effect manifests in the observation that at the same level of ionization energy losses, high-velocity ions produce less damage than low-velocity ions. Data on track radii in Y3Fe5O12 used to formulate the VE conjecture was obtained mostly through (RBS/C) measurements which is an indirect and highly averaged method for obtaining such data. These track radii and thus the VE effect itself should ideally be confirmed by more direct track imaging methods such as TEM. Recent studies based on direct and indirect measurements of swift heavy ion induced damage in GeS, HOPG and graphene have demonstrated that VE manifests itself differently for these materials. In this work, the results of a TEM study of the morphology of latent tracks in Y3Al5O12 and Y3Fe5O12 formed by Kr and Xe ion irradiation in high- and low-velocity regimes will be presented. Additionally, a possible effect of near surface stress induced by high energy ion irradiation on the results of RBS/C measurements, which may affect the reliability of deduced track sizes from damage cross-sections, is discussed.

Authors : Alessio Lamperti 1, Anna P. Caricato 2, Christina Trautmann 3 4, Paolo M. Ossi 5
Affiliations : 1 Laboratorio MDM, IMM-CNR, 20864 Agrate Brianza (MB), Italy; 2 Dip. di Fisica, Università del Salento, 73100 Lecce, Italy; 3 GSI Helmholtzzentrum für Schwerionenforschung, 64291 Darmstadt, Germany; 4 Technische Universität Darmstadt, 64287 Darmstadt, Germany; 5 Dip. Energia and Centre for NanoEngineered MAterials and Surfaces – NEMAS, Politecnico di Milano, 20133 Milano, Italy

Resume : Cubic ZrO2 single crystals have been reported to exhibit excellent radiation resistance both in the elastic and inelastic collision regimes. However, the use of Yttria Fully Stabilized Zirconia (FSZ) in realistic scenarios requires to study its radiation resistance at the nanoscale. FSZ thin films 600 nm nominally thick were grown on (100) Si by UV pulsed laser ablation. FSZ films are polymorphous, as shown by X-ray diffraction (XRD). They were irradiated with 2.6 GeV Uranium ions at different fluences in the range 5-20×1011 ions cm−2. XRD and μ-Raman spectroscopy evidenced a change in FSZ crystalline structure depending on the irradiation fluence. While low fluences do not modify film structure, at progressively higher fluences the relative fraction of monoclinic to cubic/tetragonal phases evolves towards the latter phase. Across the mid-range fluences of 8-15×1011 ions cm-2, partial amorphization is also observed. Further, the irradiation modifies FSZ crystalline structure as a function of film depth. XRD at synchrotron at different incidence angles (0.2-1°) shows that the contribution of the monoclinic phase is enhanced in the sub-surface region while the cubic/tetragonal phase dominates in depth. These observations evidence that FSZ radiation tolerance is stressed at particularly high fluences of swift heavy ions, especially in the region of few hundreds nm in the proximity of the surface

Authors : L.N. Kolotova, S.V. Starikov
Affiliations : Joint Institute for High Temperatures of Russian Academy of Sciences; Moscow Institute of Physics and Technology (State University)

Resume : At irradiation of swift heavy ions, the defects formation frequently takes place in crystals. High energy transfer into the electronic subsystem and relaxations processes lead to the formation of structural defects and cause specific effects, such as the track formation. There is a large interest to understanding of the mechanisms of defects/tracks formation due to the heating of the electron subsystem. In this work, the atomistic simulation of defects formation and structure transitions in UO2 and U-Mo alloys at irradiation of swift heavy ions has been carried out. We use the two-temperature atomistic model with explicit account of electron pressure and electron thermal conductivity. This two-temperature model describes ionic subsystem by means of molecular dynamics while the electron subsystem is considered in the continuum approach. The various mechanisms of structure changes at irradiation are examined. In particular, the simulation results indicate that the defects formation may be produced without melting and subsequent crystallization. Also it is shown that the mechanism of surface track formation differs from the mechanism of track formation in the bulk. The threshold values of the stopping power for track formation are estimated.

