Multiscale Modeling of Compositional Stresses in Nonstoichiometric Oxides

氧化物材料在能量转换和能量存储技术中具有重要意义。它们的工作原理是基于离子和电子之间输运的耦合。相关的用途包括固体氧化物燃料电池、催化剂和电解槽，这些效应也被用于化学传感器、电化学换能器以及先进的电子存储器和计算设备。这项工作的目标是定义新的计算方法来研究氧空位如何与晶界，位错和切面等缺陷相互作用。这将在电子和能源系统中使用的多晶二氧化铈薄膜以及用于催化的纳米晶体中进行研究，从而影响功能特性。目前，人们正在投入大量的精力和资源来开发有效的方法来改善氧化物材料的催化性能和传输。因此，从界面和晶界缺陷力学知识的增加中获得的见解可能具有经济影响，主要是在能源和电子工业中。结果和方法将嵌入到大学和研究生阶段的教育中。将制作互动软件，将力学概念与更广泛的公众联系起来。由于氧化物材料中缺陷之间的相互作用是由原子尺度现象和数百纳米长度范围内缺陷的弹性和静电相互作用决定的，因此该项目将采用多尺度方法。氧化物材料的晶界和缺陷结构（以二氧化铈为具体例子）将使用一种新的遗传算法技术进行预测，并通过高分辨率测量进行验证。基于该结构，本项目将研究晶界附近应力和空间电荷对缺陷形成能和相互作用的影响。利用最先进的量子模拟和确定带电缺陷应变的新方法相结合，将确定表面和晶界附近氧空位和掺杂物的分布。利用这些原子尺度模拟的信息，该项目将开发一个完全耦合的连续电化学-力学模型，以预测多晶氧化膜和纳米晶体中的应力，并模拟应力对氧空位密度和传输的影响。对于纳米晶体和多晶薄膜，该项目研究了应力对催化活性的影响，将通过库仑量热法研究和HRTEM观察来验证。最后，将使用完全耦合的电化学-力学模型来模拟和预测应变模式和位错等缺陷如何影响氧化物（以NiO为例）中的金属-绝缘体转变，并将通过实验验证预测。该项目将为研究生和本科生提供一个在领先的工业实验室进行实验工作和发展先进计算技能的机会。在计算方法方面取得的进展将包括在PI创建的课程中，以促进动手模拟经验。将开发仿真模块，使复杂的力学概念能够向更广泛的公众传播。

Oxide materials are of immense importance for energy conversion and energy storage technologies. Their working principle is based on the coupling of transport between ions and electrons. Relevant use includes solid oxide fuel cells, catalysts and electrolyzers, and these effects have also been employed in chemical sensors, electrochemical transducers, and in advanced electronic memories and computing devices. The goal of this work is to define novel computational methods to study how the oxygen vacancies interact with defects such as grain boundaries, dislocations and facets. This will be studied in polycrystalline ceria films used in electronic and energy systems and in nanocrystals used in catalysis, thus influencing functional properties. A large effort and many resources are now being invested to develop efficient methods to improve the catalytic properties and transport in oxide materials. Thus, the insights gained from increased knowledge of defect mechanics at interfaces and grain boundaries could have economic impact, mostly in the energy and electronics industry. Results and methods will be embedded into college and graduate level eductation. Interactive software will be produced to relate mechanics concepts to the broader public.Since the interactions between defects in oxide materials are determined both by atomic-scale phenomena and by the elastic and electrostatic interactions of defects over length scales of hundreds of nanometers, the project will adopt a multiscale approach. The structure of grain boundaries and defects in oxide materials (with ceria as a concrete example) will be predicted using a novel genetic algorithm technique and validated with high-resolution measurements. Based on the structure, this project will study how the formation energies and interaction of defects are influenced by stresses and space charges near the grain boundaries. The distribution of oxygen vacancies and dopants near surfaces and grain boundaries will be determined using a combination of state of the art quantum simulations and a new method to determine the strains of charged defects. Using the information from these atomic-scale simulations, the project will develop a fully-coupled continuum electro-chemo-mechanical model to predict the stresses in polycrystalline oxide films and nanocrystals and to model the influence of stresses on oxygen vacancy density and hence transport. For nanocrystals and polycrystalline films, the project study the effect of stresses on catalytic activity, which will be validated by coulombic calorimetry studies and HRTEM observations. Finally, the fully-coupled electro-chemo-mechanical model will be used to model and predict how strain patterning and defects such as dislocations influence metal-insulator transitions in oxides (with NiO as an example) and the predictions will be validated with experiments. The project will provide an opportunity for graduate and undergraduate students to both carry out experimental work in a leading industrial lab and to develop advanced computational skills. The progress made in the computational methods will be included in the course that the PI has created to promote hands-on simulation experience. Simulation modules enabling the communication of complex mechanics concepts to the broader public will be developed.