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

技术这个项目的目的是系统地研究在AMO_3钙钛矿中从定域电子行为到巡回电子行为的交叉时遇到的不寻常的物理性质，在M原子上只有p-键的3d或4d电子具有/不具有t-轨道简并。特别强调的是钙钛矿由于大的A位阳离子而具有伸展的M-O键。几乎所有这些氧化物都需要高压合成。我们还将使用高压变量来微调交叉和轨道或电荷顺序/无序转变的物理性质，在这些转变中，在较低的温度下发现量子临界点行为。更广泛的影响包括将我们的高压设备升级到250kbar的容量，这将使材料设计的几个关键基本问题得到解决。学生将接受高压技术的实践培训，并将为相关学科的年轻科学家和研究人员编写一本教科书，以使广大读者了解我们对过渡金属化合物的结构、磁性和传输(电子和离子)性质的最新进展。本提案使用高压技术来阐明过渡金属化合物中从磁绝缘体到金属行为的关键交叉以及电荷或轨道有序-无序转变时所遇到的不寻常物理性质的特征和演变。它还将使用高压来合成具有拉伸化学键的材料，这种现象与技术上重要的介电和铁电行为有关，其中d球是空的，但尚未探索它们所在的位置。例如，在磁性绝缘体到金属的转变中遇到的典型的不寻常的物理性质是一些铜氧化物的高温超导以及在一些锰氧化物和钴氧化物中发现的巨大磁阻现象。这项工作的更广泛影响包括将我们的高压能力提升到250 Gpa，这将使我们能够探索地球内部材料的属性，并在材料科学研究中增加新的能力。此外，澄清正在研究的不同寻常的物理性质的起源将使材料能够设计出具有技术价值的新性质。这项工作还将培训学生高压技术。将为相关领域的年轻科学家和研究人员编写教科书。

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.