Dynamical Localization in High Temperature Crystals as Measured by Inelastic Neutron Scattering

*非技术摘要*一个重要的科学概念是能量或热和功的等效性；这是工业革命的核心概念。目前，太阳辐射可以通过技术手段转化为多种形式的能源；但是，要使以这种方式产生的能量对我们的国家能源供应做出经济贡献，需要了解材料的长期稳定性，特别是那些在高温下的材料。康奈尔-劳伦斯-利弗莫尔国家实验室合作在高温下对一种盐晶体进行的初步中子散射实验发现了晶体中意想不到的能量局部化或热点。这些发现表明，这种简单的离子晶格具有高温复杂性，并表明需要对真实材料中原子之间的能量分配和传输方式有新的理解。这一个人研究计划将利用位于各种国家设施的复杂测量工具，以系统的方式检查和表征高温晶体中的热点行为。关于这种材料固有缺陷的知识可能最终会影响高温材料的科学。研究生和本科生都将发展适合这个新的交叉学科领域的研究方法和各种实验技术的专业知识。凝聚态科学和非线性动力学中一个长期存在的问题是，依赖于非线性和晶格离散的本征定域振动模(ILM)是否可以出现在热平衡的三维原子晶格中，这种振动模已经在宏观的一维晶格中得到了详细的探索。康奈尔-劳伦斯-利弗莫尔国家实验室合作的利用晶体固体的非弹性中子散射的初步实验已经确定，具有明确定义的离散能量的动态局域化是高温晶格动力学的一个新的、必要的组成部分。由于高温材料现在似乎是动态局域化的自然环境，而且这种激发是材料中的局部热点，它们代表了材料的本征缺陷，可能会影响高温扩散，并最终影响材料的强度。这一个人研究人员奖支持一个项目，用非弹性中子散射测量高温下晶体中出现的振动局部化。该项目的一个目标是了解各种高温晶体中ILM的性质和后果。该实验计划将涉及一名博士后、一名研究生和本科生，并将采用一套位于国家设施中的散射测量技术，从散裂源中子散射到反应堆源热中子散射，以扩大关于介质晶体中此类激发的知识。

****NON-TECHNICAL ABSTRACT****An important scientific idea is that of energy or the equivalence of heat and work; a concept central to the industrial revolution. At present solar radiation can be converted to many forms of energy by means of technology; but, to make energy produced this way an economical contribution to our national energy supply requires understanding the long-term stability of materials, especially those at high temperatures. Preliminary neutron scattering experiments on a crystal of salt at high temperatures by the Cornell-Lawrence Livermore National Laboratory collaboration have identified unexpected energy localization or hot spots in the crystal. These findings indicate a high temperature complexity for such a simple ionic lattice and point to the need for new understanding about the way energy is distributed and transported amongst atoms in real materials. This individual investigator program will make use of sophisticated measurement tools located at a variety of national facilities to examine and characterize in a systematic manner the hot spot behavior in high temperature crystals. The knowledge about such intrinsic material defects may be expected to ultimately impact the science of high temperature materials. Both graduate and undergraduate students will develop expertise in research methods and a variety of experimental techniques appropriate to this new interdisciplinary field.****TECHNICAL ABSTRACT****A long standing question in condensed-matter sciences and nonlinear dynamics is whether or not intrinsic localized vibrational modes (ILMs), which rely on nonlinearity and lattice discreteness and which have been explored in detail in macroscopic 1-D lattices, can appear in a 3-D atomic lattice in thermal equilibrium. Preliminary experiments using inelastic neutron scattering from crystalline solids by the Cornell-Lawrence Livermore National Laboratory collaboration have identified dynamical localization with well-defined discrete energies as a new, necessary component of high temperature lattice dynamics. Since high temperature materials now appear to be a natural habitat for dynamical localization and since such excitations are localized hot spots in the material they represent intrinsic material defects that may be expected to influence high temperature diffusion and ultimately the strength of materials. This individual investigator award supports a project to measure, with inelastic neutron scattering, the vibrational localization that appears in crystals at high temperatures. A goal of the project is to understand the properties and ramifications of ILMs in a variety of high temperature crystals. The experimental program will involve a postdoc, a graduate and undergraduate students, and will employ a suite of scattering measurement techniques located at national facilities, ranging from spallation source neutron scattering to reactor source thermal neutron scattering, to expand the knowledge about such excitations in dielectric crystals.