Stoichiometric Lithium Niobate Research Articles

Growth, Optical and Switching Characteristics of Ferroelectric Pure and Mn Doped Near SLN Crystals

Pure and Mn doped single domain near stoichiometric lithium niobate crystals have been grown by top seeded solution growth from 55 mol% Li solution. A uniform segregation of Mn throughout the crystal was obtained. Doping concentration decreases the Curie temperature while the absorption edge shift towards the longer wavelength region. Two color holographic recording was examined in Mn doped samples. Improved sensitivity, dynamic range and lifetime of the hologram for the doped crystal have been determined. The effect of Mn doping on the switching properties has been analyzed.

EPR of Nd3+ in congruent and nearly stoichiometric lithium niobate

AbstractThe cover picture refers to the article by Galina Malovichko et al. which has been selected as Editor's Choice for this issue [1]. The lower part of the figure shows a section of the angular dependence of the EPR spectra in the xy‐plane for nearly stoichiometric LiNbO3:Nd3+. The solid lines correspond to non‐magnetic neodymium isotopes of axial C3 symmetry (green) and low C1 symmetry (purple and blue), respectively; the symbols represent experimental data. The upper part of the figure shows possible structures of the nearest surrounding for the C3 and C1 centers and their correspondence to the observed line positions.The first author Galina Malovichko is Associate Professor in the Physics Department at the Montana State University, USA. Her scientific activity is devoted to experimental condensed matter physics, particularly to the study of structures of extrinsic, intrinsic and radiation defects and their influence on crystal prop‐erties. Her group is involved in the characterization of various materials and optimization of their parameters for advanced ap‐plications.

EPR of Nd3+ in congruent and nearly stoichiometric lithium niobate

AbstractLithium niobate crystals doped with neodymium were studied with the help of electron paramagnetic resonance, EPR in the temperature range of 4.2–20 K. Tremendous narrowing of the EPR lines in nearly stoichiometric samples in comparison with congruent ones allowed us to distinguish four non‐equivalent centers, as well as line splitting caused by hyperfine interaction of neodymium electrons with nuclear spins of both magnetic isotopes 143Nd and 145Nd. It is shown that one of the centers has axial C3 symmetry, whereas all others have lowest C1 symmetry due to presence of intrinsic defects or/and charge compensation defects in the near neighborhood of Nd3+. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

SIMS-depth profile and microstructure studies of Ti-diffused Mg-doped near-stoichiometric lithium niobate waveguide

Ti-diffused planer waveguides have been fabricated on pure and Mg-doped near stoichiometric lithium niobate (SLN). Secondary ion mass spectroscopy method was applied to study the Ti diffusion in 1 mol% Mg-doped Z-cut SLN crystal. 100 nm Ti film has been deposited on LN substrate by e-beam evaporation at room temperature. Diffusion constant value for Mg-doped SLN is lower (1.84×10 −13 cm −2/s) than that of pure SLN. Mg-doped CLN also possesses low diffusion constant value of 1.27×10 −13 cm −2/s due to higher doping concentration of Mg (5 mol%). AFM topographic observation reveals that Mg-doped SLN shows lower surface roughness than Mg-doped CLN. The roughness (peak to valley) of the Ti-diffused Mg:SLN is 20 nm compared to 62 nm for the congruent LN waveguide. These features make Mg:SLN highly attractive for the fabrication of efficient waveguides.

Deterministic beam fanning in Fe-doped stoichiometric lithium niobate crystals

We investigated the beam-fanning effect in Fe-doped stoichiometric lithium niobate (Fe:SLN) crystals that were grown by the top-seeded solution growth method. Deterministic beam fanning (DBF) was measured in Z-cut Fe:SLN crystal for incident light propagating along the c+ and c- axes. The dependence of beam-fanning factors on incident power density was also studied. The experimental results of DBF in the Z-cut Fe:SLN crystal were in good agreement with a theoretical simulation based on a two-wave mixing model. The results compared with those for Fe-doped congruent lithium niobate crystals indicate that the beam-fanning process in Fe:SLN is deterministic because of its much-reduced intrinsic density of defects.

