Ionic thermocurrent investigations of CdF2

When heated at a rate of 2 deg/min CdF2-crystals doped with Na+, Ag+, and Li+ exhibit peaks of the ionic thermocurrents (ITC) at 103.5, 93 and 85.5 K, owing to the reorientation of monovalent cation-fluorine vacancy dipoles (DO-signals). In addition, comparatively larger ITC-peaks due to the redisplacement of free fluorine vacancies (CD-signals) are found between 180 and 220 K on the same crystals and on undoped ones. In the case of CdF2-cyrstals doped with La3+, In3+, and Gd3+ redisplacement signals are observed between 300 and 350 K corresponding to the lower conductivity of these samples, whereas DO-signals due to a reorientation of trivalent cation-fluorine interstitial dipoles could not be detected in the whole range between 20 K and the temperature of the redisplacement signals. A comparison is made with ITC results on CaF2.