ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
The contrast of electron microscope lattice images of a vanadium monosulphide with superstructures was dynamically calculated on the basis of the multislice method. Interactions of 80 waves were analysed. It was shown that the vacancy-rich vanadium sites were imaged as white spots not only at the very thin part but also at the thicker part inside the first equal-thickness contour, which appeared at the thickness of 60 Å. A non-stoichiometric vanadium monosulphide, VS1.155, quenched imperfectly from the preparation temperature at 1217 °C, was examined on the basis of the lattice image observation by a 100 kV high-resolution electron microscope. Orderings in the inter- as well as intralayers could be recognized directly from the arrangement of the white spots. Interpretable lattice images appeared exclusively inside the first equal-thickness contour. A mixture of some different types of images was observed in a crystal fragment; in some band-like regions the 4C-type superstructure was found with almost the same structure as Fe7S8. Each band extended parallel to the (001) plane with thickness of at most 50 Å and the orientation was in a twin relation to that of the adjoining one. The other regions showed less well-defined lattice images, although they gave the broad diffraction peaks ranging from the 4C- to 3C-type reflexions. In order to determine the phase relations at high temperatures the specimen was heated by focusing an electron beam on the portion slightly apart from the area under examination. The technique enabled us to observe only the heating effect. Upon heating, the 4C type first increased in volume, seen by the thickening of some bands. On further heating the 3C type increased in intensity on the diffraction pattern. The structure of the 3C type was estimated to be almost the same as Fe7Se8 except that the vacancy concentration fuctuated among the partially occupied vanadium layers.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0567739476001228
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