EPR, NMR and ENDOR study of intrinsic and extrinsic defects in disordered and regularly ordered lithium niobate crystals

The spectra of EPR, NMR, ENDOR of lithium niobate crystals with different compositions, diverse modifiers and various probe impurities have been analysed. Congruent crystals with a high concentration of intrinsic defects have strong structural disorder and a random distribution of crystal fields and their gradients. Crystals with small contents of intrinsic defects offer extraordinary informative opportunities for their investigation by means of different spectroscopic techniques. As an example of the resolution enhancement in Li-rich crystals the EPR spectra of Yb3+ were considered in detail. Two new low-symmetry centers were found and their parameters were determined. The investigated strong interrelation of the intrinsic and extrinsic defect subsystems becomes especially apparent when concentrations of both defect classes are comparable.