Lattice vibrations and phase-transition soft mode in near stoichiometric lithium niobate crystals

At room temperature, Raman-scattering investigations of near stoichiometric lithium niobate (S-LN) crystals theoretically and experimentally reveal an effect of the lattice vacant positions on the Raman spectra. At high temperature, Raman peaks of the mode ν5 vary sensitively and intensely with the increase of the temperature. A condensed soft optical-phonon mode originates from the triply degenerate symmetric in-plane O–Nb–O bending. The paraelectric-ferroelectric structural transition occurs at about 1170°C. The composition homogeneity and optical uniformity of the S-LN crystals are demonstrated to be excellent compared with those of the congruent lithium niobate.

Growth of near stoichiometric LiNbO 3 crystals by a modified zone melting method

Near stoichiometric Lithium niobate (LiNbO 3) bulk crystals have been grown by a modified zone melting method. In this method, a platinum strip immersed in melting zone was used as heater. The Li content in the crystal was achieved to 49.95 mol%, which was determined by the UV absorption edge of the grown crystal. The characteristics of this technique have been discussed.

A comparative study on the domain switching characteristics of near stoichiometric lithium niobate and lithium tantalate single crystals

For pure SLN and SLT crystals the coercive field measured from ferroelectric hysteresis loop was found to be independent of ramp rate. Decreased lithium concentration in pure SLN samples, the coercive field and internal field are strongly enhanced. Nb Li antisites are the major contribution to the internal field. Coercive field depends strongly on the ramp rate in case of MgSLN and MgSLT samples, because of domain pinning. The coercive field is considerably reduced in Mg doped SLN and SLT compared to pure samples, indicating that the switching fields are strongly dependent on the nonstoichiometry of the crystals. The coercive field values were found to be constant under multiple cycling in case of Mg (1 mol%) doped SLN crystal. A strong correlation is found to exist between coercive field value and the Curie temperature.

Chemical synthesis of stoichiometric lithium niobate powders

Lithium niobate powders with an ideal stoichiometry are prepared from the raw powders of Li 2CO 3 and Nb 2O 5. An organic combustion technique is utilized to synthesize lithium niobate powders at reduced temperature, viz. 500–600°C. Urea is used as the thermal resource in the present work, which can lead to stoichiometric lithium niobate powders due to its very fast chemical reactions involved in the whole process. IR spectral characteristics strongly support the stoichiometric composition of our present powder samples.

Investigations of the growth mechanism of stoichiometric LiNbO 3 fibers grown by the laser-heated pedestal growth method

In this study, stoichiometric lithium niobate (LiNbO 3) single-crystal fibers were grown by the laser-heated pedestal growth (LHPG) method using different compositions with [Li 2CO 3]/[Nb 2O 5]=48.6:51.4, 50:50, 55:45 and 58:42 seeds. X-ray/CCD and ICP-AES were used to confirm the crystalline structure and the composition of the fibers, respectively. Electron spectroscopy for chemical analysis (ESCA) was used to analyze the [Li]/[Nb] ratio along the axis of the fibers. Based on these measurements, the growth mechanism that produces stoichiometric LiNbO 3 fibers from stoichiometric feeding rods was investigated. The results show that the growth of stoichiometric LiNbO 3 fibers using the LHPG method followed the equilibrium phase diagram concept.

A novel technique to grow stoichiometric lithium niobate single crystal

Stoichiometric LiNbO 3 crystal has received much attention because of its excellent properties. Here we reported a novel growth technique to grow near-stoichiometric LiNbO 3 single crystal. This technique also uses a double-chamber crucible including a growth chamber and a melt supply chamber, here melt supply is executed by lowering down a Pt-made mould in the melt supply chamber to push the melt to the growth chamber, not by adding raw material powders to the melt supply chamber. The near-stoichiometric LiNbO 3 crystal grown by this novel technique was clear without inclusion, free of crack and in light yellow. The composition of as-grown crystal and its homogeneity were characterized by the optical methods of measurement of UV absorption edge and the Li 2O composition in the whole crystal thus characterized was 49.774±0.016 mol%. The test by Raman band wide method and Curie temperature method also verified the homogeneous composition. Etching morphologies of the crystals shown that they were single domain. The novel growth technique is promising for batch production of stoichiometric lithium niobate single crystal and also shown the potential application for other incongruent melting crystals.

