A preliminary electron microscope study of chemical twinning in the system MnS+Y₂S₃, an analogue of the mineral system PbS+Bi₂S₃ (galena + bismuthinite)

Abstract

Examination in the electron microscope of various mixtures of MnS and Y₂S₃ after heating confirms the existence and structures of the phases MnY₂S₄ and MnY₄S₇. It also reveals the existence of at least one phase intermediate between these two, viz. Mn₂Y₆S₁₁ whose structure is an ordered intergrowth of the other two intermediate phases. Low proportions of Y₂S₃ produce isolated {113} twin planes in a B1 type matrix, and these tend to aggregate into thin lamellae (domains) of MnY₂S₄. Thus the twin plane is a structural unit in all cases (as previously forecast), and may occur in an ordered or disordered fashion. The necessity for a ‘cation-vacancy’ model is therefore minimized, or even eliminated.