Study of Transport Properties in (CrO4)2 Doped KI Crystals

Abstract

The ionic conductivity of pure and chromate anion doped KI crystals was measured in the temperature range 200 to 600 °C. A large contribution of conductivity in pure KI crystals due to cation as well as anion vacancies was observed at high temperature. The solubility of (CrO(CrO4)2— in KI crystals was also examined and it is shown that the solubility is good compared to other alkali halide systems like KCl, KBr, NaCl, NaBr, etc. The ionic conductivity measurements were made on pure KI crystals and KI crystals doped with 0.1, 0.3 and 0.5 mol% of chromate ion in the as-grown state. Further the conductivity is measured on KI crystals doped with 0.5 mol% of chromate ion and also on samples quenched from higher temperature and on annealed ones. From the conductivity (log σ T versus temperature (103/T plots, it is observed that the conductivity decreases in low and high temperature regions with increasing concentration of impurity ions. The decrease in conductivity in the low temperature region is explained on the basis of the formation of complexes with background impurities, formation of neutral pairs, etc. The increase and decrease in conductivity due to quenching and annealing is explained on the basis of dissociation and aggregation of complexes etc. The corresponding activation energies are evaluated and compared with previously reported values on various alkali halides.