X-ray diffraction and Ir-absorption characteristics of lanthanide orthophosphates obtained by crystallisation from phosphoric acid solution

Powders of LnPO(4).H2O (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) prepared by crystallisation from boiling phosphoric acid (2 M H3PO4/1) Solution were characterised by X-ray diffraction and FTIR-spectroscopy. Hexagonal LnPO(4) . H2O (La --> Tb), tetragonal (Ho --> Lu and Y) and orthorombic DyPO4 . H2O crystalline modifications were identified. Ir-spectra of the hydrated hexagonal, anhydrous tetragonal LnPO(4) . H2O (Dy, Ho, Er, Tm, Yb, Lu and Y) and anhydrous monoclinic (La --> Tb) are consistent with those reported in the literature. However, the hydrated tetragonal LnPO(4) . H2O (Ho, Er, Tm, Yb, Lu and Y) display a surplus band (625 cm(-1)) in the region of nu(4), which was not reported in the literature. The band disappears after ignition at 950degreesC, while the tetragonal structure is still maintained, which may imply that it is attributed to hydrogen bonding of H2O molecules to the phosphate oxygen in hydrated salts. Some of the phosphates, after ignition at 950degreesC, display additional P2O74- band at 1265-1267 cm(-1). That may be resulted from HPO42- for PO43- substitution in the phosphates crystallised in acidic (2 M H3PO4/1) solution. (C) 2003 Kluwer Academic Publishers.