Fluorescence properties of Nd3+ doped stoichiometric LiNbO3 fiber single crystals by micro‐pulling down method

AbstractUsing the micro‐pulling down (μ‐PD) method, 1 and 3 mol% Nd2O3 doped near stoichiometric lithium niobate (LiNbO3) single crystal fibers were grown in 1 mm diameter and 35∼40 mm length. The grown crystal fibers were free of cracks and the homogeneous distribution of Nd3+ ion concentrations were confirmed by the electron probe micro analysis. The changes of fluorescence spectra were measured with respect to the Nd3+ ion doping concentration. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Complex dispersion relation of phonon‐polariton in stoichiometric LiNbO 3

Complex polariton dispersion relations were studied in the nearly stoichiometric lithium niobate crystals grown by the double crucible Czochralski method using the terahertz (THz) time domain spectroscopy. The intensity and phase delay of transmitted THz radiation have been accurately measured for the propagation along the x-axis from 0.1 to 2.3 THz. The dispersion relation of phonon-polariton frequency and damping factor have been determined for A1(z) and E(x,y) symmetry polaritons. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ternary system Li 2O–K 2O–Nb 2O 5: Part II: Growth of stoichiometric lithium niobate

Growth conditions of stoichiometric or near-stoichiometric lithium niobate (sLN) from K 2O containing fluxes have been studied by investigating phase equilibria in the ternary system Li 2O–K 2O–Nb 2O 5. The crystallization area of LiNbO 3 was confirmed by growth experiments on the g1 (LiNbO 3–K 2O), g2 (LiNbO 3–ternary eutectic liquid ( E t: 45.0 ± 1.5 mol% Nb 2O 5, 26.0 ± 1.5 mol% K 2O and 29.0 ± 1.5 mol% Li 2O)) and g3 (LiNbO 3–KNbO 3) joins. The yield and the composition of LiNbO 3 single crystals were tested for a wide range of starting compositions. From these experiments, the starting compositions leading to stoichiometric lithium niobate have been determined.

Ternary system Li 2O–K 2O–Nb 2O 5: Part I: Phase equilibria around the lithium niobate existence field

In order to optimize the growth conditions of stoichiometric lithium niobate from K 2O–Li 2O–Nb 2O 5 fluxes, the limits of its crystallization field were determined by investigating phase equilibria in the ternary system Li 2O–K 2O–Nb 2O 5. For this purpose, suitable parts of four vertical sections were studied using DSC experiments and X-ray powder diffraction allowed to identify all the solid phases involved. The lithium niobate liquidus surface is delimited by four monovariant lines: Liq + Li 3NbO 4 + LiNbO 3, Liq + KNbO 3 + LiNbO 3, Liq + KLN solid solution + LiNbO 3 and Liq + LiNb 3O 8 + LiNbO 3. In the region investigated, three ternary invariant reactions were found. The first < LiNb O 3 > + < KNb O 3 > ⇄ < β -L i 3 Nb O 4 > + < KLN solid solution > is a quasi-peritectoid reaction occurring at 966 °C, the second is the eutectic reaction at 997 °C: Liq ⇄ < β -L i 3 Nb O 4 > + < KNb O 3 > + < LiNb O 3 > and the last one is the quasi-peritectic reaction: Liq + < KLN solid solution > ⇄ < KNb O 3 > + < LiNb O 3 > at about 1050–1055 °C.

