New Transition Metal Oxides Near Localized-Itinerant, Insulator-Metal Transitions

在复杂的铜氧化物中高温超导性的发现使人们普遍认识到过渡金属氧化物的化学、晶体结构、电子和磁性之间的关系还只是粗略的认识。由于d电子之间存在强相互作用，以及电子，磁自旋和底层原子晶格之间存在相互作用，通常基于能带结构的图像（例如，不包括电子-电子相关的影响）通常不能正确描述观察到的电子和磁性。这个固态化学研究项目的目标是发现新的复合氧化物，它们具有奇异的电子和磁性，因为它们接近绝缘体-金属的转变。详细地考虑了两类化合物。研究项目包括：(1)发现和表征新的三元和季系氧化钌、氧化卤化物和相关化合物。总的来说，以往的研究强烈表明，钌和氧是元素周期表上的一对原子之一，由于金属-氧键的特征和三元化合物形成时出现的晶体结构类型而导致其不寻常的物理性质。(2)低维铜氧阵列新型氧化铜超导体及相关材料的发现。该程序寻找在高氧压力下合成的新型铜基氧化物，其中铜-氧平面不具有通常的Cu02棋盘状几何形状。人们正在寻找新的材料，其中CuO的几何结构在电子上比Cu02平面“更简单”。这些材料的特性将允许与量子力学自旋系统行为模型的预测进行直接比较，这是一个激烈的理论活动领域，许多人认为这可能是高温超导微观机制的关键。今天的许多技术系统都是基于使用复杂的电子材料。随着这些系统复杂性的增加，它们所基于的材料类型也增加了复杂性。本项目使用固态化学的方法，在我们对固体的化学、晶体结构、电子和磁性之间的基本关系的理解的边界上寻找新的材料。将研究两种有前途的过渡金属氧化物，希望获得的见解最终有助于确定凝聚态科学和电子技术的未来方向。＊＊＊

9725979 Cava The discovery of high temperature superconductivity in complex copper oxides led to the widespread realization that the relationships between the chemistry, crystal structure, and electronic and magnetic properties of transition metal oxides was understood at only a cursory level. Due to the presence of strong interactions between the d electrons, and the interactions between the electrons, magnetic spins, and the underlying atomic lattice, the usual band structure based picture (which, for example, does not include the effects of electronelectron correlations) often can not properly describe the observed electronic and magnetic properties. This research program in solid state chemistry has the goal of discovering new complex oxides with exotic electronic and magnetic properties due to their proximity to insulator-metal transitions. Two classes of chemical compounds are considered in detail. The research program consists of: (1) The discovery and characterization of new ternary and quaternary ruthenium oxides, oxyhalides, and related compounds. Taken as a whole, previous studies strongly suggest that ruthenium and oxygen represent one of the pairs of atoms in the periodic table for which unusual physical properties result due to the characteristics of the metal-oxygen bond and the types of crystal structures which occur when compounds with ternary elements are formed. (2) The discovery of new copper oxide superconductors and related materials with low-dimensional copper- oxygen arrays. This program searches for new copper based oxides synthesized at high oxygen pressures, in which the copper-oxygen plane does not have the usual Cu02 checkerboard geometry. New materials are sought in which the CuO geometry is electronically "simpler" than the Cu02 plane. The characterization of these materials will allow direct comparison to the predictions of models for the behavior of quantum mechanical spin systems, an area of intense theoretical activity, whic h many believe may hold the key to the microscopic mechanism of high temperature superconductivity . %%% Many of today's technological systems are based on the use of sophisticated electronic materials. As those systems increase in complexity, the types of materials they are based on also increase in complexity. This project uses the methods of solid state chemistry in the search for new materials at the borders of our understanding of the fundamental relationships between the chemistry, crystalline structure, and electronic and magnetic properties of solids. Two promising classes of transition metal oxides will be studied, with the hope that the insight gained will ultimately help define the future directions of both condensed matter science and electronics technology. ***