A coprecipitation technique to prepare NaNbO3 and NaTaO3

A simple coprecipitation technique has been used successfully for the preparation of pure, ultrafine, single phases of NaNbO₃ (NN) and NaTaO₃ (NT). An alcoholic solution of ammonium carbonate and ammonium hydroxide was used to precipitate Na⁺ and Nb⁵⁺ (or Ta⁵⁺) cations under basic conditions as carbonate and hydroxide, respectively. On heating at 700°C, these precursors produce respective products. For comparison, both NN and NT powders were also prepared by the traditional solid state method. The phase purity and lattice parameters were studied by powder X-ray diffraction (XRD). The particle size and morphology were studied by scanning electron microscopy (SEM).     

LiTaO3 and LiNbO3 Epitaxial Films

The preparation of film-forming peroxide solutions of LiTaO₃ and LiNbO₃ precursors is described. The solutions are used to produce LiTaO₃ films on single-crystal corundum and LiNbO₃ substrates by the spinning process and dip coating, followed by heat treatment, and LiNbO₃ films on single-crystal corundum substrates by the spinning process.     

LiNbO3和LiTaO3晶体电子结构、平面声波和光折射特性

本研究基于密度泛函理论的第一性原理超软赝势平面方法计算了LiNbO₃和LiTaO₃的晶格参数、电子结构和弹性常数, 并利用Christoffel方程研究了二者平面声波特征。结果表明: 两者的理论计算晶格参数和弹性常数与实验值接近, 禁带宽度分别为3.78和3.98 eV, 导带底和价带顶主要由O-2p和Nb-4d(Ta-5d)态电子贡献。化学键理论揭示Li和Nb(Ta)与O原子之间有两种成键类型。 电荷布局分析结果显示有两种相应的重叠布居数, Nb(Ta)-O键呈现强共价键作用, 并且Nb-O(Ta-O)键长小于Li-O键长。LiNbO₃和LiTaO₃晶体平面声波有两支横波和一支纵波, 纵波速度大于横波速度, 在xy平面呈现六重对称性, 在xz和yz平面各向异性程度强于xy平面, 沿[001]、晶向上两支横波振动速度相等。最后利用模守恒赝势(Norm-conserving)计算了介电常数和静态折射率, 计算表明LiNbO₃晶体的折射性能和非寻常光(e光)离散程度均强于LiTaO₃晶体。     

Annealing behavior of barriers in ion-implanted LiNbO3 and LiTaO3 planar waveguides

We formed planar waveguides in LiNbO(3) and LiTaO(3) crystals by megaelectron volt He-ion implantation. The dark modes of both waveguides are measured and their refractive-index profiles are described according to the parameterized index profile reconstruction method. The extraordinary indices of both ion-implanted waveguides exhibit quite different profiles. We compare the thermal stability of barriers in ion-implanted LiNbO(3) and LiTaO(3) waveguides by annealing at different temperatures. The results show that the barrier in a LiTaO(3) planar waveguide has higher thermal stability than that in a LiNbO(3) waveguide. The experiments also show that annealing at a temperature higher than 400 degrees C results in recrystallization of the barrier.     

Crystallization characteristics of LiNbO3 derived from sol-gel

A sol-gel process for lithium niobate using lithium ethoxide and niobium ethoxide precursors was investigated. Nitric acid and acetic acid were used as catalysts, respectively. The crystallization characteristics of the sol-gel-derived lithium niobate is influenced intensively by catalysts, and the crystallization of LiNbO₃ from the nitric-acid-catalyzed sol-gel can occur at a low temperature near to 300 C.     

Powder synthesis and properties of LiTaO3 ceramics

The LiTaO₃ powders with sub micrometer grade grain size have been synthesized successfully using a molten salt method. Lithium tantalate began to form at 400 °C reaction temperature and transformed to pure phase without residual reactants when it was processed at 500 °C for 4 h in static air. The undoped LiTaO₃ ceramics with a Curie temperature about 663 °C were obtained by pressureless sintering at 1300 °C for 3 h. The relative dielectric constant (ɛ_r) increases from 50 to 375 at temperature ranging from 30 to 663 °C and then decreases quickly as the temperature increases above 663 °C. The ceramics shows a relative dielectric constant of 49.4, a dielectric loss factor (tan δ) of 0.007, a coercive field (Ec) of 28.66 kV/cm and a remnant polarization (Pr) of 32.48 μC/cm² at room temperature.     

pH值对溶胶凝胶-燃烧合成纳米晶LaMnO_3粉末的影响

以硝酸镧、硝酸锰和柠檬酸为原料,采用溶胶凝胶燃烧合成技术制备了超细LaMnO3粉末。借助XRD、DTA、SEM、FT-IR等分析仪器研究了溶胶凝胶-燃烧合成技术合成超细LaMnO3粉末的过程,着重讨论了前驱体溶液不同pH值对溶胶凝胶燃烧合成过程及合成产物的影响。结果发现,采用溶胶凝胶燃烧合成技术能合成纳米晶的LaMnO3粉末,随前驱体溶液pH值增加,燃烧反应速率增加,合成粉体的平均晶粒尺寸随pH值增加而减小。通过控制前驱体溶液pH值能一步合成超细LaMnO3颗粒(粒径200nm)。     

