Crystal structure, chemical stability and electrical properties of Sr2MnNbO6 − δ, Sr2Cr0.5Mn0.5NbO6 − δ and Sr2CuNbO6 − δ perovskites

The 3d-cation-substituted perovskites Sr2MnNbO6 − δ, Sr2Cr0.5Mn0.5NbO6 − δ and Sr2CuNbO6 − δ were synthesized using the solid state technique. Conductivity measurements showed that the investigated phases exhibited mixed-electronic-ionic conductivity, and the total conductivity decreased in the row Sr2MnNbO6 − δ–Sr2Cr0.5Mn0.5NbO6 − δ–Sr2CuNbO6 − δ. The O2−-conductivity was measured by oxygen permeation technique, and it was found that the Cu- and Cr-containing samples exhibited ∼0.5 order of magnitude higher ionic conductivities at 500 °C, and lower activation energies, 0.85 ± 0.02 and 0.90 ± 0.02 eV, respectively, than Mn-containing compound Sr2MnNbO6 − δ (1.16 ± 0.03 eV). The conductivity, thermogravimetry and Raman measurements showed that these compositions did not intercalate the water and did not exhibit proton conductivity, but showed good chemical stability at high water vapour pressure. In contrast, the solid solution Sr2.9 − xCuxNb1.1O5.65 (x = 0.07; 0.15) with double perovskite structure was able to water uptake and to proton transport, but had a low chemical stability.