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Oxynitrides have been shown to be promising visible light water splitting photocatalysts, but rapidly degrade under operating conditions. With a custom designed photoelectrochemical cell, we perform operando grazing incidence X-ray absorption spectroscopy measurements on the oxynitride semiconductor SrTaOxNy during photocatalytic solar water splitting. We show that the nature of the A-site (Sr) and its evolution during operation have large impacts on the overall stability and catalytic activity of the material, leading to an enriched BO2 (Ta(OH)/TaO(OH)) like surface. However, this usually beneficial effect with respect to increased surface hydrophilicity has complications for the efficiency of the photocatalytic process, as the OH and O(OH) intermediates formed are in competition between O2 generation and NOx species formation in the initial stages of operation. Operando characterisation of the evolution of the electronic structure of the photocatalyst proves to be an invaluable tool for the rational design and discovery of new and better performing materials.

Nanoscale thin films are widely implemented across a plethora of technological and scientific areas, and form the basis for many advancements that have driven human progress, owing to the high degree of functional tunability based on the chemical composition. Pulsed laser deposition is one of the multiple physical vapour deposition routes to fabricate thin films, employing laser energy to eject material from a target in the form of a plasma. A substrate, commonly a single-crystal oxide, is placed in the path of the plume and acts as a template for the arriving species from the target to coalesce and self-assemble into a thin film. This technique is tremendously useful to produce crystalline films, due to the wide range of atmospheric conditions and the extent of possible chemical complexity of the target. However, this flexibility results in a high degree of complexity, oftentimes requiring rigorous optimisation of the growth parameters to achieve high quality crystalline films with desired composition. In this tutorial review, we aim to reduce the complexity and the barrier to entry for the controlled growth of complex oxides by pulsed laser deposition. We present an overview of the fundamental and practical aspects of pulsed laser deposition, discuss the consequences of tailoring the growth parameters on the thin film properties, and describe in situ monitoring techniques that are useful in gaining a deeper understanding of the properties of the resultant films. Particular emphasis is placed on the general relationships between the growth parameters and the consequent structural, chemical and functional properties of the thin films. In the final section, we discuss the open questions within the field and possible directions to further expand the utility of pulsed laser deposition., Chemical Society Reviews, 52 (7), ISSN:0306-0012, ISSN:1460-4744

The growth of crystalline Li-based oxide thin films on silicon substrates is essential for the integration of next-generation solid-state lithionic and electronic devices including on-chip microbatteries, memristors, and sensors. However, growing crystalline oxides directly on silicon typically requires high temperatures and oxygen partial pressures, which leads to the formation of undesired chemical species at the interface compromising the crystal quality of the films. In this work, we employ a 2 nm gamma-alumina (γ-Al

There has been significant interest in the bilayer system formed by Ceria (CeO2) and yttria-stabilized zirconia (YSZ). Multiple studies have explored these two materials individually, however, the ...

La1–xSrxCoO3-δ perovskites are potential catalysts for the anodic reaction of alkaline water electrolyzers, i.e., the oxygen evolution reaction (OER). It is well-known that La1–xSrxCoO3−δ perovskit...

This work reveals that photoanodes based on TiNb2 O7 (TNO) powder show remarkable water-oxidation properties including nearly ideal charge-transfer and charge-injection efficiencies. Furthermore, using a simplified photoanode construction and carefully surveying the structural and morphological characteristics of oriented and polycrystalline thin films and powder-based samples revealed that the water-splitting kinetics of TNO is negligibly effected by surface morphology; instead, internal grain boundaries likely play a driving role. The current powder-based TNO photoanodes exhibit ideal water-oxidation kinetics and oxidize water at minimal applied biases under illumination; consequently, TNO exhibits an early onset photocurrent voltage (0.4 V vs. RHE) that rivals that of other state-of-the-art photoanode materials.

