Specific Features of Strengthening Phenomena in NaCl:Eu$\text{}^{2+}$ Crystals

Mechanical strength of europium doped NaCl crystals was studied as a function of both the dopant concentration (c$\text{}_{2+}$) and the kind of obstacles effective in hindering the motion of dislocations. It has been found that the yield strength (σ$\text{}_{0}$) of solution treated samples is determined by Snoek reorientation of both isolated dipoles and linear dimers within the stress fields of moving dislocations. The deviation of the σ$\text{}_{0}$ (c$\text{}_{2+}$) plot from linearity is probably due to the presence of quadripoles cutted through the moving dislocations. Also for as- received specimens two precipitation strengthening mechanisms are postulated; these are the Kelly-Nicholson cutting and the Orowan looping, respectively.