The growth striations and ferroelectric domain structures in Czochralski-grown LiNbO3 single crystals

The rotational striations and power striations are studied in LiNbO₃ crystals and one-to-one correspondence between the striations and temperature fluctuations is demonstrated. The ferroelectric domain structures related to the rotational striations and the power striations have been observed. The distribution of solute concentration in rotational striations is measured by means of energy dispersive X-ray analysis in the scanning electron microscope, and it has been concluded that the ferroelectric domain structures depend on the solute concentration gradient.     

Variation of electro-optic coefficients in MgO-doped LiNbO3 single crystals

Maker fringe experiment was performed to investigate a variation of second-harmonic generation by external DC field as a function of MgO content in MgO-doped LiNbO₃ crystals. The 4 mol% MgO-doped LiNbO₃ has the largest value of the electro-optic coefficient (Γ) among all MgO-doped LiNbO₃ crystals, which is 1.05 × 10^− 5 cm/kV. The threshold phenomena was revealed in between 4 mol% MgO-doped LiNbO₃ and 5 mol% MgO-doped one.     

近化学计量比Mn:LiNbO3晶体的助熔剂坩埚下降法生长研究

以K2O为助熔剂,在较大的温度梯度(90～100℃/cm)条件下进行引种和晶体生长,应用坩埚下降法技术成功地生长出了初始Mn2 掺杂浓度为0.5%(摩尔分数)的近化学计量比的铌酸锂晶体.用X射线衍射表征了获得的晶体,并计算了晶体的结构参数.与同成分的铌酸锂晶体相比,样品的晶格常数略变小,紫外吸收边向短波方向发生了移动.测定了晶体的吸收与发射光谱,观测到吸收中心在571nm(6A1g(6S)→4T1g(4G))的吸收宽带以及发光中心约620nm(4T1g(4G)→6A1g(6S))的红色荧光带.从晶体上部与下部的颜色以及吸收强度的变化,可初步推测出沿着晶体生长方向Mn2 离子浓度逐渐增加,Mn2 离子在晶体中有效的分凝系数＜1.     

Local polarization reversal in LiNbO3 crystals

Local polarization reversal has been investigated in a thin surface layer of a ferroelectric and preliminary results are presented for lithium niobate. The polarization reversal is accomplished by using a moving pointed electrode. Pis’ma Zh. Tekh. Fiz. 23, 54–58 (June 12, 1997)     

Phononic crystals based on LiNbO3 realized using domain inversion by electron-beam irradiation.

We report in this paper about the realization of domain inversion in z-cut lithium niobate by electron beam irradiation in order to perform phononic crystals. The fabrication of these phononic crystals on z-cut LiNbO3, which is, in our case, a periodic repetition of voids and LiNbO3, was achieved by domain inversion followed by wet etching, taking advantage of the large difference in etching rate between z+ and z- faces. A pertinent choice of irradiation conditions such as accelerating voltage, beam current, and charge density was determined and optimized. Two-dimensional structures at the micrometer scale were then realized on z-cut LiNbO3. We demonstrate the achievement of hexagons with diameters between 2 microm and 18 microm, with a very important depth close to 30 microm, which depends on the etching time and the hole size. The obtained structures, which exhibit a filling fraction varying from 1% to 64%, were characterized before etching by polarizing microscope to visualize the inverted domains. After HF etching, scanning electron microscopy was used to observe the obtained phononic structures. Taking into account the obtained filling fraction values and the size of created hexagons, the frequency band gap of these structures is expected at a range of 200 to 350 MHz. As expected in this frequency range, we have proven experimentally the existence of the phononic band gap on z-cut LiNbO3 by combination of a realized phononic crystal with a surface acoustic wave (SAW) device.     