The perovskite yttrium tantalum oxynitride is theoretically proposed as a promising semiconductor for solar water splitting because of the predicted band gap and energy positions of band edges. In experiments, however, we show here that depending on the processing parameters, yttrium tantalum oxynitrides exist in multiphases, including the desired perovskite YTaON2, defect fluorite YTa(O,N,□)4, and N-doped YTaO4. These multiphases have band gaps ranging between 2.13 and 2.31 eV, all responsive to visible light. The N-doped YTaO4, perovskite main phase, and fluorite main phase derived from crystalline fergusonite oxide precursors exhibit interesting photoelectrochemical performances for water oxidation, while the defect fluorite derived from low-crystallized scheelite-type oxide precursors shows negligible activity. Preliminary measurements show that loading an IrOx cocatalyst on N-doped YTaO4 significantly improves its photoelectrochemical performance, encouraging further studies to optimize this new material for solar fuel production.

Hematite as promising photoanode for solar water splitting suffers from severe bulk and surface charge recombination. This work describes that a protonation-annealing treatment can effectively suppress both bulk and surface charge recombination in hematite. Protons/electrons are electrochemically incorporated into hematite under 0.2 VRHE followed by annealing at 120 oC. The photocurrent density increases from ~0.9 mA cm-2 to 1.8 mA cm-2 at 1.23 VRHE under 1 sun, and further to 2.7 mA cm-2 after loading cobalt phosphate, stabilizing at round 2.4 mA cm-2. A cathodic shift of the onset potential of photocurrent is also observed. H2O2 oxidation, impedance spectroscopy and Mott-Schottky measurements show that the protonation suppresses bulk recombination and enhances donor density, but introducing more surface recombination. The annealing reduces surface recombination, while preserving relatively high bulk charge separation efficiency. Different from previous reports on the electrochemically reduced hematite, this work demonstrates that the performance improvement should be ascribed to the proton incorporation instead of the formation of Fe3O4 or metal Fe. This facile treatment by protonation and annealing could be applied in other semiconductors to promote the development of high performing photoelectrodes.

Free-standing solid-state ion conducting thin film membranes are key components in micro-energy conversion devices such as micro-solid oxide fuel cells or electrolyzers. Through this work, we explore the design and fabrication of thin film architectures with either straight, zigzag or spiral-shaped columnar grain nanostructures of 8 mol% doped Yttria stabilized zirconia (8YSZ) in order to modify the ceramics elastic properties and mechanical stability for MEMS integration. We report that the zigzag and spiral-shaped nanomorphologies' can be engineered with a ∼44% reduced elastic modulus. Ultimately, this results in an increased fabrication yield when the thin ionic conductor thin film structures are turned into free-standing membranes as required for different micro energy converter applications. Raman spectroscopy reveals that the symmetry is lowered by the existence of monoclinic distortions in the cubic phase which modifies the elastic moduli of films with straight columnar structures. Fundamentally, we show here evidence that for yttria-stabilized zirconia modifications in membrane nano-architectures and strain can lead to phase changes, which agrees well with findings published in the 1970s based on applied external stress's on macroscopic structures (i.e. pellets). The influence of the change in nano-morphology on the cross-plane ionic conductivity is minor. The oxygen ion conducting thin film nanomorphology design exhibits potential to optimize grain connectivity and tortuosity by growth as either columnar, zigzag or spiral-shaped morphologies, in order to obtain membranes with controllable phases and elastic moduli for micro-energy conversion devices.

Understanding the mechanism of oxygen evolution reaction (OER) on perovskite materials is of great interest to tailor the synthesis of better catalyst materials. Despite the huge amount of literature reports, the complexity of catalytic systems and scarce in situ and operando surface sensitive spectroscopic tools render the detection of active sites and the understanding of the reaction mechanisms challenging. Here, we carried out and compared in situ and ex situ ambient pressure X-ray photoelectron spectroscopy experimental procedures on a La0.2Sr0.8CoO3 perovskite OER catalyst. Experimental results show that segregated surface strontium, which is present in the as prepared sample, is leached into the electrolyte after immersion, leading to surface cobalt active sites enrichment. Such cobalt-enriched oxide surface evolves into a new phase, whose spectral feature is detected in situ, during/after OER. With the help of theoretical simulations, such species is assigned to cobalt oxyhydroxide, providing a direct evidence of its crucial role in the reaction.

