Defects and their interactions in congruent, stoichiometric and regularly ordered lithium niobate

G.Malovichko, V.Grachev, O.Schirmer

The technical scope of congruent LiNbO3 (LN) and LiTaO3  single crystals for many applications is limited, because of their Li-deficiency, leading to a great number of intrinsic defects (vacancies, antisite defects etc.) and essential microscopic disorder. To change the properties of this conventional crystal a high concentration of dopants-modifiers, for instance, Mg, Zn, Sc or In have to be introduced into the crystal, to prevail over the influence of intrinsic defects.

Just opposite situation occurs in case of LN crystals of stoichiometric composition (SLN), recently became available. Since SLN has an extremely low concentration of intrinsic defects, its properties can be tailored with the enormously smaller dopant concentrations than for the congruent crystals. For example, the doping of SLN with low concentrations of both the photoactive ions or/and damage-resistant impurities leads to the macroscopically homogeneous, damage free samples. Many physical properties of SLN are more favorable than those of congruent crystals, therefore it is expected that a doped SLN will be the excellent materials for the effective generation of quasi phase matched harmonics and for miniature multifunctional solid-state sources of visible light.

The project will be concentrated on studies of defect structures in correlation with the properties induced by controlled variation of defect subsystems, and mutual influence of intrinsic and extrinsic defects. Electron Paramagnetic Resonance (EPR) and Electron Nuclear Double Resonance (ENDOR) are unique, indispensable for the determination of the position, local surrounding of optically active impurities; EPR-optical simultaneous spectroscopy, developed in our laboratory, gives an essential vital information about EPR-silent defects. Systematic studies of samples with different compositions and concentrations of various dopants are able to provide a complete set of results needed for the understanding of the important defect related features of the crystals. We expect with the help of optical and radiospectroscopic techniques to clarify the structures of defects in  relatively new sLN  (impurity locations, charge states, mechanisms of charge compensation, correlated entering etc.) and to find the ways for tailoring fundamental properties by means of special doping of the crystals with regard to advanced applications.