Phase-Field Modeling of Mobile Species Coupled with Reactions and Phase Microstructures
Open Access
- Author:
- Wang, Rui
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 10, 2022
- Committee Members:
- Michael Lanagan, Outside Unit & Field Member
Ismaila Dabo, Major Field Member
Clive Randall, Major Field Member
Long-Qing Chen, Chair & Dissertation Advisor
John Mauro, Program Head/Chair - Keywords:
- Phase-field modeling
mobile species
charge
dielectric degradation
ferroelectric
alloy oxidation - Abstract:
- This dissertation focuses on the phase-field modeling of mobile species under different conditions and different material systems coupled with phase microstructures. The mobile species are modeled in dielectric degradation problem, ferroelectric problem and alloy oxidation problem. In the first part, phase-field method is used to study the defect behavior in dielectric degradation problem with a prototypical system, Fe-doped SrTiO3. The model treated the perovskite oxide as a wide-band gap semiconductor, in which the defect equilibria can be simulated after the local Fermi energy is determined in each time step, where Poisson equation and drift-diffusion-reaction equation are solved. The mechanism of dielectric degradation is studied using this model, and the impact of charge injection as well as the interfacial condition on the leakage current are also investigated. The simulation results are consistent with experiments with the degradation mechanism elucidated. The second part focuses on the modeling introduction on a XYO3 perovskite ferroelectric with certain dopants and mobile charges. The thermodynamics and kinetic evolution equations are rigorously derived which involves first-principal calculation, Landau theory and statistical mechanics. In this part, the treatment of wide-band gap semiconductor is still adopted and the defect evolutions with BiFeO3 109° normal domain wall and 71° charged domain wall are studied and compared with existing analytical models. In the third part, a phase-field model is developed to study the behavior of mobile species in alloy oxidation at high temperatures. In the multi-phase multi-component system, the mobile components are reactive which help form or grow the oxide phases while the species no longer share the same defect chemistry in semiconductors. This model is firstly validated by comparing with analytical models, then impact of nuclei size, shape distribution as well as composition on the oxidation results are simulated and analyzed.