SusChEM: Collaborative Research: experimental and computational study of structure and thermodynamics of rare earth oxides above 2000 C

非技术概述：航空航天、能源和其他技术中的应用需要在非常高的温度下稳定的材料。许多此类材料含有稀土氧化物，这是潜在短缺的关键材料。新的实验和计算方法正在研究这类稀土氧化物的结构和稳定性。该方法包括对悬浮在气流中且不受与其他材料接触污染的激光加热样品的衍射(确定晶体结构)和量热(测量与熔化和其他反应有关的热效应)，以及理论计算。这样的研究提供了一个独特的机会，以获得对结构、相变和熔化性质的基本了解，以及在技术问题上的应用。该项目还将推进高温研究的一般实验和计算技术。它将为材料科学、化学、物理和工程学的本科生和研究生提供机会，在大学和国家实验室环境中参与最先进的研究。稀土氧化物是“关键材料”，在技术上不可或缺，但供应量有限。“从摇篮到坟墓”，或者更好的是“从摇篮到摇篮”(包括回收)，开发节能、环保的流程对于资源和技术的可持续管理至关重要。技术细节：稀土氧化物是许多重要技术必不可少的关键材料，但此类应用所需的高温性能却鲜为人知。采用新的实验和计算方法相结合的方法研究了它们在2000°C以上的结构和热力学。空气动力悬浮和激光加热正被用于先进光子源的原位X射线衍射、散裂中子源的原位中子衍射以及加州大学戴维斯分校彼得·A·罗克热化学实验室的滴量热。用量热法测量了固相相变和熔融的热焓，用衍射法测定了高温相变和热膨胀的体积变化。高温热分析是滴量热法的补充。为了可靠地计算含稀土的多元体系的共晶物，熔化热是必需的。布朗大学正在使用混合泛函和DFT+U等后密度泛函理论方法，结合团簇展开、晶格动力学分析和分子动力学等统计力学技术，对高温热容、热膨胀、相变和聚变的温度和热焓进行从头计算。计算的相变和聚变的热膨胀和热焓正在与实验测量相比较，计算正在扩展到尚不能在实验中获得的稀土氧化物的高温性质。热力学是优化稀土氧化物工艺的核心；因此，该项目有助于可持续性。

NON-TECHNICAL SUMMARY: Materials which are stable to very high temperatures are needed for applications in aerospace, energy, and other technologies. Many such materials contain rare earth oxides, critical materials in potential short supply. Novel experimental and computational methods are studying the structure and stability of such rare earth oxides. The methodology includes diffraction (determination of crystal structure) and calorimetry (measurement of heat effects associated with melting and other reactions) on laser heated samples levitated in a gas stream and not contaminated by contact with other materials, as well as theoretical calculations. Such studies offer a unique opportunity to obtain fundamental understanding of structures, phase transitions, and melting properties and applications to technological problems. The project will also advance general experimental and computational techniques for high temperature research. It will offer opportunities for both undergraduates and graduate students in materials science, chemistry, physics, and engineering to take part in state-of-the-art research in both university and national laboratory settings. Rare earth oxides are "critical materials" in the sense of being technologically indispensable, but with limited supply. Developing energy-efficient, and environmentally-friendly processes "from cradle to grave" or, better still "from cradle to cradle" (involving recycling) is essential to sustainable management of resources and technology. TECHNICAL DETAILS: Rare earth oxides are critical materials essential to many important technologies yet their high temperature properties, needed for such applications, are poorly known. Their structure and thermodynamics above 2000°C are being studied using a combination of novel experimental and computational methods. Aerodynamic levitation and laser heating are being used for in situ X-ray diffraction at the Advanced Photon Source, in situ neutron diffraction at the Spallation Neutron Source and for drop calorimetry at the UC Davis Peter A. Rock Thermochemistry Laboratory. Enthalpies of solid state phase transitions and fusion are being measured by calorimetry, and volume changes on phase transitions and thermal expansion of high temperature phases are being determined by diffraction. High temperature thermal analysis complements drop calorimetry. Fusion enthalpies are required for reliable calculations of eutectics of multi-component systems containing rare earths. Ab initio computations of high temperature heat capacities, thermal expansion, and temperatures and enthalpies of phase transitions and fusion are being performed at Brown University using post-density functional theory (DFT) methods, such as hybrid functionals and DFT+U, in conjunction with statistical mechanics techniques such as cluster expansion, lattice dynamics analysis and molecular dynamics. Computed thermal expansion and enthalpies of phase transitions and fusion are being compared to experimental measurements and calculations are being extended to high temperature properties of rare earth oxides not yet accessible experimentally. Thermodynamics are central to optimizing the processes for the rare earth oxides; as such this project contributes to sustainability.