Ionic Conductivity of Potassium Bromide Crystals

Abstract

The electrical conductivity of single crystals of potassium bromide was measured as a function of temperature, and as a function of the concentration of calcium bromide or potassium carbonate impurity. The results were analyzed on the assumption that the observed conductivity was due entirely to the motion of separated anion and cation vacancies (Schottky defects), with Coulomb interactions between charged defects. Agreement between measured and calculated conductivities at all temperatures showed that this assumption was reasonable. The values obtained for transport parameters were: Schottky-defect formation enthalpy hs = 2.53 eV, entropy Ss = 10.3k; positive ion vacancy migration enthalpy Δh1 = 0.65 eV, entropy Δs1 = 1.89k; negative ion vacancy migration enthalpy Δh2 = 1.22 eV, entropy Δs2 = 7.30k; association of calcium ions and positive ion vacancies enthalpy x = 0.61 eV, entropy η = 2.23k, where k is Boltzmann's constant.