Study of thermally activated polarization effects in purified and magnesiumhyphen;doped lithium fluoride

摘要

Thermally activated polarization (TAP) and thermally activated depolarization (TAD) effects resulting from impurityhyphen;vacancy dipole reorientation occur in Mghyphen;doped and undoped lithium fluoride in the temperature region 200ndash;250deg;K. These polarizations appear related radiationhyphen;induced thermally activated depolarization (RITAD) effect in the same samples. We measure reorientation rate activation parameters of activation energyEaequals;0.44plusmn;0.03 eV and preexponential factorW0equals;108.5plusmn;1.5secminus;1for simple divalent impurityhyphen;vacancy dipole reorientation. Conversion to a second polarization phenomenon, stabilizing atEaequals;0.86plusmn;0.03 eV andW0equals;1019plusmn;1.5secminus;1is 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.