The reorientation of Cd 2+-vacancy and Pb 2+-vacancy complexes in KCl

The relaxation of Pb ²⁺-vacancy and Cd ²⁺-vacancy dipoles in purified KCl crystals was studied using a double crystal dc polarization method which self-corrects relaxation effects due to spurious causes. In the radius range from Cd ²⁺ to Ba ²⁺ these results and most others support Dreyfus' model. The reciprocal relaxation times for each impurity are given by τ ^-1_Cd=2.06x10 ¹²{exp(-s0.64±0.01 eV) }/{kT}; τ ^-1_Pb=1.19x10 ¹³{exp(-0.69±0.01 eV) }/{kT}. It is also shown that the presence of H ₂O or its products greatly perturb the relaxation times observed.