Determination and redetermination of the crystal structures of chromium tellurides in the composition range CrTe1.56–CrTe1.67: Trigonal di-chromium tri-telluride Cr2Te3, monoclinic penta-chromium octa-telluride Cr5Te8, and the five layer superstructure of

Single crystals of trigonal Cr2Te3, monoclinic Cr5Te8, and trigonal Cr5Te8 were prepared and the single crystal structures were determined. The structures are related to the NiAs structure type by successive removal of Cr in every second metal atom layer parallel to the c axis. The strong relationship between the structures is evidenced by their very similar X-ray powder patterns. In trigonal Cr2Te3 excess Cr occupies only one of the two possible sites. In monoclinic Cr5Te8 the Cr atoms occupy four different crystallographic sites. The resulting ordering of the vacancies is significantly different from the hitherto reported crystal structures of transition metal chalcogenides M5X8. A slight increase of the tellurium content leads to an order-disorder transition from the monoclinic to a trigonal phase. The Cr atoms are located on four crystallographically different sites leading to the formation of a five layer superstructure of the CdI2 type. A possible explanation is given why Cr5S8 and Cr5Se8both with the monoclinic structure type cannot be prepared under normal conditions.