High Oxide-ion Conductivity in Cubic Perovskite Na- and Ga-doped BaZrO3

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, Ba_1-xNa_xZr_1-xGa_xO_3-x (BNZG), as a potential oxide-ion conductor. Compared to La_0.8Sr_0.2Ga_0.8Mg_0.2O_2.8 (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 BaZr_0.8Y_0.2O_2.9 (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 water vapor partial pressures. Furthermore, BNZG is stable in CO₂/air and compatible with active perovskite cathodes such as La_1-xSr_xCoO_3-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.