IONIC CONDUCTIVITY OF POTASSIUM BROMIDE

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Abstract
The conductivity of four crystals of KBr - one pure and three doped with SrBr2 - have been fitted to the conventional model which allows for short range interactions between M2+ ions and cation vacancies via complex formation and long range defect interactions in the Debye-Hückel approximation. The cation vacancy migration parameters derived from the analysis of the pure crystal data do not agree with those derived from the data for doped crystals. Also the anion migration parameters found from the pure crystal data are too high. The effects of uniaxial stress have been investigated and it has been demonstrated that stress increases the conductivity of pure KBr crystals at high temperatures. This enhancement of the conductivity is attributed to anion migration down dislocations. The effect survives moderate annealing but can be removed by a prolonged anneal. The conductivity of pure KBr was therefore analyzed on a model which includes a dislocation contribution : the cation migration parameters are closer to the values deduced from the doped crystal data than were those from the Debye-Hückel model but the agreement is still not satisfactory. However, the anion migration parameters have more reasonable values. In view of the discrepancies in the cation migration parameters and in particular the big variations in the entropy found from the doped crystal data, two other models for the short-range defect interactions wcre examined. One of these allowed for three different configurations of complexes and the other for the formation of clusters of impurity ions and cation vacancies. Neither of these models, however, gave satisfactory fits to the data

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