Synthesis and characterization of mixed fluoride Y1-xSr2+1.5xF7 (-1.0 < x < 0.5)

A series of mixed fluorides with the general formula Y1-xSr2+1.5xF7 (x = -1 .0 < x < 0.5) was synthesized and characterized by powder X-ray diffraction (XRD). It was found that the compound with the stoichiometry Y0.5Sr2.75F7 shows a cubic symmetry (fluorite-type structure) with a = 5.776 Angstrom. O n decreasing the Sr2+ content or increasing the Y3+ content in Y1-xSr2+1.5x F7, a phase with tetragonal symmetry with a = 11.416 Angstrom and c = 13.29 1 Angstrom was observed in the composition YSr2F7, whereas in the compositi on Y2Sr0.5F7, a phase with hexagonal symmetry with a = 6.882 Angstrom and c = 7.032 Angstrom was observed. The existence of phases such as YSr2F7 and Y2Sr0.5F7 was confirmed. We observed a coexistence of rhombohedral and hexa gonal phases beyond a particular nominal composition in this series of comp ounds. (C) 1999 Elsevier Science Ltd.