Order and Disorder in Rocksalt and Spinel Structures in the MgS−Yb2S3 System

Abstract

The MgS−Yb2S3 solid solution, which can be formulated as Mg1-xYb(2/3)x□(1/3)xS (□, cation vacancy), was studied in a wide composition range (0 ≤ x ≤ 0.75). The structure and microstructure characterizations of the samples were mainly performed via transmission electron microscopy (TEM) and associated techniques, such as X-ray energy dispersive spectroscopy (XEDS) and electron energy-loss spectroscopy (EELS). At low Yb3+ contents (x ≤ 0.30), the system presents an average NaCl-type structure. The selected area electron diffraction (SAED) patterns corresponding to these crystals show diffuse scattered intensity, which is related to short-range order in the cation sublattice. EELS studies indicate the existence of Mg2+ in tetrahedral coordination, in addition to the octahedral coordination of the basic NaCl-type structure. Extended defects were observed perpendicular to 〈111〉 in the NaCl matrix for the x = 0.30 sample. When x ≥ 0.35, a phase with spinel-type structure is observed and characterized. Besides, ...