The phase relations in the range of non-stoichiometric pyrrhotite, Fe1-xS (0≤x≤0.125) have been studied in detail using the X-ray diffraction technique at high temperatures. During this time, some attractive phenomena have been found, e. g., there are nine closely related superstructures below 320°C and in that range of composition the super-cells are “non-integral” multiples of the NiAs-type fundamental cell. The size of the super-cells is variable corresponding to the change in T-X conditions. Because the usual procedures of X-ray single crystal structure analysis are not generally appropriate to the non-integral superstructures, an attempt has recently been made to draw qualitative models of the vacancy distributions of the non-integral super-structures on the basis of a four- (or n-) dimensional description of the modulated structure. Wave distribution of vacancies is a characteristic of the models for the NC- and NA-type superstructures. The waves were successfully observed in high resolution electron micrographs. Further refinement of the NC-type structure has also been successful by using the X-ray intensity data. We can thus understand that the structures shuld be described as four-dimensionally periodic and three-dimensionally nonperiodic structures. The structure variation of pyrrhotite, which is indicated by the displacements of the satellite reflections, depending on temperature and composition, is realized by the change in the period and the direction of the vacancy distribution wave.
A 100 kV field emission electron microscope has been developed which has lattice resolution of 0.62 Å. Electron holography was put to practical use utilizing the high coherence of this electron beam. The coherence of the electron beam was demonstrated by photographing 3, 000 bi-prism interference fringes, which is an order of magnitude greater than the number obtained previously. Spherical aberration of the electron lens, which has been the main obstacle to improving the performance of electron microscopes, was compensated for in the optical reconstruction stage of holography. Furthermore, an interference microscope was realized by means of holography. The electron microscopic image of an object contains information on object thickness in the phase of the electron beam which is not expressed in usual electron microscopic images photographed on film. Using the interference electron microscopy, the thickness distribution of fine polyhedron particles could be derived and their three-dimensional shapes determined.
Relationships between the rotation angle θ and the reciprocal density of coincident sites Σ in the coincidence site lattice (CSL) model for the ideal hexagonal crystal in which the axial ratio c/a=√8/3 were calculated for three rotation axes of low indices: ,  and  . For determining the Burgers vectors of grain boundary dislocations, the displacement shift complete (DSC) lattices were also calculated for the above cases. Results of the calculations in the range of Σ<50 were tabulated in Tables 2-4 besides the generating equations in Table 1. The structure and behavior of grain boundaries in ice crystals, especially those found experimentally by the present authors with artificially grown ice bicrystals of <1010 >/34°were well explained by the model presented above.