High Oxide-Ion Conductivity in Cubic Perovskite Na- and Ga-Doped Bazro3

Abstract

Solid oxide ion electrolytes (SOEs) play a crucial role in determining the operating temperature, cost, and lifetime of solid oxide electrochemical devices. The most competitive SOEs are typically found in cubic-structured fluorides (e.g., ZrO2-based and CeO2-based) and perovskites (e.g., LaGaO3-based and Ba(Zr,Ce)O3-based). However, the discovery of new high-conductivity SOE systems has been very limited in the history of solid state ionics. Here, we explore a new cubic-structured perovskite, Ba1-xNaxZr1-xGaxO3-x (BNZG), as a potential oxide-ion conductor. Compared to La0.8Sr0.2Ga0.8Mg0.2O2.8 (LSGM), a state-of-the-art perovskite electrolyte, BNZG exhibits a comparable bulk ionic conductivity (~0.01 S/cm at 600°C) while reducing Ga content by 40%. Additionally, compared to BaZr0.8Y0.2O2.9 (BZY), another widely studied perovskite electrolyte, BNZG shows excellent sinterability at lower temperatures. Ab Initio molecular dynamics (AIMD) simulations suggest that BNZG is an oxide-ion conductor, particularly at higher temperatures, which is also confirmed by high oxide-ion transport number (>0.99) and conductivity independent of oxygen and moisture partial pressures. Furthermore, BNZG is stable in CO2/air and compatible with active perovskite cathodes such as La1-xSrxCoO3-δ without the use of barrier layer. We also show that the high grain-boundary resistance originated from Ga segregation could be one critical issue for BNZG application in intermediate temperature solid oxide cells.

Keywords: oxide-ion conductivity, bulk, Grain boundary, ionic transport number, molecular dynamics simulations