Raman spectra and structural perfection of nominally pure lithium niobate crystals

Сидоров, Н. В.; Палатников, М. Н.; Gabrielyan, V. T.; Chufyrev, P. G.; Калинников, В. Т.

doi:10.1134/s002016850701013x

Cited by 27 publications

(13 citation statements)

References 2 publications

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“…Due to continuous miniaturization of the modern devices based on single crystals, assessment of the crystalline perfection becomes more and more important in the modern advanced technology. Different direct and indirect techniques such as Raman spectroscopy, FT-IR, X-ray topography, EPR, NMR, optical homogeneity, transmission electron microscopy [20][21][22][23][24][25] techniques have been employed to analyze the structural defects in lithium niobate single crystals. HRXRD has also been found to be one of the most suitable methods to assess the crystalline perfection and to reveal the presence of commonly observed structural grain boundaries in bulk crystal domain.…”

Section: Introductionmentioning

confidence: 99%

Crystalline perfection, EPR, prism coupler and UV-VIS-NIR studies on Cz-grown Fe-doped LiNbO3: A photorefractive nonlinear optical crystal

2011

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The Fe-doped (0.05 mol%) lithium niobate (LiNbO 3 ) bulk single crystal was gown by the Czochralski (Cz) method using a co-axial two zone low thermal gradient furnace. The crystalline perfection of the grown crystal was evaluated by high resolution X-ray diffractometry which showed that it does not contain any structural grain boundaries, and the dopants predominantly occupied vacancy sites of Li + in the lattice. Electron paramagnetic resonance studies revealed the incorporation of Fe 3+ ions at Li sites. The Z-cut optically polished 450 mm thick wafer was used for birefringence measurements on a prism coupler spectrometer with 632.8 nm wavelength and it was found that the difference in refractive index (Dn) for ordinary and extraordinary rays is 0.0833. The optical transmission/ absorption spectra were studied by UV-VIS-NIR spectroscopy and this showed that the grown crystal has good optical sensitivity for 482 nm wavelength radiation. The present studies reveal that the crystal grown with a two zone low thermal gradient furnace has very good device properties which are needed for holographic data storage applications.

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Section: Introductionmentioning

confidence: 99%

Crystalline perfection, EPR, prism coupler and UV-VIS-NIR studies on Cz-grown Fe-doped LiNbO3: A photorefractive nonlinear optical crystal

2011

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“…In NSLN, the transition from the 30 μm interval to the 20 μm interval resulted in that a significant fraction of domains grew to the opposite +z side of the sample 0.75 mm thick [6]. The found differences in the formation of individual domains can be associated with both differences in the crystal compositions and features of SLN and NSLN defect structures [4], having an effect on the electron trap concentration in the irradiation region and hence, on the electric field induced by charges intro duced by the electron beam and captured by traps.…”

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confidence: 84%

“…The melt contains almost 58 mol % (in recalculation) of related alkali components (48.6 mol % Li 2 O + 9.3 mol % K 2 O), which determines its structure and makes it possible to obtain LiNbO 3 crystals that are very similar in compo sition and properties to stoichiometric ones (NSLN) but simultaneously are no worse than congruent crys tals (CLN) in homogeneity [2,3]. According to [4], NSLN is slightly more defective than SLN and exhib its a lowered photorefractive effect in comparison with SLN and CLN.…”

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Regular domain structures fabricated by an electron beam in stoichiometric LiNbO3 crystals

