High-Pressure Synthesis and Physical Properties of New Perovskite Oxides with Stretched Bonding

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TechnicalThis project aims to systematically investigate unusual physical properties encountered at the crossover from localized to itinerant electronic behavior in AMO3 perovskites having only p-bonding 3d or 4d electrons at the M atoms with/without a t-orbital degeneracy. Particular emphasis is placed on perovskites that have a stretched M-O bond as a result of large A-site cations. Almost all these oxides require high-pressure synthesis. We will also use the high-pressure variable to fine-tune physical properties at the crossover and at orbital or charge order/disorder transitions where quantum critical-point behavior is found at lower temperatures. Broader impacts include up-grading our high-pressure apparatus to a capacity of 250 kbar, which will allow solution of several critical fundamental problems for material design. Students will be given hands-on training in high-pressure techniques, and a text book for young scientists and researchers in related disciplines will be undertaken to up-date a broad audience on recent advances in our understanding of the structural, magnetic, and transport (electronic and ionic) properties of transition-metal compounds.Non-technicalThis proposal uses high-pressure techniques to clarify the character and evolution of unusual physical properties that are encountered at critical crossovers from magnet-insulator to metallic behavior and at charge or orbital order-disorder transitions in transition-metal compounds. It would also use high pressure to synthesize materials with stretched chemical bonds, a phenomenon associated with technically important dielectric and ferroelectric behavior where the d orbtials are empty, but unexplored where they are occupied. Typical of the unusual physical properties that are encountered at magnetic-insulator to metal transitions, for example, are the high-temperature superconductivity of some copper oxides and the colossal magnetoresistance phenomenon found in some manganese and cobalt oxides. The broader impact of the work includes an up-grading of our high-pressure capacity to 250 GPa, which will allow us to explore the properties of materials in the interior of the earth as well as to add new capability in the materials science research. In addition, clarification of the origins of the unusual physical properties under study will allow design of materials exhibiting new properties of technical interest. The work will also train students in high-pressure techniques. Writing of a textbook for younger scientist and researchers in related fields will be undertaken.