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

We report on the determination of the crystal structure of Mn 9 Co 3 Ge 5 from single crystal X-rays diffraction (SG: R32; a = 6.9697 Å; c = 16.4707 Å). The new phase is isotypic of the binary compound Mn 12 Ge 5 and it is also observed in the ternary diagrams Mn–Fe–Ge and Mn–Ni–Ge. According to powder X-rays diffraction, the compound Mn 12 Ge 5 corresponds to the unknown Mn 7 Ge 3 ( κ ) phase previously reported in the Mn–Ge binary phase diagram. The new type may be viewed as a Ge deficient Ni 2 In-type Mn 2 Ge 1 − x structure with an ordering of the Ge vacancies in a rhombohedral 9-times larger cell. [ABSTRACT FROM AUTHOR]