Effect of tetravalent cation substitution on oxide-ion conduction and chemical stability of perovskite-related material Ba3Y4O9

We have reported that Zr substitution for Y in Ba₃Y₄O₉ enhances the chemical stability in humidified atmospheres at intermediate temperatures and the Zr-substituted Ba₃Y₄O₉ exhibits oxide-ion conduction probably mediated by oxide-ion vacancies. However, in addition to the problem of Si contamination in the samples, the long-time chemical stability and the transport number of ionic conductions were uncleared. In this work, we revisited the chemical stability and conductivity behavior of Ba₃Y₄O₉ with Zr substitution prepared by a modified procedure to suppress the contamination. Besides, we prepared Ba₃Y₄O₉ substituted by the other tetravalent cations (Ce, Sn, and Ti) and investigated the difference in the material properties from the Zr substitution samples. We carried out powder X-ray diffraction analyses for the evaluation of chemical stability in humidified atmospheres and electrochemical impedance spectroscopy to measure total conductivities of the substituted Ba₃Y₄O₉. As a result, we confirmed that Ce and Sn as well as Zr can substitute 20 mol% Y in Ba₃Y₄O₉ whereas the solubility of Ti in Ba₃Y₄O₉ is about 3 mol% at 1600 °C. Besides, the chemical stability of the substituted Ba₃Y₄O₉ strongly depended on not only the substitution level but also the substitution elements. Moreover, the substituted Ba₃Y₄O₉ was considered to be an almost pure oxide-ion conductor because of the little sensitivity of electrical conductivity to both humidity and partial oxygen pressure.