The crystal structures and phase transitions in Y-doped BaCeO 3: their dependence on Y concentration and hydrogen doping

Abstract

The crystal structures and phase transitions in BaCe 1− x Y x O 3− δ (0≤ x≤0.3) that occur in response to heat treatment in oxidizing, reducing, and water-vapor-containing atmospheres were determined by neutron powder diffraction at room temperature. Single-phase BaCe 1− x Y x O 3− δ ( δ≅ x/2) can be synthesized by O 2-annealing samples prepared by a solid-state reaction method, wherein they crystallize into perovskite-type structures (orthorhombic Pmcn for x≤0.1 and rhombohedral R3̄ c for x≥0.15). Within the composition range of 0.15≤ x≤0.25, where maximum total conductivity is observed, the rhombohedral structure converts partially to a monoclinic I2/m structure upon exposure to water- or H 2-containing atmospheres (including laboratory air) at elevated temperatures. This study may suggest a correlation between the crystal structures, particularly the I2/m phase, and the proton transport properties.