Nickel scandium germanide Sc3Ni4Ge4: a new ternary germanide with the Gd6Cu8Ge8-type structure

Abstract

ScaNi4Ge 4, orthorhombic, Immm, Z = 2, a = 12.910 (9), b = 6.598 (4), c = 3.908 (2)/~,, V = 332.88 A a, # = 31.1 mm -1 (Mo K~ ;t = 0.7107/k). The compound crystallizes with the Gd6CusGes-type structure. The structure was refined from single-crystal data. The final R = 0.042 for 205 reflections with isotropic thermal parameters for all atoms. Introduction. During the investigation of the Sc- Ni-Ge system, among several new ternary germanides, a compound with the approximate composition Sc3Ni4Ge 4 was found. Its powder diffractogram was very similar to that of ScaNi4Si4 (Bodak, Kotur & Gladyshevsky, 1976), the crystal structure of which was reported to be of the Gd6CusGe s type (Rieger, 1970). As the crystal structure of Sc3Ni4Si4 had been determined from powder data and the atomic param- eters had not been refined, we decided to perform a full structure investigation of Sc3Ni4Ge4 from single-crystal data. A single crystal of prismatic shape with dimensions 0.024 x 0.008 x 0.066 mm was isolated from a crushed ingot of stoichiometry close to ScaNiaGe 4. The sample was prepared by arc melting. The single crystal was examined by Laue and rotation photographs. The Laue class mmm and the systematic absences (hkl with h + k + l= 2n, hkO with h + k = 2n, hOlwith h + l= 2n, Okl with k + l = 2n, h00 with h = 2n, 0k0 with k = 2n, 00l with l = 2n) indicate Immm, Imm2, I222 and 1212121 as the possible space groups. The space-group symmetry together with the lattice parameters indicated the Gd6CusGes-type structure. Intensity data were collected by means of a Philips PW 1100 four-circle diffractometer (graphite-mono- chromatized Mo K~ radiation). Integrated intensities of 205 reflections were collected in the 0-20 scan mode up to a limit of sin 0/2 = 0.70 A -1. Lattice parameters (see Abstract) were obtained from the 20 values for 13 reflections by means of the least-squares method. The parameters of Gd6CusGe 8 given by Rieger (1970) were used as starting values for a least-squares