Growth and characteristics of LiNbO3 plate crystals

LiNbO₃ plate crystals were grown by the edge-defined, film-fed growth (EFG) technique. Growth conditions and domain structure observed are given. The quality and piezoelectric properties of crystals obtained are reported and discussed, compared with those of crystals grown by conventional Czochralski technique.     

Optical properties of Sm doped Mg:LiNbO3 and Zn:LiNbO3 single crystals

Sm³⁺ doped Mg:LiNbO₃ and Zn:LiNbO₃ are grown by Czochralski method. Optical transmittance and emission spectra are measured and Judd-Ofelt theory is applied to determine phenomenological intensity parameters, oscillator strengths, radiant transition rates, total radiant lifetimes, and branching ratios. The calculations show that Judd-Ofelt parameters with the relation of Ω₄ > Ω₂ > Ω₆ exist, and ΣΩ_ξ (ξ = 2, 4 and 6) in Sm:Zn:LiNbO₃ decreases. Fluorescence spectra indicate that visible fluorescence of Sm³⁺ is made up of 570, 606, 613 and 654 nm emission bands in these crystals under 409 nm excitation.     

Spectroscopic investigation of Nd ion in LiNbO3, MgO:LiNbO3 and LiTaO3 single crystals relevant for laser applications

The polarized absorption and luminescence properties of Nd³⁺ doped isostructural LiNbO₃, MgO:LiNbO₃ and LiTaO₃ nonlinear bulk single crystals are reported. Pump-probe experiments associated with the Judd-Ofelt approach are used to estimate two types of room temperature cross sections: polarized emission cross sections of the dominant ⁴F_3/2 → ⁴I_1//2 transition near 1085 and 1093 nm and polarized excited-state absorption cross sections in the same spectral domain and in the green spectral range corresponding to self frequency doubling. Self frequency-doubling results are also given in Nd:LiNbO₃ and Nd:MgO:LiNbO₃ versus sample temperature.     

Cu ion in-diffusion in congruent LiNbO3 single crystals

Congruent LiNbO₃ (LN) crystals were grown by Czochralski technique. Thermal in-diffusion of transition metal ion Cu²⁺ into crystal wafers was performed at various temperatures. The absorption peaks in transmission spectra indicates the Cu²⁺ ion diffusion in LN crystal wafer. A broad absorption band centered at 948 nm was observed in the absorption spectra due to the vibronic transition associated with Cu²⁺ centers. The significant red shift in absorption edges indicates the decrease in Li/Nb ratio in Cu in-diffused crystal wafers. Powder XRD of pure and Cu in-diffused LN samples show no structural change during thermal diffusion.     

Pulsed laser deposition of La0.67Ca0.33MnO3 thin films on LiNbO3 and surface acoustic wave studies

Surface Acoustic Waves on piezoelectric substrates can be used to investigate the dynamic conductivity of thin films in a non-contact and very sensitive way, especially at low conductivities. Here, we report on such surface acoustic wave studies to characterize thin manganite film like La_0.67Ca_0.33MnO₃, exhibiting a Jan Teller effect with a strong electron phonon interaction and a metal insulator transition at high temperatures.

We report on the deposition of La_0.67Ca_0.33MnO₃ on piezoelectric substrates (LiNbO₃ in different crystal cuts, employing a pulsed laser deposition technique. The structural quality of the thin films are examined by X-Ray Diffraction, Scanning Electron Microscope and Energy Dispersive X-ray spectroscopy. For the electrical characterization, we employ the surface acoustic wave technique, accompanied by conventional direct current resistance measurements for comparison.     

The growth of LiNbO3 crystals using an automated puller

Large single crystals of LiNbO₃ are readily pulled from the melt using a closed r.f. furnace and electronic diameter control to insure uniform growth. C-axis crystals ～ 1″ in diameter and 3″ long grown from the congruent melt emerged water clear and did not require in place annealing to avoid cracking. Furnace conditions and controls are also discussed.     

