Concentration Dependence of the Octahedral Ti sup (4+) Center in LiNbO sub 3; Its Effect on Refractive Indices

X-ray absorption spectra of titanium-diffused LiNbO sub 3 indicate that a strong change in the Ti center appears as the concentration is increased above 5x10 sup 20 cm sup -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 (n sub o) with increasing Ti concentration reported in the literature.