The crystal structures of the Mn9T(=Fe, Co, Ni)3Ge5 and Mn12Ge5 germanides: New examples of partially filled Ni2In-type derivatives

Abstract

We report on the determination of the crystal structure of Mn9Co3Ge5 from single crystal X-rays diffraction (SG: R32; a=6.9697Å; c=16.4707Å). The new phase is isotypic of the binary compound Mn12Ge5 and it is also observed in the ternary diagrams Mn–Fe–Ge and Mn–Ni–Ge. According to powder X-rays diffraction, the compound Mn12Ge5 corresponds to the unknown Mn7Ge3 (κ) phase previously reported in the Mn–Ge binary phase diagram. The new type may be viewed as a Ge deficient Ni2In-type Mn2Ge1−x structure with an ordering of the Ge vacancies in a rhombohedral 9-times larger cell.