2014 Fall Meeting
Oxide materials for energy harvesting: In-silico study coupled with experiment
Scientists of different communities exploring the new possibilities for energy materials through their investigations, especially on the oxide based materials. Hence, there should be a symposium dedicated to the connection between theory and experiments of energy materials in E-MRS for a new flavor.
The prolific growth of energy demand all over the world can be procured by the renewable energy harvesting. Oxide materials promise great potential for helping to solve important technological challenges in energy efficiency and the conversion of renewable energy into useable forms. Performing experiments in the laboratory can be quite expensive to test wide range of materials and their physical and chemical properties, which paves the way of computer aided theoretical prediction. Thus materials modeling come into the picture of our daily scientific life. In this symposium, computational and experimental materials scientists throughout the world can discuss profoundly the future of oxides materials for energy applications. We will also know the desired computation from a development perspective, which will be needed for such theoretical predictions. We know quite a few renowned scientists of this area who can give Plenary and Invited talks, which will enrich our symposium scientifically and motivate the young researchers in this field as well. The proposed workshop aims at bringing together world-leading experts in all these fields to improve interdisciplinary cooperation overcoming traditional boundaries between scientific disciplines.
The scientific objectives of the proposed workshop are:
- Bring together researchers from materials science, chemical synthesis, catalysis, electrochemistry and photovoltaics to highlight recent progress and discuss challenges and opportunities in the materials aspect of oxides research and development for energy applications.
- To discuss possibilities for optimizing the materials properties and device design. The interdisciplinary character of the workshop will help finding solutions for overcoming current limitations.
- Provide opportunity to form new worldwide interdisciplinary collaborations on nanostructured oxide materials for the mutual benefit of theoretical, experimental and applied researchers.
Hot topics to be covered by the symposium:
According to the theme of our symposium, which is primely motivated by the fact of energy applications of oxides materials, the following area would be given emphasize in our symposium:
i. Solar hydrogen fuel production based on oxide materials;
ii. Organic and inorganic solar cell and photovoltaic;
iii. Hybrid interfaces for the quest of novel energy efficient materials;
iv. Catalytic mechanism of hydrogen evolution reaction and oxygen reduction reactions
v. Organic and inorganic battery materials
Tentative list of invited speakers:
- Ulrike Diebold (University Vienna) firstname.lastname@example.org
- Wey Yang Theo (City-University Hongkong) email@example.com
- Yasushi Hirose (University of Tokyo) firstname.lastname@example.org
- Detlef Bahnemann (Hannover University) email@example.com
- Tobias Voss (University of Bremen) firstname.lastname@example.org
- Carsten Ronning (University of Jena) Carsten.Ronning@uni-jena.de
- Anja Bieberle-Hütter (FOM Institute DIFFER - Dutch Institute for Fundamental Energy Research) email@example.com
- Arij van Berkel (TNO - Netherlands Organisation for Applied Scientific Research) firstname.lastname@example.org
- Katarzyna Wiesenhütte (Helmholtz-Zentrum Dresden-Rossendorf)email@example.com
- W.G. Haije (Delft University of Technology - Energy Research Center of the Netherlands) W.G.Haije@tudelft.nl
- John F. Zevenbergen (TNO - Netherlands Organisation for Applied Scientific Research) firstname.lastname@example.org
- Yaroslav Romanyuk (Empa - Swiss Federal Laboratories for Materials Science and Technology) email@example.com
B. Theory and Computation:
- Puru Jena (Virginia Commonwealth University) firstname.lastname@example.org
- Maurizia Palummo (University Tor Vergata Rome)email@example.com
- Filip Tuomisto (Aalto Helsinki) firstname.lastname@example.org
- Jisoon Ihm (Seoul National University) email@example.com
- Michael Nolan (Tyndall Natl. Institute, Cork) firstname.lastname@example.org
- Friedhelm Bechstedt (University Jena) email@example.com
- Christian Elsässer (Fraunhofer IWM Freiburg)firstname.lastname@example.org
- Peter Deak (University of Bremen) email@example.com
- John Robertson (University of Cambridge) firstname.lastname@example.org
- Michael Lorke (University of Bremen) email@example.com
- Thomas Bredow (University of Bonn) firstname.lastname@example.org
- Benjamin J. Morgan (The University of Liverpool) email@example.com
- Hideyuki Kamisaka (University Tokyo) firstname.lastname@example.org
- Julia E. Medvedeva (Missouri University of Science and Technology)email@example.com
- Sheng Meng (Chinese Academy of Sciences Beijing) firstname.lastname@example.org
- Stefano Leoni (Cardiff University) LeoniS@Cardiff.ac.uk
Tentative list of scientific committee members:
- T. K. Kang
- K. V. Rao
- B. Johansson
- C. G. Granqvist
Papers of Symposium A will be published in Cogent Physics. "Cogent Physics is an innovative, open access, scientific journal helping researchers publish their work for a global audience and discover new connections. Taking an objective and constructive approach to peer review, Cogent Physics considers original research across the full spectrum of physics and materials science".
