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

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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.