Effect of the internal field on polarization and depolarization experiments on SrF2:La3+

Abstract

Thermally stimulated depolarization [ionic thermal current (ITC)] and thermally stimulated polarization current (TSPC) methods are compared, and the results obtained for ${\mathrm{SrF}}_{2}$ crystals doped with La are reported in this paper. It is shown that for normal dipolar peaks such as the low-temperature relaxation caused by the movement of the interstitial ${\mathrm{F}}_{\mathrm{i}}^{\mathrm{\ensuremath{-}}}$ bound to a ${\mathrm{La}}^{3+}$ cation to form a nearest-neighbor dipole, both techniques give the same information, provided that for the ITC case, the polarization temperature is below the temperature range where the very intense and somewhat anomalous high-temperature peak occurs. For an ITC experiment a current reversal is observed in the high-temperature tail of the dipolar peak if the sample is polarized at a temperature above the high-temperature peak. This current reversal, typical of a TSPC peak, is clearly observed and its height is useful in determining the effective polarization field applied to the sample when an ITC run is performed. The presence of the current reversal indicates the existence of a frozen-in polarization due to processes occurring in the high-temperature part of the relaxation spectrum. Also, information on the origin of the observed relaxation processes at high temperature can be deduced from a comparison of the two spectra.