Find out more about Cogent Physics at: http://explore.cogentoa.com/cogent-physics-hub.
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Authors : Dong-Ho Kim, Young-Joo Lee, Sung-Gyu Park, and Yongsoo Jeong
Affiliations : Advanced Functional Thin Films Dept., Korea Institute of Materials Science
Resume : Si-based thin film solar cells can be one of major photovoltaic technologies, considering the building integrated photovoltaics (BIPV) applications in future. Even though the power conversion efficiency of amorphous Si thin film solar cells is lower than those of crystalline-Si or compound semiconductor PV cells, their advantages of low-cost and large-area manufacturing as well as long-term reliability would be more critical in the case of the direct integration of PV technologies into window panes. Recently we have proposed a new type of a-Si solar cells with doping-free concept, which enables simple and eco-friendly production. The conventional p-type window layer and n-type a-Si layer are replaced by a transition metal oxide thin film and a dielectric/metal bilayer contact, respectively. Transition metal oxides with a high work function such as MoO3, V2O5, and WO3 can be used as the window layer. In this presentation, our recent progresses in dop-ing-free a-Si solar cells will be given, especially on V2O5-x window layer. It was found that the deposition of i-a-Si layer on V2O5-x without vacuum-breaking results in higher open-circuit voltage (Voc, ~860 mV). In addition, the annealing of sputter-deposited films prior to the i-layer deposition resulted in the improvement of fill factor (FF, ~0.68). Consequently, the cell efficiency has improved from 7.0% to 9.2%. The experimental details and properties of the oxide material for our doping-free solar cells will be discussed.
Session 3 : -
Authors : Marco Bernardi (1), Maurizia Palummo (2), Jeffrey C. Grossman(3)
Affiliations :  LBNL , Dept of Physics, Univ. of California, Berkeley USA  ETSF, Dept. of Physics University of Rome Tor Vergata Italy  DMSE Massachusetts Institute of Technology , 77 Mass. Avenue , Cambridge USA
Resume : After the discovery of graphene, new emerging two-dimensional materials including layers of BN, hybridized graphene-BN (CBN) and dichalcogenides (MoS2,MoSe2,WS2 ect.) have been the focus of strong interest for their tunable opto-electronic properties, their high carrier mobility and the envisaged possibility to use them as ultrathin optoelectronic and photo-voltaic (PV) devices. Ab-initio DFT and Many-Body Perturbation Theory (MBPT) calculations can provide a very useful scheme to understand and predict their very promising electronic and opto-electronic properties. In this talk, we will focus first on a study on CBN hybridized monolayers [1-2], then we will present candidate interfaces and device architectures to implement these 2D sheets  into efficient and photostable excitonic solar cells, alternative to those based on conjugated polymers and small molecules. In the second part of the talk we will show how TMD monolayers like MoS2, MoSe2, and WS2 can absorb up to 5−10% incident sunlight in a thickness of less than 1 nm and propose new PV devices based on just two stacked monolayers: (1) a Schottky barrier solar cell between MoS2 and graphene and (2) an excitonic solar cell based on a MoS2/WS2 bilayer. Our simulations suggest that such 1 nm thick active layers can, in principle, attain power conversion efficiencies of up to ~1-2%, corresponding to 1-3 orders of magnitude higher power densities than the best existing ultrathin solar cells. We further discuss our very re
Authors : Daragh Mullarkey Elisabetta Arca Igor Shvets
Affiliations : School of Physics, Trinity College Dublin, Ireland
Resume : Chromium oxide and N-doped chromium oxide have been often reported to improve the efficiency of both dye sensitized (DSSC) and organic solar cells (OSC). In particular it was demonstrated that despite being almost an insulator, Cr2O3 and its modifications can substitute PEDOT:PSS as buffer layer in OSC, with comparable or higher device performance. Recently we reported on a method to improve both optical and electrical properties of chromium oxide by co-doping it with Mg and N by spray pyrolysis. Doping with Mg has a major impact on enhancing the conductivity, while both optical and electrical properties can be improved simultaneously by co-doping with N, with potentially great benefit for the performance of the OSC. These films, however, could not be directly implemented in devices because of the poor morphology. In order to overcome this shortcoming, Cr2O3 and Mg-doped Cr2O3 have been deposited by physical vapour deposition techniques on different substrates (ITO and FTO) and their effect on improving the devices efficiency will be discussed in terms of an adjustment of the band alignment at the interface between the organic active layer and the electrode. The effect of the band alignment and of the deposition parameters on the device efficiency will be presented.
