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

Princeton University, Princeton NJ

Investigators

Abstract

TECHNICAL SUMMARY Transition 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 SUMMARY Discovering 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.