15:40 Coffee Break    
Defect Formation in Ionic-Covalent Materials : G. Baldinozzii
Authors : E.A. Kotomin (1,2), V.N. Kuzovkov (2), A.I. Popov (2), J. Maier (1), and R. Vila (3)
Affiliations : 1) Max Planck Institute for Solid State Research, Stuttgart, Germany 2) Institute of Solid State Physics, University of Latvia, Riga, Latvia 3) CIEMAT, Madrid, Spain

Resume : Al2O3 (sapphire, corundum) is a promising material for fusion reactors, mainly for diagnostics as a general insulator or optical components. Anion-deficient sapphire doped with carbon is also used in personal dosimeters. Thus, it is very important to predict and simulate the kinetics of defect accumulation in sapphire under neutron irradiation as well as long-time defect structure evolution. There were numerous experimental measurements of the primary defect accumulation kinetics (first of all, F color centers—oxygen vacancy with two trapped electrons) as a function of radiation dose rate and temperature with subsequent post-irradiation annealing. As is well known, the F center mobility is much smaller than that of the complementary Frenkel defects – interstitial oxygen ions. Thus, at moderate radiation doses and temperatures, the kinetics of the F center annealing is controlled by their diffusion-controlled recombination with mobile oxygen interstitials. Despite numerous experimental data, very few theoretical efforts were devoted so far to the quantitative analysis of available kinetics, in order to extract main kinetic parameters- interstitial migration energy Ea and diffusion pre-exponent Do, necessary for further prediction of the secondary defect kinetics and radiation stability of sapphire and related materials. Such theory was developed and applied to irradiated insulators in our recent studies [1,2]. In this paper, we analyzed carefully the annealing kinetics for neutron irradiated sapphire available from literature. The extracted migration energies in different experiments vary from 0.8 eV (close to theoretical prediction [3]) down to 0.3 eV, as radiation dose increases. The pre-exponent Do is also much smaller than the estimate for a regular diffusion in crystalline solids. This could be attributed to a strong spatial correlation of radiation-induced defects along neutron trajectories. Moreover, we have observed a strong correlation between the activation energy Ea and pre-exponent Do (Ea) which is no longer constant but fits very well to the exponential function of Ea. In fact, as radiation dose increases, both the migration energy Ea and Do decrease, as the defect diffusion rate effectively grows. Moreover, we demonstrate this correlation for two other neutron irradiated ionic materials- MgO and MgF2. These results are analysed in terms of the Meyer-Neldel rule [4] observed earlier in glasses and disordered materials. [1] V.N. Kuzovkov, E.A. Kotomin, A.I. Popov, R.Villa, Nucl. Inst. Meth. B 374, 107 (2016). [2] V.N. Kuzovkov, A.I. Popov, E.A. Kotomin et al, Low Temp. Phys., 42, 748 (2016). [3] A. Platonenko, D.Gryaznov, S.Piskunov, E.A.Kotomin , Phys. Stat. Sol. C 13, 932 (2016) [4] W. Meyer, H. Neldel, Phys. Zeitschrift, 38, 1014 (1937).

Authors : A.I. Popov (1), V.N. Kuzovkov (1), A. Ch. Lushchik (2), and E.A. Kotomin (1)
Affiliations : (1) Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga LV1063, Latvia; (2) Institute of Physics, University of Tartu, W.Ostwald Str. 1, 50411 Tartu, Estonia

Resume : The radiation-resistant oxide insulators (MgO, Al2O3, MgAl2O4, BeO etc) are important materials for applications in fusion reactors. It is very important to predict/simulate not only the kinetics of diffusion-controlled defect accumulation under neutron irradiation, but also a long-time defect structure evolution including thermal defect annealing after irradiation. In thus work, the kinetics of the F-type center annealing after electron, heavy ions or neutron irradiation was treated as the bimolecular process with equal concentrations of the complementary F and Oi defects. It is controlled by the interstitial oxygen ion mobility, which is much higher than that of the F centers. The F center annealing begins in binary oxides at temperatures 500-700 K, when both F and F centers are practically immobile, due to the recombination with mobile Oi defects. It is demonstrated how the shape of the F-annealing curves is determined by two control parameters: Ea and effective pre-exponential factor and strongly depends on irradiation conditions. The appropriate migration energies were obtained from available from literature annealing kinetics for electron, neutron and ion irradiated MgO, Al2O3, MgAl2O4, BeO, ZnO, PLZT etc. The results obtained are compared with recent ab initio calculations of interstitial oxygen migration. Special attention is paid to: (1) dose effects on F center annealing in neutron and fast electron irradiated MgO and MgF2; (2) a detailed comparison of diffusion-controlled F center thermal annealing in neutron, electron and heavy-ion irradiated MgO, MgF2, Al2O3, ZnO and MgAl2O4; (3) the F center annealing and metal colloid formation in thermochemically reduced MgO, Al2O3 and BeO.

