Thermodynamics and Phase Equilibria of Heusler and half-Heusler Alloys

A2BC型Heusler化合物和ABC型半Heusler化合物，其中A和B是过渡金属，C是III-V族元素，它们的功能性质如形状记忆、热电、铁磁和自旋极化效应引起了人们的极大兴趣，可能导致新的机械和电子设备。拟议研究的目的是准确地确定这类三元化合物的生成热，对热容、相平衡、熔点和晶格参数进行补充测量，并对这些数据进行分析，以了解这些系统中的合金化行为。化合物的生成热能将通过使用Kleppa型量热计的直接合成反应量热法来确定。比热将在一定的温度范围内通过在赛塔拉姆高温滴量热计中测量的热焓来确定。尽管可能有230种化合物，但将使用扩散倍数和相图系统分析来快速筛选组成空间，以确定哪些体系包含这些化合物。所获得的热力学数据将纳入一个在线数据库，供科学界查阅。这些数据将被纳入化合物的计算热力学吉布斯能量描述中，用于预测相平衡。这些数据在为第一性原理计算和优化化合物的热力学描述提供基准方面也很重要，从而使未来计算合金的发展扩展到更高阶系统。非技术摘要：使用基于三种金属元素的化合物可能会有新的机械和电子设备。这些化合物通常表现出诸如磁或热形状记忆和磁场的大形状变化等性质，可用于机械致动器和半金属-半半导体性质，可用于制造所谓的自旋电子器件或将热能转换为电能，从而有可能减少电子设备中的能量消耗和浪费热损失。将对大量此类化合物进行基本性质测量，其中许多以前没有合成过。该项目的成果可以被更广泛的科学界用于这些材料的进一步合金开发和设备应用。伊利诺伊州数学与科学学院的研究生、本科生和高中生将直接参与这项研究。芝加哥当地一所公立学校将安排3-8年级的学生参观实验室。该项目涉及与中国和韩国的研究人员进行大量的国际合作，并将为研究人员提供访问IIT的机会，为我们的学生举办研讨会，并与教职员工和研究生互动。所有科学家都可以通过网络访问热力学数据库。实验技术的视频教程将被制作、编辑并在网络和iTunes U上提供。

TECHNICAL SUMMARY: Heusler compounds of type A2BC and 'half-Heusler' compounds of type ABC, where A and B are transition metals and C is a group III-V element are of great interest for their functional properties such as shape memory, thermoelectric, ferromagnetic and spin polarization effects which could lead to new mechanical and electronic devices. The objectives of the proposed research are to accurately determine heats of formation for ternary compounds of this type, to make complementary measurements of heat capacity, phase equilibria, melting points and lattice parameters and to analyze these data to provide understanding of the systematic alloying behavior in these systems. The enthalpies of formation of the compounds will be determined by direct synthesis reaction calorimetry using a Kleppa type calorimeter. The specific heats will be determined over a range of temperature from enthalpy measurements made in a Setaram high temperature drop calorimeter. Although potentially there are 230 compounds, rapid screening of composition space to identify which systems contain these compounds will be performed using diffusion multiples and systematic analysis of phase diagrams. The thermodynamic data obtained will be incorporated into an on-line database for access by the scientific community. The data will be incorporated in computational thermodynamic Gibbs energy descriptions of the compounds for use in predicting phase equilibria. Such data are also of importance in providing benchmarks for first principles calculations and for optimization of thermodynamic descriptions of compounds to permit future computational alloy development extending to higher order systems.NON-TECHNICAL SUMMARY: Novel mechanical and electronic devices may be possible using compounds based on three metallic elements. These compounds often exhibit properties such as magnetic or thermal shape memory and large shape change in magnetic fields which can be used for mechanical actuators and half metal-half semiconductor property which can be used to produce so-called 'spintronic' devices or conversion of thermal energy to electrical energy which have the potential to reduce energy consumption and waste heat loss in electronic devices. Basic property measurements will be made on a large number of such compounds, many of which have not been synthesized previously. The results of this project can be used by the wider scientific community for further alloy development of these materials and application to devices. Graduate and undergraduate students and high school students from the Illinois Mathematics and Science Academy will be directly involved in the research. Laboratory tours will be arranged for 3-8th grade classes from a local Chicago public school. The project involves a substantial international collaboration with researchers in both China and Korea and will provide opportunity for researchers to visit IIT to give seminars to our students and interact with faculty and graduate students. The thermodynamic database is available for all scientists to access via the web. Video tutorials of experimental techniques will be produced, edited and made available on the web as well as through iTunes U.