Electron microscopic study of the chimney ladder structures MnSi2−x and MoGe2−x

Manganese disilicides MnSi2−x as well as molybdenum digermanides MoGe2−x have been studied by electron diffraction and electron microscopy. Both materials, known as Nowotny phases or “chimney ladder” structures, are shown to possess structures based on two in-commensurable sublattices. Dark field electron microscopy reveals that a strictly commensurable superstructure does not exist. The presence of moiré fringes is related unambiguously to the presence of irrational diffraction spots, forming either orientation anomalies, spacing anomalies or both.