Understanding the effect of water transport on the thermal expansion properties of the perovskites BaFe0.6Co0.3Nb0.1O3-δ and BaCo0.7Yb0.2Bi0.1O3-δ

In this paper, we report a study of the perovskite phases, BaFe0.6Co0.3Nb0.1O3-δ (BFCN) and BaCo0.7Yb0.2Bi0.1O3-δ (BCYB), as possible air electrode materials for solid oxide cells (SOCs). The crystal structures and thermal and chemical expansion properties are reported, and the stability evaluated in different atmospheres. The thermal expansion data show unusual behaviour, with apparent negative thermal expansion (NTE) behaviour at low temperatures (100-240oC) up to -11.6x10−6 K−1 for BFCN and up to -17.3x10−6 K−1 for BCYB. This NTE behaviour is related to water
incorporation at lower temperatures, which is then lost in this temperature range upon heating. In order to examine the potential of these materials for use in a solid oxide electrolyser (SOE), the stability at elevated temperatures in the presence of water was evaluated, which indicated that water vapour leads to increased degradation at SOC operation temperatures.