Polymorphism of scandium, yttrium and rare earth oxyfluorides under high pressure

Oxyfluorides MeOF (M = Sc, Y, Tb, Dy Ho, Er, Yb, Lu) were prepared under pressure 100 kbar at 800 and 1000 deg C. Phase analysis of the final products was base on the study of X-ray spectra of the powders. In all experiments scandium oxyfluoride was obtained in the form of tetragonal modification. Yttrium and REE oxyfluorides have rhombic structure of PbCl2 type. Prepared phases were annealed under vacuum at 450 deg for 5 hour. Scandium oxyfluoride transformed into the structure of type XrO2. Lutecium oxyfluoride gave two phases; tetragonanal and rhombic, terbium oxyfluoride afforded rhombic modification TbOF and the phase of solid solution with cubic structure. All other oxyfluorides have been transformed into the state with rhombic structure