Oxygen-ion and proton transport in Y<SUP>3+</SUP>-doped hexagonal perovskite Ba<sub>7</sub>In<sub>6</sub>Al<sub>2</sub>O<sub&gt

In this work, the thermal and electrical properties of the Y3+-doped Ba7In5.9Y0.1Al2O19 phase, characterized by a hexagonal perovskite structure (a = 5.935(7) Å, c = 37.736(8) Å), were studied. It has been established that the phase is capable of incorporating protons and exhibiting proton conductivity. The introduction of an isovalent dopant, yttrium, led to an increase in the concentration of protons (up to the limiting values of Ba7In5.9Y0.1Al2O19 ·0.55H2O), as a result of an increase in the unit cell volume and, accordingly, the free space for the placement of OH–-groups in an oxygen-deficient block containing coordination-unsaturated polyhedra [BaO9]. Isovalent doping led to an increase in the oxygen-ion conductivity, which is due to an increase in interatomic distances and a decrease in the migration activation energy. In a humid atmosphere (pH2O = = 1.92·10–2 atm), the Ba7In5.9Y0.1Al2O19 phase exhibited higher values of proton conductivity compared to the matrix compound Ba7In6Al2O19 and below 500°C it was characterized by dominant proton transport both in air and in a wide range of pO2 (10–18–0.21 atm).