Some observations on the synthesis and electrolytic properties of (Ba_1-xCa_x) (M_0.9Y_0.1)O₃, M = Ce, Zr-based samples modified with calcium

In this paper, the impact of partial substitution of calcium for barium in (Ba_1-xCa_x) (M_0.9Y_0.1) O₃, M = Ce, Zr on physicochemical properties of the powders and sintered samples was investigated. The powders, with various contents of calcium (x = 0, 0.02, 0.05, 0.1), were prepared by means of thermal decomposition of organometallic precursors containing EDTA. All of the BaCeO₃-based powders synthesised at 1100 °C were monophasic with a rhombohedral structure, however, completely cubic BaZrO₃-based solid solutions were obtained at 1200 °C. A study of the sinterability of BaZr_0.9Y_0.1O₃ and BaCe_0.9Y_0.1O₃-based pellets was performed under non-isothermal conditions within a temperature range of 25 to 1200 °C. The partial substitution of barium for calcium in the (Ba_1-xCa_x) (M_0.9Y_0.1) O₃, M = Ce, Zr solid solution improved the sinterability of the samples in comparison to the initial BaCe_0.9Y_0.1O₃ or BaZr_0.9Y_0.1O₃. The relative density of calcium-modified BaCe_0.9Y_0.1O₃-based samples reached approximately 95 to 97 % after sintering at 1500 °C for 2 h in air. The same level of relative density was achieved after sintering calcium-modified BaZr_0.9Y_0.1O₃ at 1600 °C for 2 h. Analysis of the electrical conductivity from both series of investigated materials showed that the highest ionic conductivity, in air and wet 5 % H₂ in Ar, was attained for the compositions of x = 0.02 to 0.05 (Ba_1-xCa_x)(M_0.9Y_0.1)O₃, M = Zr, Ce. The oxygen reduction reaction on the interface Pt│BaM0.9Y0.1O3, M = Ce, Zr was investigated using Pt microelectrodes. Selected samples of (Ba_1-xCa_x) (M_0.9Y_0.1)O₃, M = Zr, Ce were tested as ceramic electrolytes in hydrogen-oxygen solid oxide fuel cells operating at temperatures of 700 to 850 °C.