Progressive Lattice Distortion in Stressed Crystal Lamellae

The literature contains many references to the appearance of fringe patterns on crystals, under examination in the electron microscope, which are attributed to bending of the crystal. An unusually detailed and extensive but still incomplete pattern is presented in an electron micrograph of a sodium...

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Bibliographic Details
Published in:Proceedings of the Royal Society of London. Series A, Mathematical and physical sciences Mathematical and physical sciences, 1959-04, Vol.250 (1263), p.427-438
Main Author: Cuckow, F. W.
Format: Article
Language:English
Subjects:
Bending
BRAGG REFLECTION
Chlorides
Crystal lattices
CRYSTALS
DEFECTS
Diffraction patterns
ELECTRON MICROSCOPY
ELECTRONS
Geometric planes
LATTICES
LOSSES
MATERIALS SCIENCE
MEMBRANES
MONOCRYSTALS
REFLECTION
ROTATION
Shear stress
Single crystals
Sodium
SODIUM CHLORIDES
STRESSES
Wave diffraction
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Summary:The literature contains many references to the appearance of fringe patterns on crystals, under examination in the electron microscope, which are attributed to bending of the crystal. An unusually detailed and extensive but still incomplete pattern is presented in an electron micrograph of a sodium chloride crystal sheet. The corresponding electron diffraction pattern was of the ‘two-dimensional’ type. Diffraction and fringe patterns were present throughout extensive rotation of the specimen. The fringe pattern is repetitive and cannot be explained by reasonable degrees of bending of the sheet. It is shown to be consistent with the loss of electrons by Bragg reflexion from a lamellar single crystal in a special state of shear strain. Ideally, the strain progresses uniformly in all radial directions but is considered to have been induced experimentally by the contraction of a membrane attached to one side acting in opposition to the natural rigidity of the crystal. For the ideal state of strain it is shown that the fringe pattern is an enlargement by a two-dimensional vernier coincidence process of the intersections of origin reflecting planes with the basal plane, the magnification being simply related to the shear strain. The pattern is identical geometrically with Neumann’s linear crystallographic projection.
ISSN:1364-5021
0080-4630
1471-2946
2053-9169
DOI:10.1098/rspa.1959.0074