Oxynitrides have been shown to be promising visible light water splitting photocatalysts, but rapidly degrade under operating conditions. With a custom designed photoelectrochemical cell, we perform operando grazing incidence X-ray absorption spectroscopy measurements on the oxynitride semiconductor SrTaOxNy during photocatalytic solar water splitting. We show that the nature of the A-site (Sr) and its evolution during operation, have large impacts on the overall stability and catalytic acitivity of the material, leading to an enriched BO2 (Ta(OH)/TaO(OH)) like surface. However, this usually beneficial effect with respect to increased surface hydrophilicity has complications for the efficiency of the photocatalytic process, as the OH and O(OH) intermediates formed are in competition between O2 generation and NOx species formation in the initial stages of operation. Operando characterisation of the evolution of the electronic structure of the photocatalyst proves to be an invaluable tool for the rational design and discovery of new and better performing materials.

Solid-state electrolytes for Li-ion batteries are attracting growing interest as they allow building safer batteries, also using lithium-metal anodes. Here, we studied a compound in the lithium superionic conductor (LISICON) family, i.e., Li4-xGe1-xPxO4 (LGPO). Thin films were deposited via pulsed laser deposition, and their electrical properties were compared to those of ceramic pellets. A detailed characterization of their microstructures shows that thin films can be deposited fully crystalline at higher temperatures but also partially amorphous at room temperature. The conductivity is not strongly influenced by the presence of grain boundaries, exposure to air, or lithium deficiencies. First-principles molecular dynamics simulations were employed to calculate the lithium-ion diffusion profile and the conductivity at vario temperatures of the ideal LGPO crystal. Simulations give the upper limit of conductivity for a defect-free crystal, which is in the range of 10(-2) S cm(-1) at 300 degrees C. The ease of thin-film fabrication and room-temperature Li-ion conductivity in the range of a few mu S cm(-1) make LGPO very appealing electrolyte material for thin-film all-solid-state all-oxide microbatteries.

We report results from visible and UV Raman spectroscopy studies of the phonon spectra of a polycrystalline sample of the prototypical perovskite type oxide BaZrO

In the present study, morphological and electrical properties of BaZrO3 were investigated as a function of the ionic radii mismatch between Zr and the different B-site dopants (Al, Sc, In, Lu, Tm, Y, Gd, Sm, Nd, and La) for the same solute concentration and valence. Our study highlights the critical role of the ionic radius of the acceptor dopant on stability, sinterability, and proton conductivity of barium zirconate. From our study, Gd-doped barium zirconate emerges as a novel promising material for proton conductor electrolytes.

The nitrogen substitution into the oxygen sites of several oxide materials leads to a reduction of the band gap to the visible light energy range, which makes these oxynitride semiconductors potential photocatalysts for efficient solar water splitting. Oxynitrides typically show a different crystal structure compare to the pristine oxide material. Since the band gap is correlated to both the chemical composition and the crystal structure, it is not trivial to distinguish what modifications of the electronic structure induced by the nitrogen substitution are related to compositional and/or structural effects. Here, X-ray emission and absorption spectroscopy is used to investigate the electronic structures of orthorhombic perovskite LaTiOxNy thin films in comparison with films of the pristine oxide LaTiOx with similar orthorhombic structure and cationic oxidation state. Experiment and theory show the expected upward shift in energy of the valence band maximum that reduces the band gap as a consequence of the nitrogen incorporation. But this study also shows that the conduction band minimum, typically considered almost unaffected by the nitrogen substitution, undergoes a significant downward shift in energy. For a rational design of oxynitride photocatalysts the observed changes of both the unoccupied and occupied electronic states have to be taken into account to justify the total band gap narrowing induced by the nitrogen incorporation.