高掺镁LiNbO3晶体抗光折变性能研究

在LiNbO3中掺进MgO以提拉法生长Mg(1mol%)LN,Mg(3mol%)LN,Mg(5mol%)LN,Mg(7mol%)LN,和Mg(9mol%)LN晶体.改进晶体生长工艺条件,解决了在生长中出现的脱溶,散射颗粒,生长条纹等缺陷.生长出高质量高掺镁LiNbO3晶体.测试MgLiNbO3晶体的红外光谱,当Mg2+的浓度达到或超过阈值浓度的MgLiNbO3晶体,OH-吸收峰移到3535cm-1,晶体抗光损伤能力比LiNbO3晶体提高两个数量级以上.测试MgLiNbO3晶体的倍频性能(相位匹配温度,倍频转换效率)MgLiNbO3晶体的相位匹配温度随Mg2+浓度的增加而改变,Mg(5mol%)LN,晶体的相位匹配温度达到116℃,Mg(9mol%)LN晶体在室温附近.     

Stoichiometry and doping effects on cation ordering in LiNbO3 crystals

The cation disorder in stoichiometric and congruent lithium niobate crystals and also in congruent crystals doped with Y³⁺ or Gd³⁺ has been studied by X-ray diffraction and Raman scattering spectroscopy using vacancy models. The results indicate that the structural disordering induced by doping with Y³⁺, revealed by both X-ray diffraction and Raman spectroscopy, can be understood in terms of the mechanism of yttrium incorporation into the cation sublattice of the crystal. Yttrium substitution for Nb⁵⁺ on its normal lattice site causes Nb⁵⁺ to occupy vacant octahedra, thereby increasing the cation and vacancy disorder along the polar axis and distorting the octahedra because the ionic radius of Y³⁺ exceeds that of Nb⁵⁺.     

掺Mn近化学计量比铌酸锂晶体生长及其性质

采取中频加热和TSSG的方法,从掺入了6%(质量分数)K2O的同成分Li2O-Nb2O5熔体中生长出了近化学计量比铌酸锂单晶,其铁电畴结构为单畴结构,居里温度为1191.5℃.在此基础上,分别掺入0.05%(质量分数),0.16%(质量分数)和0.32%(质量分数)的氧化锰,生长了掺Mn近化学计量比的铌酸锂晶体,其铁电畴结构也均为单畴结构,居里温度分别为1195.3、1201.5和1219℃.对这4个晶体进行的红外光谱测试的结果表明均在3466cm-1有一吸收峰.通过二波耦合实验,我们对不同掺杂浓度的4种晶体进行了光折变性能测试.     

Strong d-d electron interaction inducing ferromagnetism in Mn-doped LiNbO3

Mn-doped LiNbO₃ was prepared by ion beam implantation with Mn content of 1 to 5 at.%. The samples were ferromagnetic. The maximum atomic magnetic moment was 5.83 μ_B/Mn for the samples with Mn content of 3 at.% in the implanted layer. Structure characterization using X-ray absorption near edge structure determined that the Mn atoms substituted principally the Li atoms in the LiNbO₃ lattice. The magnetic mechanism was understood with the aid of electronic structure calculation using local density approximations plus U method. The calculated results demonstrated that the Mn:LiNbO₃ with Mn atom on the Li site is half-metallic ferromagnetic. The calculated magnetic moment per cell agreed well with the experimental results. Spin splitting of the d-states occurred for both the Mn dopant and the Nb atoms. The doped Mn atom interacts strongly with its neighboring Nb atoms. This strong d-d electron interaction can work at long range through the whole crystalline cell.     

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.     

Fabrication of ferroelectrics LiNbO3 thin films by pseudospark electron beams

The films of ferroelectrics LiNbO₃ have been prepared by pseudospark electron beam deposition at different substrate temperatures. The pseudospark electron beams possess high power density of 10⁹ W/cm² and nanosecond duration. The phase composition, crystallinity, and surface morphology of the films were investigated. It was found that both the substrate temperature and the crystallization treatment play important roles in the composition control and crystallization of the films. The study indicates that the technique of the film preparation has some unique advantages and will be promising in photoelectric integrated circuit with further improvement.     