Authors : A. Azarov (1), E. Wendler (2), E. Monakhov (1), and B. G. Svensson (1)
Affiliations : (1) University of Oslo, Department of Physics, Centre for Materials Science and Nanotechnology, P.O. Box 1048 Blindern, N-0316 Oslo, Norway (2) Friedrich-Schiller-Universität Jena, Institut für Festkörperphysik, Max-Wien-Platz 1, 07743 Jena, Germany

Resume : ZnO is a wide and direct band gap semiconductor with potential applications in electronic devices able to work in harsh environments including fusion/fission reactors. However, despite that ZnO exhibits efficient dynamic annealing even at cryogenic temperatures, radiation-induced defects of different types accumulate and can affect device performance. In the present contribution, we study the role of buried pre-existing extended defects on damage formation and annealing in ZnO single crystals implanted with N ions at RT and 15 K. A crystal c-axis aligned 500 keV Ag implantation was used to create a dense band of extended defects in the samples [1]. After that 80 keV N implantations were performed in the region between the sample surface and the Ag peak. Damage evolution was analyzed by RBS/C. The results show that thermally activated migration of point defects from the implanted volume and subsequent trapping/annihilation by the pre-existing defects determine the defect accumulation in the pre-damaged samples at RT. In particular, this leads to the suppression of the defect formation around the projected range of N ions and enhanced radiation tolerance of the material in this region. In its turn, annealing leads to an apparent increase of the damage in all the N implanted samples i.e. a reverse annealing takes place and the role of the pre-existing defects on reverse annealing is discussed. [1] A. Azarov et al., Appl. Phys. Lett. 110, 022103 (2017). [2] A. Azarov et al., Appl. Phys. Lett. 110, 172103 (2017).

Authors : E.V. Savchenko1*, O. Kirichek2, C.R. Lawson2, I.V. Khyzhniy1, S.A. Uyutnov1, M.A. Bludov1
Affiliations : 1Institute for Low Temperature Physics and Engineering NASU, 61103 Kharkiv, Ukraine 2ISIS Neutron and Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot, OX11 0QX, UK

Resume : Radiation-induced degradation processes in solid methane have aroused particular interest in connection with its use as a moderator of hot neutrons in advanced neutron sources [1]. Another aspect of the interest is related to planetary and interstellar astrophysics [2]. Dramatic changes of solid CH4 under ionizing radiation were discovered in 80’s [3,4]. Here we present new trends in the study of radiation damage of CH4 solids with an accent on relaxation processes in the films pre-irradiated with a 1 keV electron beam. Because there is no thermoluminescence from pure solid CH4 we focused on measurements of relaxation currents to discriminate charge recombination reactions. Thermally stimulated exoelectron emission TSEE was measured at T from 5 to 120 K. Two strong peaks of TSEE at about 18 and 43 K were detected from solid CH4 for the first time and activation energies were estimated. Measured in a correlation manner (similar to used in [5]) thermally stimulated particle ejection (post-desorption) from pre-irradiated solid CH4 was found. Strong peaks of anomalous low-temperature post-desorption ALTpD were observed starting at temperatures much lower than the characteristic sublimation temperature. The ALTpD and TSEE yields were compared with the temperature behavior of “burps” in solid CH4 moderator. Basic mechanisms behind of these phenomena are discussed. [1] E. Kulagin, S. Kulicov, V. Melikhov, E. Shabalin. NIM B 215 (2004) 181. [2] R. Miles Icarus 272, (2016) 387. [3] J.M. Carpenter Nature 330, (1987) 358. [4] G. Foti, L. Calcagno, K. Sheng, G. Strazzulla, Nature, 310 (1984) 126. [5] E.V. Savchenko, I.V. Khyzhniy, S.A. Uyutnov, A.N. Ponomaryov, G.B. Gumenchuk, V.E. Bondybey, Low Temp. Phys. 39 (2013) 446.

