Growth and characterization of MgO:LiNbO3 crystals

Congruent MgO:LiNbO₃ (MLN) single crystals doped with 0, 2.5, 5.0, 7.5 and 10.0 mole% of MgO were grown by the Czochralski method. The density and Curie temperature (T_c) for MLN crystals were measured. It was found that the density curve has a minimum and maximum at 2.5 mole% and 5.0 mole%, respectively. The Curie temperature increases first with the MgO concentration and decreases again when the concentration of MgO goes beyond the threshold limit ([Mg]_c, 5.0-7.5 mole%). We also measured optical absorption edges and IR absorption spectra at room temperature for MLN crystals. There existed a threshold concentration of nearly 6.0 mole%. The IR absorption peak appeared at 3470 cm^-1 in 0-5.0 mole% and 3534 cm^-1 in 7.5-10.0 mole% and peak shifts at about 60 cm^-1 toward the shorter wavelength side. We assumed that the substitution of Mg²⁺ for Nb⁵⁺ would weaken the cation-oxygen bond with its neighbouring O^2- ion, and the distortion of oxygen octahedron of MLN crystals would change in some degrees with the increasing MgO ratio. This distortion of oxygen would affect many physical properties of the MLN crystals