Concentration and mobility of fluorine ion vacancies in CaF2

The electrical conductivity of sodium doped CaF2 crystals was investigated between 20 and 900 °C. Experimental formulas for the intrinsic and extrinsic regions are derived from spectral-analytically determined sodium concentrations. They are used to determine the concentration and mobility of the fluorine ion vacancies as well as the formation, mobility, and association entropies of the defects. The jump frequencies show that in the intrinsic region the charge transport is governed by the fluorine ion vacancies. The contribution of the interstitial fluorine ions at 900 °C is only about 1%. The results are corroborated by comparative considerations and the absorption behaviour of the crystals after X-ray irradiation.