Collaborative Research: Experimental and Computational Study of Structure and Thermodynamics of Rare Earth Oxides above 2000 C

非技术描述：能够承受超高温的材料对陶瓷加工、航空航天和核应用非常重要。含有稀土元素的氧化物熔点高，不易蒸发，化学性质一般不活泼。这种难熔性质有利于高温应用，但同时也使其热和能量关系（热力学）性质的确定具有挑战性，目前的数据是不完整的。这些数据对于预测材料在各种极端环境（如高温或高压环境）的简单和复杂系统中使用期间的稳定性或降解至关重要。新的实验和计算方法来确定2000摄氏度以上的热力学是这个项目的主要焦点，它代表了加州大学戴维斯分校的Navrotsky小组进行热化学测量和结构研究，而布朗大学的van de Walle小组进行计算和相图评估。该项目为大学水平的学生提供了参与应用于高温过程的最先进的实验和计算研究的机会。技术细节:目标是开发、测试和应用新的方法(i)确定稀土氧化物和碳化物在2000摄氏度以上的相变温度和热（固体-固体和熔化），（ii）在1500摄氏度以上的悬浮样品上通过同步加速器x射线衍射测量结构参数，包括相变时的热膨胀和体积变化。（iii）利用从头算密度泛函理论（含混合泛函）和分子动力学，结合统计力学技术计算高温热力学性质；（iv）基于理论和实验，生成热力学性质的统一图像，并公开用于相图（CalPhaD）模型的计算和其他应用。量热法、x射线衍射和计算的结合为耐火稀土氧化物的性质提供了所需的热力学数据和物理见解，并扩展到更复杂的系统。除了有关陶瓷的国际期刊和会议外，还通过在其网站上举行的小型重点会议和讲座进行传播。新开发的从头计算技术正被集成到广泛使用和免费分发的ATAT软件中。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL DESCRIPTION: Materials that can withstand ultrahigh temperatures are important to ceramic processing, aerospace, and nuclear applications. Oxides containing rare earth elements have high melting points, do not evaporate easily, and are generally chemically unreactive. This refractory nature favors high temperature applications, but at the same time makes the determination of their heat and energy relationships (thermodynamic) properties challenging, and current data are incomplete. Such data are essential for prediction of material stability or degradation during use in both simple and complex systems in a variety of extreme environments (such as high-temperature or high-pressure environments). New experimental and computational approaches to determine thermodynamics above 2000 degrees C form the primary focus of the project, which represents collaboration between Navrotsky's group at University of California at Davis performing thermochemical measurements and structural studies, and van de Walle's group at Brown University undertaking calculations and phase diagram assessments. The project provides university-level students an opportunity to participate in state-of-the-art experimental and computational research applied to high temperature processes. TECHNICAL DETAILS: The goals are to develop, test and apply new methodology (i) to determine temperatures and heats of phase transitions (both solid-solid and melting) of rare earth oxides and oxycarbides above 2000 degrees C, (ii) to measure structural parameters, including thermal expansion and volume change upon phase transition by synchrotron X-ray diffraction on levitated samples above 1500 degrees C, (iii) to calculate high-temperature thermodynamic properties using ab initio density functional theory (with hybrid functionals) and molecular dynamics in conjunction with statistical mechanical techniques, and (iv) to generate a unified picture, based on both theory and experiment, of thermodynamic properties, to be made publicly available for use in calculation of phase diagrams (CalPhaD) modeling and other applications. The combination of calorimetry, X-ray diffraction, and computation provides both needed thermodynamic data and physical insight into the properties of refractory rare earth oxides, with extensions into more complex systems. In addition to international journals and meetings on ceramics, dissemination is taking place through smaller focused conferences and lectures on their websites. Newly developed ab initio computational techniques are being integrated within the widely used and freely distributed ATAT software.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.