NEW TERNARY PHOSPHIDES LN(3-X)CU(8-Y)P(8) (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 synthes ized. The crystal structure of Y3Cu8-yP8 (y = 0.35(1)), which belongs to a new structure type, was determined by single crystal methods: spa ce 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 l attice parameters were determined. The structure of Y3Cu8-yP8 is const ructed from fragments of Cu3P, with one of the fragments containing ad ditional P atoms, and a close packing of RE atoms. The structure can a lso be considered as an intercalation of additional P atoms in the Yb3 Cu8-xP6 structure. (C) 1998 Published by Elsevier Science S.A. All rig hts reserved.