The structures of the chromium sulphides

The system Cr-S has been studied at room temperature. In the range CrSo.95-CrS~.50--previously thought to be a berthollide rango---six phases, each with a narrow homogeneity range, were established: namely, monocl{n~c CrY, tr~gona[ ~rT~s ~, tr{gonal Crsg e, monocI~nle Cr3S4, tr~gonal Cr2S 3 and rhombohedral Cr2S 3. The structure of CrS is intermediate between the NiAs and PtS types. 'CrTS s' probably has a partly disordered structure intermediate between the NiAs and Cd(OH)2 types. The structures of the other chromium sulphides are also intermediate between those of NiAs and Cd(OH) 2, but the lattices are completely ordered. CrsS e is ferrimagnetic within a limited temperature range; at 5 C. the magnetic anisotropy is fotmd to be of negative sign. The magnetic properties of structures related to the NiAs type are discussed in connection with geometrical aspects. It is suggested that in the chromium sulphides both ionic Cr-S bond, ~. and metallic Cr-Cr bonds are present. Phase Symmetry :Homogeneity range a-Cr Cubic b.c. Very narrow CrS Monoclinic Probably ~ CrSo.9~ 'Cr7S s' Trigonal Cro.ssS-Cro.87S CrsS 6 Trigonal Cro.85S Cr3S 4 Monoclinic Cro.79S-Cro.TeS CreS 3 tr. Trigonal Cro.6sS Cr2S a rh. Rhombohedral Cro.