Ionic conductivity of potassium iodide crystals

The electrical conductivity of pure KI, KI + SrI 2 , and KI + K 2 CO 3 single crystals was measured as a function of temperature. A method for calculating ionic transport parameters from these results was developed, assuming that the conductivity was due entirely to the motion of positive and negative ion vacancies, and including the effect of association and Coulomb interaction between oppositely charged defects. It was shown that the Coulomb interaction had an appreciable effect on the high-temperature intrinsic conductivity, and the extrinsic conductivity of heavily doped crystals. Calculation of transport parameters from intrinsic-conductivity measurements alone gave erroneous results. From the agreement (within experimental error) between the experimental and calculated results, it was concluded that the only defects taking part in the conduction process were Schottky defects. The following parameters were calculated: Schottky-defect formation enthalpy h s = 2.21 eV, entropy s s = 0.765 × 10 −3 eV/deg; positive ion vacancy migration enthalpy Δh 1 = 0.63 eV, entropy Δs 1 = 0.136 × 10 −3 eV/deg; negative ion vacancy migration enthalpy Δh 2 = 1.29 eV, entropy Δs 2 = 0.805 × 10 −3 eV/deg; association of divalent cations and positive ion vacancies enthalpy χ = 0.54 eV, entropy η = 0.190 × 10 −3 eV/deg.