Poster session-2 : J. M. Costantini-E. Kotomin-C. Trautmann-G. Baldinozzi
Authors : A. Antuzevics (1), J. Gabrusenoks (1), E. Elsts (1), U. Rogulis (1), Ya.Zhydachevskii (2,3), S. Ubizskii (2), D. Sugak (2), A.I. Popov (1)
Affiliations : (1) Institute of Solid State Physics, University of Latvia, 8 Kengaraga, 1063 Riga, Latvia; (2) Lviv Polytechnic National University; Ukraine (3) Institute of Physics, Polish Academy of Sciences; Warsaw, Poland

Resume : Yttrium orthoaluminate YAlO3 (YAP) crystals doped by rare earth ions have long-term interest for thermoluminescent (TL) dosimetry of ionizing radiation as well as fast scintillator detection. Recently, application potential of Mn-doped YAP for TL dosimetry of ionizing radiation has been clearly demonstrated. In this presentation, after introducing some basics on the radiation point defects and impurities in YAlO3, we will summarize the current status of luminescence studies (PL, OSL, TSL, TR-OSL, and dose dependence of OSL) of YAlO3:Mn single crystals and ceramics. Then, we will report the recent results of Raman and EPR measurements of the set of undoped YAlO3 and YAlO3:Mn samples, prepared and characterized in [1, 2]. Finally, detailed comparison with earlier published data will be presented. [1] Ya.Zhydachevskii, et al., Radiation Measurements 45 (2010) 516. [2] Ya. Zhydachevskii, et al., Radiation Measurements 94 (2016) 18. The financial support of Latvian-Ukrainian Joint Research Project No LV-UA/2016/1 is greatly acknowledged.

Authors : Dmitry Bocharov1, Matthias Krack2, Alexei Kuzmin1, Juris Purans1
Affiliations : 1 Institute of Solid State Physics, University of Latvia, Riga, Latvia 2 Paul Scherrer Institute, Laboratory for Reactor Physics and Systems Behaviour, Villigen, Switzerland

Resume : Uranium dioxide (UO2) is an important industrial material which is employed as a fuel in most nuclear reactors world-wide. The doping of UO2 with small amounts of chromium sesquioxide (Cr2O3) is technically applied to obtain a larger average grain size after the fuel sintering process. In this study the local environment of cromium in UO2 was investigated using X-ray absorption spectroscopy. An interpretation of the X-ray absorption spectra is a non-trivial task, especially for so complicated systems like doped fuel. Here we will address this challenging problem using two approaches, in which the ab initio EXAFS theory is combined with classical molecular dynamics (MD) or ab initio molecular dynamics (AIMD) as well as electronic structure simulations based on density functional theory (DFT). The atomic scale MD and DFT simulations were carried out using the CP2K code. Alternatively, DFT simulations were performed to determine the influence of the chromium doping on the fuel matrix. The atomic structure around the chromium impurity was relaxed, and the resulting structures were used to calculate the Cr K-edge EXAFS spectra. The comparison of the simulated EXAFS spectra derived from DFT results with the experimental one allows the identification of valid atomic configurations. The limitations of this approach are discussed.

Authors : V. Savchyn (1), C Balasubramanian (2), I Karbovnyk (1), O.I. Aksimentyeva (1), H. Klym (3), E. Elsts (4), A. Akilbekov (5), A. Dauletbekova (5) and A. I. Popov (4)
Affiliations : (1) Ivan Franko National University of Lviv, 107 Tarnavskogo str., 79017 Lviv, Ukrain (2) Institute for Plasma Research, Bhat, Gandhinagar, 382 044. India (3) Lviv Polytechnic National University, 12, Bandera str., Lviv, 79013, Ukraine (4) Institute for Solid State Physics, University of Latvia, Kengaraga 8, LV-1063 Riga, Latvia (5) L.N. Gumilyov Eurasian National University, 3 Munaitpasova Str., Astana, Kazakhstan

Resume : Cathodoluminescence (CL) spectra of the aluminum nitride nanotubes and nanoparticles, synthesized by using a highly nonequilibrium dc-arc plasma method have been measured at 80 K and room temperature (RT) under electron irradition with 10 keV energy. Low-temperature CL spectra of nanostructured AlN have been compared with those of the commercially available AlN powder. The significant difference between emission spectra of the three investigated samples has been established. Commercial AlN has been found to emit a band peaked at 3.47 eV which is commonly ascribed to oxygen impurities. Emission of the AlN nanoparticles is centered around 3.66 eV while CL spectrum of AlN nanotubes show complex character with at least three peaks at 2.2, 3.0 and 3.5 eV in the photon energy range of 1.8 – 3.8 eV. CL intensity of the nanostructured samples has been found to decrease significantly at RT, most probably due to a combination of non-irradiative relaxations at the surface, electron-phonon interactions and the reabsorption of the emitted light. CL of AlN-nanotube/CsI-scintillator composites has been also studied. Energy transfer via luminescence emission from CsI scintillator to AlN nanotube is demonstrated. Luminescence properties AlN nanotube/polymer composites were also studied and compared with those obtained for AlN nanotubes and nanoparticles.

