4d and 5d Oxides at the Border between Localized and Itenerant Electronic Behavior

过渡金属氧化物继续对我们理解复杂固体中化学、晶体结构和物理性质之间的关系提出了巨大的挑战。这些挑战是由于氧化物中d电子之间的相互作用通常非常强，这种相互作用仍然很难或不可能通过理论模型来处理。此外，所发现的电子态和晶体结构往往是几乎能量相等的力之间微妙平衡的结果；化合物的电子、磁性和结构特征经常以复杂、微妙和令人惊讶的方式相互作用。这个固态和材料化学支持的项目直接解决了导致一些过渡金属氧化物显示局部电子行为和局部矩磁性的关键因素，而其他的，非常相似，显示流动电子行为和非磁性或外来磁性状态。特别感兴趣的将是基于4d和5d族过渡金属的氧化物，在这些氧化物中，磁性不像在更频繁研究的3d化合物中那样常见。该研究集中于钌、铱和铼基氧化物的发现和表征，这些氧化物有望跨越局部和巡回电子行为之间的边界。这些特殊的材料可以从不同的角度解决这些不同行为之间的平衡：例如，钌酸盐通常是金属导体，具有流动的电子，尽管有时显示局部电子状态，而铱酸盐和铼酸盐更倾向于局部行为，尽管5d轨道名义上更延伸，预计会形成流动的电子状态。发现新材料并确定其物理特性是科学和工程链中的一个关键环节，它导致引入新技术，大大提高我们的生活质量，从消费电子产品，计算和通信系统到医疗成像和诊断系统。现在这些技术中日常使用的材料是经过数十年的基础和应用研究开发出来的，其中固态和材料化学家发挥了主导作用。我们目前的许多技术，以及未来的许多技术，都是基于过渡元素的化合物——元素周期表中心的金属元素。最近在过渡金属氧化物方面的革命性科学发现，如高温下的超导性，材料的巨大响应-对外加磁场的抵抗力，以及在温度梯度中产生大电流，都表明科学界对这些化合物的理解令人惊讶地贫乏。这个固态和材料化学支持的项目直接解决了我们对过渡金属基材料理解中的一个不足之处——是什么关键因素导致一些材料具有磁性，而另一些材料非常相似，却没有磁性？这将通过研究几类介于磁性和非磁性之间的过渡金属氧化物来实现。参与该项目的研究生和本科生将被训练成为技术应用材料关键领域的未来研究人员，这是美国前瞻性行业广泛寻求的技能。除了技术成果和直接的本科生和研究生教育和培训外，PI将继续与中小学生一起工作，帮助促进学生进入科学管道，并将积极鼓励妇女和少数民族参与该项目。

TECHNICAL SUMMARYTransition metal oxides continue to pose great challenges to our understanding of the relationships among chemistry, crystal structure, and physical properties in complex solids. These challenges arise due to the often very strong interactions between d electrons in oxides, an interaction that continues to be difficult or impossible to treat by theoretical models. In addition, the electronic states and crystal structures that are found are often a consequence of delicate balances between nearly energetically equivalent forces; the electronic, magnetic, and structural characteristics of the compounds often interact in complex, subtle, and surprising ways. This Solid State and Materials Chemistry supported program directly addresses the critical factors that cause some transition metal oxides to display localized electron behavior and local moment magnetism, while others, quite similar, display itinerant electron behavior and non-magnetic or exotic magnetic states. Of particular interest will be oxides based on transition metals in the 4d and 5d family, where magnetism is not as commonly encountered as in the more frequently studied 3d compounds. The research concentrates on the discovery and characterization of ruthenium, iridium and rhenium-based oxides that are expected to straddle the border between localized and itinerant electronic behavior. These particular materials allow addressing the balance between these different behaviors from different perspectives: ruthenates for example are very often metallic conductors, with itinerant electrons, though sometimes displaying localized electronic states, while iridates and rhenates tend more toward localized behavior in spite of the fact that 5d orbitals are nominally more extended and expected to form itinerant electronic states. NON-TECHNICAL SUMMARYDiscovering new materials and determining what their physical properties are is a critical link in the scientific and engineering chain, which leads to the introduction of new technologies that greatly enhance our quality of life, ranging from consumer electronics, computing, and communications systems to systems for medical imaging and diagnosis. The materials, now daily used in these technologies were developed through decades of basic and applied research, with solid state and materials chemists taking a leading role. Many of our current technologies, and many of those proposed for the future, are based on chemical compounds of the transition elements - the metallic elements at the center of the periodic table. Revolutionary scientific discoveries in the recent past in oxides of the transition metals, such as superconductivity at high temperatures, giant responses of materials - resistance to applied magnetic fields, and the generation of large currents in temperature gradients, have shown that the scientific communities' understanding of such compounds is surprisingly poor. This Solid State and Materials Chemistry supported program directly addresses one of the deficiencies in our understanding of transition metal based materials - What are the critical factors that cause some of these materials to be magnetic, while others, quite similar, are not? This will be accomplished through the study of several classes of transition metal oxides that straddle the border between magnetism and non-magnetism. Graduate and undergraduate students who work on this project will be trained to become future researchers in the critical area of materials for technological applications, a skill widely sought by forward looking American industries. Beyond the technological results and direct undergraduate and graduate student education and training, the PI will continue his work with primary and secondary school students to help to promote students to enter the science pipeline, and will actively encourage the participation of women and minorities in the project.