SYNTHESIS AND CHARACTERISATION OF A NEW NIOBATE COMPLEX WITH CHROMIUM(III)

Abstract

A new hexaniobate complex with chromium(III) was prepared and characterised by analytical and spectroscopic techniques. The compound is a violet, non-crystalline solid, formulated as [Cr₂(μ-OH)(H₃Nb₆O₁₉)(en)₃(H₂O)]. It was synthesised in aqueous solution by reaction of [Cr(en)₃]³⁺, en = ethylenediammine, with the hexaniobate anion [Nb₆O₁₉]^8-, at pH 8. Thermal decomposition yielded a mixture of CrNbO₄ and Nb₂O₅. The synthesis of this compound shows that the hexaniobate anion may form complexes at lower pH values than previously reported.     

铌酸锂晶体性能的组成依赖性(英文)

总结了铌酸锂晶体的各项性能指标,显示了其对晶体实际组成的强烈依赖性.利用化学键模型定量地解释了这种依赖性产生的根源,从而说明了制约该晶体性能提高的关键因素是晶体结构中的缺陷控制.     

Processing and characterization of Pb(Mg,Nb)O3-PbTiO3 thin films from metal alkoxide-derived gels

The sol-gel processing is one of promising methods to fabricate well-derived integrated thin films at relatively low temperature. Ferroelectric niobates films do afford the possibilities for adding the values by the hybridization with semiconductor and/or electro-optic systems. The molecular level designing of the precursor solution was stressed as well as the control of key processing factors. The advantages of this sol-gel have been extended to prepare the ferroelectric Pb(Mg, Nb)O₃-PbTiO₃ solid solution films integrated on Si wafers. The crystallization of the films with desired crystal structure could be promoted by the controlled partial hydrolysis of designed alkoxide solution in the intermediate state and the pre-heated treatment of alkoxide-derived films in flow of water vapor and oxygen gas mixture.     

Synthesis and Structure of Ba[ZrN2] and Ba2[NbN3]

Ba₃N₂ reacts at 950°C under pure N₂ with Zr to yield dark red, air-sensitive Ba[ZrN₂]. This new compound crystallizes in the tetragonal space group P4/nmm with a = 416.10(2), c = 839.2(1) pm and Z = 2. The crystal structure was solved and refined using X-ray and neutron powder diffraction data. In the nitrido zirconate [ZrN₂]^2? the Zr atoms exhibit a square-pyramidal coordination by five N atoms at distances of 201(3) and 220.2(2) pm. The pyramids share all the edges in the basal plane to form layers parallel to (001) with their apices alternately pointing up and down. The Ba²⁺ cations are integrated into these layers at the levels of the pyramidal apices. The structure can be interpreted as a stuffed PbFCl type. Ba₂[NbN₃] is formed by the reaction of Ba₃N₂ and NbN or of Ba and Nb at 1 000°C under N₂. Isostructural to Ba₂[TaN₃] it crystallizes in the monoclinic space group C2/c with a = 613.2(3), b = 1 176.8(3), c = 1 322.9(4) pm, β = 91.65(2)°, Z = 8. The nitrido niobate anions form chains of corner sharing NbN₄ tetrahedra with distances Nb? N between 188(1) and 199.9(9) pm.     

Optical and Electrical Properties of Ferroelectric SBN Thin Films Prepared by Sol-Gel Process

Strontium barium niobate thin films were prepared by sol-gel method on various substrates using an improved process, two-step heating process. The two-step heating process applies an additive heat-treatment before crystallization for enhancement of the densification and the nucleation of films. Also, highly c-axis oriented SBN thin films with various compositions were obtained on MgO(100) and Pt(100)/MgO(100) substrates. Their optical and electrical properties such as optical propagation loss, refractive index, P-E hysteresis, and dielectric constant, were characterized as a function of the film composition.     

The ridge waveguide fabrication with periodically poled MgO-doped lithium niobate for green laser

Ridge waveguides were fabricated using an external field, a precision lapping machine and neutron loop discharge (NLD) in magnesium-oxide-doped lithium niobate. The measured quasi-phase-matching (QPM) wavelength of the second-harmonic generation (SHG) in a 30 mm long periodically poled magnesium-doped lithium niobate (PPMgLN) ridge waveguide which has a domain period of 6.8 μm is about 532 nm. A fabricated periodically poled magnesium-doped lithium niobate ridge waveguide was duty cycle of 51.9 ± 2.83% and demonstrated second-harmonic generation. By using this periodically poled magnesium-doped lithium niobate ridge waveguide, highly effective, low-cost optical devices with high power or short wavelength can be achieved.     

非线性光学晶体铌酸钾锂的二次谐波产生

研究铌酸钾锂晶体的近经这过光谱：利用铌酸钾锂晶体对８９０￣９６０ｎｍ的Ｔｉ：ｓａｐｐｈｉｒｅ近红外激光进行倍频,获得蓝得蓝绿光输出;研究了晶体的倍频特性,探讨了提高晶体倍频效率的方法。     

Lattice vibration and photoinduced light scattering in Co-, Cr- and Fe-doped lithium niobate

Raman scattering and photoinduced light scattering in Co-, Cr- and Fe-doped lithium niobate were examined. The A₁(TO) modes appear in E symmetry spectrum of the doped lithium niobate. Their intensities vary with different dopings. In the spectrum of z(yy)x geometry, the properties of the lowest-frequency E(TO) mode of the Cr-doped lithium niobate are different from those of pure, Co- and Fe-doped lithium niobate. The intensity of the A₁(TO) mode at 637cm^-1 I is decreased in doped lithium niobate compared with the pure crystal. We attribute these properties to both the photorefractive effect which is enhanced by dopants and to the different occupation of the doping ions. A light climbing effect was observed in Co- and Cr-doped lithium niobate for the first time. A higher photodamage threshold and quicker light climbing speed were found in Co- and Cr-doped lithium niobate in comparison with the light climbing effect in the Fe-doped lithium niobate. The results from the photoinduced light scattering experiments were compared with those from a Raman spectroscopic study.     

Inhomogeneity of composition in near‐stoichiometric LiNbO3 single crystal grown from Li rich melt

A near‐stoichiometric LiNbO₃ single crystal has been grown by the Czochralski technique from a melt of 58.5 mol% Li₂O. Its composition homogeneity was assessed by measuring the UV absorption edge. It was found that the maximum composition difference is about 0.03 mol% in the radial direction and 0.05 mol% in the axial direction. Differential scanning calorimetry (DSC) analysis was performed on the powder from the synthesized raw material and the frozen melt after crystal growth. The analytical results indicate that, during crystal growth, the magnitude of lithium volatilization from the melt surface is more than the degree of segregation from the crystal. The volatilized lithium diffuses into the crystal to compensate for the lithium segregation in the LiNbO₃ crystal. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

铌酸锂质子交换波导中切伦科夫倍频实验研究

报道了质子交换铌酸锂平板波导中切伦科夫倍频蓝绿光输出研究。理论上计算了质子交换波导参数对不同基波波长倍频转换效率的影响。制备出适合于蓝绿光输出的铌酸锂质子交换波导并观测到较高转换效率的倍频光产生,实验中我们测量了倍频转换效率与抽运动率以及抽运波长的关系,实验结果与理论预测吻合。