A novel route to enhance the sinterability and its effect on microstructure, conductivity and chemical stability of BaCe0.4Zr0.4Y0.2O3-δ proton conductors

BaCeO3 based perovskites exhibit highest protonic conductivity in their class but suffer from low chemical stability. Addition of more stable BaZrO3 to BaCeO3 has been explored to obtain a good combination of conductivity and chemical stability. BaZrO3, however, is unfavourable towards densification due to its poor sinterability. In this study, a two-step sintering process and Zn addition have been explored vis-à-vis conventional sintering to obtain dense Y-doped BaCeO3-BaZrO3 solid solution (BaCe0.4Zr0.4Y0.2O3-δ) at comparatively lower temperatures. The conventional single-step sintering at 1450 °C for different sintering times (5, 10, 15 h) could not provide a dense sample. The two-step sintering process (1550 °C-5 min, 1450 °C-15 h), on the other hand, yielded a relative density of 95%. Addition of 4 mol.% Zn resulted in high sintered density (97%) at 1300 °C though it was not effective at 1200 °C due to insufficient shrinkage (densification). Zn addition also improved the chemical stability against CO2. The grain size of the sintered samples decreased with decreasing sintering temperature and or time. As a result the specific grain boundary conductivity decreased with decreasing sintering time. The overall conductivity was higher in the two-step processed sample compared to the Zn-doped sample. ▪ •Two-step sintering of BCZY vis-à-vis conventional and Zn-aided sintering was evaluated.•Conventional sintering was ineffective and density decreased with decreasing sintering time.•Two-step sintering was found very effective yielding 95% relative density.•Zn-doping also improved the densification but the conductivity was adversely affected.•Two-step sintered samples showed highest conductivity.