Lithium niobate (LiNbO₃ or LN) has found numerous applications in electro-optics and other fields. We have studied the influence of point defects on the Curie temperature (Tc) of pure LiNbO₃ (LN) and LN doped with impurities of different valencies (divalent and tetravalent) using our newly proposed vacancy model and the theory of ferroelectric phase transition developed by Safaryan. Doping non-stoichiometric LN samples with MgO reduces point defects in the LiNbO₃ crystal, particularly at low magnesium concentrations approaching 3 mol%, bringing the LN closer to stoichiometric composition.

Analyses of the defect composition reveal a decrease in the concentration of Nb_Li with divalent doping, which leads to an increase in Tc and confers quasi-stoichiometry on the LN. Conversely, the concentration of Nb_Li increases with doping with tetravalent impurities, leading to a reduction in Tc and making the material more non-stoichiometric. These results highlight the impact of doping lithium niobate with divalent and tetravalent impurities on the structure of point defects in LN.

Index Terms-Defect structure; Doping; Lithium niobite; Acousto-optic materials; vacancy model