Novel mid-temperature Y3+ → In3+ doped proton conductors based on the layered perovskite BaLaInO4

The possibility of isovalent substitution in the In-sublattice of layered perovskite BaLaInO₄ was experimentally investigated. The yttrium doping leads to the increase of total and protonic conductivity up to 2 orders of magnitude. The solid solution BaLaIn_1?xY_xO₄ (0 ≤ x ≤ 0.5) is mixed ionic-electronic (hole) conductor at the dry air. The increase in the water vapor partial pressure leads to the appearance of protons in the structure below 600 °C, which is confirmed by the decrease of activation energy from ～0.75 eV to ～0.52 eV for doped samples. Both undoped and doped BaLaIn_1?xY_xO₄ samples are nearly pure (～95%) proton conductors under wet air conditions below 400 °C. The most conductive Y-doped compositions BaLaIn_0.8Y_0.2O₄ demonstrates the proton conductivity value 4?10^?5 S/cm at the 400 °C.