Processing and characterisation of BaZr0.8Y0.2O3- δproton conductor densified at 1200 °c

Abstract

Barium zirconate-based perovskites (BZY) are intensely studied proton conductors for high-temperature electrochemical applications; however, their refractory nature means excessive temperatures are required for sintering (∼1700 °C). Although different strategies have been employed to improve densification, a high-temperature step (1300-1700 °C) is generally required to achieve sufficient grain growth and good electrical properties. Here, sol-gel synthesis using alkoxide precursors is employed to obtain BaZr0.8Y0.2O3-δ sinter-reactive powders with Ba excess at 750 °C. High relative densities (∼98%) of ceramic bodies with an average grain size ∼190 nm were obtained on sintering isostatically-pressed pellets at the uniquely low temperature of 1200 °C for 4 hours on addition of 4% mol ZnO as a sintering agent to the Ba-excess sol-gel powders. Impedance spectroscopy indicates that the resistance of the greater grain-boundary volume arising from the low densification temperature is largely offset by a higher specific grain-boundary conductivity than that of the same composition sintered at 1650 °C with larger grain size. Conductivity measurements for prolonged periods in dry and wet (pH2O ∼ 0.022 atm) 90% N2 : 10% H2 and 90% Ar : 10% CO2 atmospheres at 500 °C verified that Ba excess in the starting composition did not contribute to deteriorating chemical stability. Processing of sol-gel BZY nanopowders with Ba excess combined with ZnO sintering aid is thus demonstrated as a successful low-temperature route for obtaining BZY with high density, stability and sufficient grain growth for electrochemical applications. This journal is