Impurity-concentration effects on the dielectric relaxation of alkali halides

The effect of the impurity concentration on the reorientation parameters of impurity-vacancy complexes ($I-V$) in alkali halides has been studied. The systems considered have been LiF:Ni, LiF:Co, NaCl:Pb, KCl:Ca, and KBr:Sr, with concentrations up to ${10}^3$ ppm. A systematic decrease of the reorientation energy with increasing dipolar concentration has been detected. These effects are clear above 100 ppm of free dipoles. The experimental results have been analyzed in terms of the monoenergetic ionic-thermocurrent equations as well as with the modified theory including dipole-dipole interaction. The incidence of such correction of the experimental conditions is also discussed.