Effects of Heavy Doping of MgO on Characteristics of LiNbO₃

Heavily doped LiNbO 3 single crystals were successfully grown using the Czochralski technique. The MgO solubility was, as determined from transmittance and X-ray diffraction data, less than 30 mol% in this crystal. The site-occupancy refinement study reveals that all of the Mg 2+ ions incorporated into LiNbO 3 will occupy A-site lattices. They first expel the Nb 5+ ions which reside in this site and then create vacancies at the same site. The Curie temperature thereafter increases firstly with the MgO content and decreases again when the concentration of MgO goes beyond a certain limit. The C-constant of the Gallagher model, T c = K - C · C v , is estimated to be C b =3333.3 for lightly doped materials and C a =300.0 for heavily doped materials. The former is due to the decrease in B-site vacancies, while the latter is ascribed to the increase in A-site vacancies.