INCOMMENSURATE MISFIT LAYER COMPOUNDS OF THE TYPE MTS3 (M = SN, PB, BI, RARE-EARTH ELEMENTS, T = NB, TA) - A STUDY BY MEANS OF ELECTRON-MICROSCOPY

Incommensurate misfit layer structures of the type "MTS3" (M = Sn, Pb, Bi, rare earth elements; T = Nb, Ta) were studied by means of electron diffraction and high resolution electron microscopy. It is demonstrated how the electron diffraction patterns along the zone perpendicular to the layer planes can be interpreted in terms of the misfit between the constituent layers. Diffraction evidence for orientation variants is presented; their occurrence is directly related to the degree of deformation of the corresponding sublattices. With the use of image calculations it is shown how high resolution images in the layer plane directly reveal the incommensurate misfit through the varying coincidence of the atom columns of the two substructures. The shift of successive layers as reported from X-ray diffraction is found not to occur systematically in all crystals but it can give rise to stacking disorder. © 1990.