Thermal treatment and light illumination effects in EPR spectra of KtaO3:Cu

In order to understand the manner of incorporation of oxygen vacancies into perovskite structure oxides, KTaO3 crystals containing Cu2+ impurity ions were investigated following thermal treatments in atmosphere of H-2, air, and vacuum. The results of thermal treatments were controlled by EPR. The influence of light illumination on copper centres in these crystals was studied also. The thermal treatment and light illumination effects in EPR spectra of Cu impurity centres are studied for the incipient perovskite-like ferroelectric KTaO3 single crystals. It was found that thermal treatment at similar to 950 degrees C in hydrogen atmosphere and in vacuum strongly depresses EPR signal of both types of Cu2+(1) and Cu2+(2) axial centres substituting Ta5+ in the B-sublattice positions. Subsequent high-temperature treatment in air restores EPR signals of Cu2+ centres, but changes the ratio between Cu2+(1) and Cu2+(2) centres concentration. These effects, together with UV light illumination effects observed for T < 80 K, are connected with the possibility of the Cu2+ <--> Cu+ thermal and photo-induced transformations of the Cu impurity centres.