Conductivity studies of dense yttrium-doped BaZrO₃ sintered at 1325^oC

High-temperature proton conductors have wide applications in the areas of fuel cells, electrolysis and hydrogen separation. Barium zirconate-based materials are of interest due to their good stability and high protonic conductivity. The reported conductivity of these ceramic materials is generally less than 10(-2) S/cm, even at high temperatures. This is not high enough for an electrolyte-supported device to achieve an ASR of less than 0.2 Omega cm(2) therefore thin film electrolytes are required for successful application. As BaZrO3-based materials have to be sintered at temperatures as high as 1700 degrees C, this makes it difficult to find a suitable supporting electrode which will not undergo significant chemical reaction with the BaZrO3-based electrolyte during fabrication of the required electrode supported electrolyte. In this paper, proton-conducting BaZr0.8Y0.2O2.9 was successfully sintered at 1325 degrees C with a relative density of 96% via addition of 1 wt% ZnO. Fabrication of electrochemical cells using proton-conducting BaZr0.8Y0.2O2.9 as the electrolyte thus becomes possible. The formula of the 1 wt% ZnO added sample is Ba0.97Zr0.77Y0.19Zn0.04O3-delta which exhibits a tetragonal structure with space group P4/mbm (127); a = 5.9787(1) angstrom, c = 4.2345(1) angstrom, V = 151.36(1) angstrom(3). It was found that a solid solution was formed for a limited range of Zn doping. Conductivity has been studied as a function of atmosphere (air, dry and wet 5% H-2/Ar) with the changes in bulk and grain boundary on changing atmosphere being monitored as a function of time. The total conductivity of Ba0.97Zr0.77Y0.19Zn0.04O3-delta is 1.0 x 10(-3) S/cm above 600 degrees C therefore it may be used as a proton-conducting thin film electrolyte for efficient electrochemical devices at such temperatures. The grain boundary resistance is insigniticant at high temperature for the well-sintered sample. (C) 2007 Published by Elsevier Inc.