Towards the Rational Design of Materials Exhibiting Colossal Metal-Insulator Transitions

非技术性概述很少有物质的物理性质在不同材料之间表现出像电导率那样大的变化。材料可以是绝缘体、半导体和金属，事实上，不同材料携带电荷的独特能力支撑着现代技术的大多数方面。一类相对罕见的材料包括响应于所施加的外部刺激（例如温度升高、电压施加、光源照射或经受拉伸应变）而突然从绝缘体转变为金属的固体。更罕见的是，材料在接近室温的温度下经历了如此戏剧性的性质转变。在材料研究部门的固态和材料化学计划的支持下，该项目的重点是破译这些突然转变中原子结构和化学键的变化，以期合理设计材料，这些材料可以被诱导以响应外部刺激而在许多数量级上切换其导电性。该活性利用了过渡金属氧化物的结构多样性，这是一类可以精细控制化学组成和原子结构精确细节的材料。该项目预计将大大扩展现有材料的库，这些材料在接近室温的温度下显示出与技术相关的可切换性，同时还涉及与此类固体中电子之间相互作用相关的基础科学。首席研究员专注于让从社区学院转学的学生在大学生涯的早期参与研究，以更好地利用这个经常被忽视的人才库。最后，该项目正在开发启发性材料，让小学生体验纳米科学的技术可能性。技术概要该项目的重点是金属-绝缘体转变的有趣现象，即材料的导电性会随着温度、压力、电压、光激发或化学成分的变化而突然从绝缘状态转变为金属状态。电导率的这种突然不连续的变化源于材料中局部价电子向巡回电子的转变，并且通常由电子-电子相互作用支撑。理解和调整电子相关性仍然是物理科学的重大挑战之一。 研究活动的基本前提是，原子间的距离，电荷有序图案，和掺杂剂的比例可以精确地调制在复杂的过渡金属氧化物通过嵌入阳离子的大小，电荷，化学计量和极化率的变化的想法。该活动涵盖复杂氧化物的化学合成，精确控制组成和结构，结构和组成特征与金属-绝缘体转变的相关性，应用衍射和光谱工具来探测这些转变的机理基础，以及通过定义嵌入梯度来调制转变。一项夏季研究活动将吸引从社区学院转到德克萨斯州A M的本科生。将在公共科学活动中开发和传播以纳米科学为重点并旨在激励小学生的图形小说。

Non-Technical SummaryThere are few physical properties of matter that show as much variation across different materials as electrical conductivity. Materials can be insulators, semiconductors, and metals, and indeed the distinctive abilities of different materials to carry electronic charge underpin most aspects of modern technology. A relatively rare class of materials comprises solids that abruptly switch from being insulators to metals in response to an applied external stimulus such as an increase in temperature, application of a voltage, illumination with a light source, or being subjected to a tensile strain. Rarer still are materials that undergo such dramatic switching of properties close to room temperature. With support from the Solid State and Materials Chemistry program in the Division of Materials Research, this project focuses on deciphering the changes in atomic structure and chemical bonding across these abrupt transformations with a view towards rationally designing materials that can be induced to switch their conductivity across many orders of magnitude in response to external stimuli. The activity takes advantage of the structural versatility of transition metal oxides, a class of materials where the chemical composition and the precise details of the atomic structure can be finely controlled. The project is anticipated to greatly expand the available repertoire of materials that show such technologically relevant switchability of properties close to room temperature while also addressing fundamental science related to the interaction between electrons in such solids. The principal investigator is focused on engaging students transferring from community colleges in research early on in their college careers to better tap into this often overlooked talent pool. Finally, the project is developing inspirational material to provide elementary school students a flavor of the technological possibilities of nanoscience.Technical SummaryThe project is focused on the intriguing phenomenon of metal-insulator transitions wherein the electrical conductivity of a material abruptly switches from insulating to metallic behavior in response to temperature, pressure, voltage, photo-excitation, or change in chemical composition. Such an abruptly discontinuous change in electrical conductivity arises from the transformation of localized valence electrons to itinerant electrons in the material, and is often underpinned by electron-electron interactions. Understanding and tuning electron correlation remains one of the grand challenges of the physical sciences. The fundamental premise of the research activity is the idea that inter-atomic distances, charge-ordering motifs, and dopant ratios can be precisely modulated in complex transition metal oxides through variation of the size, charge, stoichiometry, and polarizability of intercalating cations. The activity spans chemical synthesis of complex oxides with precise control of composition and structure, correlation of structural and compositional characteristics to metal-insulator transitions, the application of diffraction and spectroscopic tools to probe the mechanistic basis for these transitions, and modulation of the transitions by defining intercalation gradients. A summer research activity will engage undergraduates transferring to Texas A&M from community colleges. Graphical novels focused on nanoscience and designed to motivate elementary school students will be developed and disseminated at public science events.