Possible deuterium positions in the high-temperature deuterated proton conductor Ba3Ca1+yNb2-yO9-delta studied by neutron and X-ray powder diffraction

High-temperature proton conductors with perovskite structures are a class o f well-known systems with high protonic conductivity, which is of high tech nological interest in view of the possible applications in solid oxide fuel cells. We present neutron and X-ray diffraction studies of the crystal str ucture of the Ba3Ca1.18Nb1.82O9-delta + zD(2)O (BCN18) system that exhibits high proton conductivity. It is assumed that the mechanism of proton condu ctivity in BCN18 is connected with trapping of protons at some interstitial positions in the crystal lattice as deduced from earlier quasielastic neut ron scattering and muon spin rotation studies published in the literature. In order to get more information on the location of deuterium, systematic h igh-resolution neutron diffraction studies of the stoichiometric Ba3Ca1Nb2O 9 and non-stoichiometric BCN18 compounds with and without D2O were performe d. The ROTAX time-of-flight (TOF) diffractometer at the ISIS neutron spalla tion source and the SW double-axis diffractometer at the DIDO reactor at Ju lich were used. Refinements of the crystal structures were performed by usi ng the FULLPROF and GSAS programs. The possible deuterium positions in the crystallographic unit cell are discussed. (C) 2001 Elsevier Science B.V. Al l rights reserved.