Absolute refractive index and oscillator model of dispersion for some ferroelectrics with pseudoilmenite structure

The interferometric method for measurement of the absolute refractive index of the optical media with the accuracy of 0.00001 has been developed. The range of index and thickness measurements is not limited in principle. This method allows testing LiNbO3and LiTaO3

Anisotropy of induced birefringence in ferroelectrics with pseudoilmenite structure

An analysis of the nature of anisotropy of the optical properties of LiTaO3 is presented on the basis (of the features) of its intrinsic crystallographical properties. Electrooptically induced refractive-index change in the regular and reverse-poled LiTaO3 is calculated. Specifically we determine how the index change depends on electric field magnitude and direction in y-propagating extraordinary modes. To accomplish this, changes in index-ellipsoid shape and orientation are determined by use of a numerical eigenvalue procedure for diagonalizing the impermeability tensor; then the refractive index is calculated by vector reference-frame transformation and small perturbation approximation. The general formula is inferred from calculations for specific field directions. Electrooptic coefficients for the reverse-poled LiTaO3 are obtained tensor reference-frame transformation of those of LiTaO3

Electrical Conductivity and Dielectric Properties of Bi4_{4}Ti3_{3}O12_{12}

The present paper deals with the investigation of electrical and dielectric properties of structures based on Bi$_{4}$Ti$_{3}$O$_{12}$ films. It has been found that the nonlinearity of the $I - U$ characteristics in Me-Bi$_{4}$Ti$_{3}$O$_{12}$-Me structures is attributed to intercrystalline potential barriers. The height of the intercrystalline barrier ($\Phi_{0}=0.12$ eV) and the mean size of crystallise ($L=0.3~\mu$m) have been determined. At rather low temperatures, the hopping conductivity with a mean length of hopping, $\sim 2.6 \times 10^{19}$ cm$^{-3}$ eV$^{-1}$, is shown to be a dominant process at the charge transfer. It has been found that the electrical conductivity ($\sigma$) in the direction parallel to the $C$-axis (“sandwich” configuration) shows an anomaly in the phase transition region ($\sim 950$ K), while in the direction perpendicular to the $C$-axis, a simple bending of $\sigma$ vs. $T$ is observed. The latter is explained by the change of spontaneous polarization in Bi$_{4}$Ti$_{3}$O$_{12}$ films. The temperature dependence of the dielectric constant and the dielectric loss tangent have the maxima in the range of the phase transition temperature. The dielectric constant values are $\sim 650 \sim 120$ for the structures of “sandwich” and planar configurations, respectively. This fact indicates the presence of a polarization component in the given direction. The diffusion of the phase transition is explained by the imperfection of the film structure

Electronic structure and phase transition effects in some ABO3 materials

In this work a new theoretical study is undertaken of the electronic structure of ABO 3 materials and role of the BO 6 octahedron containing Ti, Nb, and Ta in paraelectric and ferroelectric phases. The results of this work show that, cluster calculations by the X ? method (in ferroelectric and paraelectric phases) even for a minimum cluster can describe the nonlocal electronic properties of ABO 3 and can be used in discussions of the physical properties of these compounds. © 2002 Taylor & Francis