Study on the temperature dependence of the O[H.sup.-] absorption band in Hf-doped LiNb[O.sub.3] crystals

We study in this paper the temperature dependence of the O[H.sup.-] absorption band in LiNb[O.sub.3] crystals with different Hf-doping concentrations. It is found that the shoulder at 3500 [cm.sup.-1] appears in the doping level of 2.6 mol%, becomes more evident at 3 and 4 mol%, and then gradually faints when the doping concentration increases. This result is explained by the non-monotonic change of Nb vacancy density in the three stages of the defect evolution involved in the Hf incorporation of LN lattice. Moreover, the absorption difference analysis of the O[H.sup.-] bands is consistent with this explanation and reveals that the mobility of H? ions may be reduced by the strong trapping of the highly electronegative Nb vacancies.