Protonic and electronic hole conductivity of grain interior and grain boundaries in BaZr0.9Y0.1O3-δ: Effect from sample processing

Abstract

BaZr0.9Y0.1O3-δ (BZY10) is a popular composition for the electrolyte in protonic ceramic cells, due to its relatively high proton conductivity, excellent chemical stability, and good compatibility with NiO negatrode substrate during high temperature co-sintering. The microstructure of BZY10 is highly dependent on sample processing, leading to large discrepancy of the electrochemical performance of BZY10 in literature. In this work, three BZY10 samples were prepared by different sample processing and sintering conditions, and the grain interior (bulk) and grain boundary partial conductivities of protons and holes were separated. The sintering processes influenced the transport properties of pristine BZY10 samples significantly, and longer sintering time at high temperature (1650 – 1700 °C) leads to lower proton conductivity in both bulk and grain boundary. However interestingly, longer sintering time resulted in higher ionic transport number of bulk conduction, but lower ionic transport number of grain boundary conduction, possibly due to increasing Ba-deficiency in bulk by longer annealing at high temperature. Besides, adding ZnO into BZY10 decreased the proton conductivity in both bulk and grain boundary, but its ionic transport number of bulk conduction increases. A further analysis based on the theory of space charge layer indicated that adding ZnO leaded to decreased Schottky barrier height in the grain boundary core, and the highest Schottky barrier height was observed in the pristine sample which was sintered for longer time. The results obtained in this work suggest a potential strategy to regulate the transport properties of BZY10 by choosing appropriate approaches for sample processing to control the microstructure and local composition of the polycrystalline BZY10 ceramic electrolyte.