Processing and characterization of lithium niobate with second phase addition

Lithium niobate (LiNbO{dollar}sb3{dollar}) is a material whose electro-optic coefficients make it useful for optical switching. High quality single domain single crystals are prepared from the congruent composition. The congruent composition is markedly lithium deficient and this lithium deficiency lowers the ferroelectric transition temperature from 1210{dollar}spcirc{dollar}C to about 1135{dollar}spcirc{dollar}C for the stoichiometric composition.; In order to scribe a light guide into the LiNbO{dollar}sb3{dollar} crystal, titanium dioxide is diffused into the surface to alter the refractive index and form the desired light pipe. At the limit of solid solubility of TiO{dollar}sb2,{dollar} the T{dollar}sb{lcub}rm c{rcub}{dollar} is reduced to 960{dollar}spcirc{dollar}C, below the temperature normally employed to achieve satisfactory rate of diffusion. This leads to the destruction of the single domain structure and a concomitant reduction in transmission quality.; It is now believed that the cation vacancy concentration controls the T{dollar}sb{lcub}rm c{rcub}{dollar}. In this research the effect of different dopants on the T{dollar}sb{lcub}rm c{rcub}{dollar} of lithium niobate was investigated. The current theories about the role of cation vacancy content and the c/a ratio in controlling the T{dollar}sb{lcub}rm c{rcub}{dollar} of LiNbO{dollar}sb3{dollar} was also investigated.; The experimental tools used in this study include x-ray diffraction for phase analysis and lattice parameter measurement, thermal analysis for T{dollar}sb{lcub}rm c{rcub}{dollar} measurement, neutron diffraction, microscopy and refractive index measurement.; It has been determined by neutron diffraction that vacancies of lithium compensate for lithium deficiency in congruent lithium niobate. This is in conflict with the Abrahams and Marsh model to account for non-stoichiometry in LiNbO{dollar}sb3{dollar}. Addition of MgTiO{dollar}sb3{dollar} causes an increase in the T{dollar}sb{lcub}rm c{rcub}{dollar} of LiNbO{dollar}sb3{dollar} and a uniform reduction in both the a and the c lattice parameters. MgTiO{dollar}sb3{dollar} also increases the refractive of LiNbO{dollar}sb3{dollar} and thus seems to be a suitable dopant for waveguide applications. The diffusion temperature for waveguide formation can be increased without affecting the quality of the crystal and this can lead to the formation of well defined channel waveguides. It has also been determined that the T{dollar}sb{lcub}rm c{rcub}{dollar} is not dependent only on the cation vacancy concentration or does not correlate directly to the c/a ratio.