Effects of Heavy Doping of MgO on Characteristics of LiNbO3

Abstract
Heavily doped LiNbO3 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 Mg2+ ions incorporated into LiNbO3 will occupy A-site lattices. They first expel the Nb5+ 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.

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