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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.

The study of ionic conductivity vs reciprocal temperature of pure KCl and KCl crystal doped with 0⋅ ⋅1, 0⋅ ⋅3 and 0⋅ ⋅5 mole% gadolinium has been carried out in as grown, quenched from elevated temperatures (100, 350 and 500°C) and annealed at various timings i.e. 2-3 h and deformed by different percentages. The plots exhibit three well-known regions, II, III and IV (extrinsic regions). The intrinsic region I was not observed in the plots as the conductivity measurements were taken up to 575°C. From the analysis of these plots, activation energies for the migration of cation vacancy and the association of gadolinium ion with cation vacancy in the lattice of KCl crystals are calculated. These values are compared with previously reported values. Further, an attempt is made to explain the existence of oxidation state of gadolinium ion in + 3 state rather than in + 2 state as reported earlier. The variation in conductivity with effect of concentration of impurity ion, quenching and annealing and deformation with various percentages are explained on the basis of formation of impurity vacancy dipoles, vacancy-vacancy pairs (which appear in the form of precipitation), storage of cation vacancies in the form of defects, introduction of fresh dislocations, etc.

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