Anatase ${\mathrm{TiO}}_{2}$ (a-${\mathrm{TiO}}_{2})$ exhibits a strong x-ray absorption linear dichroism in the pre-edge, the XANES and the EXAFS at the titanium $K$ edge. In the pre-edge region, the behavior of the A1--A3 and B peaks originating from the $1s\ensuremath{-}3d$ transitions is due to the strong $p$-orbital polarization and strong $p\ensuremath{-}d$ orbital mixing. An unambiguous assignment of the pre-edge peak transitions is made in the monoelectronic approximation with the support of ab initio finite difference method calculations and spherical tensor analysis in quantitative agreement with the experiment. Our results suggest that several previous studies relying on octahedral crystal field splitting assignments are in accurate due to the significant p-d orbital hybridization induced by the broken inversion symmetry in a-${\mathrm{TiO}}_{2}$. It is found that A1 is mostly an on-site $3d\ensuremath{-}4p$ hybridized transition, while peaks A3 and B are nonlocal transitions, with A3 being mostly dipolar and influenced by the $3d\ensuremath{-}4p$ intersite hybridization, while B is due to interactions at longer range. Peak A2, which was previously assigned to a transition involving pentacoordinated titanium atoms, is shown to exhibit a quadrupolar angular evolution with incidence angle, which implies that its origin is primarily related to a transition to bulk energy levels of a-${\mathrm{TiO}}_{2}$ and not to defects, in agreement with theoretical predictions [Vorwerk et al., Phys. Rev. B 95, 155121 (2017)]. Finally, ab initio calculations show that the occurence of an enhanced absorption at peak A2 in defect-rich a-${\mathrm{TiO}}_{2}$ materials originates from defect-related $p$ density of states due to the formation of doubly ionized oxygen vacancies. The formation of peak A2 at almost the same energy for single crystals and nanomaterials is a coincidence while the origin is different. These results pave the way to the use of the pre-edge peaks at the Ti $K$ edge of a-${\mathrm{TiO}}_{2}$ to characterize the electronic structure of related materials and in the field of ultrafast x-ray absorption spectroscopy where the linear dichroism can be used to compare the photophysics along different axes.

This work reveals that photoanodes based on TiNb

We study the oxo-hexametallate Li$_7$TaO$_6$ with first-principles and classical molecular dynamics simulations, obtaining a low activation barrier for diffusion of $\sim$0.29 eV and a high ionic conductivity of $5.7 \times 10^{-4}$ S cm$^{-1}$ at room temperature (300 K). We find evidence for a wide electrochemical stability window from both calculations and experiments, suggesting its viable use as a solid-state electrolyte in next-generation solid-state Li-ion batteries. To assess its applicability in an electrochemical energy storage system, we performed electrochemical impedance spectroscopy measurements on multicrystalline pellets, finding substantial ionic conductivity, if below the values predicted from simulation. We further elucidate the relationship between synthesis conditions and the observed ionic conductivity using X-ray diffraction, inductively coupled plasma optical emission spectrometry, and X-ray photoelectron spectroscopy, and study the effects of Zr and Mo doping.

We performed a comparative study on the photoelectrochemical performance of LaTaON2 loaded with NiOx, Ni0.7Fe0.3Ox, CoOx and IrOx as cocatalysts. Ni-based oxides lead to the highest improvement on the photoelectrochemical performance, while CoOx and IrOx also enhance the performance though to a lower extent, but they simultaneously introduce more pseudocapacitive current thus resulting in an inefficient utilization of the photo-generated holes. Repetitive voltage cycling between 1.0 VRHE and 1.6 VRHE transforms the NiOx and Ni0.7Fe0.3Ox into oxyhydroxides known to possess higher catalytic activities. However, these oxyhydroxides lead to lower photoelectrochemical performance compared to the as-loaded oxides, most probably due to the decay of the passivation centers at the photoelectrode–cocatalyst interface. High catalytic activities cannot be achieved without sufficient passivation of surface recombination states. Despite that the photoelectrochemical performance of LaTaON2 can be improved by cocatalysts, the maximum achievable photocurrent density is still not comparable to that reported for other oxynitride compounds. Our study suggests that poor electronic conductivity or severe bulk recombination of the photo-generated electron–hole pairs are the main limiting factors for the photon-to-current conversion efficiency in LaTaON2 photoanodes.

