Quenching of cation vacancies in doped crystals of sodium chloride

Abstract

As is well known, the thermodynamic defects developed by alkali halide crystals at high temperatures are predominantly of the Schottky type. The number of cation and anion vacancies in equilibrium with the crystal, at temperatures near the melting point, for example, may be as large as 10^-4 of the total number of atoms. Attempts have, therefore, been made to quench these vacancies by very rapid cooling from these high temperatures, but without success, judging from the very similar values obtained for the electrical conductivities of the quenched and the annealed specimens1. (From the melt, however, some of the defects can be quenched.) This, however, is not surprising, since the relaxation times corresponding to the migration of vacancies, leading either to formation of pairs or to their exit from the crystal, remain small, even at temperatures several hundred degrees below the melting point.