STUDIES OF HIGH-TEMPERATURE IONIC THERMOCURRENTS OBSERVED IN CAF2 ANDCAF2-EU

A strong and thermally stable ionic thermocurrent (ITC) band peaked at 316 K was observed in europium-free CaF2 crystals. The experimental I TC spectrum can be described by an ionic conduction kinetic expression of the type tau = tau(0) exp(E(a)/kT), with tau(0) = 1.90 x 10(-13)s and E(a) = 0.93 eV. This new band was very sensitive to europium dopin g, the ITC peak intensity being drastically reduced with the addition of only 0.002 mol.% europium. At the same time, a high-temperature typ ical ionic thermocurrent (HT ITC) band due to mobile interstitial fluo rine ions appeared at 416 K. The decrease of the new band at 316 K is explained by assuming that mobile fluorine vacancies are compensated w ith fluorine ions introduced into CaF2 as charge compensators for the trivalent europium ions. The dependence of the temperature T-m on the ITC peak in the higher-temperature ITC band on europium concentration is determined and the kinetic parameters are estimated.