IONIC CONDUCTIVITY OF POTASSIUM BROMIDE CRYSTALS

Abstract

The conductivity of single crystals of potassium bromide has been measured as a function of temperature. Potassium carbonate was found to be sufficiently soluble at high temperatures in KBr to cause a conductivity due to negative ion vacancies. The ionic conductivity parameters of KBr were calculated from conductivity measurements on crystals containing known concentrations of potassium carbonate and calcium bromide without recourse to transport number experiments. A simple theory of association was found to be adequate to describe the interaction between calcium ions and positive ion vacancies. The solubility of free divalent impurities in KBr was also calculated from conductivity measurements. The following enthalpy values were found: for formation of a pair of Schottky vacancies, 2.53 eV; for the motion of positive ion vacancies, 0.665 eV; for the motion of negative ion vacancies, 0.87 eV; for the association of calcium ions and positive ion vacancies, 0.46 eV.