铌酸锂晶体的生长研究

近年来,铌酸锂晶体由于其自身所具有的多种优异性能和巨大的应用前景而受到了人们的广泛关注,但生长出满足不同市场要求的高质量铌酸锂单晶体比较困难.本文从晶体生长技术的角度综述了铌酸锂单晶体不同的生长方法以及各自的特点,并分析了在生长铌酸锂晶体时出现的一些问题.     

大尺寸光学级铌酸锂晶体生长及检测方法

本文着重介绍了大尺寸光学级铌酸锂晶体生长方法,实验中采用中频感应加热方式,利用下电子秤自动控制系统,自制热场.成功地解决了以往生长大尺寸铌酸锂晶体时易出现的晶体头部有汽泡,易开裂,生长过程中多晶等难题,生长出了80mm×60mm的优质光学级铌酸锂晶体.并对晶体的消光比、锥光图、居里温度、透过率、抗激光损伤阈值等性能指标进行了测试,得出了相关的结果.     

激光晶体炉上称重法自动直径控制(ADC)技术

自动直径控制(ADC)技术是直拉法晶体生长设备的一项动直径控制方法,并从理论上分析了上称重法自动直径控制(ADC)原理,着重介绍了在传统TDL-J50A及TDL-J60激光晶体炉上自主开发的上称重法自动直径控制系统的机械结构及控制系统.使用上称重法自动直径控制系统已成功地生长出φ51～76mmYAG晶体及φ51～76mm铌酸锂晶体,取得了良好的控制效果.     

提拉法生长晶体的自等径控制

采用JPG技术有限公司所开发的自等径控制程序,利用上称重法实现了晶体生长的自等径控制(ADC).通过对生长曲线PID的具体分析及其他晶体生长相关参数的设置,以铌酸锂晶体为对象,成功实现了按预设程序进行的晶体生长自等径控制.     

大直径、高掺镁铌酸锂晶体的生长及其紫外光折变性能研究

我们生长了掺镁量分别为3.0mol;、5.0mol;、7.8mol;、9.0mol;的76mm高掺镁铌酸锂晶体,检测了这些晶体的生长条纹情况,并利用双光耦合配置测试了这些晶体在351nm紫外光下的光折变性能.从实验结果看,采用同成分共熔点铌锂配比的高掺镁铌酸锂晶体生长条纹比较多;虽然高掺镁铌酸锂晶体在可见光波段有很好的抗光折变能力,但是在紫外光下具有良好的光折变性能,可以作为优良的紫外光折变材料使用.同时,实验结果表明,掺镁量在5.0mol;的铌酸锂晶体具有最佳的紫外光折变性能.     

非线性晶体铌酸锂钾的性质和生长

用提拉法生长出铌酸锂钾(KLN)晶体;探讨了KLN晶体生长时开裂的主要原因;对钛宝石激光倍频获得蓝光输出.     

铌酸锂晶体的缺陷及其控制

针对铌酸锂晶体中的缺陷研究,本文总结了国内外学者提出的不同晶体缺陷模型及各自的特点,并介绍了我们提出的铌位依赖、锂位敏感模型.在分析晶体缺陷研究的基础上提出了对铌酸锂晶体进行缺陷控制的意义及理论依据,指出缺陷控制的主要任务是保护锂格位.本文还简要概括了铌酸锂晶体缺陷控制的主要手段,并建议从反映铌酸锂晶体性能的角度来研究缺陷结构.     

晶体材料中的常青树——铌酸锂晶体

正从上世纪70年代开始,我国科研人员就开始了铌酸锂晶体生长、缺陷、性能及其应用研究。南开大学是国内最早开展研究的单位之一,几十年来,围绕通讯、激光、国防等领域对高光学均匀性、高抗光损伤、高温度适用性光学级铌酸锂晶体的需求,将铌酸锂晶体的光学均匀性提高了近2个数量级,发明了掺镁铌酸锂晶体,将抗光损伤能力提高6个数量级以上,并实现了高光学质量近化学计量比铌酸锂晶体的实用化制备。     

四价掺杂铌酸锂晶体抗光折变性能研究

我们在同成份铌酸锂晶体中掺入四价离子铪,生长了掺杂浓度分别为2、4、6mol;的掺铪铌酸锂系列晶体.掺铪浓度达到4mol;时,晶体的抗光损伤能力为5×105W/cm2,比同成份纯铌酸锂晶体提高了4个数量级.应用全息法测得掺4、6mol;铪的铌酸锂晶体最大折射率变化为8.7×10-6,与高掺镁(6.5mol;)铌酸锂晶体的类似.晶体的红外吸收谱和紫外-可见光吸收谱也显示,掺杂浓度为4mol;时具有明显的阈值特征.由此可以确定铪离子在铌酸锂晶体中的阈值浓度约为4mol;.     

