ORTHOSCOPIC INVESTIGATION OF THE AXIAL OPTICAL AND COMPOSITIONAL HOMOGENEITY OF CZOCHRALSKI GROWN LINBO3 CRYSTALS

The orthoscopy has been used to analyse the chemical homogeneity of [10.0]- and [00.1]-grown LiNbO3 single crystals by utilization of the sensitive correlation between compositional deviations and the variation of the extraordinary refractive index. It has been shown that a strong dependence of the resulting orthoscopic fringe patterns along the growth direction with the chemical axial distribution following Pfann's segregation occurs. A linear parallel fringe pattern corresponds to no segregation and hence with the adjustment of the congruent melt composition which was determined as 48.470+/-0.005 mol% Li2O for [00.1] growth orientation. In the case of [10.0]-grown crystals, a distribution-free homogeneous crystal composition was found at 48.490+/-0.005 mol% Li2O in the melt. This difference could be a result from various kinetic segregation coefficients k(kin). A localized deviation from Pfann's law at g almost-equal-to 0.1 is affected by the break of the mass transfer regime during the pulling process.