Influence of sintering activators on electrical property of BaZr_0.85Y_0.15O_3-δ proton-conducting electrolyte

In this study, the influence of CuO and ZnO sintering activators on the densification behavior, distribution of sintering activators, and electrical properties of Y-doped BaZrO_3−δ proton conducting oxide were examined over a wide range of oxygen and water vapor partial pressures. With the use of 1 mol% CuO and 4 mol% ZnO, a relative density above 97% was achieved at sintering temperatures of 1500 °C and 1300 °C, respectively. The bulk and grain boundary conductivities of fully sintered BaZr_0.85Y_0.15O_3−δ, Ba(Zr_0.84Y_0.15Cu_0.01)O_3−δ, and Ba(Zr_0.81Y_0.15Zn_0.04)O_3−δ were assessed using electrochemical impedance spectroscopy. The amount of sintering activators incorporated into the bulk was investigated using an energy dispersive spectrometer equipped with a high-resolution transmission electron microscope, whereas the equilibrium concentrations of proton and oxygen vacancies as a function of water vapor pressure were estimated by thermogravimetric analysis. Using these results, the total electrical conductivities of the three compositions at 800 °C over a wide range of oxygen and water vapor partial pressures were analyzed via a non-linear fitting based on the defect structure of Y-doped BaZrO_3−δ. As a result, the proton, oxygen ion, and hole partial conductivities were calculated, and the proton transference numbers of the three compositions were compared.