Interactions of Point Defects with Dislocations in Sodium Chrolide Crystals. I

The internal friction of pure NaCl crystal has been measured to study the processes of pinning and unpinning of point defects around a dislocation. The specimens were prepared by cleaving. They were compressed about 1.5% at room temperature after annealing at 700°C for 10 hours, and then used as the specimens. The measurements have been carried out on both pinning and unpinning processes by the Marx's oscillator method using an automatic control circuit. The results indicate that the number of pinners on dislocation increases or decreases proportionally to 1/3 power of time with the activation energy, 0.25 ±0.05 eV, in both processes. On the basis of calculation on the defect distribution around a vibrating dislocation, the t 1/3 dependence is quantitatively explained.