Developing novel materials for the conversion of solar to chemical energy is becoming an increasingly important endeavour. Perovskite compounds based on bandgap tunable oxynitrides represent an exciting class of novel photoactive materials. To date, literature mostly focuses on the characterization of oxynitride powder samples which have undeniable technological interest but do not allow the investigation of fundamental properties such as the role of the crystalline quality and/or the surface crystallographic orientation toward photo-catalytic activity. The challenge of growing high quality oxynitride thin films arises from the availability of a suitable substrate, owing to strict material and processing requirements: effective lattice matching, sufficiently high conductivities, stability under high temperatures and in strongly reducing environments. Here, we have established the foundations of a model system incorporating a TiN-buffer layer which enables fundamental investigations into crystallographic surface orientation and crystalline quality of the photocatalyst against photo(electro)chemical performance to be effectively performed. Furthermore, we find that TiN as current collector enables control over the nitrogen content of oxynitride thin films produced by a modified pulsed laser deposition method and allows the growth of highly ordered LaTiO3−xNx thin films.

We report results from visible and UV Raman spectroscopy studies of the phonon spectra of a polycrystalline sample of the prototypical perovskite type oxide BaZrO3 and a 500 nm thick film of its Y-doped, proton conducting, counterpart BaZr0.8Y0.2O2.9. Analysis of the Raman spectra measured using different excitation energies (between 3.44 eV and 5.17 eV) reveals the activation of strong resonance Raman effects involving all lattice vibrational modes. Specifically, two characteristic energies were identified for BaZrO3, one around 5 eV and one at higher energy, respectively, and one for BaZr0.8Y0.2O2.9, above 5 eV. Apart from the large difference in spectral intensity between the non-resonant and resonant conditions, the spectra are overall similar to each other, suggesting that the vibrational spectra of the perovskites are stable when investigated using an UV laser as excitation source. These results encourage further use of UV Raman spectroscopy as a novel approach for the study of lattice vibrational dynamics and local structure in proton conducting perovskites, and open up for, e.g., time-resolved experiments on thin films targeted at understanding the role of lattice vibrations in proton transport in these kinds of materials.

There has been significant interest in the bilayer materials used as Solid Oxide Fuel Cell Oxides (SOFCs) electrolytes. Multiple studies have explored the two participating materials in bilayer electrolytes, individually. However, the interfaces formed by them remain largely unexplored due to their complex nature. In order to advance the fundamental science of bilayer electrolytes, in this work a multiscale modeling study of the interface formed in commonly used SOFC electrolyte- ‘Ceria (CeO2)/yttria-stabilized zirconia (YSZ)’, was conducted. First, a realistic YSZ/CeO2 interface model containing all the important microstructural features of the interface such as dislocations, point defects, and lattice strains was prepared by using classical molecular dynamics (MD) simulations. Then, density functional theory was implemented to analyze the electronic properties of the realistic YSZ/CeO2 interface model prepared by MD. It was found that, at the interface, the overall strain in CeO2 and YSZ is compressive and tensile, respectively, as expected; however, the local strain at the core of the dislocation is converse. At dislocations, CeO2 was found to have tensile strain whereas YSZ has compressive strain. The presence of tensile strain in CeO2 at the core of the dislocations might contribute to the formation of O vacancies and reduction of Ce4+ to Ce3+, as observed in experiments. Overall, this work for the first time integrates the classical and quantum simulations to prepare and analyze a realistic working-class YSZ/CeO2 interface, resulting in the long-sought explanation for the experimentally observed Ce reduction at the YSZ/CeO2 interface.1 Acknowledgments This work was supported in part by the International Institute for Carbon-Neutral Energy Research (I2CNER) sponsored by the World Premier International Research Center Initiative (WPI) and the JSPS Core-to-Core Program, A. Advanced Research Networks and Paul Scherrer Institut. The computations were performed by using Computational Science Research Center, Okazaki, Japan, and the HPC supercomputers at I2CNER, Kyushu University, Japan. References [1] Kulbir K. Ghuman, Elisa Gilardi, Daniele Pergolesi, Aleksandar Staykov, John Kilner, Thomas Lippert, Microstructural and Electronic Properties of YSZ/CeO2 Interface via Multiscale Modelling , Acta Materialia (2019) Submitted.

