Date of Award

8-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Materials Science and Engineering

Committee Chair/Advisor

Dr. Kyle S. Brinkman

Committee Member

Dr. Jianhua Tong

Committee Member

Dr. Dong Hou

Committee Member

Dr. Fei Peng

Abstract

Garnet-type Li7La3Zr2O12 (LLZO)  is a promising solid Li-ion conductor for solid-state batteries and high-temperature lithium-containing electrochemical systems. Its performance, however, depends strongly on synthesis route, phase purity, density, lithium stoichiometry, dopant chemistry, microstructure, and operating environment. This dissertation investigates the synthesis, compositional control, and molten Li-Pb stability of Ga- and Ta-doped LLZO.

First, a rapid, solvent-free, urea-assisted combustion route was developed to synthesize cubic Ga-doped LLZO powder. The optimized fuel-lean condition produced powder with no detectable crystalline secondary phases, a crystallite size of approximately 62 nm, and a yield of about 90%. Pellets sintered at 1100 °C for 5 h reached 94.2% relative density and a total Li-ion conductivity of 5.8 × 10-4 S cm-1.

Second, Ga-doped LLZO closed-end tubes were fabricated by 3D printing and reactive sintering and exposed to molten eutectic Li-Pb. At 350 °C, no detectable bulk phase transformation occurred for up to 100 h under the tested conditions. At 450 °C, the material exhibited bulk blackening, cubic-to-tetragonal transformation, microcracking, lithium enrichment, Pb penetration, and reduction-related defect formation. Ta-doped LLZO showed mainly surface-localized degradation while retaining a comparatively intact bulk.

Finally, lithium-deficient and lithium-excess Ga-doped LLZO compositions were studied. Lithium deficiency promoted incomplete garnet formation, whereas higher lithium excess promoted Li-rich and Ga-rich secondary phases. Under the processing conditions used, 10% excess lithium provided the best balance of cubic-phase stability, densification, and ionic conductivity. Overall, the findings establish coupled processing–composition–microstructure relationships governing LLZO performance in battery and fusion-related environments, providing guidance for material and process optimization.

Author ORCID Identifier

0009-0002-4662-9560

Download

Available for download on Tuesday, August 31, 2027

Share

COinS