2012

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In this work, we study the capability of electron beam writing of regular domain structures (RDSs) in stoichiometric LiNbO 3 crystals. Domain structures were formed in two crystal types. The first type sto ichiometric LiNbO 3 crystal (SLN) was grown by the Czochralski method from a Li 2 O enriched melt (~58.6 mol % Li 2 O) [1]. Such crystals, due to the sig nificant difference in melt and crystal compositions, are characterized by a highly nonuniform refractive index along the growth axis and are hardly applicable in practice. The second crystal was grown from the congruent composition melt containing an additive of 6 wt % K 2 O alkali solvent (flux) [2]. The melt contains almost 58 mol % (in recalculation) of related alkali components (48.6 mol % Li 2 O + 9.3 mol % K 2 O), which determines its structure and makes it possible to obtain LiNbO 3 crystals that are very similar in compo sition and properties to stoichiometric ones (NSLN) but simultaneously are no worse than congruent crys tals (CLN) in homogeneity [2,3]. According to [4], NSLN is slightly more defective than SLN and exhib its a lowered photorefractive effect in comparison with SLN and CLN.To pattern RDSs, optically polished Z cuts 0.75 mm thick, fabricated from SLN and NSLN crys tals, were irradiated in a scanning electron microscope with a controlled electron beam (E = 25 keV, I = 0.1-0.25 nA). To provide a uniform electric field, Al was deposited on the opposite +z surface, and samples were grounded. The local irradiated areas S = 1 × 1 and 1.5 × 1.5 μm were aligned along lines with interval of 1.0 or 1.5 μm. The distances between lines for differ ent structures varied from 6.5 to 10 μm. Periodic lines were patterned in parallel to the X or Y direction on a crystal area of ~500 × 500 μm 2 . After that, samples were etched for ~60 s in a HF + 2HNO 3 solution upon heating. Then RDSs were studied using a Zeiss Axioplan 2 optical microscope and a Nano R2TM atomic force microscope.The threshold charges necessary for individual domain nucleation slightly differed in SLN and NSLN at 25 keV, but were close, Q NSLN ≤ 1 × 10 -11 C and Q SLN ~ 1.2 × 10 -11 C. In both crystals at threshold and close to threshold charges Q, the domain shape was triangular. The average radius of triangular domains, determined by their area, was r d ~ 2.5 μm for SLN and ~4 μm for NSLN. Despite their difference, switching region sizes for both crystals exceed irradi ated area sizes, which is probably caused by electron drift in the irradiated region [5]. In SLN, in contrast to NSLN [6], no gradual transformation of triangular nuclei to the hexagonal form was detected as the intro duced charge increased. In SLN, only an increase in the number of fine triangular nuclei formed in the irra diation region (Figs. 1a and 1b) occurred with increas ing introduced charge. Individual domains in SLN did not grow to the opposite side at distances between irra diations of 30, 20, and 10 μm. In NSLN, the transition from the 30 μm interval to the 20 μm interval resulted in that a significant frac...

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“…The photorefractive effect in lithium niobate (LiNbO 3 ) single crystals of different compositions (nominally pure and doped with a broad range of "photorefractive" and "non-photorefractive" cations) has been studied rather thoroughly in the literature using the Raman spectra only for excitation of the spectra in the visible region [1][2][3][4][5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%

“…1a). The intensity of this line is maximum in the spectrum of the crystal of stoichiometric composition, which has the greatest photorefractive effect among the studied crystals [1,[6][7][8], and the intensity is minimum in the spectrum of the LiNbO 3 [Y(0.46 wt.%)] crystal.…”

Section: Introductionmentioning

confidence: 99%

Raman spectra of photorefractive lithium niobate single crystals

et al. 2010

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We have conducted comparative studies of the Raman spectra of lithium niobate (LiNbO 3 ) crystals of different compositions for excitation in the visible and near IR regions. We have observed that the photorefractive effect is one of the factors leading to line broadening. For this reason, the linewidths may be greater upon Raman excitation in the visible region than for excitation in the near IR region. This may be explained by formation in the crystal, when illuminated by laser radiation in the visible region, of a three-dimensional sublattice of nanostructures and microstructures (with refractive index and other physical parameters different from the parameters of the host crystal) from which photorefractive light scattering occurs. Formation of nanostructures and microstructures makes an additional contribution (besides the contribution due to random and dynamic disorder in the arrangement of the structural units) to the broadening of the Raman lines in the visible region of the spectrum. Illumination of the crystal by radiation in the near IR region does not induce a sublattice of nanostructures and microstructures, due to a significantly smaller photorefractive effect.Keywords: Raman light scattering, photorefractive effect, nominally pure and doped single crystals, defect structure, lithium niobate. Introduction.Raman light scattering is one of the most informative methods for simultaneously studying the structural features of ferroelectric single crystals and the photorefractive effect [1]. The photorefractive effect in lithium niobate (LiNbO 3 ) single crystals of different compositions (nominally pure and doped with a broad range of "photorefractive" and "non-photorefractive" cations) has been studied rather thoroughly in the literature using the Raman spectra only for excitation of the spectra in the visible region [1-8].** Due attention has not been paid to studies of

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Raman spectra and structural perfection of nominally pure lithium niobate crystals

Cited by 27 publications

References 2 publications

Crystalline perfection, EPR, prism coupler and UV-VIS-NIR studies on Cz-grown Fe-doped LiNbO3: A photorefractive nonlinear optical crystal

Crystalline perfection, EPR, prism coupler and UV-VIS-NIR studies on Cz-grown Fe-doped LiNbO3: A photorefractive nonlinear optical crystal

Regular domain structures fabricated by an electron beam in stoichiometric LiNbO3 crystals

Raman spectra of photorefractive lithium niobate single crystals

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