X-ray diffraction study of an as-grown crystal of a two-phase sample of Lu0.65Ca0.35F2.65

The X-ray diffraction study of an “as-grown” crystal of Lu0.65Ca0.35F2.65 revealed for the first time two phases with a regular mutual orientation. The c axis of the hexagonal phase (a = 3.88 A, c = 6.89 A) is oriented along the body diagonal to the cubic phase (a = 5.50 A). The hexagonal phase has a tysonite-type structure with a “small” unit cell (P63/mmc, Z = 2). The cubic phase has a fluorite structure (\(Fm\bar 3m\), Z = 4).