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Abstract
The surfaces of single crystals of sodium chloride and potassium bromide have been studied, by a decoration technique, in electron microscopy. Features on the decoration figures observed are interpreted as twist grain boundaries at (110) planes. Under most reasonable assumptions concerning the Burgers vectors of the dislocations forming the boundary the angles of twist are calculated and they always have the same values: 17′, 41′ or 50′. These rotation angles of the boundary are explained ä crystal positions of minimum energy. This has been done by using a rigid lattice approximation taking into account only the Coulomb interaction between some ions belonging to a cell of the superlattice created by the dislocation network associated with the grain boundary.