Equivalent electric circuit analyses of ionic thermocurrent in sodium-doped CaF 2 crystals

Abstract

The characteristics of high-temperature ionic thermocurrent (HT ITC) in CaF 2 doped with different sodium concentrations were studied by the Teflon-insulated electrode ITC method. It was shown that, with increasing sodium concentration, the HT ITC band moved toward a Na +–F V dipole band with a peak at 162 K. The results of analyses of the HT ITC spectra using an equivalent electric circuit proved that the activation energy of space charge migration related to HT ITC was also strongly dependent on the doped sodium concentrations if varied from 0.94 to 0.46 eV with increasing sodium concentration in our ITC study. In addition, the broadening of the Na +–F V dipole band was observed in 3 nominal mole% NaF-doped CaF 2, which was accompanied by a considerable decrease of the activation energy from 0.46 to 0.29 eV without showing marked temperature shifts of the peak ITC bands.