Pyroelectric Electron Emission Behaviors of Congruent and Stoichiometric Lithium Niobate Single Crystals

Pyroelectric electron emission current measurements and current distribution collecting were performed on congruent and stoichiometric lithium niobate single crystals. Electron emission behaviors were found to be gap distance (crystal-detector) dependent. For small gaps, in both crystal compositions, emission was accompanied by a partial superficial domain inversion, triggered by surface plasma ignition. For large gaps (> 2 mm) in congruent single crystals the emission was activated by a true pyroelectric effect.

Domain structures and etching morphologies of lithium niobate crystals with different Li contents grown by TSSG and double crucible Czochralski method

AbstractStoichiometric lithium niobate single crystals with different Li contents have been grown both by the top‐seeded solution growth (TSSG) method from potassium containing flux and by the double crucible Czochralski (DC Cz) method. Spectroscopic properties (e.g. the UV absorption edge, Raman linewidth) and the Curie temperature measurement have been used for the characterization of the crystal composition. The double crucible Czochralski method is found to be suitable for mass production of stoichiometric LiNbO3 with Li content larger than 49.7 mol% and homogeneity of 0.03 mol%. The domain structures and etching morphologies on negative and positive c‐surface were also investigated by chemical etching method. A new domain structure of three‐fold symmetric sectors were observed in near‐stoichiometric LiNbO3 grown by TSSG method. The straight line arrangement hillocks on negative c‐surface and the net‐like arrangement etch lines were observed and explained by stress etching mechanism. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Anisotropic thermal expansion of stoichiometric lithium niobate crystals grown along the normal direction of facets

Abstract In this paper, a stoichiometric lithium niobate (SLN) crystal with the size up to 20 × 20 × 18 mm3 was grown along the normal direction of the ( 0 1 2 ) facet from the 16 mol% K2O fluxed melt by the top-seeded solution growth method. The anisotropic thermal expansion of the SLN crystal and congruent lithium niobate (CLN) crystal was measured along different directions by using a Shimadzu thermomechanical analyzer. As compared with CLN, the SLN crystal exhibited slightly larger thermal expansion along the Z-axis and slightly smaller expansion along the X-axis. Both the SLN and CLN crystals showed strong anisotropy in the thermal expansion. The thermal expansion coefficient of SLN along the X-axis (∼16.7 × 10−6 °C−1 at 300 °C) is much larger than that along the Z-axis (∼2.5 × 10−6 °C−1 at 300 °C). Based on the experimental data and polynomial fitting results, we calculated the thermal expansion coefficients for different directions. In the case of growing the SLN crystal along the normal direction of ( 0 1 2 ) facet, we studied the radial anisotropic thermal expansion and discussed the cracking problem of the crystal according to its actual growth morphology. It is found that the cracks of SLN can be suppressed by growing the crystal along the W-axis due to its reduced radial anisotropy in the thermal expansion.

Preparation and characterization of high-quality stoichiometric LiNbO 3 thick films prepared by the sol–gel method

Stoichiometric lithium niobate (SLN) thick films were deposited on z-cut LiNbO 3 using the sol–gel method from a precursor solution containing various polyvinyl alcohol (PVA) concentrations and their characteristics were investigated. The film thickness increases linearly and the roughness decreases with the increase in PVA concentration. The refractive indexes of the films prepared with PVA were n 0=2.28±0.02 and n e=2.19±0.02 at a wavelength of 632.8 nm. The transmission loss was 0.61±0.05 dB/cm

Studies on the crystal growth aspects of efficient optical data storage material: Mn doped near-stoichiometric lithium niobate (Mn:SLN)

Optical quality pure and Mn doped near stoichiometric lithium niobate (SLN) crystals were grown by top seeded solution growth using induction heating system. The growth parameters like temperature field, pulling and rotation rate have been optimized. Transmission studies revealed a shift in optical absorption towards longer wavelength for increased doping concentration. Curie temperature was found to decrease with Mn concentration. The effect of Mn doping on two-color sensitivity and dynamic range (M/#) on gating and writing intensities are also investigated. Long dark storage time has been obtained for the doped crystal.