<i>AB</i> ₂ <i>X</i> ₂-Verbindungen im CaAl₂Si₂-Typ, VI Zur Struktur von ThCu₂P₂, YbZn₂P₂ und YbZnCuP₂ sowie der verwandten Verbindungen YbCu₃P₂ und YbCu₂P₂

Abstract

Abstract X-Ray investigations on the trigonal crystallizing compounds YbZn 2 P 2 ( a = 4.035 Å, c = 6.774Å), YbZnCuP 2 ( a = 3.946 Å, c = 6.462 Å) and ThCu 2 P 2 ( a = 4.028 Å, c = 6.469 Å) revealed a CaAl 2 Si 2 -type structure. In order to establish the limits of existence of the CaAl 2 Si 2 -type, the new compounds YbCu 2 P 2 and YbCu 3 P 2 have been prepared and structurally solved. YbCu 3 P 2 crystallizes in a trigonal-rhombohedral structure (hexagonal axes: a = 3.964Å, c = 40,296Å, c / a = 10.165, S.G. R[unk]m, Z = 6, all atoms in 6c) with a structure in which Yb-atoms are surrounded by 6 P-atoms in form of a distorted octahedron. They embrace two kinds of blocks, as they are observed in the CaAl 2 Si 2 -structure (CuP-blocks) and recognized in Cu 3 P (Cu 2 P-blocks). CuP- and Cu 2 P-blocks show a regular alternating sequenze. YbCu 2 P 2 , for which the structural determination showed the approximate stoichiometry YbCu ≈2.2 P 2 , was obtained besides YbP and crystallizes also in a trigonal-rhombohedral structure (hexagonal axes: a = 3.951 Å, c = 59.46 Å, c / a = 15.05, S.G. R[unk]m, Z = 9, Yb(l) in 3a, all other atoms in 6c, three of four Cu-positions partially occupied). The Yb-atoms are also surrounded by P-atoms in a distorted octahedron and include, as in the copper-rich compound, CuP- and Cu 2 P-blocks. However there are twice as many CuP-blocks as Cu 2 P-blocks. As the atomic distances show, Ytterbium is probably trivalent in both compounds.