Structural transformation of the oxygen and proton conductor Ba2In2O5 in humid air: an in-situ X-ray powder diffraction study

摘要

The oxygen and proton conductor Ba2ln2O5is known to undergo a structural transformation inhumid atmosphere at about 3000C. The resulting phaseBa2ln2O5·H2O was investigated by in-situ high-temperature X-ray diffraction. During thetransformation, a transient structure existing near3200C in a narrow temperature interval is formed.Ba2ln2O5·H2O is stable from ≈3000C gown to roomtemperature and may be characterized by S.G. P4/mmm,No. 123, tetragonal, with a = 4.1827(10) A, b=4.1827(10) A and c = 8.9617(10) A. The atomicrearrangement during the transformation together withthe change of the coordination of one half of the inatoms from tetrahedral to octahedral symmetry reducesthe unit cell volume of Ba2ln2O5·H2O to one quarterof the initial value. Linear thermal expansioncoefficients of both phases show a strong anisotropy.