Proton conductivity of Ca-doped Ba2R1-xCaxNbO6-δ (R = La, Nd, Sm, Gd, Dy, Y, and Yb) ceramics with double perovskite structure

The influence of Ca substitution for R (R = La, Nd, Sm, Gd, Dy, Y, and Yb) on the electrical conductivity of double perovskite-structured Ba₂R_1-xCa_xNbO_6-δ (x = 0 and 0.2) ceramics was characterized in this study. Crystal structure analysis of Ba₂R_0.8Ca_0.2NbO_6-δ showed three types of lattices, monoclinic (R= La and Nd), tetragonal (R= Sm, Gd, and Dy) and cubic (R= Y and Yb), resulting the reduction of structural distortion for monoclinic structure by the Ca substitution for R. The significant differences in the electrical conductivity between the Ba₂LaNbO₆ and Ba₂La_0.8Ca_0.2NbO_6-δ ceramics may be related to the decrease in the structural distortion, as suggested by the changes in HT-XRPD patterns. Ba₂La_0.8Ca_0.2NbO₆ ceramic exhibited the highest electrical conductivity of 2.21 × 10⁻³ S/cm at 800 ℃ measured under a wet 1 % H₂/Ar atmosphere. EMF measurements using a hydrogen concentration cell with water vapor and a water vapor concentration cell revealed that the predominant charge carriers in the Ba₂R_1-xCa_xNbO_6-δ ceramics were protons in the temperature range of 600–800 ℃.