A study was made of the behavior of absorption bands that were due to the O-H bond-stretching vibration and its polarization. It was found that the O-H bond-stretching vibrational frequencies were closely related to the Nb concentration. The O-H bond-stretching vibrational frequencies shifted to higher frequencies when the Sc concentration in the crystal exceeded some 2.5mol%. The frequency shift was smaller, and the polarization dependence of the absorption bands due to O-H bond-stretching was weaker, in Sc2O3-doped material than in MgO-doped material. These results were attributed to the difference in charge of Sc3+ and Mg2+. An ideal defect structure model was proposed, for Sc2O3-doped material, which was based upon the Li-site vacancy model. The observed behavior of the O-H bond-stretching vibrational frequencies could be consistently explained by this proposed defect model.

S.Shimamura, Y.Watanabe, T.Sota, K.Suzuki, N.Iyi, Y.Yajima, K.Kitamura, T.Yamazaki, A.Sugimoto, K.Yamagishi: Journal of Physics - Condensed Matter, 1996, 8[37], 6825-32