Planar optical waveguides obtained in Z-cut LiNbO3 and LiTaO3 by proton exchange in LiHSO4 vapors

A new proton source – LiHSO₄ vapors at low temperature – was used in forming optical waveguides in LiNbO₃ and LiTaO₃. The proton-exchanged layers were investigated by mode spectroscopy and infrared absorption spectroscopy. An estimate of the optical losses and phase contents of the waveguides was made. The diffusion parameters were determined for both types of crystal, and were compared to those obtained when benzoic acid melt was used as a proton source. The results presented could contribute to the realization of waveguides with controled phase compositions. The method proposed allows the use of a very simple and safe chamber construction, and the production of low-loss waveguides in a single technological step.     

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.     

溶胶凝胶钽酸锂薄膜热释电红外探测器的设计与制备

在带微桥结构的石英玻璃基底上设计了一种新型Al-LiTaO3-ITO红外探测结构。在响应/参考双单元结构框架下,由振动、环境温度变化和日照变化引起的无效信号输出在前置放大电路处被消除掉了。用醋酸锂和乙醇钽作为起始反应物,通过溶胶凝胶工艺生成了对红外敏感的钽酸锂薄膜,并详细讨论了基于钽酸锂薄膜的红外探测器件制备工艺。用ITO衬底作下电极,蒸镀的Al点作上电极,在室温条件下测试了薄膜的介电特性,在1kHz处,介电常数为53.28,在40~10kHz内,介电损耗和介电系数呈下降趋势。器件的电压响应和比探测率测试结果表明75Hz处得到响应电压峰值9685V/W,器件的比探测率在70~100Hz区域保持在6.12×108cmHz1/2W-1附近。     

溶剂对溶胶-凝胶燃烧法合成YAG粉体的影响

以Y(NO3)3.6H2O、Al(NO3)3.9H2O和柠檬酸为原料,分别以去离子水和无水乙醇为溶剂,采用溶胶-凝胶燃烧法合成YAG粉体。借助FT-IR、XRD、SEM等分析仪器研究了溶胶-凝胶燃烧法合成YAG粉体的过程,重点讨论了前躯体溶液不同溶剂对溶胶-凝胶燃烧法合成过程及合成产物的影响。结果表明:去离子水和无水乙醇对合成的YAG粉体的形貌和分散性有重要的影响。     

Preformed sol-gel synthesis and characterization of YAlO3

The synthesis of YAlO₃ is described from commercially-available yttria and alumina preformed sols which have nanometer particle-size ranges. The products have been characterized by X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform (DRIFT) spectra, thermogravimetry—derivative thermogravimetry—differential thermal analysis (TG-DTG-DTA), scanning electron microscopy (SEM) as well as CHN-analysis, and are similar to those prepared by the alkoxide, nitrate and citrate routes. The proposed method is a simple, cheap and rapid synthetic route.     

质子导体SrCe0.95Yb0.05O3-α溶胶凝胶燃烧合成的研究

综合利用溶胶凝胶及燃烧合成的优点制备了质子导体SrCe0.95Yb0.05O3-α粉体,发现柠檬酸的添加量是金属离子的2倍的情况下所制干凝胶燃烧时温度最高,合成产物最好;在燃烧合成中,柠檬酸作还原剂,而硝酸根离子作氧化剂;氧气不是燃烧反应的必要条件,但氧气可以加剧反应进行.XRD结果表明,1000℃即形成斜方钙钛矿结构,较高温固相反应合成温度降低了约400℃.     

Structural developments during heating in LiNbO3 precursors synthesized by the sol-gel method

LiNbO₃ precursor gels with a variety of molecular structures were prepared by the sol-gel method by changing the amount of added water and other conditions of synthesis. The molecular structures, as well as the thermal behaviour of the amorphous precursors, were studied by Raman spectroscopic analysis and differential thermal analysis-thermogravimetry in order to determine the influence of the structures on the resulting LiNbO₃ formation. The crystallization to LiNbO₃ by the combustion heat of the residual unhydrolysed alkyls was observed at 300 °C for the homogeneous precursors prepared from a double alkoxide (LiNb(OC₂H₅)₆) without added water, but the LiNbO₃ formed had low crystallinity. When using the hydrolysed double alkoxide, the synthesized precursors transformed to LiNbO₃ at 480 °C after the structural relaxation. This temperature can be assigned to the real crystallization point. Indeed the unhydrolysed double alkoxide is necessary to prepare the high-quality LiNbO₃ films, and heat treatment above 500°C is required to obtain good crystallinity. Even for the inhomogeneous precursors prepared from LiOC₂H₅ and NbO(C₂H₅)₅, lithium ion diffusion and the structural relaxation occur, to form the uniform molecular structures from 300–400 °C.