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Abstract—LiNbO3:Mg(~5.3 mol %) crystals grown from directly and homogeneously doped charges have been studied using a number of characterization techniques. Both crystals offer high chemical homogeneity, with an even Mg distribution over the boule. At the same time, the estimated effective distribution coefficient is larger in the homogeneously doped LiNbO3:Mg crystal. Moreover, the homogeneously doped crystal has a more ordered system of hydrogen bonds. Our results suggest that the distinctions between the fine structural features and chemical homogeneity of the crystals can be due to the effect of organic inclusions with rigid covalent bonds on the structure and physical characteristics of the growth charge prepared using a homogeneously doped Nb2O5:Mg precursor. [ABSTRACT FROM AUTHOR]

We have observed that LiNbO3:Mg (0.19–5.91 mol % MgO) crystals experience rearrangements in their defect structure with increasing concentration of Mg and exhibit optical anomalies related with them, which have a threshold character. We have shown that, at Mg concentrations close to the first concentration threshold at ~3.0 mol % MgO, the optical homogeneity of the crystals increases. When the Mg concentration approaches the second concentration threshold, we have revealed a significant shift (by ~50 cm–1 compared to that in other crystals) of the entire IR absorption spectrum in the range of stretching vibrations of OH groups to the high-frequency range, a sharp decrease in the number of protons, and a jumpwise shift of the absorption edge in the short-wavelength range. We have shown that the shift occurs because all NbLi point defects are replaced by Mg cations near the concentration threshold at 5.5 mol % MgO, and, subsequently, Mg cations occupy only positions of Li and Nb cations of an ideal stoichiometric structure, forming MgLi and MgNb point defects. [ABSTRACT FROM AUTHOR]

Abstract—The congruent charge LiNbO3:Zn (2.44 wt %) was synthesized using precursor Nb2O5:Zn (2.83 wt %) by the method of homogeneous doping. The LiNbO3:Zn crystal (2.12 wt %) was grown from this charge by the Czochralski method. The crystal demonstrates high chemical uniformity of Zn dopant distribution along the growth axis. The same distribution is characteristic of crystals obtained by usual direct doping. The homogeneously doped LiNbO3:Zn crystal (2.12 wt %) and the LiNbO3:Zn (2.02 wt %), LiNbO3:Zn (2.05 wt %), and LiNbO3:Zn (2.12 wt %) crystals close to this composition obtained by method of direct doping, as well as LiNbO(3cong), were compared to study defectiveness and optical and structural homogeneity. The method of IR absorption spectroscopy, photoinduced light scattering, and laser conoscopy were used for the study. All studied crystals show no photorefractive response, as can be seen from photoinduced light scattering. The conoscopic patterns of a crystal LiNbO3: Zn (2.12 wt %, homogeneous doping) are strained, which can be connected with a greater photoinduced ability to scatter light than in other crystals. The ability is caused by microstructures, clusters, and residual domain structures. However IR spectra demonstrate narrowing of bands, which can be explained by the fact that homogeneous doping of a Nb2O5 precursor with zinc contributes to the ordering of the lithium sublattice of a LiNbO3:Zn crystal and ordering of H+ protons compared to the ordering in a LiNbO3cong crystal. This effect is highly unusual at this concentration of the dopant. [ABSTRACT FROM AUTHOR]

IR absorption spectra of zinc-doped LiNbO3 crystals in the stretching region of OH groups, Raman spectra of the crystals, and their optical absorption spectra provide evidence of drastic changes in the mechanism responsible for the incorporation of Zn into the structure of the crystals and the nature of hydrogen bonds and the corresponding proton-containing charged defect complexes ( –OH–, NbLi–OH−, and –OH−) near a concentration threshold at ≈6.76 mol % ZnO in the melt. [ABSTRACT FROM AUTHOR]

The IR absorption spectrum of LiNbO3:Mg(5.05 mol %):Fe(0.009 mol %) crystals has been shown to be noticeably shifted (by ~50 cm–1) to higher frequencies, corresponding to stretching vibrations of OH– groups, in comparison with the spectrum of congruent LiNbO3 crystals. Analysis has shown that the shift is due to the formation of – –OH– and – –ОН– defect complexes. [ABSTRACT FROM AUTHOR]