Theoretical and experimental study of primary radiation defects in KNbO3 perovskite crystals

The results of large-scale computer simulations of point defects - F-type electron centers and hole polarons bound to a potassium vacancy - in perovskite KNbO3 crystals are presented. One-site polarons and two-site (molecular) polarons are expected to coexist, both are characterized by close absorption energies around 1 eV. The transient absorption spectra and decay kinetics observed after ns-pulsed electron beam irradiation have been measured for different KNbO3 crystals. The relaxation kinetics of the optical density vary considerably for different impurity concentrations and sample stoichiometries. Experimental data are discussed in the light of the presented calculations