A measurement of the charge on edge dislocations in a sodium chloride crystal

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Abstract
Single crystals of NaCl were plastically bent, and specimens were then cut from them in which the dislocations were almost entirely of the same mechanical sign. These specimens were subjected to a cyclic tensile and compressive stress such that the dislocations moved to produce a plastic strain and an electrical polarization. The charge on the dislocations was determined by measuring these quantities. On first testing it lay in the range—(6 to 12) × 10−-4 e.s.u./cm, but it was approximately doubled as a result of cyclic stressing at high amplitudes. The results are compared with two approximate models : one in which the dislocation acquires a charge by sweeping up otherwise immobile positive-ion vacancies, and another in which the dislocation is in thermal equilibrium with mobile positive-ion vacancies. Both models give results of the order of magnitude found experimentally.