An electron microscope study on substitutional order and disorder in the system MnSLn2S3 (Ln = Yb or Y)

The substitution of 2 Ln³⁺ (Ln is Yb or Y) for 3Mn²⁺ at about 1873 K in the α-MnS structure (cubic close packing) was investigated by means of electron diffraction (at room temperature). Diffuse intensity contours suggest that clusters of Mn²⁺ and Ln³⁺ around a vacancy are formed. In the close-packed plane, the cluster is a hexagon of 4Mn²⁺ and 2Ln³⁺ around a vacancy, a seven-point cluster. Clusters remain independent up to composition 4MnS · Ln₂S₃. With higher Yb₂S₃ content spinel domains in the short-range-order matrix are formed. Samples of MnSY₂S₃ heated at 1873 K showed formation of extended defects (in this case twin planes) when they contained more than 20 mole% Y₂S₃ (14% vacancies).