Oxide Ion Conduction in Ca-Doped Yb₃Ga₅O₁₂ Garnet

Developing oxide ion conductors with new structural families is important for many energy conversion and storage techniques. Herein, a series of Ca-doped Yb₃Ga₅O₁₂ garnet-type materials are prepared through a traditional solid-state reaction method, with their oxide ion conduction properties being reported for the first time. The results revealed that Ca substitution for Yb would significantly improve the conductivity of Yb₃Ga₅O₁₂ from 3.57 × 10^-7 S/cm at 900 °C under air to 1.66 × 10^-4 S/cm, with an oxide ion transporting number of ∼0.52. The oxygen vacancy defect formation energy (∼0.127 eV) and the local structure around an oxygen vacancy were studied by atomic-level static lattice simulations based on the interatomic potential method. The oxide ion conducting mechanism was studied by the bond-valence-based method, which revealed three-dimensional pathways for oxide ion migration in both the parent and Ca-doped structures. The simulated activation energy of oxide ion migration decreased slightly from ∼0.358 eV in the parent structure to 0.346 eV in the doped one. These discoveries in the Ca-doped Yb₃Ga₅O₁₂ will stimulate extensive exploitation and fundamental research on garnet-type materials.