Evidence of Screw Dislocations in KCl Single Crystals

Abstract

(100) cleavage faces of KCl single crystals have been etched in a solution of 90% absolute ethyl alcohol, 5% n-butanol, 3% distilled water and 2% formaldehyde, and spiral etch pits both clockwise and anticlockwise are produced. By etching matched pairs of faces in the same conditions one to one correlation in the number, position, shape, and sense of the spirals are obtained. By re-etching a cleavage face on which spiral depressions were produced, in another etchant, square shaped pits exactly at the centres of each spiral depression are produced, indicating thereby that the centres of the spiral depressions are the sites of screw dislocations. It is observed that when a cleavage face is successively etched for two different periods, the spiral depressions produced during the first etch grow in size while their shape and sense remains the same. The implications are discussed.