Authors : 1. Seung-Jae Lee, 1. Kwang-Young Lim, 2. Young-Wook Kim
Affiliations : 1. Korea Nuclear Fuel R&D Center, 2. University of Seoul

Resume : High Temperature Oxidation Behavior of Silicon Carbide Ceramics for Enhanced Performance Fuel in Hydrothermal Exposure Conditions Seung-Jae Lee1, Kwang-Young Lim1, Young-Wook Kim2 1Materials Development Section, KEPCO Nuclear Fuel, Daejeon 305-353, Republic of Korea 2Functional Ceramics Laboratory, Department of Materials Science and Engineering, The University of Seoul, Seoul 130-743, Republic of Korea Keywords : SiC, Nuclear Fuel, PBAT, TRISO, ATF The recent investigations focus on the nuclear ceramic fuels with enhanced accident tolerance under severe accidents. In this sense, the use of particle-based accident tolerant (PBAT) fuels is an alternative strategy for overcoming this issue by multiple silicon carbide (SiC) barriers such as SiC layer in TRISO particle and the dense SiC matrix of the ceramic capsules. The performance on high temperature oxidation of PBAT fuel is one of important factors for plant safety of nuclear reactors supposing the accidents. In this work, safety performance evaluation of SiC ceramics for accident tolerance fuel (ATF) in hydrothermal exposure condition was performed at 1200 and1700 oC for ~25hr. PBAT fuel and monolithic SiC ceramics was fabricated by hot-pressing and normal pressureless sintering, respectively. After 25hr hydrothermal oxidation, some TRISO particles in PBAT fuel were exposed and inner surface portion of PBAT fuel shows pore channel by permeated liquid phase through the grain boundary and junction. The high temperature oxidation resistance of SiC ceramics was dependent on the chemistry inside the grain structure, the additive compositions and the additive contents. More importantly, suppression of liquid phase formation by reaction between formed SiO2 and junction area is one of the essential factors for oxidation resistance performance of SiC ceramics. Detail data for oxidation behavior of SiC ceramic under hydrothermal exposure conditions will be dealed.

Authors : Shunkeyev K., Zhanturina N., Myasnikova L., Barmina A., Sagimbaeva Sh.
Affiliations : K. Zhubanov Aktobe Regional State University Aktobe, Kazakhstan

Resume : To study the effect of uniaxial deformation by <100> and <110> directions on the radiative annihilation of self-trapped excitons (STE), experiments were carried out with KI, KCl and KBr crystals. At deformation by <110> direction, in KBr spectra the emission line with the maximum at 2.95 eV was recorded. In KI and KCl under deformation by <110> and in KBr by <100> direction in the X-ray luminescence spectrum, in addition to intrinsic  -,  - luminescence, additional emission bands were not recorded. This effect was explained by the appearance of excitons with a strongly asymmetric configuration in KBr crystal. Since the ratio between the radii of the anion and the cation for KI, KBr and KCl are equal to 1.5, 1.9 and 2.2, respectively, then it is obvious that the size of the cavity containing STE will be the largest for KCl and the smallest for KI. Therefore, in KI, there are no configurational transformations of STE, since its molecular core cannot move. For KCl, the conversion effect is possible, but in this crystal the luminescence of STE is extinguished at 40K. In KBr crystal, at deformation by <110>, the core of the STE is "pushed out" into the interstitial void. Thus, STE of a less symmetrical configuration is formed than the "strong-off", which corresponds to the emission band at 2.95 eV. This effect is also explained on the basis of the difference in the energies of the exciton states by the surface of adiabatic potential [2]. Calculated energy difference for KI, KBr and KCl crystals was 0.0045 eV, 0.0016 eV, 0.0232 eV, respectively. It follows from these calculations that for the configuration transformations for KBr, the lowest energy is required, which explains the possibility of creating of STE with a less symmetrical configuration than "strong-off".