Influence of reduction on the behavior kinetics of optical inhomogeneities in LiNbO3 single crystals

An investigation was made of the influence of high-temperature annealing in vacuum on the optical homogeneity of LiNbO₃ single crystals. It was observed that the residual light transmission decreased appreciably and the temperature dependence of this parameter almost completely disappeared. Pis’ma Zh. Tekh. Fiz. 24, 81–85 (November 26, 1998)     

Eu3+:LiNbO3单晶的坩埚下降法生长及其光谱性质

选用合适的温度梯度(20～30℃/cm)与生长速度(1～3mm/h),用坩埚下降法成功地生长出了掺杂Eu3+的LiNbO3单晶.用X射线衍射及DTA分析表征了获得的晶体.生长的晶体无宏观缺陷,在He-Ne激光的照射下,无散射中心.测定了从生长初期下部到生长后期上部晶体的紫外-可见吸收光谱与荧光光谱.观测到分裂的光谱线.结果表明,沿着晶体生长方向,Eu3+浓度逐步减少.Eu3+离子在晶体中取代Li与Nb格位.     

On the preparation of large,single domain KNbO3 crystals

Crystal growth, orientation and polarization of KNbO₃ were mentioned. Crystal cracks can be divided into two types and one of them could be eliminated by polarization. The forms of etching pits were corrected. The phase matching curve at room temperature was given.     

Eu^3＋：LiNbO3Eu单晶的坩埚下降法生长及其光谱性质

选用合适的温度梯度(20～30℃／cm)与生长速度(1～3mm／h)，用坩埚下降法成功地生长出了掺杂Eu^3 的LiNbO3单晶。用X射线衍射及DTA分析表征了获得的晶体。生长的晶体无宏观缺陷，在He-Ne激光的照射下，无散射中心。测定了从生长初期下部到生长后期上部晶体的紫外一可见吸收光谱与荧光光谱。观测到分裂的光谱线。结果表明，沿着晶体生长方向，Eu抖浓度逐步减少。Eu抖离子在晶体中取代Li与Nb格位。     

Vapor transport equilibration-induced formation of micron-sized ErNbO4 precipitates in Zn/Er-codoped LiNbO3 crystals

Congruent LiNbO₃ crystals with Zn/Er-doping levels of 5.5/1, 6/0.15 and 7/0.8 mol%/mol% were thermally treated at 1100 °C over 101 h using vapor transport equilibration (VTE) technique. It is shown that the VTE treatment has brought these crystals closer to stoichiometric composition. X-ray powder diffraction and Er³⁺ spectroscopic characterizations show that the VTE treatment induced formation of micron-sized ErNbO₄ precipitates on the surface and in the bulk of all crystals studied. It was observed using an optical microscope that the precipitates grow preferably along X, Y and Z axes of the host matrix, and show different morphologies, densities and dimensions, depending on the Er³⁺ and Zn³⁺ doping level. The formation origin of the precipitate is qualitatively explained.     

Incorporation of LiNbO3 crystals into tellurite glasses

Transparent tellurite glasses containing 5–10 m diameter LiNbO₃ crystals (3–7 wt%) have been successfully prepared using an incorporation method in which LiNbO₃ crystals are directly dispersed into the 80TeO₂-15Li₂O-5Nb₂O₅ glass. The dissolution behaviour of the LiNbO₃ crystals greatly depends on the Li₂O: Nb₂O₅ ratio in the matrix glasses. In the 80TeO₂-10Li₂O-10Nb₂O₅ matrix glass, the crystals remaining after incorporation have the composition LiNb₃O₈. A small difference in the refractive indices, n, between the TeO₂-based glasses (n=2.07) and the incorporated LiNbO₃ crystals (n=2.296) is a significant reason for the transparency. It is feasible to prepare the highly transparent TeO₂-based glasses containing a large amount of LiNbO₃ crystals by controlling the incorporation process.     

掺锌铌酸锂晶体的拉曼光谱

为研究LiNbO3晶体中Zn2 浓度对拉曼光谱的影响,以及Zn2 在LiNbO3晶体中的占位和Zn:LiNbO3晶体的结构,分别在LiNbO3中掺进摩尔分数为0.02、0.04、0.06、0.08 ZnO的Zn:LiNbO3晶体,进行其A1(To)和E(To)模的拉曼光谱测试.结果表明,当掺杂ZnO的摩尔分数小于0.06时,拉曼光谱变化不大,当掺杂ZnO的摩尔分数大干8%时,晶体拉曼光谱的274 cm-1峰变得模糊,E(To)模也混入A1(To)模中,晶体峰值变化较大.     

