Phonon-Assisted Diffusion in Solids from First-Principles: Unraveling a New Mechanism for Fast Diffusion

非技术摘要分子在液体和气体中的扩散是很常见的：例如，香水可以在空气中扩散。扩散也发生在高温固体中，了解如何扩散将是新应用的关键。许多与技术相关的材料，特别是那些具有高工作温度的材料，经历了高度相关的不同集体原子振动模式。人们对这些相关振动对扩散的影响知之甚少，现有的理论模型在将它们纳入扩散描述方面也极其有限。该项目通过(A)设计一个描述受相关集体原子振动影响的质量传输行为的理论框架，以及(B)实现一个无需实验输入即可预测扩散系数的计算工具来解决这一问题。最终产品将是一个具有扩散预测能力的开放访问软件工具包，这将大大加速固态电池和燃料电池等应用的先进材料的发现和设计。教育活动包括编写关于高温材料动力学高级主题的全面教程，该教程将在PI的网站上分发，为学生提供一个世界范围的教育平台。此外，PI还将为工程师开发一门关于第一性原理建模的研究生课程。技术总结目前在对强非简谐系统中扩散现象的基本理解和理论建模方面存在很大差距。也就是说，(I)非简谐振动对扩散现象的影响还没有被很好地理解，(Ii)现有的基于零温能量的谐和近似的计算模型不能预测这些系统中的扩散系数。这个项目的目标是通过引入一个结合随机抽样技术和从头计算的理论框架来确定有效能面上的扩散路径，以解决这些差距。该项目的发现将促进对非简谐振动对扩散影响的基本理解，并将显著扩展当前扩散模拟能力的限制。此外，它将提供先验预测能力，而不需要实验输入，这将大大加快新材料的优化和设计。该项目的成果将有助于推进两个材料研究领域：(I)预测新型高温固相的扩散性质，以及(Ii)通过为其模拟提供准确的扩散迁移率数据，对各种扩散控制过程(如相变、沉淀生长和粗化、氧化和蠕变)有新的理解。该大学是一所服务于西班牙裔美国人的机构，PI将参与UIC现有的两个招收少数族裔学生和女性工程学的项目。她将培训本科生和研究生进行研究，她将在当地高中讲授入门课程，并开发一门新的研究生级别的第一原理建模工程课程。PI将发布开源软件以及使用标准存储库的扩散数据。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical SummaryDiffusion of molecules in liquids and gases is familiar: perfume, for example, can diffuse in air. Diffusion also takes place in high-temperature solids, and understanding how will be key to new applications. Many technologically-relevant materials, in particular those with high operating temperatures, experience different modes of collective atomic vibrations that are highly correlated. The effect of these correlated vibrations on diffusion is poorly understood, and existing theoretical models are extremely limited in incorporating them into the diffusion description. This project addresses this limitation by (a) devising a theoretical framework that describes the mass-transport behavior affected by the correlated collective atomic vibrations, and (b) implementing a computational tool to predict the diffusion coefficient without requiring experimental input.The end product will be an open-access software toolkit with predictive capability for diffusivity, which will substantially accelerate the discovery and design of advanced materials for applications such as solid-state batteries and fuel cells. Educational activities include the development of a thorough tutorial on advanced topics in the kinetics of high-temperature materials, which will be distributed on the PI's website to provide a world-wide educational platform for students. Also, a graduate-level course about first-principles modeling for engineers will be developed by the PI.Technical SummaryThere currently exist substantial gaps in fundamental understanding and theoretical modeling of diffusion phenomena in strongly anharmonic systems. Namely, (i) the effect of anharmonic vibrations on diffusion phenomena is not well understood, and (ii) existing computational models based on the harmonic approximation of zero-temperature energy fall short of predicting diffusivity in these systems. The goal of this project is to address these gaps by introducing a theoretical framework that combines stochastic sampling techniques and ab-initio calculations to identify the diffusion pathways on an effective energy surface.The findings of this project will advance the fundamental understanding of anharmonic vibration effects on diffusion and will significantly expand the current limits of diffusion modeling capabilities. Additionally, it will provide a-priori predictive capability without requiring experimental input, which will substantially accelerate the optimization and design of new materials. The outcomes of this project will contribute to the advancement of two lines of materials research: (i) predicting diffusion properties for novel high-temperature solid phases and (ii) gaining new understanding of various diffusion-controlled processes (e.g., phase transformation, precipitate growth and coarsening, oxidation, and creep) by providing accurate diffusive mobility data for their simulation.The university is a Hispanic-serving institution, and the PI will participate in two existing programs for recruiting minority students and women to engineering at UIC. She will train undergraduates and graduate students in research, and she will give introductory lectures at local high schools and develop a new graduate-level engineering course in first-principles modeling. The PI will release open-source software as well as data on diffusivity using standard repositories.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.