1971 Volume 44 Issue 3 Pages 643-648
Oxyfluoride phases for the rare earth Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Y have been prepared by heating a mixture of lanthanon fluorides, LnF3, and lanthanon oxides, Ln2O3. Three phases were identified. The rhombohedral phases, LnOF, have a stoichiometric composition, and the tetragonal phases, Ln4O3F6, have a comparatively large nonstoichiometric composition range. The third cubic phase, with a fluorite-type structure, was observed in the SmOF-Sm4O3F6 region after quenching from a high temperature. This establishes that both the rhombohedral SmOF and the tetragonal Sm4O3F6 transform to the cubic phase and form a complete solid solution in the high-temperature range. It is postulated that the rhombohedral and tetragonal phases are pseudo-cubic from the fact that the diffraction patterns of these two phases are closely similar to that of the fluorite type.
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