Novel Strongly Correlated-Electron Materials with Rock-Salt Related Structures

在美国国家科学基金会材料研究部固态和材料化学项目的支持下，拟议的研究重点是具有cdi2型层的过渡金属氧化物AMO2 （A =碱金属，M = 3d金属）。AMO2相表现出各种各样的物理性质，包括几何挫折磁性、自旋、电荷和轨道有序、热电性和非常规超导性。在所有已知的AMO2相中，过渡金属仅处于3+或3+/4+氧化态。β - nafe2o3是已知的唯一具有层状岩盐相关结构和双层过渡金属-氧块的化合物。本研究的主要组成部分是合成、晶体结构和物理性质的研究：(1)具有cdi2型层的新型层状相，M处于独特的低（对于这种相）2+/3+混合价氧化态；(2)新的n = 2和n = 3成员层状岩盐相关同源物。设想实现上述提议目标不仅会产生新颖的强相关电子氧化物，而且还会为制备高度不寻常的相提供新的合成方法，并对相关电子行为产生新的基本见解，从而发现具有潜在有用的热电和/或磁性质的化合物。在一类特殊的金属化合物中，电子-电子相互作用产生了从基础和技术角度看都很重要的各种物理性质。这些所谓的强相关电子材料的性质取决于晶体结构的细节，以及过渡金属的氧化和自旋态。本提案中开发的新合成方法将能够以可预测的方式制备强相关电子材料。对结构-性能关系的研究将提供对相关电子行为的深刻见解，并使能够通过温度梯度将热量转换为电能（热电材料）的新材料以及具有有趣磁性质的化合物的设计原则得以发展。研究生和本科生将接受无机合成、电化学、晶体学、磁学和各种表征技术方面的培训。该PI将领导组织中西部本科生化学研究研讨会。此次研讨会由PI牵头，以本科生到研究生院的过渡为目标，旨在增加国内申请研究生课程的人数。

TECHNICAL SUMMARYWith support from the Solid-State and Materials Chemistry Program in the NSF Division of Materials Research, the proposed research focuses on transition metal oxides AMO2 (A = alkali metal, M = 3d metal) with CdI2-type layers. AMO2 phases demonstrate a large variety of physical properties, including geometrically frustrated magnetism, spin, charge and orbital ordering, thermoelectricity, and nonconventional superconductivity. In all known AMO2 phases, transition metals are only in the 3+ or 3+/4+ oxidation states. Beta-NaFe2O3 is the only known compound with a layered rock-salt related structure and double layer transition metal-oxygen block. The main components of this proposal are synthesis, crystal structure and physical properties investigation: (1) of novel layered phases with CdI2-type layers and M in uniquely low (for such phases) 2+/3+ mixed valent oxidation states and (2) of new n = 2 and n = 3 members of the layered rock-salt related homologue. It is envisioned that implementation of the stated proposal objectives will not only result in novel strongly correlated-electron oxides, but also provide new synthetic methodologies for the preparation of highly unusual phases as well as result in new fundamental insights into correlated-electron behavior, leading to the discovery of compounds with potentially useful thermoelectric and/or magnetic properties. NON-TECHNICAL SUMMARY In a special class of metal compounds electron - electron interaction results in a variety of physical properties important from fundamental and technological points of view. Properties of these so called strongly correlated-electronic materials depend on details of crystal structure, as well as on transition metal oxidation and spin states. New synthetic methodology developed in this proposal will enable preparation of strongly correlated-electronic materials in a predictable way. Investigation of structure-property relationships will provide deep insights into correlated-electron behavior and enable development of design principles for new materials capable of converting heat via a temperature gradient into electric energy (thermoelectric materials), as well as compounds with interesting magnetic properties. Graduate and undergraduate students will be trained in the areas of inorganic synthesis, electrochemistry, crystallography, magnetism, and various characterization techniques. The PI will lead the organization of the Midwestern Symposium on Undergraduate Research in Chemistry. This symposium, spearheaded by the PI targets the undergraduate to graduate school transition and is designed to increase the number of domestic applicants to graduate programs.