Authors : M.P.F. Graça a, B.M.G. Melo a, P.R. Prezas a, S. A. Salehizadeh a, F.N.A. Freireb, M.A. Valente a, L. Bih c
Affiliations : a Physics Department (I3N), Aveiro University, Campus Universitário de Santiago, Aveiro, Portugal; c Mechanics Engineering Department, Ceará Federal University, Fortaleza, Brazil; c Equipe Sciences de Matériaux, FST-Errachidia, Maroc;
Resume : Phosphate glasses have potential to act as catalyst to dissociate water vapor into hydrogen and oxygen, and thus be able to capture hydrogen in its surface. The addition of sodium and niobium oxides to the glass composition, contributes to the depolymerization of the P-O-P chains increasing the number of non-bridging oxygen in the glass structure, whereas the tungsten plays a major role in the ability of dissociate and form hydrogen protons to bound with the non-bridging oxygen, and thus form OH groups. In the present work, glasses with a composition of 30PO_(5/2)-25NbO_(5/2)-10WO_3-25Na_2 O-10[(1-x)BaO-xSrO] (0
Authors : Vladimir Barbashov, Elizaveta Nesova
Affiliations : Dоnetsk Institute for Physics and Engineering named after O.O.Galkin of the National Academy of Sciences of Ukraine
Resume : Molecular dynamics simulations of ZrO2 - x mol .% Y2O3 (x = 0 , 4 , 8, 12) were performed in isothermal conditions at 600 , 800 and 1200 K. Calculated composition dependencies of the diffusion coefficient of oxygen ions and conductivity in the ZrO2 - Y2O3 system demonstrates satisfactory quantitative agreement with experimental data. These curves have a maximum at 8 mol .% Y2O3. The radial distribution functions of oxygen ions in the ZrO2 - Y2O3 system showed that increase of the stabilizer concentration and temperature have similar effects on disordering the anion sublattice. Discussion of results was performed in terms of the baric model of conduction of zirconia. This model assumes the control effect of hydrostatic pressure on oxygen ions diffusion.
Authors : Chabaiporn Junin, Chanchana Thanachayanont
Affiliations : National Metal and Materials Technology Center 114 Thailand Science Park, Paholyothin Rd., Klong 1, Klong Luang, Pathumthani 12120 Thailand
Resume : Titanium dioxide, TiO2, has been widely applied to energy (solar cells, fuel cells and batteries) and environmental (photocatalysis) applications due to its stability and biocompatibility. Phase, morphology and crystallite sizes have been identified as important parameters in controlling functional properties. For examples, anatase phase of TiO2 has been shown to be more photocatalytically active than the thermodynamically stable rutile phase and preform better in Dye-Sensitized Solar Cells. Degussa P25 (75% anatase and 25% rutile) has been known to outperform both pure anatase and rutile phases. In this study, TiO2 thin films on Ti substrates were prepared by sol-gel method, using titanium (IV) isoproproxide (TTIP) with isopropanol. Effects of coating techniques, i.e. dip- and spray- coating, were investigated by XRD, BET, AFM, SEM and TEM in order to study phase, surface area, morphology and crystal structure. Photocatalytic activities of the TiO2 films were tested using methylene blue and UV-VIS pectrophotometer. It was found that the TiO2 films prepared by dip coating technique resulted in mixed anatase:rutile phases. Phase ratio was found to vary with the number of cycles of dipping. On the other hand, pure anatase phase was obtained for the TiO2 films prepared by spray coating. Films prepared by both techniques went through the same heat treatment procedure. The pure anatase TiO2 films were found to have higher photocatalytic activity than the mixed-phase films.
