Variants of the X-phase in the Mn-Co-Ge system

Abstract

We report two new variants of the X-phase (ortho­rhom­bic, space group Pnnm) derived from the Mn-Co-Ge system. Two com­positionally related crystals were investigated by means of single-crystal X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The Mn14.9Co15.5Ge6.6 and Mn14Co16.2Ge6.8 inter­metallic com­pounds are part of the homogeneity region of the X-phase and adopt the Mn14(Mn0.11Co0.64Si0.25)23 structure type. The com­position obtained from refinement of the XRD data is in agreement with the EDS results. In the present study, chemical disorder was only detected on the 8h positions. The ordering is com­pared with other members of the X-phase family and shows that the degree of disordering depends on the chemical com­position. No com­pletely ordered variants of the X-phase have yet been reported.