Growth of MgF2 optical crystals and their ionic conductivity in the as-grown state and after partial pyrohydrolysis

MgF₂ single crystals have been grown from melt by the Bridgman technique in a fluorinating atmosphere. To control the presence of oxygen impurity, it was first suggested to measure the ionic conductivity in MgF₂ crystals by impedance spectroscopy. The characteristics of ionic conductivity of “as grown” (i.e., without thermal treatment) crystals and crystals obtained by commercial vacuum technology practically coincide: the volume conductivity σ_v = 1.4 × 10^?7 S/cm at 773 K and the ion-transport activation energy E _a = 1.40 ± 0.05 eV. Annealing MgF₂ crystals during electrophysical studies upon heating from 293 to 823 K in vacuum (residual pressure ～1 Pa) for 4 h led to their partial pyrohydrolisis. The influence of this thermal treatment of MgF₂ crystals on their optical transmission is studied in the wavelength range of 115–300 nm.