Authors : Jun Hee Choi 1, Jun Eon Jin 1, Junhong Na 2, Ho-Kyun Jang 1, Byung Chul Lee 1, Jong Mok Shin 1, Gyu Tae Kim*1
Affiliations : 1 School of Electrical Engineering, Korea University, Seoul, 136-701, Korea; 2 Future Convergence Research Division, Korea Institute of Science and Technology, Seoul 136-791, South Korea
Resume : Recently, 2D materials such as graphene, MoS2 and WSe2 are expected to be advantageous in future electronic devices as high mobility of channel materials. In order to measure mechanical properties of these 2D materials in nano-scale, nano-structures of the suspended configuration is required. In this presentation, we report the fabrication of sub-100nm cross-linked PMMA trench by using E-beam lithography. After then 2D materials are transferred by liquid exfoliation method on the trench. A bending test experiment is performed with the tip of an atomic force microscope (AFM). Through these measurements, we determined Youngs modules and initial pre-tension of 2D materials nanosheets suspended on the trenches.
Authors : Wei Luo
Affiliations : Physics and Astronomy Department, Uppsala University, Box 530, SE-752 12 Uppsala, Sweden
Resume : The storage of hydrogen (H2) is one of the main technological hurdles to cross in order to make it become an alternate energy carrier in fuel cell in applications. Solid-state storage of H2 based on suitable materials seem to be a workable option in this regard and posses high gravimetric density, operation at ambient conditions, reversibility and fast kinetics, which are necessary for H2 storage materials. It was found that the hydrogen desorption from MgH2 (0001) under biaxial mechanical strain  and concluded a significant improvement in the hydrogenation and dehydrogenation energies. The dehydrogenation energies of the surface were reduced most with the combined effects of doping and strain. The most 7.5% of biaxial mechanical strain could be introduced to the metal atoms (Al, Si, Ti) doping MgH2 surface . In this study, density functional theory has been employed to investigate the release or desorption of hydrogen from the MgH2 surface. To improve upon the energetic for hydrogen desorption from this system, the effects of strain and doping by Al, Si, Ti have been explored. Both of these two effects have been found to be effective. The strain applied along the X direction induces more prominent effects than along the Y direction. Regarding the doping, the system doped with Al gives the most noticeable effect. The Si doped system shows the least improvement while the Ti doped system lies in between as compared to the other two. The combination of doping and straineffects is found to be more efficacious. Reference:  J.J. Tang, X.B. Yang, M. Chen, M. Zhu, Y.J. Zhao, J. Phys. Chem. C 116 (2012) 14943.  T. Hussain, T.A. Maark, A. De Sarkar, W. Sun, R. Ahuja, Europhys. Lett. 101 (2013) 27006
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Session 5 : -
Authors : Yaroslav E. Romanyuk 1*, Harald Hagendorfer 1, Patrick Stücheli 1, Peter Fuchs 1, Shiro Nishiwaki 1, Cédric Broussilou 2, Veronica Bermudez 2, Pierre-Philippe Grand 2, and Ayodhya N. Tiwari 1
Affiliations : 1 Laboratory for Thin Films and Photovoltaics, Empa - Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland; 2 NEXCIS Photovoltaic Technology, 13790 Rousset, France
Resume : Solution processing of inorganic thin films has become an important thrust in material research community because it offers low-cost and high-throughput deposition of various functional coatings and macroelectronic devices such as thin film solar cells. There have been several examples of solar cells with solution (ink)-processed absorber materials, including Cu(In,Ga)Se2, Cu2ZnSn(S,Se)4, CdTe-CdS nanocrystal hybrids, a-Si, Cu2O-ZnO, and recently emerged organometallic halide perovskites. Solution processing of other functional layers like metal contacts and especially transparent contacts still remains a big challenge because a high-temperature annealing step is usually required. The talk will critically review solution approaches for the functional layers of inorganic thin film solar cells. As the main highlight, a proprietary low-temperature (<100 °C) chemical bath deposition route to fabricate highly conductive Al-doped ZnO (AZO) is used to fabricate transparent contacts for various types of thin film solar cells. Conversion efficiencies approaching 14% have been achieved for solar cells in which all functional layers (except the metal back contact) were processed from aqueous solutions.
