NSF-EC Activity: Studies of Defects, Disorder and Phase Transitions via Diffuse Scattering

NSF-EC 活动：通过漫散射研究缺陷、无序和相变

• 批准号: 0099573
• 负责人: Simon Moss
• 金额: $ 31.93万
• 依托单位: University of Houston
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-08-01 至 2004-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0099573&HistoricalAwards=false
• 关键词: NSF; EC; Activity; Studies; Defects

We propose here a joint University of Houston - Max Planck Institute (MPI-Stuttgart) program on the diffuse scattering of X-rays and neutrons from disordered alloys. There are three projects involved: a) The determination of detailed local and long-range static atomic displacements in a dilute random Ge(0.08)Si(0.92) alloy crystal using anomalous X-ray scattering at the ESRF in Grenoble, along with high energy-resolution X-ray or neutron measurements of the optic modes and in-band resonant modes; b) The use of a null matrix 62Ni(0.52)Pt(0.48) crystal (62Ni, which has a negative scattering length, will be supplied by the MPI) to eliminate all Bragg, thermal diffuse and Huang scattering in order to evaluate both the local order and local atomic displacements for comparison with theoretical models for this alloy. A "normal" Ni-Pt crystal will also be used to assess the phonon dispersion curves and Huang scattering. Companion theoretical work on the elastic and electronic interactions will be performed in collaboration with our MPI colleagues; c) Continuation of theoretical work to understand defect influences on phase transitions, in this case the X-ray observation of the conversion of a bulk first-order transition in V2H to a tricritical transition in a defective (dislocation-dominated) "skin" layer. Students will participate in this research.In this program of work we continue our studies of the detailed local structure of alloys - both semiconducting and metallic - through the application of diffuse (i.e. non-Bragg) X-ray and neutron scattering. The underlying physics of alloys depends on the precise nature of the interatomic interactions, both electronic and elastic. These interactions may be directly probed through a combination of scattering data and theoretical modeling, either via simulation or from first principles. The essential issues are the "size" of an atom, i.e. charge transfer, and the way in which the basic electronic structure is manifested in local order, alloy stability and, ultimately, in the prediction of phase diagrams. Statistical mechanics lies at the heart of these problems, as does the influence of defects, such as dislocations, on phase stability and phase transitions. Our scattering program, combined with theoretical modeling, will address these issues in a comprehensive way using synchrotron X-rays and reactor-based neutrons. This research will be conducted with students who will receive training in one of the contemporary forefront areas of condensed matter physics. Through this they will be prepared to enter the scientific/technological workforce of the next few decades.

我们在这里提出了休斯顿大学-马克斯·普朗克研究所(MPI-Stutgart)关于无序合金中X射线和中子的漫射散射的联合计划。它涉及三个项目：a)利用格勒诺布尔ESRF的反常X射线散射，以及光学模式和带内共振模式的高能分辨X射线或中子测量，确定稀散随机Ge(0.08)Si(0.92)合金晶体中详细的局部和远程静态原子位移；B)使用零矩阵62Ni(0.52)Pt(0.48)晶体(62Ni具有负散射长度，将由MPI提供)来消除所有的Bragg、热扩散和黄散射，以便评估局域有序和局域原子位移，以便与该合金的理论模型进行比较。一个“正常的”镍铂晶体也将被用来评估声子色散曲线和黄光散射。关于弹性和电子相互作用的配套理论工作将与我们的MPI同事合作进行；c)继续理论工作以了解缺陷对相变的影响，在这种情况下，X射线观察到V2H中的大块一级相变到缺陷(位错占主导地位的)“皮肤”层中的三临界相变。学生将参与这项研究。在这项工作计划中，我们将继续通过应用漫反射(即非布拉格)X射线和中子散射来研究合金-包括半导体和金属-的详细局部结构。合金的基本物理依赖于原子间相互作用的精确性质，包括电子和弹性相互作用。这些相互作用可以通过散射数据和理论建模的组合直接探测，可以通过模拟或从第一性原理进行。关键问题是原子的“大小”，即电荷转移，以及基本电子结构在局域有序、合金稳定性以及最终相图预测中的表现方式。统计力学是这些问题的核心，位错等缺陷对相稳定性和相变的影响也是如此。我们的散射程序，与理论建模相结合，将使用同步加速器X射线和基于反应堆的中子以全面的方式解决这些问题。这项研究将与将接受当代凝聚态物理学前沿领域之一培训的学生一起进行。通过这一点，他们将准备进入未来几十年的科学/技术劳动力大军。