Measurements of the charge acquired by dislocations in NaCl crystals of known purity

Abstract

Pure and Mn⁺⁺-doped crystals of NaCl were prepared containing 0·24 and 14 mol p.p.m. of divalent impurity and free from OH-. The room-temperature point defect concentrations were estimated from ionic conductivity and e.s.r. measurements. Edge dislocations were introduced by bending, and their charge was measured at room temperature by determining the strain and polarization produced by a small cyclic tensile and compressive stress. This charge increased with the amplitude of dislocation motion, corresponding to a sweeping up of cation vacancies from many of the impurityvacancy dipoles on the slip plane. In the 14 p.p.m. Mn++-doped crystals the charge reached a saturation at about 0·5 ionic charges per core site, but these high charges decreased on standing.