A new ternary derivative of the Laves phases in the Mg-Co-Ga system.

Crystal structures of MgCoGa, Mg 0.74 CoGa 0.52 and Mg 0.49 CoGa 0.15 phases from the Mg-Co-Ga system were investigated using single-crystal diffraction. These structures belong to the family of so-called Laves phases. Hexagonal MgCoGa crystallizes as a disordered phase within the MgZn 2 structure type. The orthorhombic structure of Mg 0.74 CoGa 0.52 is a distortion variant of MgZn 2 and URe 2 structure type, and the structural relation is demonstrated in terms of a Bärnighausen formalism group-subgroup transformation scheme. The structure of trigonal phase Mg 0.49 CoGa 0.15 is strongly disordered, as is shown by the presence of adjacent atomic sites which cannot be occupied simultaneously. In Mg 0.49 CoGa 0.15 , two subcells (A and B) were obtained in a ratio of 9:1. Subcell A is closely related to MgZn 2 -type.