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THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING
GEORGIA INSTITUTE OF TECHNOLOGY
Under the provisions of the regulations for the degree
DOCTOR OF PHILOSOPHY
on Friday, November 16, 2018
3:00 PM
in Love 295
will be held the
DISSERTATION PROPOSAL DEFENSE
for
Lei Zhang
"ATOMIC LEVEL SIMULATIONS OF PROTON CONDUCTING BAHFO3 WITH A/B-SITE DOPANTS"
Committee Members:
Prof. Meilin Liu, Advisor, MSE
Prof. Rampi Ramprasad, MSE
Prof. Ting Zhu, ME/MSE
Prof. Angus Wilkinson, CHEM/MSE
Prof. Jean Luc Bredas, CHEM
Abstract:
Barium hafnate, i.e. BaHfO3 is one of the most promising proton conducting perovskites. The material’s proton conductivity at intermediate temperature range (~500 Celsius) provides the commercialization chance for it to be solid state electrolyte in proton conducting solid oxide fuel cells (SOFCs). Although a considerable amount of computational and experimental research on similar perovskite systems, e.g. BaZrO3, BaCeO3, BaSnO3have been carried out, there is very limited research effort on BaHfO3. In this proposal, we take advantage of atomic level simulation techniques to gain electronic and atomic level insight in A/B-site doped BaHfO3. The proposed simulation technique is so-called “ab-initio thermodynamics”, coupling density functional theory based first-principles calculations with statistical thermodynamic theory. Specific theories or models include defect formation energy calculation, finite temperature vibrational energy calculation via phonon frequencies evaluation under harmonic approximation, proton migration along minimum energy pathway via transition state theory, and configurational entropy contribution via cluster-expansion and Monte-Carlo method. A variety of relevant properties are investigated, including hydration percentage governed by hydration Gibbs free energy, proton diffusivity by proton migration barrier, microscopic defect-clustering between dopant-oxygen vacancy and dopant-proton due to enthalpic and entropic balance. All the above properties are sensitive to chemical dopants in the lattice, i.e. Li, Na, K, Rb, Cs on A-site, and Sc, Y, La, Gd, Lu, Al, Ga, In on B-site. The goal is to understand the fundamental mechanism in BaHfO3 upon various chemical dopants, and achieve rational dopant selection and doping concentration optimization in BaHfO3. The computation workflow built in this proposal will be extremely useful in proton conducting solid state electrolyte design and give a broader impact to the community of solid state ionics.
