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

The results of large-scale computer simulations of point defects - F-type e lectron centers and hole polarons bound to a potassium vacancy - in perovsk ite KNbO3 crystals are presented. One-site polarons and two-site (molecular ) polarons are expected to coexist, both are characterized by close absorpt ion energies around 1 eV. The transient absorption spectra and decay kineti cs observed after ns-pulsed electron beam irradiation have been measured fo r different KNbO3 crystals. The relaxation kinetics of the optical density vary considerably for different impurity concentrations and sample stoichio metries. Experimental data are discussed in the light of the presented calc ulations. (C) 2000 Elsevier Science B.V. All tights reserved.