Authors : Jangwon Seo, Sangman Park, Young Chan Kim, Nam Joong Jeon, Jun Hong Noh, Sung Cheol Yoon* and Sang Il Seok*
Affiliations : Division of Advanced Materials Korea Research Institute of Chemical Technology 141 Gajeong-Ro, Yuseong-Gu, Daejeon 305-600, Republic of Korea
Resume : Hybrid organic/inorganic perovskite material, CH3NH3PbI3 (=MAPbI3) has received a great deal of attention due to their intrinsic properties such as appropriate band gap (1.55 eV), high absorption coefficient, long hole-electron diffusion length (~100 nm) and excellent carrier transport in photovoltaic applications. Recently, great progress has been made in the perovskite solar cells consisting of electron transporting layer/perovskite materials/hole-transporting layer/Au. Despite of high performance, most of electron transporting layer such as mesoporous (mp)-TiO2-layer process at high temperature. Therefore, many approaches have been performed to avoid high-temperature manufacturing (>450 oC) for preparing a compact or mp-TiO2 layer. In this work, we have demonstrated highly efficient perovskite-PCBM heterojunction unit cells and modules (10 x 10 cm2). The optimization of PCBM layer thickness (with ~ 55 nm) and insertion of LiF interlayer, owing to the formation of extremely uniform perovskite layers, enabled the device performance to reach 14.1% in a unit cell and 8.7% in module, respectively, which are one of the highest values reported till date for a normal-type perovskite-PCBM heterojunction solar cells. This study provides new avenues for the fabrication of more efficient perovskite thin film solar cells by solution-processing at low temperature and great potential in large-area flexible photovoltaic devices.
Authors : Denis Gryaznov
Affiliations : Institute of Solid State Physics, University of Latvia, Kengaraga 8, LV-1063, Latvia
Resume : La1-xSrxCo0.25Fe0.75O3-delta perovskite solid solutions containing reducible transition metals is known as one of the best cathode materials for permeation membranes and solid oxide fuel cells. The key properties controlling the quality of cathode materials are the concentration of oxygen vacancies and their migration energies. The first principles calculations were used in this study, in order to understand properties of oxygen vacancies in La1-xSrxCo0.25Fe0.75O3-delta and La1-xSrxFeO3-delta at two concentrations of Sr dopant, namely 12.5 and 50%. The standard GGA-type PBE exchange-correlation (ex-corr) functional and the DFT+U method, as implemented in plane wave code VASP, and hybrid ex-corr functional PBE0, as implemented in Gaussian basis set code CRYSTAL, were used for careful analysis of obtained results. The calculations were spin polarized in supercells with full structure relaxation. The analysis also included the phonon contribution to the formation energies of oxygen vacancies using direct method and supercells and, thus, temperature dependences. We give a particular emphasis to the comparison of calculated formation energies with those obtained in thermogravimetric measurements as well as permeation measurements. The role of ex-corr functional for the calculated formation energies is discussed from the viewpoint of Sr content and valence state of Fe.
Authors : Daniel I. Bilc, Cristian Morari, Calin Floare, Philippe Ghosez
Affiliations : Mol & Biomol Phys Dept, Natl Inst Res & Dev Isotop & Mol Technol, Cluj Napoca, Romania; Département de Physique, Université de Liège, Liège, Belgium
Resume : The identification of alternative and renewable sources of energy is one of the main challenges that modern society faces. One of the most promising technologies is that of thermoelectric (TE) devices, which allows one to transform heat into electrical energy or vice-versa. Several basic technological problems still need to be solved before thermoelectricity becomes a competitive energy source for large scale applications. In particular, the performance of TE materials governed by the figure of merit ZT will have to be roughly doubled before large-scale applications can be envisaged (ZT=(S2σT)/(κe + κl), where S2σ is called the power factor PF, κe and κl are the electronic and lattice contributions to the thermal conductivity, and T is absolute temperature). In practice, ZT should be greater than 3 for TE devices to become fully competitive with other energy conversion systems. New perspectives on thermoelectrics have been opened by nanostructuring, which has generated materials with ZTs ranging from 1 to 2.4. Using a new guidance idea, which exploits the highly-directional character of some orbitals to produce a low-dimensional transport, and the concept of electronic band structure engineering we predict from first-principles calculations impressive PFs in LaVO3(KNbO3) nanostructures embedded in a SrTiO3 matrix. These impressive PFs are realistically able to generate ZTs>3. The origin of these impressive PFs will be discussed in detail.
