Atomistic simulations of defects in ceramics: Dislocation, grain boundaries, and their interactions in SrTiO3 as an example.
Date
2023-08
Authors
Tran, Kiet Tuong
Major Professor
Advisor
He, Ping
Xiong, Liming
Zhou, Lin
Committee Member
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Abstract
Ceramics, such as semiconductors and oxides, are usually brittle at room temperature. Certain ceramics, SrTiO3 for instance, are found to be plastically deformable by accommodating dislocation-mediated plastic flow. The dislocation line in such ceramics under plastic deformation may be used to realize a fast ionic transport at room temperature, which can find a variety of applications in fuel cells, batteries, solar cells, and so on. However, the injection of a high density of dislocations into SrTiO3 without cracking them is not trivial and is still in a "trial and error" stage due to the lack of a mechanistic understanding of how dislocations behave and how they interact with other defects, such as solid solutions and grain boundaries, in such complex solids. To meet this need, the goal of this master thesis research is to perform a series of atomistic simulations to: (i) quantify the dislocation activation volume and activation energy in single crystalline SrTiO3 under nanoindentation through temperature- and strain rate-jump tests; (ii) measure the grain boundaries energy and correlate it with the grain boundaries cohesive strength in SrTiO3; (iii) probe the mechanisms underlying the interaction between dislocations and low-/high-angle grain boundaries and monitor the pileup-induced local stress concentration and the transmission-induced local stress release; (iv) map the atomistic simulation-revealed mechanism to the experimental observations for polycrystalline SrTiO3 under indentation. The knowledge gained from this research may be used to support: (1) the development of constitutive rules, such as dislocation mobility laws and slip transfer metrics, that can be used in higher length scale models for understanding plastic behaviors of ceramics under deformation; (2) the discovery of using oxides as superionic conductors by simply deforming them. An expansion and transfer of the knowledge/method to the other material system will also be discussed and outlooked in this thesis.
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