To determine the defect structure of ZnO-doped LiNbO3 single crystals with high doping concentrations, we obtain the measurements using the extended x-ray absorption fine structure (EXAFS) at room temperature. It indicates Zn atom is directly substituted on the Li site of the LiNbO3 crystal after Zn doping. EXAFS simulation by way of analyzing the scattering amplitudes also shows that the Zn atom does not substitute the Nb site at highly Zn-doped LiNbO3. Finally, we confirm that VNb5−, a strong charged vacancy, should be considered as an important factors in influencing the physical properties of LiNbO3 beyond 7.5mol% Zn-doped doping concentration.

A water-quenched Al73Ni22Fe5 decagonal quasicrystal was investigated by the selected-area electron diffraction, convergent-beam electron diffraction and high-angle annular dark-field scanning transmission electron microscope methods. The alloy shows very sharp spots and nearly no diffuse scattering in the diffraction patterns, belongs to centrosymmetric space group P10(5)/mmc and is constructed almost by one type of 2 nm diameter atom cluster having mirror symmetry with a highly quasicrystalline order arrangement. Although a small number of 2 nm atom clusters having five-fold symmetry exists, which are similar to those observed in melt-quenched Al70Ni15Fe15, the structure of Al73Ni22Fe5 is considered to basically be the same as that of water-quenched Al72Ni20Co8, which is constructed only by mirror symmetry clusters arranged with a very high quasiperiodicity. The number of valence electrons per atom (e/a) of the present alloy (1.92) is very close to that of Al72Ni20Co8 (1.90), but differs from those of phases constructed by only the five-fold symmetry clusters. This implies that these alloys are Hume-Rothery electron compounds, whose structures are determined primarily by e/a value.

An investigation of the OH À absorption spectra of Zn-doped LiNbO 3 single crystals with doping concentrations from 0.0 to 8.3 mol % after proton exchange (PE) is carried out. Before PE treatment, the absorption bands are found centered at approximately 3485 cm À1 for the samples with Zn-doping concentrations below 7.5 mol %, whereas two distinct bands at 3505 and 3530 cm À1 are clearly observed for the samples with Zn-doping concentrations above 7.5 mol %. After PE treatment, an absorption band at 3505 cm À1 is predominant for all the samples, and this is attributed to the high concentration of H þ ions substituting Li atoms. However, for the highly Zn-doped samples, the lineshape and intensity of the 3530 cm À1 mode remain the same during PE. A theoretical investigation using the hybrid density functional B3LYP method with a simple cluster structure shows that the origins of the 3485 and 3530 cm À1 absorption modes correspond to the Li-and Nb-vacancy models, respectively.

The proton-exchanged OH− absorption spectra of congruent and 8.1 mol % Zn-doped LiNbO3 single crystals with and without polarization inversion are presented. The variation in the proton-exchanged OH− spectra for the congruent sample is not affected by polarization inversion. This result confirms the Li-vacancy model. However, the highly doped sample shows stronger increase in intensities with polarization inversion. In our investigation, highly negative charge vacancy model confirms with proton-exchanged OH− absorption spectra and domain inversion etching experiment. Finally, we demonstrated the polarization inversion mechanism with these two samples based on extended x-ray-absorption fine structure experimental results.