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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 33: Focus Session: (Multi-)Ferroic States V

KFM 33.3: Talk

Friday, March 22, 2024, 10:10–10:30, EMH 225

An extended phase-field-drift-diffusion model for oxygen vacancy migration in single-crystal barium titanate — •Xuejian Wang and Frank Wendler — Institute of Materials Simulation (WW8), Friedrich-Alexander-Universität Erlangen-Nürnberg, Dr.-Mack-Str. 77, 90762 Fürth, Germany

Barium titanate (BTO) and its solid solutions are attractive materials for replacing lead-based piezoelectrics, exhibiting a high density of point defects. Here, we present an extended phase-field model that includes the migration of oxygen vacancies (Vo), a crucial type of point defect in ferroelectric materials, within single-crystal BTO. The model bases on the Landau-Ginzburg-Devonshire theory, considers a continuous concentration of Vo (Cv) and incorporates the drift-diffusion equation for its migration. The Finite Element Method is used to simulate domain formation with varying Cv values, where a range of phenomena is discovered. Initially, the existence of Vo induces a modification in the orientation of polarization in comparison to the defect-free crystal. The level of Cv significantly affects the evolution and structure of domain/domain walls (DWs). Systems possessing a larger Cv will generate domains of higher density and a greater variety of DWs in comparison to systems with lesser Cv. The migration of Vo occurs on both sides of the DWs and along the polarization orientation. Moreover, defect clustering is observed at the junctions of domain walls at higher Cv levels. The influence of Vo concentrations on electromechanical loading are shown, and results are compared to experimental data from literature.

Keywords: phase-field model; single-crystal barium titanate; point defect migration; drift-diffusion equation; finite element analysis