Session 7 : -
Authors : Kevin Sivula
Affiliations : Laboratory for Molecular Engineering of Optoelectronic Nanomaterials, École polytechnique fédérale de Lausanne (EPFL), Station 6, 1015 Lausanne, Switzerland
Resume : A device that can convert solar energy into a chemical fuel with good efficiency while also offering high stability and the capability to be constructed from widely available materials using inexpensive processing techniques is urgently needed. A practical, stable and inexpensive device could be fabricated with an n-type oxide photoanode in tandem with a p-type oxide photocathode. In this presentation I will present our progress in the development of solution-processed, stable oxide photoelectrodes and their application toward overall photoelectrochemical water splitting tandem cells. I will discuss the feasibility of employing BiVO4, WO3, or Fe2O3 as the n-type photoanode and Cu2O or CuFeO2 as the p-type photocathode. Combinations of these materials have potential solar-to-fuel conversion efficiencies higher than 10%. However, specific drawbacks have limited their performance in solar water splitting to date. I describe these limitations and our efforts to overcome them. In detail, by employing water oxidation and reduction catalysts (Co-Pi and RuOx, respectively) together with an operating point analysis we show that an unassisted solar photocurrent density on the order of 1 mA cm2 is possible and moreover gain insight into routes for improvement. We further demonstrate the unassisted 2-electrode operation of a tandem cell in this system and show that light harvesting is an important limiting factor.
Authors : A. Bieberle-Huetter
Affiliations : FOM Institute DIFFER
Resume : Electrochemical interfaces are present in many emerging energy applications, such as fuel cells, batteries, or solar fuel conversion devices. In most studies, experimental methods are used in order to characterize the interface and the processes taking place at the interface. However, a combined approach of experiments and modelling & simulations does significantly improve the understanding of these interfaces and gives guidelines for advanced processing of electrochemical interfaces. We will illustrate this with two examples: In solid oxide fuel cells, we have prepared patterned Ni thin film model electrodes and have characterized them in detail by electrochemical impedance spectroscopy as a function of pattern geometry. In combination with electrochemical modelling of the Ni, H2-H2O | YSZ interface, we could exclude seven possible reaction mechanisms to be limiting the kinetics at the interface and could pinpoint the rate limiting reaction step at the fuel cell anode to hydrogen spillover. In photoelectrochemical solar fuel conversion, we are pursuing a similar approach. We are fabricating and electrochemically characterizing well-defined, nanostructured photoelectrodes by impedance spectroscopy. In parallel, we are doing electrochemical modelling & simulations of the photoelectrode ? electrolyte interface. Combining both aspects will allow us to identify the electrochemical limitations at solar fuel conversion electrodes and to process highly efficient photoelectrodes in the future.
