The crystal structures and phase transitions in Y-doped BaCeO3: their dependence on Y concentration and hydrogen doping

The crystal structures and phase transitions in BaCe1-xYxO3-delta (O less t han or equal to x less than or equal to 0.3) that occur in response to heat treatment in oxidizing, reducing, and water-vapor-containing atmospheres w ere determined by neutron powder diffraction at room temperature. Single-ph ase BaCe1-xYxO3-delta (delta congruent tox/2) can be synthesized by O-2-ann ealing samples prepared by a solid-state reaction method, wherein they crys tallize into perovskite-type structures (orthorhombic Pmcn for x less than or equal to 0.1 and rhombohedral R (3) over barc for x greater than or equa l to 0.15), Within the composition range of 0.15 less than or equal to x le ss than or equal to 0.25, where maximum total conductivity is observed, the rhombohedral structure converts partially to a monoclinic 12/m structure u pon 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 12/m phase, and the proton transp ort properties, (C) 2000 Elsevier Science B.V. All rights reserved.