Radiation-induced Schottky defects in NaCl

Abstract

It has been found in nominally pure NaCl single-crystal samples that have been either gamma irradiated, plastically deformed or quenched into liquid nitrogen from 700 degrees C, that an additional quenching with a short residence time at the quenching temperature reveals the presence of dipolar defects by means of ionic thermocurrent (ITC) measurements. This procedure does not induce ITC signals in untreated samples. Since the occurrence of divacancies and divacancy clusters in plastically deformed or quenched samples is expected. It is pointed out that gamma irradiation may also form divacancies. The fact that all the ITC spectra of the samples treated in the above-indicated ways exhibit peaks at similar temperatures also supports this view. The parallelism observed between the stored energy spectra of these samples and the evolution of the ITC areas against the quenching temperature indicates that the two phenomena are related. The occurrence of dipolar defects is consistent with a previous proposal: that the stored energy release is due to the recombination of divacancies with alkali halide molecules.