The solar water splitting process assisted by semiconductor photocatalysts attracts growing research interests worldwide for the production of hydrogen as a clean and sustainable energy carrier. Due to their optical and electrical properties several oxynitride materials show great promise for the fabrication of efficient photocatalysts for solar water splitting. This study reports a comparative investigation of particle- and thin films-based photocatalysts using three different oxynitride materials. The absolute comparison of the photoelectrochemical activities favors the particle-based electrodes due to the better absorption properties and larger electrochemical surface area. However, thin films surpass the particle-based photoelectrodes due to their more suitable morphological features that improve the separation and mobility of the photo-generated charge carriers. Our analysis identifies what specific insights into the properties of materials can be achieved with the two complementary approaches.

Photoelectrochemical solar water splitting is a promising approach to convert solar energy into sustainable hydrogen fuel using semiconductor electrodes. Due to their visible light absorption properties, oxynitrides have shown to be attractive photocatalysts for this application. In this study, the influence of the preparation method of CaNbO2N particles on their morphological and optical properties, and thereby their photoelectrochemical performance, is investigated. The best performing CaNbO2N photoanode is produced by ammonolysis of Nb enriched calcium niobium oxide. The enhanced photoactivity arises from an enlarged surface area and superior visible light absorption properties. The photoactivity of this photoanode was further enhanced by photodeposition of Co-Pi co-catalyst and by atomic layer deposition of an Al2O3 overlayer. A photocurrent density of 70 microA.cm-2 at 1.23 V vs RHE was achieved. The observed enhancement of the photoelectrochemical performance after Co-Pi/Al2O3 deposition is the combined effect of the improved kinetics of oxygen evolution due to the Co-Pi co-catalyst and the reduced surface recombination of the photogenerated carriers at the Al2O3 surface layer.

Multilayered heterostructures of Ce0.85Sm0.15O2-delta and Y0.16Zr0.92O2-delta of a high crystallographic quality were fabricated on (001) - oriented MgO single crystal substrates. Keeping the total thickness of the heterostructures constant, the number of ceria-zirconia bilayers was increased while reducing the thickness of each layer. At each interface Ce was found primarily in the reduced, 3+ oxidation state in a layer extending about 2 nm from the interface. Concurrently, the conductivity decreased as the thickness of the layers was reduced suggesting a progressive confinement of the charge transport along the YSZ layers. The comparative analysis of the in-plane electrical characterization suggests that the contribution to the total electrical conductivity of these interfacial regions is negligible. For the smallest layer thickness of 2 nm the doped ceria layers are electrically insulating and the ionic transport only occurs through the zirconia layers. This is explained in terms of a reduced mobility of the oxygen vacancies in the highly reduced ceria.

Many physical properties of oxides can be changed by inducing lattice distortions in the crystal through heteroepitaxial growth of thin films. The average lattice strain can often be tuned by changing the film thickness or using suitable buffer layers between film and substrate. The exploitation of the full potential of strain engineering for sample or device fabrication rests on the understanding of the fundamental mechanisms of stress generation and evolution. For this study an optical measurement of the substrate curvature is used to monitor in situ how the stress builds up and relaxes during the growth of oxide thin films by pulsed laser deposition. The relaxation behavior is correlated with the growth mode, which is monitored simultaneously with reflection high-energy electron diffraction. The stress relaxation data is fitted and compared with theoretical models for stress evolution which were established for semiconductor epitaxy. The initial stage of the growth appears to be governed by surface stress and surface energy effects, while the subsequent stress relaxation is found to be fundamentally different between films grown on single-crystal substrates and on buffer layers. The first case can be rationalized with established theoretical models, but these models fail in the attempt to describe the growth on buffer layers. This is most probably due to the larger average density of crystalline defects in the buffer layers, which leads to a two-step stress relaxation mechanism, driven first by the nucleation and later by the migration of dislocation lines.

