Soft chemistry routes for the synthesis of Sr_0.02La _0.98Nb_0.6Ta_0.4O₄ proton conductor

Proton conducting Sr_0.02La_0.98Nb_0.6Ta _0.4O₄ powders were prepared by auto-combustion or co-precipitation methods from aqueous solutions using citrates and oxalates as complexing agents. After calcination at 1100C the two methods lead to powders with sub-micrometric average particle size, 0.5 μm and 0.7 μm, respectively. Upon sintering at 1600C, pellets with an average grain size of 11 m for the auto-combustion method and of 7 μm for the co-precipitation method were obtained. The electrical conductivity measured on sintered pellets at 800C in wet argon atmosphere was 1.9 ×10^-4 S cm^-1 for the material obtained by co-precipitation method, 1.8× 10^-4 S cm^-1 for the one derived from auto-combustion method, and 7.4× 10^-5 S cm^-1 for the one produced by solid state reaction. The improvement in conductivity of the wet chemistry methods with respect to the solid state reaction was ascribed to the better control of the cation mixing with the synthetic conditions.