Growth, Stucture And Properties Of Lithium Niobate And Lithium Tantanlum Doped With Magnesium

Lithium tantalum, due to excellent electrics and optical properties, good electromechanical coupling, temperature coefficient, etc. It was generally used in the manufacture of high-frequency surface acoustic wave devices and in mobile phones, walkie-talkie and satellite communications, aerospace, etc. lot of high-end communications fields. It has been widely applied to volume holographic memory. However, light scattering can be induced by high light intensity in lithium tantalum, which results in serious holograph distortion. In this paper, Mg:LiTaO3 single crystals were grown by the Czochraski method using intermediate frequency heating, and as-grown boules had no macroscopic and had good optical homogeneity.X-ray powder diffraction experiment showed that the Mg:LiTaO3 crystals held the same lattice structure as the congruent sample. In Mg:LiTaO3 crystals, calculation results of unit cell parameters indicated that the lattice constant increased with the MgO concentration increasing. Curie temperature of the Mg:LiTaO3 crystals was obtained from DTA measurement, which increased with MgO concentration increasing when MgO concentration was below the threshold concentration. When MgO concentration reached the threshold concentration, the Curie temperature began to decrease.The change mechanism of the UV-V absorption edge and the IR absorption peak was also discussed in the Mg:LiTaO3 single crystals. Analysis showed Mg2+ ions took priority of replacing anti-site Ta ( TaL 4i+), firstly. When the MgO concentration reached the threshold concentration, all of the TaL 4i+ ions were completely replaced, and Mg2+ ions began to occupy the normal Li and Ta sites simultaneously, thus formed self-compensation defect structure, ( Mg 3T-a+3 Mg +Li).The photorefractive properties of the Mg:LiTaO3 crystals, e.g., diffraction efficiency, photorefractive response time, were obtained by two-beam coupling experiment. With the MgO concentration increasing, diffraction efficiency and erasure time decreased, the photorefractive response speed increased.The light scattering resistance of the Mg:LiTaO3 crystals was studied by the transmission facula distortion method. When the MgO concentration was below threshold concentration, the light scattering resistance of samples showed no obviously change. In contrast, when the MgO concentration reached threshold concentration, the light scattering resistance of samples increased significantly. It is higher than that of pure LiTaO3 crystals.