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Apgar B.A.,University of Illinois at Urbana - Champaign | Martin L.W.,International Institute for Carbon Neutral Energy Research
Crystal Growth and Design | Year: 2014

We explore the evolution of epitaxial TiO2 films on a wide range of (001)-oriented perovskite substrates. We observe epitaxial stabilization of anatase to >150 °C above the bulk anatase-to-rutile transition temperature for films grown on substrates with -2.0% to 6.0% lattice mismatch. Continuum elastic models are used to calculate the strain energy density and to construct a model for the preferred epitaxial orientation of anatase. This model is consistent with experimental observations that the strain energy density dominates and leads to the stabilization of 00l- and h00-oriented anatase below and above lattice mismatch values of 5%, respectively. Additionally, TiO 2 nanocrystallite size is found to decrease with lattice mismatch and is discussed in terms of energy competition and possible changes in the nucleation and growth process. To further probe the competition between bulk free, surface, interface, and strain energies in metastable (kinetically limited) as-grown TiO2 films, ex post facto annealing was completed to assess the equilibrium state of the films. These studies confirm the continuum elastic model and highlight the relative importance of the different energies. We then implement our understanding of energy competition to deterministically increase surface area and enhance light absorption via in situ growth processes and ex post facto annealing. © 2014 American Chemical Society.

Wilson R.B.,Urbana University | Apgar B.A.,Urbana University | Apgar B.A.,University of California at Berkeley | Apgar B.A.,International Institute for Carbon Neutral Energy Research | And 6 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

We report the results of time-domain thermoreflectance (TDTR) measurements of two strongly bonded metal-oxide systems with unusually large thermal conductances. We find that TDTR data for the epitaxial SrRuO3/SrTiO3 interface is consistent with an interface conductance G>0.8GWm-2K-1. For an Al/MgO interface at a pressure of 60 GPa, we find G≈1.1GWm-2K-1. Both are within 40% of the maximum possible conductance for these systems, as predicted by simple theory. © 2015 American Physical Society.

Oishi J.,University of Tokyo | Otomo J.,University of Tokyo | Oshima Y.,University of Tokyo | Koyama M.,Kyushu University | And 2 more authors.
Journal of Power Sources | Year: 2015

It is known that the minor elements affect the performance of solid oxide fuel cell (SOFC). In this study, we focus on the influence of minor elements on the SOFC cathode properties. The Ca, Ba, Al, and Si, which originate from raw materials and production processes for SOFC cathodes, are investigated as minor elements that may have effect on the properties of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode. To examine the effects of minor elements on the cathode properties, Ca, Ba, Al, and Si with a controlled concentration are added to the LSCF reference sample. Conductivity relaxation measurements are conducted to determine the chemical diffusion coefficient (Dchem) and surface exchange coefficient (ktr), which governs the overpotential characteristics of the LSCF cathode. The results show that Al and Si have negative effects on both Dchem and ktr while Ca and Ba do not alter Dchem and show weakly positive effects on ktr. The effects of Ca and Ba for the cathode properties are discussed on the basis of XPS measurements. © 2014 Elsevier B.V. All rights reserved.

Zapata J.,Catalan Institute of Nanoscience and Nanotechnology | Burriel M.,Imperial College London | Garcia P.,Catalan Institute of Nanoscience and Nanotechnology | Kilner J.A.,Imperial College London | And 2 more authors.
Journal of Materials Chemistry A | Year: 2013

The layered structure of the orthorhombic GdBaCo2O 5+δ (GBCO) double perovskite compound, currently considered as a promising cathode material in Solid Oxide Fuel Cells (SOFCs), is believed to induce a high degree of anisotropy in the oxygen diffusion coefficient, being maximum along the a-b plane in comparison to the diffusion along the c-axis direction. In this study we have deposited films with different orientation: pure c-axis and a-axis orientation on SrTiO3(001) and NdGaO 3(110) single crystals, respectively. The oxygen diffusion was analysed by isotopic 18O exchange depth profiling (IEDP) and Time-of-flight Secondary Ion Mass Spectrometry (ToF-SIMS) in the films along the longitudinal and transverse directions at different exchange temperatures and exposure times. The magnitude of longitudinal D* at low temperatures shows a clear anisotropy. The oxygen diffusion along the a-axis shows comparable values to the bulk polycrystalline GBCO, while it is about one order of magnitude lower along the c-axis of the structure. The corresponding oxygen surface exchange rates k* do not show any anisotropy having comparable values for c-axis and a-axis orientation. These k* values are slightly larger than those reported for bulk material showing that thin film textured cathodes may have enhanced activity for oxygen reduction at low temperatures. This journal is © The Royal Society of Chemistry 2013.

Otsu T.,Kurume National College of Technology | Tanaka H.,Kyushu University | Sugimura J.,International Institute for Carbon Neutral Energy Research
Toraibarojisuto/Journal of Japanese Society of Tribologists | Year: 2014

This paper describes the effect of surrounding temperature on the behavior of cavitation formed in lubrication film. Point contact sliding tests were conducted in the vacuum chamber in which surrounding temperature and gas were controlled. Temperatures used in this study were in the range between 295 K and 350 K, and gases used were helium, argon, carbon dioxide and air. Two stage cavity growths, i.e. initial stage and second stage as reported in previous report, was found at elevated temperature. Although cavity length was not changed by temperature at initial time after its generation, the cavity length at higher temperature was longer than that at lower temperature in the second stage. Cavity growth in the second stage is affected by gas solubility; cavity length in temperature with higher gas solubility is longer. These results suggest that cavity growth in initial stage is related with rapid evolution of negative pressure at outlet of conjunction and that in second stage is related with gradual release of dissolved gas into cavity.

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