Thermodynamic Measurements of Binary and Ternary Intermetallic Compounds

基于金属的非技术化合物是一种重要的功能材料，它为社会提供了许多有价值的特性，是一类智能材料的一部分。例如，它们的性能可以通过将废热转化为电力来收集能量，通过消除移动部件来实现高效制冷，通过热或磁场操作的机械定位器和医疗设备，如用于治疗循环问题的支架、用于矫直牙齿的支架和用于治疗眼病的微型机器人。这些材料的开发需要了解科学家所说的相平衡，这意味着合金成分在特定温度下由什么结构组成，这样才能开发出合适的加工工艺，从而提供可能的多功能。对结构的了解也是必要的，因为这确定了可以通过通过调整成分和工艺热处理来改变结构来调节的性质。本项目致力于确定一类基于金属的化合物的相平衡、结构和性质。这项工作包括对这些化合物的性质和性质的实验和计算研究。对于器件制造商来说，这项研究的结果将使他们能够将这些材料整合到现有器件中，作为现有材料的替代品，或者使他们能够开发有利于社会的新器件。技术摘要金属间化合物，如X2YZ型Heusler化合物和XYZ型“Half-Heusler”化合物，其中X和Y是过渡金属，Z是III-V族元素，Laves相因其形状记忆、热电、铁磁和自旋极化效应而引起人们的极大兴趣，这可能导致新的机械和电子器件。在这个项目中，我们将系统地测定这些化合物的热力学性质、晶体结构和相平衡。用滴量热法测定化合物的标准生成热和热容作为温度的函数。相平衡和晶体结构将用差示扫描量热法、能量色散x射线分析和x射线衍射法确定。这些数据将被用来对这些化合物的第一性原理计算进行基准测试，并评估DFT预测的总体准确性。数据库将扩大到包括DFT结构和能量结果，作为对实验数据的验证。尽管可能存在数千种化合物，但将使用相图的系统分析和高通量第一原理计算来快速筛选组成空间。所获得的热力学数据将纳入一个在线数据库，供科学界直接访问，用于合金开发和计算材料设计。这些数据将被纳入化合物的热力学吉布斯能量描述中，用于使用CALPHAD方法预测相平衡。实验数据将为DFT社区提供一个独特的机会来评估他们计算的准确性。本项目中进行的非化学计量金属间化合物的密度泛函缺陷计算将使社会各界更好地了解结构缺陷对结构稳定性的影响。该项目涉及与中国、捷克共和国和奥地利的研究人员进行大量的国际合作。所有人都可以通过网络公开访问热力学数据库。

Non-Technical Abstract Compounds based on metals are important functional materials that provide many properties of value to society and are part of a class of "smart materials". Their properties can, for example, provide energy harvesting through conversion of waste heat to electricity, efficient refrigeration through the elimination of moving parts, mechanical positioners operated by heat or magnetic field and medical devices such as stents for circulatory problems, braces for straightening teeth and micro-robots for treatment of eye diseases. The development of these materials requires a knowledge of what scientists call phase equilibria, which means what structure an alloy composition consists of at a particular temperature, so that suitable processing can be developed and so it can provide possible multi-functionality. A knowledge of the structure is also necessary as this determines the properties which may be tuned by modifying the structure through adjustment of composition and process heat treatments. This project is focused on the determination of the phase equilibria, structure and properties of a class of compounds based on metals. The work involves both experimental and computational research into the nature and properties of these compounds. For device manufacturers, the results of this research will enable them to incorporate these materials into existing devices as replacements for current materials or enable them to develop new devices for the benefit of society.Technical AbstractIntermetallic compounds such as Heusler type X2YZ and "half-Heusler" compounds of type XYZ, where X and Y are transition metals and Z is a group III-V element and Laves phases are of great interest for their properties such as shape memory, thermoelectric, ferromagnetic and spin polarization effects which could lead to new mechanical and electronic devices. In this project the thermodynamic properties, crystal structures and phase equilibria of these compounds will be systematically determined. Using drop calorimetry the standard heat of formation and heat capacity as a function of temperature of the compounds will be determined. Phase equilibria and crystal structures will be determined using differential scanning calorimetry, energy dispersive x-ray analysis and x-ray diffraction. The data will be used to benchmark first-principles calculations for these compounds and to assess the general accuracy of DFT predictions. The database will be expanded to include DFT structural and energy results as validations for experimental data as well. Although potentially there are thousands of compounds, rapid screening of composition space will be performed using systematic analysis of phase diagrams and high-throughput first principles calculations. The thermodynamic data obtained will be incorporated into an on-line database for access by the scientific community directly for use in alloy development and computational materials design. The data will be incorporated in thermodynamic Gibbs energy descriptions of the compounds for use in predicting phase equilibria using the Calphad approach. The experimental data will provide a unique opportunity for the DFT community to assess the accuracy of their calculations. DFT defect calculations for non-stoichiometric intermetallics performed in this project will provide the community with a greater understanding of the effect of constitutional defects on structural stability. The project involves a substantial international collaboration with researchers in China, Czech Republic, and Austria. The thermodynamic database is publicly available for all to access via the web.