New ionic conductor: Ba-deficient Ba₃Y₄O₉ with Zr substitution

Abstract

To lower operating temperatures of solid oxide fuel cells (SOFCs), the development of ion-conducting oxides with high conductivity and durability is desired. In this work, we investigated Zr-substituted “Ba₃Y₄O₉” as an ionic conductor at intermediate temperatures and found that the Zr substitution for Y dramatically improves the phase stability in humidified atmospheres at 300–800 °C. The total electrical conductivity of nominally 20 mol% Zr-substituted Ba₃Y₄O₉ sample is about 0.1 mS/cm at 500 °C in both dry H₂ and O₂ atmospheres. Because an increase in the conductivity in a humidified atmosphere was not observed, the conducting carriers may be oxygen ions. Besides, in the Zr-substituted “Ba₃Y₄O₉” samples, we observed that BaO-rich phase coexists with the main phase whose composition is estimated to be Ba:(Y + Zr) ~ 2:3. Therefore, the main conducting phase might be Ba-deficient Ba₃Y₄O₉. The mechanism of the ionic conduction and the improvement of chemical stability has not been revealed yet due to the lack of crystallographic information about the Ba-deficient phase. While we are now working on further investigation, we promptly report the characteristic of the new compound.