New ternary phosphides Ln3-xCu8-yP8 (Ln=Y, Gd, Tb, Dy, Ho, Er, Tm) and their crystal structure

Phosphides RE3-xCu8-yPa (RE=Y, Gd, Tb, Dy, Ho, Er and Tm) were synthesized. The crystal structure of Y3Cu8-yP8 (y = 0.35(1)), which belongs to a new structure type, was determined by single crystal methods: space group R (3) over bar m, a=3.968(1), c=60.14(1) Angstrom, R = 0.0571 for 210 independent reflections. The isotypic compound Gd3-xCu8-yP8 (x=0.28(3), y=1.0(1), R=0.097) was studied by X-ray powder methods and for other phosphides RE3-xCu8-yP8 (RE =Y, Tb, Dy, Ho, Er and Tm) the lattice parameters were determined. The structure of Y3Cu8-yP8 is constructed from fragments of Cu3P, with one of the fragments containing additional P atoms, and a close packing of RE atoms. The structure can also be considered as an intercalation of additional P atoms in the Yb3Cu8-xP6 structure. (C) 1998 Published by Elsevier Science S.A. All rights reserved.