Authors : Valiev D., Stepanov S., Khasanov O., Khasanov A., Dvilis E. and Polisadova E.
Affiliations : National Research Tomsk Polytechnic University, Lenin Avenue 30, 643050 Tomsk, Russia

Resume : The modern development of optical materials is impossible without the development of optical materials of a new generation. Therefore, the creation of new optical materials is an important, relevant and strategic objective in an optical instrument and optical material science. Great interest for the modern element base of photonics, represent transparent ceramic materials. This is explained by a better technological performance of transparent ceramics compared with single crystals and transparent glass. Spinel oxides find many applications as magnetic, electric, ceramic, catalysis and optical materials. MgAl2O4 has received a great deal of attention as a technologically important material because of its mechanical strength, chemical inertness, wide band gap, relatively low density, high melting point and thermal shock resistance, low thermal expansion coefficient, resistance to neutron irradiation. In this work, we investigated the optical and cathodoluminescent properties of MgAl2O4 ceramics. The polycrystalline MgAl2O4 spinel from nanopowder was consolidated by the spark plasma sintering (SPS) technique using the installation SPS-515S with different temperature and pressure. The integrated cathodoluminescence spectra and decay kinetics were investigated with the pulsed optical spectrometer based on a high-current electron accelerator GIN-600 (Еex=0.25 MeV, FWHM=15 ns, W=3 mJ/cm2) and AvaSpec-2048 fiber spectrometer. The dependences of luminescent properties on the conditions of sintering of ceramics are established. Nature of luminescent centers and mechanisms of luminescence are discussed. This work is financially supported by the project of Russian Science Foundation No 17-13-01233.

Authors : I. Karbovnyk, I. Bolesta, S. Velgosh, R. Lys, H. Klym, A.I. Popov
Affiliations : I. Karbovnyk, I. Bolesta, S. Velgosh, R. Lys - Ivan Franko National University of Lviv, 50, Dragomanova str., Lviv, 79005 Ukraine; H. Klym - Lviv Polytechnic National University, 12 Bandery str, 79000 Lviv, Ukraine; A.I. Popov - Institute of Solid State Physics, University of Latvia, Kengaraga 8, Riga, LV, 1063, Latvia

Resume : MX2 (where M is a metal and X typically denotes Iodine or Bromide) halogenides with pronounced layered structure are interesting materials due to their capability of transforming ionizing radiation into visible light. Specific structure of these compounds provides a number of ways for doping with different impurities. Localization of impurities at interlayer voids and formation of complex aggregates involving intrinsic defects stimulate grow of nanostructures in these materials. Since micron and submicron sized clusters are quantum systems, their discrete energy spectra need to be taken into account when one deals with optical absorption or luminescence of MX2. Unlike thoroughly studied semiconductors, for example, GaSe or InSe, formation and properties of nanostructures in wide band gap halogenides are rather unexplored, while definitely represents a subject of interest. This interest is not only fundamental, as the morphology of clusters in layered MX2 change luminescence color, intensity and kinetics opening several possibilities for designing adjustable scintillators or efficient UV detectors. This report is focused on luminescence properties of a representative crystal from MX2 family – cadmium iodide. Results of spectroscopic experiments at different temperatures are discussed and mechanisms of non-radiative and radiative recombination centers formation are analyzed.

Authors : U. Rogulis, A. Fedotovs, A. Antuzevics, Dz. Berzins, Ya Zhydachevskyy, D. Sugak, A.I.Popov
Affiliations : Institute of Solid State Physics, University of Latvia, 8 Kengaraga St., Riga, Latvia; U. Rogulis, A. Fedotovs, A. Antuzevics, Dz. Berzins, A.I.Popov Institute of Physics, Polish Academy of Sciences, Warsaw, Poland; Ya Zhydachevskyy Lviv Polytechnic National University, Lviv, Ukraine; Ya Zhydachevskyy, D. Sugak

