Novel Vibrational Modes and Thermal Properties in Systems with Large, Open Unit Cells

这个个人研究者奖是颁给加州大学圣克鲁斯分校的一位资深教授。该项目涉及对具有大型开放式单元格的系统进行一系列局部结构（XAFS）测量。这些材料具有丰富的振动运动，其中许多在简单结构中是观察不到的。特别是，可以有大量的低能光学声子模式，其中一些涉及近刚性原子的旋转。这种刚性单元振动模式解释了ZrW2O8和其他开放结构的新型负热膨胀系数。另一种开放结构材料是部分填充的角钼矿化合物。在这种情况下，稀土原子可以被纳入到单元电池的空隙中，并强烈地抑制热导率。XAFS测量将澄清所提出的结构模型是否正确，并为开发更好的热电化合物和低热膨胀材料提供基础。这项工作将为研究生和本科生提供在PI下作为一个团队工作的教育机会。学生将获得在国家机构工作的经验，并在家乡UCSC学习实验设计和数据分析。许多复杂的材料，在晶体结构中含有开放空间，表现出不同寻常的热性能。它们对各种实际应用具有潜在的重要意义，包括更好的热电冷却器和冷却时不收缩的材料。这些材料中的空隙允许原子以新的方式振动，许多不寻常的和增强的热性能都归因于这种运动。在一组材料中，原子团被认为几乎作为一个单位振动；在另一些研究中，有人提出，每个添加的杂质原子都在结构的空隙中“摇来摇去”。这是授予加州大学圣克鲁斯分校一位资深教授的个人研究者奖，以资助对这些类型的运动进行详细的实验测量，这对了解这些不寻常的热特性至关重要。这项工作将为研究生和本科生提供在PI下作为一个团队工作的教育机会。学生将获得在国家机构工作的经验，并在家乡UCSC学习实验设计和数据分析。* * *

This individual investigator award is to a senior professor at the University of California in Santa Cruz. The project involves a series of local structure (XAFS) measurements on systems whichhave large, open unit cells. Such materials have a rich array of vibrational motions, many of which are not observed in simple structures. In particular, there can be a large number of low energy optical phonon modes, some of which involve rotations of nearly rigid atomic. Such rigid unit vibrational modes have been proposed explain the novel negative thermal expansion coefficient of ZrW2O8 and other open structures. Another set of open structure materials are the partially filled skutterudite compounds. Here rare earth atoms can be incorporated into a void in the unit cell and strongly suppress the thermal conductivity. The XAFS measurements will clarify whether the proposed structural models are correct and provide a basis for developing better thermoelectric compounds and low thermal expansion materials. The work will provide educational opportunities for both graduate and undergraduate students to work as a team under the PI. Students will gain experience working at a national facility as well as learn experimental design and data analysis at the home institution, UCSC. %%%A number of complex materials, containing open spaces within the crystal structure, exhibit unusual thermal properties. They are potentially important for a variety of practical applications, including better thermoelectric coolers and materials that do not shrink when cooled.The voids in such materials allow the atoms to vibrate in new ways and many of the unusual and enhanced thermal properties are attributed to such motions. In one set of materials, clusters of atoms are thought to vibrate nearly as a single unit; in others it has been proposed thateach added impurity atom "rattles around" inside a void in the structure. This is an individual investigator award to a senior professor at the University of California at Santa Cruz to fund the detailed experimental measurements of these types of motion crucial for developing an understanding of these unusual thermal properties. The work will provide educational opportunities for both graduate and undergraduate students to work as a team under the PI. Students will gain experience working at a national facility as well as learn experimental design and data analysis at the home institution, UCSC. ***