Optical anisotropy induced by torsion stresses in LiNbO3 crystals: appearance of an optical vortex

We report the results of studies of the torsion effect on the optical birefringence in LiNbO(3) crystals. We found that the twisting of those crystals causes a birefringence distribution revealing nontrivial peculiarities. In particular, they have a special point at the center of the cross section perpendicular to the torsion axis where the zero birefringence value occurs. It has also been ascertained that the surface of the spatial birefringence distribution has a conical shape, with the cone axis coinciding with the torsion axis. We revealed that an optical vortex, with a topological charge equal to unity, appears under the torsion of LiNbO(3) crystals. It has been shown that, in contrast to the q plate, both the efficiency of spin-orbital coupling and the orbital momentum of the emergent light can be operated by the torque moment.     

Accurate measurements of the acoustical physical constants of LiNbO (3) and LiTaO(3) single crystals

The acoustical physical constants (elastic constant, piezoelectric constant, dielectric constant, and density) of commercial surface acoustic wave (SAW)-grade LiNbO(3) and LiTaO(3) single crystals were determined by measuring the bulk acoustic wave velocities, dielectric constants, and densities of many plate specimens prepared from the ingots. The maximum probable error in each constant was examined by considering the dependence of each constant on the measured acoustic velocities. By comparing the measured values of longitudinal velocities that were not used to determine the constants with the calculated values using the previously mentioned constants, we found that the differences between the measured and calculated values were 1 m/s or less for both LiNbO(3) and LiTaO(3) crystals. These results suggest that the acoustical physical constants determined in this paper can give the values of bulk acoustic wave velocities with four significant digits.     

Growth of large LiNbO3〈Mg〉 crystals

We have analyzed conditions for the growth of large (≥80 mm in diameter) LiNbO₃〈Mg〉 crystals in a wide range of dopant concentrations in the melt (2.9–5.8 mol % MgO). We have established conditions for the growth of large LiNbO₃〈Mg〉 crystals uniform in doping level from melts containing magnesium concentrations above a certain threshold (C _melt 5.0–5.8 mol % MgO) and optimized the high-temperature electrodiffusion annealing process, which allowed us to obtain single-domain, microstructurally homogeneous, large LiNbO₃〈Mg〉 crystals containing 4.9–5.15 mol % magnesium.     

A method for obtaining single domain superconducting YBa2Cu3O7−x single crystals

A method is reported for producing an orthorhombic YBa₂Cu₃O_7–x single crystal comprised entirely of a single untwinned domain. The transformation from a polydomain to a single domain single crystal is carried out by applying uniaxial pressure of approximately 25 MPa for about one minute at 450°C in an oxygen atmosphere. We report on some of the superconducting properties of crystals produced in this way.     

Nano-sized domain inversion characteristics in LiNbO3 group single crystals using SNDM

This is, we believe, the first report on nano-sized domain inversion characteristics in congruent LiNbO₃ (CLN), MgO doped LiNbO₃ (MgO:LN) and stoichiometric LiNbO₃ (SLN) single crystals brought out using scanning dielectric nonlinear microscopy method. Thin crystal plates for forming nano-sized domain inversions were prepared by chemical mechanical polishing and an ion beam etching process. The small domain dot of 13 nm in radius was formed in CLN. However, the domain dots in CLN tended to disappear. The smallest domain dot of 6.1 nm in radius was obtained in MgO:LN. The domain dot array was also successfully formed at a density of 558 Gbit/in.². In case of higher application voltage, a unique result was obtained in MgO:LN showing that the sizes of domain inversions were almost constant against the voltage pulse width. It is not easy to form domain dot array in SLN since the sidewise growth speed in SLN is very fast.     

Low-temperature pyroelectric anomalies in single domain crystals of triglycine sulphate

The pyroelectric coefficient along the ferroelectric axis, of single-domain samples of triglycine sulphate has been determined on heating by means of the static technique from 85 K to within a few degrees below the Curie point,T _c. Dielectric and ferroelectric measurements carried out on some representative specimens in the vicinity ofT _c revealed a normal second-order ferroelectric transition. Anomalies in the pyroelectric signal were observed at temperatures of the order of 125, 165 and 270 K which have analogues in previous electrical and structural measurements.