CRYSTAL-STRUCTURES OF GADOLINIUM-DOPED AND YTTRIUM-DOPED BARIUM CERATE

The crystal structures of two doped, oxide ion and protonic conducting perovskites, BaCe0.9M0.1O2.95 with M = Gd or Y, have been refined from room-temperature neutron powder diffraction data. Both compounds are orthorhombic, space group Pmcn, Z = 4, with lattice constants a = 8.7705(4) angstrom, b = 6.2233(3) angstrom, c = 6.2393(3) angstrom for BaCe0.9Y0.1O2.95 and a = 8.7728(16) angstrom, b = 6.2219(12) angstrom, c = 6.2443(14) angstrom for BaCe0.9Gd0.1O2.95. The lattice constants and fractional coordinates of both compounds are shifted only slightly from the undoped compound indicating the good lattice match of Y3+/Gd3+ for Ce4+ . For Y-doping, the extrinsic anion vacancy has been found to lie on only one of the two crystallographically distinct oxygen sites but the extreme absorption cross-section of Gd precluded refinement of the oxygen site occupancies in BaCe0.9Gd0.1O2.95.