Study of thermally activated polarization effects in purified and magnesium-doped lithium fluoride

Abstract

Thermally activated polarization (TAP) and thermally activated depolarization (TAD) effects resulting from impurity-vacancy dipole reorientation occur in Mg-doped and undoped lithium fluoride in the temperature region 200–250°K. These polarizations appear related radiation-induced thermally activated depolarization (RITAD) effect in the same samples. We measure reorientation rate activation parameters of activation energy Ea=0.44±0.03 eV and preexponential factor W0=108.5±1.5 sec−1 for simple divalent impurity-vacancy dipole reorientation. Conversion to a second polarization phenomenon, stabilizing at Ea=0.86±0.03 eV and W0=1019±1.5 sec−1 is observed during annealing for several days at room temperature. This seems to be caused by aggregation into dipolar complexes for which the activation energy becomes significantly temperature dependent.