Resume : Usually the correlation between the optical and paramagnetic properties of point defects has been studied by the optically detected magnetic resonance (ODMR) in crystalline materials, where the angular dependencies of the magnetic resonances are well pronounced [1]. Nevertheless, the correlation of optical and paramagnetic properties of activator centres is an actual task also in glass-ceramics and ceramic samples [2]. In this work, we present the results of the magnetic circular dichroism (MCD) and the MCD-detected EPR measurements of the Er3+, Gd3+[3] and Mn2+ doped oxyfluoride glass-ceramics. Through the MCD-EPR, the direct correlation between the optical absorption and the local structure of the activator centres in these glass-ceramics has been established. More complicated task with the estimation of the correlation between the optical spectra and paramagnetic centres is for the ceramics, e.g. Mn-doped YAP ceramics [4]. The MCD is not available due to the opacity of the ceramics. In this case the only possibility is to establish the correlation by the MCD-EPR first in the crystalline analogous and then to verify it for the corresponding ceramics. [1] J.-M. Spaeth, H. Overhof, Springer-Verlag, Berlin, Heidelberg (2003). [2] U. Rogulis, Low temperature physics, 2016, 42, 689-693. [3] A. Fedotovs, et al, J. of Non-Crystalline solids, 2015, 429, 118-121. [4] Ya. Zhydachevskii, et al, Optical Materials, 2014, 37, 125?131.

Authors : H. Klym (1), A. Ingram (2) , O. Shpotyuk (3), L. Calvez (4), I. Karbovnyk (5), A.I. Popov (6)
Affiliations : (1) Lviv Polytechnic National University, 12, Bandera str., Lviv, 79013, Ukraine (2) Opole University of Technology, 75, Ozimska str., Opole, 45370, Poland (3) Vlokh Institute of Physical Optics, 23, Dragomanova str., Lviv, 79005, Ukraine (4) Equipe Verres et et Céramiques, UMR-CNRS 6226, Institute des Sciences chimiques de Rennes, Université de Rennes 1, 35042 Rennes Cedex, France (5) Ivan Franko National University of Lviv, 50, Dragomanova str., Lviv, 79005, Ukraine (6) Institute of Solid State Physics, University of Latvia, Riga, Latvia

Resume : The GeS2–Ga2S3 and GeSe2–Ga2Se3 chalcogenide glasses (ChG) have shown many advantages for potential applications of optical modulator, fiber-optical amplifier in the IR region, etc. Atomic arrangement in such ChG can be studied with numerous techniques, while number of probes available to study atomic-deficient distribution is rather limited, especially at a sub-nanometer scale. One of the best techniques capable to probe such fine free volumes is the positron annihilation lifetime spectroscopy (PALS). In the present paper, we imply the PAL method to study of free-volume structure of GeS2-Ga2S3 ChG. The PALS spectra were recorded with conventional ORTEC system. The PALS spectra of ChG were processed with standard LT 9.0 computer program, the obtained curve being fitted by two components with tau1, tau2 lifetimes and I1, I2 intensities. The positron trapping modes in the studied ChG were calculated using a formalism of two-states trapping model. Since (1, I1) component has no strong physical meaning, we focused our analysis on second component, where tau2 lifetime is directly related to a size of defect free-volume entity and the intensity I2 is proportional to the number of such “defects”. At values of PALS fitting parameters for Ge-Ga-S/Se system, bulk positron lifetime is near 0.28 ns and average lifetime is 0.32 ns. It is shown that the size of free-volume trapping centers in the ChG is higher than in the 80GeSe2-20Ga2Se3 glasses, weak increases of I2 intensities testify growing behaviour in the number of defect-related entities. Other positron trapping parameters for Ge-Ga-S system are similar to Ge-Ga-Se glasses.

Authors : M. Elkady, M. Khorolskiy and A. Sanin
Affiliations : Department of Manufacturing Engineering for Space Launch Vehicles, Dnipropetrovs’k National University

Resume : Nowadays, one of the most important materials are elastomeric materials and their products. These materials are playing a serious role in almost types of machines. Once, there is no common material could be used for manufacturing details for any working conditions. Science researches are doing their best to promote technical properties. It is known that elastomeric materials products which ensure the capacity of many aggregates of rocket and space equipment that can be operated in extreme conditions. Definitely it involves high heat resistance materials for solid propellant rocket motors that must withstand high temperatures. Nowadays, a special rubber produced by various rubber fillers which have different activities is using as internal thermal insulation material. At the same time, their heat-shielding properties need to be improved. One of methods for improving protective properties of rubber composite materials is using carbon nanotubes (CNTs) as filler. CNTs structure makes ability for creating more effective heat resistance coating of rubber composite. According to our estimation vulcanizates with CNTs as an active filler will improve heat-shielding properties such strength and elastomer properties, abrasion and tear resistance. Moreover, the thermal insulation coating volume in solid rockets is substantial and density of CNTs does not exceed 1400 kg/m3 . These properties of CNTs make them auspicious to be used as filler. As well it can be used for reducing the structure net weight of solid propellant rock

