Transport Properties of Intergrowth Structures Ba5In2Al2ZrO13 and Ba7In6Al2O19

The development of solid oxide fuel cells operating at medium temperatures (500–700 °C and even lower) requires the search for proton conductors based on complex oxides that would have a wide range of required properties. This task stimulates the search for new promising phases with proton conductivity. The new hexagonal perovskite-related compound Ba7In6Al2O19 was synthesized by the solid-state method. The phase was characterized by powder X-ray diffraction, thermogravimetric analysis, FT-IR spectroscopy, and impedance spectroscopy (in a wide range of temperatures, and partial pressures of oxygen at various atmospheric humidities). The investigated phase had a hexagonal structure with a space group of P63/mmc; the lattice parameters for Ba7In6Al2O19 are a = 5.921(2) Å, c = 37.717(4) Å. The phase is capable of reversible hydration and incorporates up to 0.15 mol H2O. IR-data confirmed that protons in the hydrated compound are presented in the form of OH–-groups. Electrical conductivity data showed that the sample exhibited dominant oxygen-ion conductivity below 500 °C in dry air and dominant proton conductivity below 600 °C in wet air.