Distribution Coefficients of Various Impurities in Alkali Halides

Abstract

Distribution coefficients of several monovalent and divalent impurities were obtained for NaCl, KCl, NaBr and KBr by the method of zone melting performed in the respective halogen atmosphere. Dependence of the impurity distribution on the speed of a zone pass and on the concentration of impurity were studied in KCl doped with lead ions, whose concentration was determined by the measurements of optical absorption as well as by the usual chemical analysis. For the monovalent impurities, the distribution coefficients obtained from distribution curves agree well with those calculated from the thermodynamical expression of distribution coefficient using the theoretical energy of solid solution. The energy of solid solution of divalent impurities was calculated from the experimentally obtained distribution coefficients taking the equilibrium of Schottky defects into account and was compared with that of lattice calculation.