Determination of the sign of the intrinsic surface charge in alkali halides from ionic sublimation measurements

A novel method of determining the sign of intrinsic surface charge in alkali halides is proposed. The basis for this method is the analysis of the shape of temperature dependence of thermal ion currents emitted by single crystals of these salts and measured by a mass-spectrometric technique. It is found that such charge is positive in the KCl and CsI cases (the Gibbs free energy of formation of anion vacancies, g+, is greater than that of cation vacancies, g−), whereas it is negative in the NaCl and KBr cases (g+<g−).