Concentration dependence of the octahedralTi4+center inLiNbO3: Its effect on refractive indices

X-ray absorption spectra of titanium-diffused ${\mathrm{LiNbO}}_3$ indicate that a strong change in the Ti center appears as the concentration is increased above 5×${10}^{20}$ ${\mathrm{cm}}^{\mathrm{-}3}$, involving a tendency toward displacement in the x-y plane and disorder. This change in the Ti center occurs within the concentration range used for integrated-optical-device fabrication, and may account for the abrupt decrease in rate of change of the ordinary optical index (${\mathrm{n}}_0$) with increasing Ti concentration reported in the literature.