New Good Ionic Conductor: Ba-Deficient Ba3Y4O9 with Zr Substitution

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 “Ba 3 Y 4 O 9 ” 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 20 mol% Zr-substituted Ba 3 Y 4 O 9 is about 1 mS/cm at 700 °C in dry H­ 2 and O 2 atmospheres and the contribution of electronic conduction (both hole and electron) is relatively small compared with Y-doped BaZrO 3 (BZY) and Gd-doped CeO­­ 2 (GDC) which are typical intermediate-temperature ionic conductors. Besides, in the Zr-substituted “Ba 3 Y 4 O 9 ” samples, we observed that BaO-rich amorphous 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 Ba 3 Y 4 O 9 . 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.