High-Pressure Synthesis and Physical Properties of New Oxides with Perovskite or Perovskite-Related Structure

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DMR 0904282High-pressure synthesis and physical properties of new oxides with perovskite or perovskite-related structureTECHNICAL SUMMARY:Unquenched orbital angular momentum in the 4d and 5d transition-metal oxides with the perovskite or the perovskite-related structure leads to a new type of Mott insulator and anomalous metallic phases. Their exotic physical properties due to strong spin-orbit coupling have attracted broad attention in recent years. The A-site cation in these perovskites does not contribute directly to the electronic states near the Fermi energy. However, as shown in high-Tc cuprates and the magnetoresistive manganites, superconductive transition temperature, the magnetic transition temperature, and the magnetization are highly sensitive to the A-cation disorder as well as the mean A-cation size. The A-cation effect on the physical properties of the 4d and 5d transition-metal oxides has not been studied systematically. Introduction of A-cation size variance and the change of mean A-cation size in a wide range is normally limited by the geometric tolerance factor at ambient pressure. A complete study of this subject requires synthesis at pressures as high as P ~ 20 GPa in some cases. The high-pressure synthesis with a large volume at P 20 GPa has been developed in the field of geoscience to study the earth?s lower mantle. However, it remains essentially a virgin field to apply pressure over 10 GPa in a broad range of solid-state synthesis. This funding will allow the PIs not only to address key factors determining physical properties in the 4d and 5d metal oxides with unquenched orbital angular momentum, but also to explore systematically solid-state synthesis under pressure to 20 GPa. NON-TECHINICAL SUMMARY:Perovskite oxides are technically important materials that are widely used in the microelectronic industry, in chemical plants as catalysts, and in solid-state fuel cells as both electrolyte and electrodes. The basic research outlined in this project will lead to a better understanding of perovskite oxides, which in turn benefits greatly their application. What is unique about the PIs? laboratory is that they have established several sophisticated instruments for material synthesis, characterization, and measurements and they have a long history of emphasis on the relationship between crystal structures, chemistry, their physical properties, and their engineering application. Experimental results are compared directly with theoretical calculations. The PIs emphasize high-pressure synthesis and crystal growth in the project. These characteristics have attracted scholars around the world to the laboratory. Students, post-docs, and visiting scholars with diversified backgrounds of materials science, chemistry and physics have a chance to interact with each other and to develop their own strategy of material research while working on the project. Visiting researchers have also brought with their specialties developed in their home laboratories. All these factors create a very rich environment for learning and research. In this project, the PIs also collaborate with scientists in Spain, Japan, China and Canada.