Conduction properties and transport number of double perovskite barium tantalate ceramic

Abstract Ba3Ca1·18Nb1·82O9-δ(BCN18), which has a high conductivity and protonic conductive dominant above 600 °C, is regarded as a promising double perovskite-type proton conductor for solid oxide fuel cells, catalysis, and electrochemical sensors. To further increase the conduction properties of the double perovskite-type proton conductor, it can be considered to decrease the electronegativities of A and B site elements. In this study, Ba and Ta, which have lower electronegativities than those of Ca and Nb, were introduced to totally substitute Ca and Nb. The double perovskite-type proton conductor Ba4·3Ta1·7O8.55 (BBT30) was prepared by solid-state sintering. We found that the total conductivities increased linearly with the increase of the temperature, with the total conductivities being in the range of 1.2 × 10−5−8.7 × 10−4 S cm−1 in humid air at 400 °C−800 °C; the estimated activation energy of proton was obviously lower than those of oxide ion and hole. The standard molar hydration enthalpy of BBT30 was calculated to be −79.9 kJ/mol. Additionally, the transport numbers were determined systematically by defect equilibria model. Our results indicated that both the transport numbers of oxide ion and hole remarkably increased with increasing oxygen partial pressure, while the protonic conduction was always predominant in those atmospheric conditions, with the protonic transport number being 0.64 at 700 °C, and it was significantly higher than those of other double perovskite-type proton conductors. This indicates that BBT30 is an excellent candidate for an electrochemical sensor, and our work has demonstrated a new direction in developing a high conductivity and protonic transport number perovskite-type proton conductor.