Investigation of electrical conductivity and oxygen relaxation behavior for BaBi_0.98Sr_0.02Nb_5-xTi_xO_15-δ ceramics

BaBiNb₅O_15- based oxide ion conductors have shown promise for solid fuel cell applications at medium temperatures. In this study, BaBi_0.98Sr_0.02Nb_5-xTi_xO_15-δ (x = 0.02, 0.04, 0.05, 0.06, 0.08) samples were prepared by the conventional solid-state synthesis with two-step sintering method. The electrical properties and oxygen relaxation behaviors of the BaBi_0.98Sr_0.02Nb_5-xTi_xO_15-δ samples were investigated. With increasing the Ti content, the bulk conductivity of the BaBi_0.98Sr_0.02Nb_5-xTi_xO_15-δ samples showed a trend of increasing first and then decreasing. When the doped Ti content reached 5 mol%, the highest bulk conductivity of BaBi_0.98Sr_0.02Nb_5-xTi_xO_15-δ samples can be got, 5.27 × 10⁻⁵ S/cm at 773 K. According to the dielectric relaxation spectroscopy measurement, the BaBi_0.98Sr_0.02Nb_4.95Ti_0.05O_15-δ sample exhibits the higher moveable oxygen vacancy concentration and mobility of oxygen vacancies. This could be the possible reason that there is the highest bulk conductivity in the BaBi_0.98Sr_0.02Nb_4.95Ti_0.05O_15-δ sample. Additionally, the influence of sintering temperature on the electrical properties of the BaBi_0.98Sr_0.02Nb_4.95Ti_0.05O_15-δ compound was investigated. When the BaBi_0.98Sr_0.02Nb_4.95Ti_0.05O_15-δ sample is sintered at a temperature of 1423 K, it exhibits the best bulk conductivity and total conductivity.