An investigation was made of defects in single crystals. It was found that randomly distributed intrinsic point imperfections predominated in conventional congruent crystals. This led to a perturbation of the surroundings of optically or acoustically active impurities, and to a broadening of their spectral lines. A marked narrowing of resonance lines in almost stoichiometric samples increased the spectral resolution enough to permit the study of non-controlled trace impurities and satellite centres which consisted of impurity and intrinsic defects. The disappearance of satellite centres, and the appearance of new centres due to changes in the charge compensation mechanism, was observed in stoichiometric crystals.

Point Imperfections and Clusters of Intrinsic and Extrinsic Defects in Non-Stoichiometric and Stoichiometric Lithium Niobate: the Regularly Ordered Crystal. G.Malovichko, V.Grachev, E.Kokanyan, O.Schirmer: Radiation Effects and Defects in Solids, 1999, 150[1-4], 619-23