Authors : Hang Si*, Yaqi Ji, George Beridze, Evgeny Alekseev, Yulia Arinicheva1, Robert J. Baker2, Sarah Finkeldei1, Nina Huittinen3, Stefan Neumeier, Bin Xiao , Dirk Bosbach & Piotr M. Kowalski
Affiliations : 1Institute of Nuclear Waste Management and Reactor Safety, Forschungszentrum Jülich GmbH, Jülich, Germany, (*correspondence:, 2Trinity College Dublin, Ireland 3Institute of Resource Ecology, Helmholtz-Zentrum Dresden –Rossendorf, Dresden, Germany

Resume : With the steady increase in the availability of supercomputing power and capabilities of computational software the computer-aided modeling techniques become popular research tools in many research fields. They are also frequently used in the research on nuclear materials, including the ones relevant to nuclear waste management [1]. In our research we aim at joint computational and experimental investigation of nuclear materials which allows for a superior characterization of properties of nuclear waste. In this presentation we will show the results of joint investigation of selected ceramic waste forms (monazite, xenotime, pyrochlore) and potential secondary phases that may form in the spent nuclear fuel under disposal conditions (studtite/metastudtite & coffinite). We will discuss the structural incorporation of actinides into these materials and the derivation of related thermodynamic [2] and thermochemical parameters [3]. We will also show the results on the structural and disordering effects [4], on the stability of selected solid solutions and on the derivation of phase diagrams of actinide-bearing compounds [5]. The discussed materials properties are important for assessment of long-term durability and stability of disposed nuclear waste. [1] Chroneos et al., J. Nucl. Mater. 441, 29 (2013). [2] Kowalski et al., J. Nucl. Mater. 464, 147 (2015). [3] Kowalski et al., J. Eur. Ceram. Soc. 36, 2093 (2016). [4] Finkeldei et al., Acta Materialia 25, 166 (2017). [5] Xiao et al., Chem. Eur. J. 22, 946 (2016).

Authors : I. Isakovica, S. Piskunov, A. I. Popov
Affiliations : Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga LV1063, Latvia

Resume : The YAlO3 single crystals and ceramics have a long interest for scintillator detectors, laser and optical recording media as well as a substrate for the high-temperature superconductor thin films growth. Among them Mn-doped YAlO3 is a promising material for thermoluminescent dosimetry of ionizing radiation. In this presentation we report the results of the first principles calculations obtained within the formalism of hybrid Density Functional Theory and Hartree-Fock method (using the HSE0 Hamiltonian as implemented in total energy LCAO-CO CRYSTAL14 computer code [1]) properly adapted and carefully verified for atomic, electronic and phonon structure of pristine YAlO3 bulk. The YAlO3 crystal is described by the Pbnm space symmetry group. Equilibrium lattice constants obtained in our study a = 5.189 Å, b = 5.317 Å, c = 7.388 Å are in good agreement with those experimentally observed: a = 5.167 Å, b = 5.315 Å, and c = 7.354 Å. Band gap calculated for the YAlO3 bulk is equal 7.26 eV vs. 7.1 eV known from the experiment. Doping of YAlO3 with Mn ions results in the formation of mid band gap states that alter its electronic properties. In this study we discuss electronic structure of YAlO3 having host Al substituted with both divalent and trivalent Mn ions. In the later case neutral F-center has been inserted to keep the unit cell neutral. Careful comparison with available experimental data is provided. [1]

Authors : alma dauletbekova et al.
Affiliations : kazakstan

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Symposium organizers
Christina TrautmannGSI Helmholtzzentrum & Technische Universität Darmstadt

Planckstr. 1 64291 Darmstadt Germany

+49 6159 712716
+49 6159 713266
Eugene KOTOMINInstitute of Solid State Physics, University of Latvia; Max Planck Institute for Solid State Research, Stuttgart, Germany

Kengaraga 8, Riga LV-1063, Latvia; Heisenbergstr. 1, Stuttgart 70569, Germany

+371 67187 480; +49 711 689 176;
Gianguido BaldinozziCNRS, SPMS, LRC Carmen, Ecole Centrale Paris

92295 Châtenay-Malabry France

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Jean-Marc Costantini - MAIN ORGANIZERCEA-Saclay, DMN/SRMA

91191 Gif-sur-Yvette cedex France

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+33 (0)1 69 08 71 67