ITC technique to monitor interactions between dislocations and aliovalent cations in alkali halides

The features of C-peak appearing in the ITC spectra (300–370 K) of alkali halides doped with divalent cations are unusual. Its position and amplitude Hc are functions of thermal treatment, plastic deformation, impurity concentration, sample thickness and nature of contacts. Hc is strongly reduced by plastic deformation, according to the square root of the screw dislocation density; it is partially recovered by sample annealing in the 290–350 K range. Most of the results, obtained in a wide class of systems (such as LiF:Be, KC1 and NaCl:Eu, Pb, Ni), can be explained in terms of interfacial polarization induced by Cottrell atmosphere surrounding dislocations. The role of air gaps between sample and electrodes is also considered.