Mineralogical applications of electron diffraction. 1. Theory and techniques

Trace Elements Investigations 597

This report concerns work done on behalf of the Division of Research of the U.S. Atomic Energy Commission



The small wavelengths used in electron-diffraction experiments and the thinness of the crystals necessary for the transmission of the electron beam combine to require a somewhat different diffraction geometry for the interpretation of electron-diffraction patterns than is used in the interpretation of X-ray diffraction patterns. This geometry, based on the reciprocal lattice concept and geometrical construction of Ewald, needed for the interpretation. of transmission electron-diffraction single-crystal patterns is here reviewed.

Transmission electron-diffraction single-crystal patterns of two monoclinic substances, colemanite [CaB3O3(OH)3•H2O] and potassium chlorate (KC103), are examined and the .theory necessary for their interpretation is given in detail. The study of these patterns furnishes a basis for the interpretation of single-crystal patterns of materials belonging to any crystal system. It is shown that useful unit-cell data, accurate to a few tenths of a percent, can be obtained from the patterns of colemanite and KClO3. A method of evaluating unit-cell data from measurements of such single-crystal patterns is given.

The transmission electron-diffraction powder pattern obtained from an oriented aggregate of thin crystals gives the same unit-cell data as are given by the electron-diffraction single-crystal pattern obtained from one crystal of the aggregate., A graphical method is given for precisely evaluating unit-cell constants from measurements of such a powder pattern.

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USGS Numbered Series
Mineralogical applications of electron diffraction. 1. Theory and techniques
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Trace Elements Investigations
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U.S. Geological Survey
54 p.