The mixed ionic and electronic conductor Sr(Ti,Fe)O 3 - α (STF) exhibits fast oxygen surface exchange kinetics, with electron concentration potentially playing a key role. The effect of La donor doping on electron concentration, Fermi level, and overall defect chemistry of STF is investigated on Sr 1 - y La y Ti 0.65 Fe 0.35 O 3 - α (LSTF, 0 ≤ y ≤ 0.5) thin films. Defect chemical modeling, optical absorption, and electrical conductivity measurements in oxidizing conditions indicate compensation of donors by an increase in oxygen and electron concentrations, increase in Fermi level, decrease in oxygen vacancy and hole concentrations, and formation of cation vacancies (for [La] > [Fe]). The surface exchange coefficient, measured by impedance spectroscopy, decreased with increasing donor concentration, suggesting that oxygen exchange kinetics in LSTF are limited by low oxygen vacancy and/or hole concentrations, rather than electron transfer.

Physical properties of materials can be significantly altered without changing their composition thereby enhancing or inhibiting properties or even invoking new functionalities. These changes can be enforced, for example, through lattice distortions (strain) in particular when grown as thin films. The growth-induced strain is typically the result of a mismatch among the lattice constants, the substrate, and the material to be grown. In the first half of this chapter, we introduce and review different models of strain and strain relaxation. In the second half, experimental techniques are presented suitable to study strain in thin films as well as in their applications of in situ strain/stress monitoring capabilities. This includes diffraction-based techniques (XRD, RHEED), as well as curvature-based techniques (cantilever, Multi-beam Optical Stress Sensor).

The need for reducing the operating temperature of solid-oxide fuel cells (SOFCs) imposed by cost reduction has pushed significant progress in fundamental understanding of the individual components, as well as materials innovation and device engineering. Proton-conducting oxides have emerged as potential alternative electrolyte materials to oxygen-ion conducting oxides for operation at low and intermediate temperatures. This article describes major recent developments in electrolytes, electrodes, and complete fuel cell performance for SOFCs based on proton-conducting electrolytes. Although the performance of such fuel cells is still relatively modest, significant improvements in the power density output have been made during the last couple of years, and this trend is expected to continue.

Donor doping of the p-type solid oxide fuel cell cathode, Sr(Ti,Fe)O3-δ, with La was pursued to examine the role of minority charge carriers (electrons) on the oxygen exchange rate. Model dense thin film cathodes of (La,Sr)(Ti,Fe)O3-δ were fabricated by pulsed laser deposition. Optical transmission spectroscopy measurements demonstrated that the addition of the donor La resulted in a change in valence state of Fe from 4+ to 3+, suggesting a rise in Fermi level. The activation energy of the cathode’s area specific resistance, studied by impedance spectroscopy, was found to be lower with La addition; however, the magnitude of the area specific resistance was not lowered.

Solid oxide oxygen ion and proton conductors are a highly important class of materials for renewable energy conversion devices like solid oxide fuel cells. Ba2In2O5 (BIO) exhibits both oxygen ion and proton conduction, in a dry and humid environment, respectively. In a dry environment, the brownmillerite crystal structure of BIO exhibits an ordered oxygen ion sublattice, which has been speculated to result in anisotropic oxygen ion conduction. The hydrated structure of BIO, however, resembles a perovskite and the protons in it were predicted to be ordered in layers. To complement the significant theoretical and experimental efforts recently reported on the potentially anisotropic conductive properties in BIO, we measure here both the proton and oxygen ion conductivity along different crystallographic directions. Using epitaxial thin films with different crystallographic orientations, the charge transport for both charge carriers is shown to be anisotropic. The anisotropy of the oxygen ion conduction can indeed be explained by the layered structure of the oxygen sublattice of BIO. The anisotropic proton conduction, however, further supports the suggested ordering of the protonic defects in the material. The differences in proton conduction along different crystallographic directions attributed to proton ordering in BIO are of a similar extent as those observed along different crystallographic directions in materials where proton ordering is not present but where protons find preferential conduction pathways through chainlike or layered structures.

