Crystal Structure of the Ternary Compound ErRe0.25Ge2

Abstract

An alloy of nominal composition Er 30.8 Re 7.7 Ge 61.5 was synthesized by arc melting and investigated by X-ray powder diffraction. A new ternary germanide of approximate composition ErRe 0.25 Ge 2 was found, which adopts the structure type CeNiSi 2 (Pearson symbol oS16, space group Cmcm, a = 4.0997(4), b = 15.7348(18), c = 3.9921(5) Å, R B = 0.0355, refined composition ErRe 0.23(2) Ge 2 , for the as-cast alloy; a = 4.1117(3), b = 15.6846(15), c = 4.0184(3) Å, R B = 0.0420, refined composition ErRe 0.28(2) Ge 2 , after annealing at 1073 K). The coordination polyhedron of the Er atoms has 21 vertexes (hexagonal prism with nine additional atoms), that of the Re atoms is a bicapped square antiprism and the two crystallographically independent Ge atoms center tricapped trigonal prisms and cuboctahedra. The crystal structure contains layers of trigonal prisms (characteristic of the structure type AlB 2) and square antiprisms (characteristic of the structure types BaAl 4 and CeAl 2 Ga 2), which alternate along the crystallographic direction [010]. The polyhedron surrounding the site partly occupied by the transition metal atoms is compared with the corresponding polyhedra in closely related structures.