Experiments on second-harmonic generation had revealed oxidation and reduction processes to have a great influence on the values of the intensities obtained. This influence was explained here by the fact that the oxidation-reduction treatment changed the concentration of the free charges connected with O vacancies, and these charges influence the impurity cluster formation, which caused changes in the second-harmonic intensities. It was shown that polarized impurity clusters were stabilized by charges placed at their boundaries because of the compensation of the depolarization field.

Polar Cluster Formation due to Point Charge Centres in KTaO3:Li. S.A.Prosandeev, V.S.Vikhnin, S.E.Kapphan: Journal of Physics - Condensed Matter, 2002, 14[17], 4407-14