A Transmission Electron Microscopy Study of the MnS-Er₂S₃ System

Abstract

A systematic search mainly by means of electron diffraction and microscopy techniques was performed to elucidate the structural behaviour of the Mn-Er-S ternary system at 1373-1773 K. At 1773 K a new phase MnEr₂S₄ with spinel structure, a = 11.97(2) Å , was found. It transforms, due to electron beam damage (400 kV), into rock-salt (α-MnS ) domains and slabs of defects formed by some unit cells of MnEr₂S₄ (CaTi₂O₄ type) and MnEr₄S₇ (Y₅S₇ type) structures. The composition range between MnEr₄S₇ (S/M = 1.333) and MnEr₄S₇ (S/M = 1.400) is covered quasi-continuously by ordered and disordered intergrowth of both phases. Two ordered phases with composition Mn₃Er₈S₁₅ (S/M = 1.3636) and Mn₂Er₆S_ll (S/M = 1.375) have been found; however, disordered crystals due to a non-uniform mixing of those structures are more commonly observed. Furthermore, a new phase with a layer structure, reminiscent of LaCrS₃ type, has been found mainly at 1373 K.