抄録
The critical shear stress for driving dislocations against dipoles (calcium ion-cation vacancy pair) is determined by the three-point bending test in sodium chloride crystals containing CaCl2 (from 330 to 900 ppm). The relationship between the stress (τ) and the concentration (Xd) of dipoles is found to be τ∝Xd2⁄3. The concentrations of dipoles at R. T. are estimated from the ionic conductivity measurements in the region III with an assumption. The concentrations of effective calcium impurities (C′) for dipole are evaluated 30 percent of the total amount of calcium impurities as doped. The degree of association of calcium ions with cation vacancies, e.g., Xd⁄C′, is estimated as 0.8–1.0 from 530 to 300 K. The contribution of dipoles to the stress increment can be separated from that of another types of aggregates of calcium ions by taking account of the stress magnitude and the concentration.
