The system MgGa2S4-MgSc2S4 and the crystal structure of olivine type MgGaScS4 with a comment on olivine type MnGaScS41

The system MgGa2S4-MgSc2S4 was studied by X-ray diffraction methods on samples quenched from 800 to 1000 degrees C. Two new compounds MgGaxSc2-xS4 are obtained: for x = 1.6 a new material with FeGa2S4 type structure (trigonal, P (3) over bar m1 (No. 164), a = 373.7(1), c = 1222.0(2) pm) and for x = 1.0 a new olivine type compound (orthorhombic, Pnma (No. 62), a = 1278.5(3), b = 741.9(1), c = 607.2(1) pm). The crystal structure of the olivine type compound MgGaScS4 was determined from single-crystal X-ray diffraction data and refined to R = 0.025. The octahedral 4a site is occupied by 0.7 Sc and 0.3 Mg, the 4c site, which is octahedrally coordinated also by 0.3 Sc and 0.7 Mg, and the tetrahedrally coordinated 4c site by Ga. An analogous cation distribution is found for the olivine MnGaScS4.