In this work we study the photorefractive and electro-optical properties of Zirconium-doped congruent lithium
niobate (LN) crystals. In order to set the ground for the utilization of these crystals in nonlinear wavelengthconversion
devices, we investigate the dependence of the photorefractive properties of the crystals on dopant
concentration and incident power. In our experiments the birefringence variations induced by a 532-nm laser beam
are measured by using the Sénarmont method, in the ZrO<sub>2</sub> concentration range 0-3mol% and intensity range 155-
1800 W/cm<sup>2</sup>. In order to investigate photorefractivity at high intensities, we have also utilized the direct observation
of the distortion of the light spot transmitted by the crystal. In presence of photorefractivity, the transmitted light
spot becomes smeared and elongated along the c-axis. Our data show that the threshold ZrO<sub>2</sub> concentration can be in
the range 2.5-3mol%. Considering that the growth of large homogeneous Zr:LN crystals should be easier than for
Mg:LN, and that electrical poling of these crystals has already been demonstrated, Zr-doped LN could represent a
more convenient choice than Mg:LN for the realization of room-temperature wavelength converters.
Several near-stoichiometric lithium niobate (LiNbO<sub>3</sub>) plates for Periodically poled lithium niobate (PPLN) were prepared by vapor transport equilibrium (VTE) technique. External electric field poling was carried out on these samples. A linear dependence of the switching field on the concentration of anti-site niobium ions was observed. This linear relationship was explained by a two-dimensional model based on the dynamics of domain wall. In this model, the bowing of domain wall and the pinning role of anti-site niobium ions to the movement of domain wall were considered. The pinning-depinning transition of domain wall was attributed to the movement of anti-site niobium ions through the oxygen plane, which is due to the change of domain environment round anti-site niobium ions . A parameter of θ, denoting the ratio between the negative and positive domains round anti-site niobium ions , was introduced. The interaction between anti-site niobium ions and rounding domain environment was analyzed associating with the parameter θ. With the help of the shell-model theory, the force needed for anti-site niobium ions to pass through the oxygen plant was given as 1.696×10<sup>-9</sup> N and the critical θc corresponding to domain reversal was calculated to be about 67° in degree. Using the fitting result of experiment data, the domain wall energy per unit area for LiNbO<sub>3</sub> was also roughly calculated as 0.41 J/m<sup>2</sup>.