Two-wave mixing of ion-implanted photorefractive waveguides in near-stoichiometric Fe:LiNbO3 crystals

We report on the two-wave mixing of light in photorefractive waveguides in H ion-implanted Fe-doped near-stoichiometric lithium niobate crystals. For pump light of 632.8 nm wavelength a gain coefficient as high as 15 cm⁻¹ is found. A response time of the order of a few seconds is achieved for micro-watt input powers.     

扫描电子声显微镜对骨组织的成像

1引言自1980年由Brandis和Rosencwaig以及Cargill分别建立扫描电子声显微镜(SEAM)以来,由于它可以高分辨率[1]地同时获得试样表面电子显微镜像(SEM)和亚表面SEAM像以及试样制备简     

Ce:Fe:LiNbO3晶体光栅热固定的研究

在LiNbO3晶体中掺进CeO2和Fe2O3,以Czchralski法生长CeFeLiNbO3晶体,对晶体进行氧化还原处理.测试CeFeLiNbO3晶体的吸收光谱,发现CeFeLiNbO3晶体的吸收边相对LiNbO3晶体发生红移.氧化态的CeFeLiNbO3晶体的吸收边相对还原态的CeFeLiNbO3晶体发生紫移.采用热固定法测试CeFeLiNbO3晶体(氧化,生长,还原)的显影效率.CeFeLiNbO3晶体(还原)的显影效率低于CeFeLiNbO3晶体(氧化)的显影效率.测算并推导出热固定光栅在常温下的寿命.     

Light-induced absorption changes in iron-doped LiNbO3

LiNbO₃: Fe and LiNbO₃: Fe,Me (Me = K, Mg, Zn) crystals are illuminated with frequency-doubled pulses of a Q-switched Nd: YAG laser. We detect light-induced absorption changes at high pulse intensities (I > 10⁹Wm^-2) utilizing cw probe lasers of different wavelengths (λ^p = 488, 633, and 785 nm). Intensity dependences as well as relazation processes after illumination are investigated. Absorption changes increase with increasing light intensity. Strongest effects are observed in reduced crystals. Doping with magnesium or zinc and an increasing lithium content, respectively, diminishes light-induced absorption changes. Our results can be described by a two-center charge transport model.     

Shapes of isolated domains and field induced evolution of regular and random 2D domain structures in LiNbO3 and LiTaO3

The variety of the shapes of isolated domains, revealed in congruent and stoichiometric LiTaO₃ and LiNbO₃ by chemical etching and visualized by optical and scanning probe microscopy, was obtained by computer simulation. The kinetic nature of the domain shape was clearly demonstrated. The kinetics of domain structure with the dominance of the growth of the steps formed at the domain walls as a result of domain merging was investigated experimentally in slightly distorted artificial regular two-dimensional (2D) hexagonal domain structure and random natural one. The artificial structure has been realized in congruent LiNbO₃ by 2D electrode pattern produced by photolithography. The polarization reversal in congruent LiTaO₃ was investigated as an example of natural domain growth limited by merging. The switching process defined by domain merging was studied by computer simulation. The crucial dependence of the switching kinetics on the nuclei concentration has been revealed.     

The congruently melting composition of LiNbO3

The congruently melting composition of lithium niobate was investigated using the measurement of phase matching temperature at the 1.06 wave length radiation and a controlled crystal growth program. It was shown to be between 48.50 and 48.60 mole % Li₂O.     

Review of proposed defect structures in LiNbO3

The problem of native defect structure in LiNbO₃ is discussed in the light of experimental data published till now. An attempt of uniform interpretation of these data has been undertaken.     

Optical spectroscopy of Dy ions in LiNbO3

A systematic spectroscopic study of Dy³⁺ doped LiNbO₃ is presented. The energy position of the Stark levels and their symmetry character is given for most of the multiplets. Luminescence of this system has been investigated in the visible and infrared. The only emitting state in this region is the metastable 4F_9/2 multiplet whose life time is temperature independent and with a value of 186 μs. Evidence about Dy³⁺ multicentres is also discussed.