MRI: Development of Multi-field Resonant Ultrasound Spectroscopy

弹性常数是任何固体材料的基本性质，了解它们随温度和/或外加磁场或电场的变化对于理解不同材料中发生的不同物理过程是至关重要的。然而，使用传统技术测量弹性常数并不总是一项微不足道的任务。它通常需要大量样品和/或大量耗时的测试，特别是在低温和高温和/或在各种外部刺激(如电场和磁场)下进行测量的情况下。该项目中正在开发的多场共振超声光谱分析(MF-RUS)设备将允许在有或没有外加电场或磁场的情况下，仅使用一个样品在宽温度范围内快速地从单一测试中确定任何固体的全套弹性常数。MF-RUS的广泛能力将使不同固体的全面表征成为可能，并加强许多领域的研究，包括材料科学和工程、物理和化学。通过快速、轻松地评估不同材料的弹性性能，MF-RUS的使用将进一步促进新材料的开发，用于广泛的不同应用，包括能源收集、存储和转换、国防和运输系统。一旦开发完成，这种独特的仪器将通过德克萨斯州农工大学久负盛名的材料表征设施用户计划向来自其他学术机构、行业和实验室的研究人员提供。德克萨斯农工大学和其他学术机构的18个研究项目，包括两个少数群体服务机构，目前由NSF和其他联邦机构支持，将立即从MF-RUS的开发中受益。弹性常数作为自由能关于应变的二次导数，不仅关系到应力和应变张量，而且提供了关于固体中原子键特征的基本信息，因此它们被认为是最基本的材料性质之一。虽然弹性常数主要代表平衡热力学性质，但衰减是与材料中各种物理过程的能量吸收有关的不可逆过程的直接表现。共振超声光谱(RUS)是一种简单、廉价和优雅的实验技术，它可以用小到1 mm~3的单晶或多晶样品同时测定各向同性固体的杨氏模数和剪切模数，或单晶的全套弹性常数(CIJ)和超声衰减。目前，商业上可用的RUS仪器仅限于室温测量，而一些现有的定制RUS系统允许在受控环境中测量高达1320°C的磁场，从低温到327°C的磁场，或在电场下但仅在室温下进行测量。该项目中正在开发的多场共振超声光谱(MF-RUS)系统将是独一无二的，因为它将允许同时测量固体材料的弹性常数和超声衰减，从液氦温度到1900°C，在有或没有高达1000V/mm的电场或高达7T的磁场的情况下，以及在各种大气(空气、高真空、惰性气体等)中。该RUS系统将是模块化的，将在3年的项目期内分阶段开发，随着每个模块的添加，将具有部分功能。该仪器将提供一个强大的新工具来观察和量化由于固体中各种物理过程引起的弹性系数和超声衰减的变化，例如一阶和二阶相变，或者由于不同过程引起的不同的非弹性松弛机制，例如点缺陷(例如间隙和空位跳跃)、线缺陷(例如位错)或平面缺陷(例如畴壁或马氏体相变相界面等)的热弹性松弛和运动。

Elastic constants are fundamental properties of any solid material and knowing their changes with temperature and/or under applied magnetic or electric field is essential for understanding different physical processes that take place in different materials. However, measurement of elastic constants using conventional techniques is not always a trivial task. It usually requires large number of samples and/or numerous time-consuming tests, especially if the measurements are performed at low and high temperatures and/or under various external stimuli such as electric and magnetic fields. Multi-field Resonant Ultrasound Spectroscopy (MF-RUS) apparatus under development in this project will allow rapid experimental determination of the full set of elastic constants of any solid from the single test using only one sample as small as 1 mm3 in the wide temperature range, with or without applied electric or magnetic fields. The broad capabilities of the MF-RUS will enable comprehensive characterization of different solids, and enhance research in many fields, including materials science and engineering, physics, and chemistry. By allowing rapid and easy evaluation of elastic properties of different materials, utilization of MF-RUS will further foster development of new materials for widely varying applications including energy harvesting, storage and conversion, defense, and transportation systems. Once developed, this unique instrument will be available to researchers from other academic institutions, industry and laboratories through a well-established Materials Characterization Facility's users program at Texas A&M University. Eighteen research projects at Texas A&M University and other academic institutions, including two minority serving institutions, currently supported by NSF and other federal agencies will benefit immediately from the development of MF-RUS.Elastic constants, as the second derivatives of the free energy with respect to strain, not only relate stress and strain tensors, but also provide fundamental information about the character of atomic bonding in solids, and thus they are considered to be one of the most fundamental materials properties. While the elastic constants represent primarily equilibrium thermodynamic properties, the attenuation is direct manifestation of irreversible processes related to energy absorption by various physical processes in the material. Resonant Ultrasound Spectroscopy (RUS) is a simple, inexpensive and elegant experimental technique that can be used to determine simultaneously Young's and shear moduli of isotropic solids, or a full set of elastic constants (Cij) of single crystals, as well as ultrasonic attenuation, using single crystal or polycrystalline sample as small as 1 mm3. Currently, commercially available RUS instruments are limited to room temperature measurements while some existing custom-made RUS systems allow measurements up to 1320ºC in controlled environments, in magnetic fields up to 7T from cryogenic temperatures to 327ºC, or under an electric field but only at room temperature. A Multi-Field Resonant Ultrasound Spectroscopy (MF-RUS) system under development in this project will be unique since it will allow simultaneous measurements of elastic constants and ultrasonic attenuation of solid materials from liquid helium temperature up to 1900ºC, with or without electric fields of up to 1000 V/mm or magnetic fields of up to 7T, and in various atmospheres (air, high vacuum, inert gases, etc.) This RUS system will be modular and will be developed in stages over the 3-year project period with partial functionality as each module is added. This instrument will provide a powerful new tool to observe and quantify changes in elastic coefficients and ultrasonic attenuation as a result of various physical processes in the solid, such as first- and second-order phase transformations or different inelastic relaxation mechanisms due to different processes such as thermoelastic relaxation and motion of point defects (e.g. interstitial and vacancy hopping), linear defects (e.g. dislocations) or planar defects (e.g. domain walls or martensitic transformation phase interfaces, etc.).