Surface-charge accumulation and clustering in fluorites

Comparative Thermally Stimulated Polarization and Depolarization studies have been carried out on SrF 2 crystals doped with lanthanum up to molar concentrations of 5x10 −2 and to temperatures of 500K. The first three peaks, attributed to nearest-neighbour dipoles and to clusters built with this basic unit (L-shaped La 3+ -F i2 − and the gettered 2:2:2 dimer) and the first high temperature peak are accurately reproduced in both spectra proving the dipolar origin of these relaxations. A fifth band at high temperature is present in the ITC spectrum but not in the TSP run where it is replaced by a steep increase in the current. The behaviour of this peak is studied and it is concluded that it is related to the relaxation of space charges accumulated near the electrodes.