We investigated the crystal structure of Ti3SiC2 by means of high-resolution electron microscopy (HREM). Two polymorphs, α– and β–Ti3SiC2, were identified. The amount of the α phase was larger than the β phase, indicating that the former has lower energy than the latter. We also found that the bright spots in HREM images of Ti3SiC2 do not necessarily correspond to the atomic columns; thus an intuitive interpretation of the image contrast in terms of the stacking sequences of the close-packed layers should be made cautiously

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Structural changes on and near surfaces of ZnTe crystals were observed by the surface profile imaging method in a high-resolution transmission electron microscope (HRTEM) with 200 kV accelerating voltage. It was found that ZnO particles form under electron irradiation on surfaces originally covered with a thin amorphous layer. For amorphous coverages thicker than about 7 nm, ZnO particles were not observed. Under the ZnO particles, 2×1 and 2×2 superstructures (about 10 nm in size) were often found in the ZnTe matrix. These superstructures can be described as a metastable Zn2Te3 having a structure similar to the ordered Ga2Te3 structure. This change can be accomplished by considering the diffusion of zinc from the ZnTe matrix to the surface to form the oxide and evaporation of tellurium out of the surface, leaving behind a matrix with an altered stoichiometry. The HRTEM computer-simulated images for the proposed Zn2Te3 superstructure matched very well the experimental images. The 2×1 and 2×2 superstructures corresponded to the HRTEM images of the new Zn2Te3 structure viewed along its [211] and [100] directions, respectively.

The results of high resolution transmission electron microscope (HRTEM) observation and image simulation show that Zr4Co4Si7 possesses the same structure type of Zr4Co4Ge7. Addition of Fe or Ni into the Zr4Co4Si7 compound, except that the dimensions changed slightly, does not change the lattice type and coordination in the crystal structure, maintaining the V-phase structure. Also, twins with coherent boundaries and partially coherent interfaces are observed. The image conditions of Zr4Co4Si7 and the structure differences between Zr4Co4Si7 and tetrahedral close-packed phases are also discussed.

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