Insight into the structure and functional application of Mg-doped Na0.5Bi0.5TiO3 electrolyte for solid oxide fuel cells

Na 0.5 Bi 0.5 TiO 3 (NBT) and its acceptor-doped perovskites , as lead-free piezoelectric materials before, have been found to be excellent oxygen-ion conductors with potential applications in intermediate-temperature solid oxide fuel cells (SOFCs). Among them, the Bi deficient and B-site Mg doped sodium bismuth titanate (Na 0.5 Bi 0.49 Ti 0.98 Mg 0.02 O 2.965 , NBTM) exhibits a remarkable oxygen ionic conductivity . Here, we report a structural analysis on NBT and NBTM ceramics using high-temperature in situ neutron diffraction (NPD) to gain insight into the effects of Mg doping on ionic conductivity and structure. Both perovskite oxides exhibit two consecutive phase transformations from R 3 c to P 4 bm at ∼400 °C and from P 4 bm to Pm 3 ¯ $\overline{3}$ m at ∼600 °C. The effects of Bi deficiency and Mg substitution on oxygen vacancy concentration and ion displacements are revealed. In addition, a NBTM supported single cell consisting of Ag-NBTM cathode and Ni-NBTM anode is fabricated to evaluate the possibility of its application in intermediate-temperature SOFCs. The structural stability of NBTM is still a major concern that hinders its utilization at high temperature and under reducing atmosphere.