Composition of Single Crystals of Chromium Chalcogenide Spinels Grown by Chemical Vapor Transport

Abstract

Compositional analyses using atomic absorption spectrophotometry were carried out on the vapor-phase grown single crystals of copper-based spinels with the nominal formulas such as CuCr2S3Cl, Cu1−xFexCr2S4 (x≤1), Cu0.5In0.5Cr2S4, CuCr2Se3Cl, and CuCr2Se3Br, and the cadmium-based spinels of CdCr2S4 and CdCr2Se4, including crystals doped with indium, silver, and copper. The grown crystal usually had a composition different from the nominal formula and a tetrahedral-site deficiency of the copper-based spinels is reported for the first time. All crystals of Cu1−xFexCr2S4 and Cu0.5In0.5Cr2S4 were contaminated with a considerable amount of chlorine and some of the crystals had a substantial cation deficiency on the tetrahedral sites; the cation deficiency increases with increasing copper or chlorine content. For the CuCr2S3Cl and CuCr2Se3Br crystals, a large copper deficiency was also found while the halogen content was close to that expected for the nominal compositions, or somewhat higher. Of all the copper-based spinels, the least tetrahedral-site deficiency was observed in the CuCr2Se3Cl crystals, but the chlorine content was much less than the stoichiometric content. The cadmium-based spinels usually satisfied the stoichiometric formula CdCr2S4 or CdCr2Se4.