Ionic conductivity of crystalline potassium thiocyanate

Studies have been made of the a.c. electrical conductivity of single crystals of potassium thiocyanate in various states of purity between 446 K and room temperature. For all samples there was a marked change in the conductivity on passing through the 'phase' transition at 414 K. The position of this break was independent of the purity of the specimens. A complete analysis of the curves was not possible due to the existence of pronounced pretransitional and prefusional effects. On the assumption that Schottky disorder predominates in both phases it is deduced that the enthalpy of cation migration is 0.49+or-0.02 eV in the low temperature phase and 0.74+or-0.02 eV in the high temperature phase. The enthalpy of formation of Schottky pairs is less than 3.2 eV in the low temperature phase and about 1.8 eV in the high temperature phase. A second transition has been detected at 444 K.