Authors : Anastasiia Novokhatska, Gennadiy Akimov
Affiliations : DONETSK INSTITUTE FOR PHYSICS AND ENGINEERING NAMED AFTER O.O. GALKIN NATIONAL ACADEMY OF SCIENCES OF UKRAINE
Resume : Interest in the study of lanthanum manganites with perovskite structure primarily associated with observed in them the effect of colossal magnetoresistance (CMR) at close to room temperature, which is promising in the practical application as highly sensitive magnetic field sensors, components of anodes of solid oxide fuel cells, catalysts of chemical reactions, etc. This work presents the results of studies of the effect of superstoichiometric manganese on density, grain size and structure as well as the phase composition and magnetoresistive properties of ceramics (La0.65Ca0.35)1-xMn1+xO3±Δ (LCMO) (x = 0, 0.2) sintered at 1000-1500 ° C. Powder manganite of LCMO had been obtained by sol-gel methods and compacted into preforms by cold isostatic pressing at a pressure of 0.1 GPa. Sintering was performed at 1000, 1200, 1300, 1400, 1450 and 1500 °C for 2-3 hours. After measuring a density the samples were split and the cleaved surfaces were thermally etched at 1000 °C for visualization of the grain and its internal structure. The x-ray diffractions were measured by the diffractometer Philips-1050/70 in CuKα radiation. The study of the microstructure of ceramics was carried out by the scanning electron microscope (SEM) JSM-6490LV. Measurements of the magnetoresistive effect was performed using four probe method in magnetic fields H=0 and 5 kOe in the temperature range 77-400 K. SEM studies were shown that with increasing the sintering temperature above 1300 °C the excess of manganese allocates on the grain boundaries in the oxides form of Mn3O4 and thus the composite material with clean LCMO and Mn3O4 grains is obtained. In addition, the presence of superstoichiometric manganese has a decisive influence on the structure of ceramics as a uniform grain growth and the emergence of nanoscale layered LCMO grain structure after sintering at 1450 °C, as well as, significantly effects on the magnetoresistive properties of ceramics. Experimental results of measurements shown that with rise in the sintering temperature in the ceramics with x=0.2 the peak value of colossal magnetoresistance increasing more in 2,5 times as compared with the ceramics with x=0. In addition, in the LCMO (x=0.2) ceramics sintered at 1450 °C having composite structure and less grain size the sloping low temperature trend of a magnetoresistance curve was detected which is typical for the single-crystal manganite.
Authors : Aadesh P. Singh, Nisha Kodan, Bodh R. Mehta
Affiliations : Thin Film Laboratory, Department of Physics, Indian Institute of Technology, Hauz Khas, New Delhi-110016, India
Resume : Efficient solar-to-hydrogen conversion in photoelectrochemical (PEC) cell is an ultimate goal for scientific community in the field of energy generation. Surface disor¬dering at nano-level is a promising tool for altering optical absorption and carrier transport in metal oxide semiconductors which can be used an efficient photoelectrode in PEC cell for solar energy harvesting. RF-sputtering technique offers a viable solution for overcoming thermodynamic impediments involved in the growth of metal oxide thin film and surface engineering through hydrogen treatment. This talk will present how ionic and molecular hydrogen incorporation in sputter deposited metal oxide thin films alters the material properties, which can be transformed into advanced material technologies. Optical absorption, XPS and KPFM studies shows that changes in the band gap, shift in valence band maximum and work function values are dependent on method of hydrogen incorporation. Enhancement in photoelectrochemical response in hydrogen treated metal oxide thin films will be explained in terms of optical and electrical properties along with energy band diagrams drawn on the basis of work function, band gaps, and valence band offsets.
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Session 8 : -
Authors : Michael Nolan
Affiliations : Tyndall National Institute, UCC, Lee Maltings, Dyke Parade, Cork, Ireland
Resume : TiO2 photocatalysts have two key challenges: (1) to shift the TiO2 band gap to the visible region, allowing solar energy to be used and (2) enhancing charge separation after photoexcitation. We discuss our simulation driven work on a new mechanism for band gap modification in TiO2: surface modification of TiO2 with metal oxide nanoclusters. Modifying TiO2 with transition metal oxide nanoclusters induces visible light activity, which is achieved by introducing nanocluster derived electronic states above the original TiO2 valence band edge, to shift the VB edge to higher energy. A model of the photoexcited state confirms the band gap reduction which is controlled by the coverage of transition metal oxide nanoclusters. For tin oxide, experiment and simulation show that the change in the band gap is controlled by two factors: the tin oxidation state and the TiO2 crystal polymorph, with rutile and anatase showing different properties when modified with SnO2. The stereochemical lone pair in SnO and PbO induces a band gap reduction. Simple rules for modifying TiO2 to induce visible light absorption are presented. Models of the photoexcited state of modified TiO2 show that the photoexcited hole localises on low coordinated oxygen in the nanocluster and the electron in the TiO2 surface; the presence of low coordinated atoms is crucial. We present initial studies of the interaction of molecules at these structures.
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