Phase relationships in the systems MSCr2S3In2S3 (M = Co,Cd, Hg)

The phase diagrams of the quaternary systems MSCr₂S₃In₂S₃, with M = Co, Cd, and Hg, were studied with the help of X-ray powder photographs of quenched samples, high-temperature X-ray diffraction patterns, DTA and TG measurements, and far-infrared spectra. Because indium sulfides do react with silica tubes, alumina crucibles must be used for annealing the samples. Complete series of mixed crystals are formed among the spinel-type compounds MCr₂S₄, MIn₂S₄ (M = Cd, Hg), and In₂S₃. HgIn₂S₄ is decomposed at temperatures above 300°C. In the sections CoCr₂S₄CoIn₂S₄ and CoCr₂S₄In₂S₃ relatively large miscibility gaps exist due to the change from normal to inverse spinel structure. But the interchangeability of both systems increases with increasing temperature, and at temperatures above 1000°C, complete series of solid solutions are formed, which can be quenched to ambient temperature. Superstructure ordering like that of ordered α-In₂S₃ has been found in the In-rich region of the MIn₂S₄In₂S₃ solid solutions. The unit cell dimensions of all stoichiometric and phase boundary compounds, e.g., Cd_1.15In_1.9S₄, including the chromium spinels MCr₂S₄ (M = Mn, Zn) and ZnCr₂Se₄, are given and discussed in terms of possible deviations from stoichiometry.