The size of the band gap and the energy position of the band edges make several oxynitride semiconductors promising candidates for efficient hydrogen and oxygen production under solar light illumination. The intense research efforts dedicated to oxynitride materials have unveiled the majority of their most important properties. However, two crucial aspects have received much less attention. One is the critical issue of the compositional/structural surface modifications occurring during operation and how these affect the photoelectrochemical performance. The second concerns the relation between the electrochemical response and the crystallographic surface orientation of the oxynitride semiconductor. These are indeed topics of fundamental importance since it is exactly at the surface where the visible light-driven electrochemical reaction takes place. In contrast to conventional powder samples, thin films represent the best model system for these investigations. This study reviews current state-of-the-art of oxynitride thin film fabrication and characterization before focusing on LaTiO2N selected as representative photocatalyst. We report the investigation of the initial physicochemical evolution of the surface. Then we show that, after stabilization, the absorbed photon-to-current conversion efficiency of epitaxial thin films can differ by about 50% for different crystallographic surface orientations and be up to 5 times larger than for polycrystalline samples.

We performed a comparative study on the photoelectrochemical performance of LaTaON

The nitrogen substitution into the oxygen sites of several oxide materials leads to a reduction of the band gap to the visible-light energy range, which makes these oxynitride semiconductors potential photocatalysts for efficient solar water splitting. Oxynitrides typically show a different crystal structure compared to the pristine oxide material. As the band gap is correlated to both the chemical composition and the crystal structure, it is not trivial to distinguish which modifications of the electronic structure induced by the nitrogen substitution are related to compositional and/or structural effects. Here, X-ray emission and absorption spectroscopy are used to investigate the electronic structures of orthorhombic perovskite LaTiO

The CRESST experiment in its first phase is using sapphire detectors with tungsten phase transition thermometers to search for dark matter WIMPs. At present Four 262 g detectors are performing first measurements under low background conditions. Detector performance as well as preliminary results from the background runs are presented. A second phase of CRESST using CaWO4 and simultaneous measurement of phonons and scintillation light is in preparation. (C) 2000 Elsevier Science B.V. All rights reserved.

BaZr0.8 − xPrxY0.2O3 − δ (BZPYx, 0.1 ≤ x ≤ 0.4) perovskite oxides were investigated for application as cathode materials for intermediate temperature solid oxide fuel cells based on proton conducting electrolytes (protonic-SOFCs). The BZPYx reactivity with CO2 and water vapor was evaluated by thermogravimetric and X-ray diffraction analyses, and good chemical stability was observed for each BZPYx composition. Conductivity measurements of BZPYx sintered pellets were performed as a function of temperature and pO2 in humidified atmospheres, corresponding to cathode operating condition in protonic-SOFCs. Different conductivity values and activation energies were measured depending on the Pr content, suggesting the presence of different charge carriers. For all the compositions, the partial electronic conductivity, calculated from conductivity measurements at different pO2, increased with increasing the temperature from 500 to 700 °C. Furthermore, the larger the Pr content, the larger the electronic conductivity. BaZr0.7Pr0.1Y0.2O3 − δ and BaZr0.4Pr0.4Y0.2O3 − δ showed mostly pure proton and electron conductivity, respectively, whereas the intermediate compositions showed mixed proton/electronic conductivity. Among the two mixed proton/electronic conductors, BaZr0.6Pr0.3Y0.2O3 − δ presented the larger conductivity, which coupled with its good chemical stability, makes this perovskite oxide a candidate cathode materials for protonic-SOFCs.

The need for reducing the solid oxide fuel cell (SOFC) operating temperature below 600 °C is imposed by cost reduction, which is essential for widespread SOFC use, but might also disclose new applications. To this aim, high-temperature proton-conducting (HTPC) oxides have gained widespread interest as electrolyte materials alternative to oxygen-ion conductors. This Progress Report describes recent developments in electrolyte, anode, and cathode materials for protonic SOFCs, addressing the issue of chemical stability, processability, and good power performance below 600 °C. Different fabrication methods are reported for anode-supported SOFCs, obtained using state-of-the-art, chemically stable proton-conducting electrolyte films. Recent findings show significant improvements in the power density output of cells based on doped barium zirconate electrolytes, pointing out towards the feasibility of the next generation of protonic SOFCs, including a good potential for the development of miniaturized SOFCs as portable power supplies.