A structural investigation of several mixed lanthanide orthophosphates

Abstract

The single crystal structures of Gd 0.5Er 0.5PO 4, Gd 0.5Y 0.5PO 4, Gd 0.5Yb 0.5PO 4 and Gd 0.75Yb 0.25PO 4 have been determined by means of single crystal X-ray diffraction techniques. These mixed phosphate compounds have the zircon-type structure and are therefore isostructural with the pure orthophosphates of the higher lanthanides (i.e. Tb, Dy,...., Lu). The subject mixed orthophosphates crystallize in space group I4 1/ amd (D 19 4h, No. 141). Anisotropic refinement of the structures using a full-matrix least-squares program yielded final reliability factors in the range of 0.040 to 0.053. The metal atoms in each compound are eight coordinated to oxygen atoms, with two distinct MO bond distances. The important bond distance PO av. was found to be 1.533(6) Å. The coordination geometry about the central metal atom is bisphenoidal (D 2 d) and is represented by two interpenetrating tetrahedra. In each mixed compound, the phosphate group is found to be a distorted tetrahedron.