We have re-examined the infrared absorption bands due to the O-H bond-stretching vibration and the polarization characteristics in undoped and MgO-doped LiNbO3 using well-characterized crystals. It has been found that the O-H bond stretching vibrational frequency nu (OH) has a strong correlation with Nb concentration in the crystals. We have also determined the position where hydrogen enters using Novak's empirical relationship between the values of nu (OH) and the length of the hydrogen bond and the structure analysis data for the undoped crystals. On the basis of those results and the polarization characteristics, we have examined the intrinsic and the extrinsic defect structure models in LiNbO3. It has been clarified that the behaviour of nu (OH) reflects the defect structures. The behaviour of nu (OH) supports the Li-site vacancy model as the intrinsic defect structure model, and the corresponding extrinsic defect model. A brief discussion is also given of the behaviour of nu (OH) in crystals simultaneously doped with two kinds of impurity.

The water content was determined for five strongly basic anion-exchange resins (trimethyammonium type having different exchange capacities and cross-linking degrees by divinylbenzene) in definite anionic forms (ten singly, three doubly, one triply, and one quadruply charged) dried at 25 °C and at a relative humidity of 50%. Incorporation of the results of the previous research on the conventional resins by X-ray absorption fine structure and diffraction methods indicated that the present method gave the number of intrinsic water molecules strongly interacting with an anion. The hydration numbers of weakly hydrating anions (Cl⁻, Br⁻, and ClO₄⁻) and a small anion (F⁻) were independent of the exchange capacity and slightly decreased with an increase in cross-linking, especially at 8%. The small and strongly hydrating ion F⁻ kept the in-water hydration structure to form a water-separated ion pair in the resins, while the other weakly hydrating ions were appreciably dehydrated to form a contact ion pair. The hydration number of a strongly hydrating ion, H₂PO₄⁻, appreciably decreased with increases in both the exchange capacity and cross-linking degree accompanied by intermolecular hydrogen bonding between the anions. This may be related to other characteristics of the H₂PO₄⁻ form resin, such as a higher concentration required for quantitative exchange, a systematic change in infrared spectra on the degree of exchange, and facile thermal dehydration, giving H₂P₂O₇²⁻. In contrast, multivalent anions were exchanged without dehydration, due to the larger space allowed for in the resins and the stronger interaction with water compared to those of monovalent anions.

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The spaces (voids) available for cations in the five exchange resins with varying exchange capacities and cross-linking degrees were estimated, on the basis of the additivity of molar volumes of the constituents. Tetraalkylammonium ions (NR(4)(+); R: Me, Et, Pr) may completely exchange potassium ion on the resin having a larger void radius. In contrast, the ratio of saturated adsorption capacity to exchange capacity of the resin having a smaller void radius decreased with an increase in size of NR(4)(+) ions, due to the interionic contacts. Alkali metal ions could be exchanged quantitatively. While the hydration numbers of K(+), Rb(+), and Cs(+) were independent of the void radius, those of Li(+) and Na(+), especially Na(+), decreased with a decrease in void radius. Interionic contacts between the hydrated ions enhance the dehydration. Multivalent metal ions have the hydration numbers, comparable to or rather greater than those in water. A greater void volume available due to exchange stoichiometry released the interionic contacts and occasionally promoted the involvement of water molecules other than directly bound molecules. The close proximity between ions in the conventional ion-exchange resins having higher exchange capacities may induce varying interactions.

We have systematically studied the behaviour of the absorption bands due to the O - H bond-stretching vibration and its polarization characteristics in with the use of well characterized crystals. It has been found that the O - H bond-stretching vibrational frequencies, , have a strong correlation with Nb concentration in the crystals as in the case of MgO-doped . The values of shift to the higher-frequency region when the Sc concentration in the crystal exceeds about 2.5 mol%. The magnitude of the frequency shift is smaller and the polarization dependence of the absorption bands due to is weaker in -doped than in MgO-doped . These features are attributed to the difference of the charge between and . We have also proposed an ideal defect structure model for -doped , which is based on the Li-site vacancy model as an intrinsic defect structure model. The observed behaviour of is consistently explained by the proposed defect structure model. This supports the justification of the extrinsic defect structure model based on the Li-site vacancy model for -doped as well as for MgO-doped .