Frustration of the dislocation density in NaCl and its implication on “Harper-Dorn” creep

Static annealing of (100)-oriented NaCl single crystals at a homologous temperature of ~0.92 showed a significant reduction in the etch-pit dislocation density during the first 100 h, which remained constant during subsequent annealing up to 225 h. The existence of the frustration of the dislocation density, at a value of ~109 m-2, in NaCl is similar to the observations in the high purity Al and LiF single crystals. The implication of the frustration dislocation density on the observation of a creep stress exponent of >1 in the Harper-Dorn creep regime is discussed.