Study of ionic conductivity in KBr: (CrO4)2- crystals

Abstract

The ionic conducti vity of pure KBr and KBr c rystals doped with chromate anion has been measured in the temperature range of 200-600 DC. In pure KBr crystals, large contribution to conductivity by cati on vacancies has been observed at hi gher temperatures. Ionic conducti vity measurements are made on pure KBr crystals and KBr crystals doped with 0 .25. 0.5 and 0. 75 mo le % of chromate a nion in as-grown state. Furthe r, the e ffects o f quenching and annealin g on conductivity of KBr crys tals doped with 0.75 mo le % chromate ion are measured. The conducti vity versus tempe rature plo ts show that. as concentrati on o f impuri ty a nions increases, the conducti vi ty decreases in cxtrin sic associated region. As the concentration increases to 0.75 mole %, the conducti vity increased to high value compared to 0.5 mole %. But, it is less than lhat of pu re c rystals. T hc extri nsic un-associated region shows a s light vari ation in conducti vit y but , tends to be same that of as-grown pure KBr c rystals. T he variation in conducti vity of doped KBr c rystals are explained on the basis of formation of complexes with background impuriti es, formation of ne utral pairs, introducti on o f fresh di s locations, etc. The variati on in conducti vity due to quenc hing and anneal ing is ex pl ained on the basis of dissociati ons and aggregati on of complexes, vanishing of newly introduced dislocations, etc. The correspondi ng ac ti vation ene rgy values a rc evaluated