Crystal Growth and Structure Refinement of SeCeO₃ Protonic Conductor

Crystals of SrCeO₃ and SrCe_0.95Yb_0.05O_3-a were grown by Xe arc-image FZ method. The crystal structures of SrCeO₃ and SrCe_0.95Yb_0.05O_3-a were determined by the powder X-ray diffraction profile refinement (Rietveld method). The trial model for the refinement was determined with the technique suggested by Glazer for distorted perovskite-type structures. The crystal data for SrCeO₃ are orthorhombic. Pnma (No. 62) and a=6.1473(2), b= 8.5803(5), c=6.0066(2)A with a^-b⁺a^- anion octahedra tilt system. SrCe_0.95Yb_0.05O_3-a has the same symmetry with SrCeO₃ and a = 6. 1409(2), b = 8.5783(7), c=5. 9997(4) A. The refined structure parameters were approximately the same between SrCeO₃ and SrCe_0.95Yb_0.05O_3-a within a standard deviations. The protonic conduction of SrCeO₃, which is caused by the partial substitution of Ce with Yb, is not accompanied by obvious structural changes. The refined structual parameters also showed that the anion octahedra tilt 13. 2° about [100] and [001] and 10.7° about [010], which are extremely large among perovskite-type compounds with similar a^-b⁺a^- tilt systems. Precession photographs and polarization micrographs showed that the grown crystals had complex twin structures which were seemed to be formed by successive transformations accompanying the tilt of the anio octahedra.