Ternary Phosphide Ho2Cu6−x P5−y , Its Crystal Structure, and RE m+n (Cu2P3) m (Cu4P2) n Relationship with Other Rhombohedral Rare-Earth Copper Phosphides

Crystals of the phosphide Ho2Cu6−x P5−y (x=0.41, y=0.50) have been prepared by annealing pressed powders of the elements at 800°C for 2 weeks. The structure was determined by single-crystal methods: space group R 3 m (No. 166), Z=3, a=3.976(1) Å, c=40.554(8) Å, R=0.045 for 243 independent reflections [F>4σ(F)]. The unit cell of Ho2Cu6−x P5−y can be built from a close packing of Ho atoms and fragments of Cu3P, with one of the fragments containing additional P atoms. It can be also considered as an intercalation of additional P atoms in the YbCu3−x P2 structure (P. Klüfers, A. Mewis, and H. U. Schuster, Z. Kristallogr. 149, 211 (1979)). The RE m+n (Cu2P3) m (Cu4P2) n relationship with other rare-earth copper phosphides, having similar structural characteristics is discussed.