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

技术综述过渡金属氧化物继续给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带来巨大的挑战。这些挑战的出现是由于氧化物中d电子之间往往存在非常强的相互作用，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近能量等效力之间微妙平衡的结果；化合物的电子、磁性和结构特征往往以复杂、微妙和令人惊讶的方式相互作用。这一固态和材料化学支持计划直接解决了导致一些过渡金属氧化物表现出局域电子行为和局域磁矩的关键因素，而另一些非常类似的过渡金属氧化物表现出巡回电子行为和非磁性或奇异的磁性状态。特别令人感兴趣的将是4d和5d族中基于过渡金属的氧化物，其中磁性不像更频繁研究的3D化合物中那样常见。这项研究集中在Ru、Ir和Re基氧化物的发现和表征上，这些氧化物有望跨越局部电子行为和巡回电子行为之间的边界。这些特殊的材料允许从不同的角度解决这些不同行为之间的平衡：例如，Ruthenate通常是金属导体，带有巡回电子，尽管有时会显示局域电子态，而Irate和Rhenate更倾向于局域行为，尽管5d轨道名义上更长，预计会形成巡回电子态。非技术总结发现新材料并确定它们的物理性能是科学和工程链中的关键一环，这导致了新技术的引入，这些新技术极大地提高了我们的生活质量，从消费电子产品、计算机和通信系统到医学成像和诊断系统。这些材料现在每天都在这些技术中使用，是通过几十年的基础和应用研究开发出来的，固体和材料化学家发挥了主导作用。我们目前的许多技术，以及许多为未来提出的技术，都是基于过渡元素的化合物--位于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，如高温超导、材料的巨大响应--对外加磁场的阻力，以及在温度梯度中产生大电流--表明，科学界对此类化合物的理解令人惊讶地糟糕。这个固态和材料化学支持计划直接解决了我们在理解过渡金属基材料方面的不足之一--是什么关键因素导致这些材料中的一些具有磁性，而其他非常相似的材料则不是？这将通过研究跨越磁性和非磁性之间的几类过渡金属氧化物来实现。参与该项目的研究生和本科生将接受培训，成为技术应用材料这一关键领域的未来研究人员，这是一项前瞻性的美国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，PI将继续他与中小学生的工作，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.