In situ high-temperature X-ray powder diffraction study of the synthetic Ca_2Sb_20_7 weberite-type compound

摘要

The crystal structure of synthetic Ca_2Sb_20_7 has been investigated by in situ X-ray powder diffraction methods within the temperature range 298-1273 K. Ca_2Sb_20_7 is orthorhombic, space group Imma, over the entire temperature range and shows only general thermal expansion. The unit-cell parameters show a monotonous increase as a function of temperature. Only slight changes occur in the individual bond distances without evidence of abrupt structural changes. The mean coefficients of thermal expansion along the various axes are: a_a= 9.49 x 10~(-6)K~(-1), a_b=10.11 x 10-~(-6) K~(-1), a_c=7.56 x 10~(-6) K~(-1) and the bulk thermal expansion coefficient a_v= 27.20 x 10~(-6)K~(-1).