Hydrothermal syntheses and crystal structure of NH4Ln3F10 (Ln = Dy, Ho, Y, Er, Tm)

Ammonium rare earth fluorides NH(4)Ln(3)F(10) (Ln = Dy, Ho, Y, Er, Tm) were synthesized by a hydrothermal method, Two polymorphs, of the hexagonal beta -KYb3F10 and the cubic gamma -KYb3F10 structure types, were formed under hydrothermal conditions for most of the rare earth fluorides except NH4Dy3F10, for which only the cubic gamma -phase was obtained. The crystal structures of MLn(3)F(10) (M = alkaline metal, NH4+ and Ln = rare earth) show a strong correlation to the ratio of ionic radii (R-M/R-Ln), which has been expressed in a structure phase diagram of the ionic radii of univalent and rare earth cations, (C) 2001 Academic Press.