近化学计量比铌酸锂晶体的研究进展

本文总结了近化学计量比铌酸锂晶体的不同生长方法及它们各自的特色,分析了锂铌摩尔比对晶体性能的影响及Li含量的各种表征方法.通过比较看出,采用K2O助熔剂生长近化学计量比铌酸锂晶体是一种较为实用的途径.基于此,我们采用K2O助熔剂提拉法和助熔剂-坩埚下降法生长了近化学计量比铌酸锂晶体,所得晶体的最大尺寸分别达到45mm×60mm和25mm×40mm.     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

Effect of alumina on enthalpy of mixing of mixed alkali silicate glasses

The enthalpy of mixing of mixed alkali (Na₂O and K₂O) silicate glasses containing various concentrations of alumina was determined using an ion-exchange equilibrium method. For glasses with a constant alkali concentration, the enthalpy of mixing was found to become less negative with alumina addition. Consistent with our previous results on the enthalpy of mixing of alumina-free mixed alkali silicate glasses, the magnitude of enthalpy of mixing exhibited a good correlation with the molar volume mismatch of the corresponding two single alkali glasses as well as with the extent of conductivity mixed alkali effect, e.g. excess activation energy of conductivity, ΔE. The reduction of the magnitude of the enthalpy of mixing with alumina addition can be attributed to the reduction of non-bridging oxygen and ionic field strength. Combining the present results with results obtained earlier, the magnitude of the enthalpy of mixing for all mixed alkali (Na₂O and K₂O) silicate glasses with and without alumina was expressed by a simple function of a modified Tobolsky parameter, which takes into account the alkali concentration and the difference in cation-to-effective anion distances. The enthalpy of mixing data of the mixed alkali glasses was then compared with reported experimental data on the conductivity of mixed alkali aluminosilicate glasses. What appears to be conflicting experimental data can be understood in terms of the magnitude of the enthalpy of mixing and we can conclude that the mixed alkali effect is closely correlated with the negative enthalpy of mixing.     

Mesomorphism Dependence on the Position of Substitution of a Pair of Esters

A novel homologous series of ethylene derivatives of thermotropic liquid crystals has been synthesized. The methoxy to octyloxy derivatives are nematogenic, the decyloxy to tetradecyloxy derivatives are smectogenic, in addition to nematogenic, and the hexadecyloxy homologue is smectogenic only. All the members of the series are enantiotropically mesogenic. Thermotropic behavior was determined by an optical polarizing microscope equipped with a heating stage and Differential Scanning Calorimetry (DSC) study. Analytical and spectral data confirm the molecular structures of homologues (infrared, nuclear magnetic resonance, mass spectra, X-ray, and DSC data). Textures of the nematic phase are threaded or Schlieren and that of smectic phase are focal conic fan-shaped of smectic A or C. Transition curves of the phase diagram behave in a normal manner except one or two deviations from the normal trend. The mesophase range (Sm+N) varies from 3°C to 44°C. The average thermal stability for smectic is 93°C and that for nematic 117.4°C. The LC behavior of the novel series is compared with a structurally similar known series.     

原位氮化法制备TiN纳米粉体

用溶胶凝胶法合成的纳米TiO2粉体作为原料,将该粉体在氨气中进行原位氮化制备了TiN纳米粉体.用XRD,TEM,化学分析等手段对合成的TiN纳米粉体的物相组成、形貌、成分进行了分析.实验分析表明:在1000℃和1100℃下分别氮化5h,可以制备粒径大约为40nm和80nm的TiN粉体,其TiN的含量分别为95.40;和98.37;;而在1000℃条件下氮化时间减少到2h时,TiN的含量仅为58.36;.氮化温度和氮化时间是合成纳米TiN的重要因素,提高合成温度和延长氮化时间均可形成纯度较高的TiN纳米粉体,但延长氮化时间更有利于获得粒径小的氮化钛粉体.     

立方晶系晶体本征铁弹相变序参量的选取

在本征铁弹相变的软模理论的基础上,依据弹性本构关系和居里原理,给出了立方晶系晶体所有可能的自发应变的种类,研究了立方晶系晶体本征铁弹相变序参量的选取问题.以Th群和Oh群为例,阐明了不同类的序参量导致晶体对称性变化相同的的原因,提出了该情况下序参量选取的“就少不就多”的原则.得到了发生本征铁弹相变时所有可能的序参量及晶体的对称性的变化.     

On the influence of structural features of DNA on the possibility of metabolic transfer of electrons

Abstract

A fragment of a DNA molecule is considered as one of the channels of metabolic electron transfer. The heterogeneity of the complementary chains is effectively taken into account. This made it possible to find the speed of the electron injected into the DNA conduction band and the current density that it creates. Estimates of electron mobility in nucleic acid chains are made. They were an order of magnitude smaller than that of typical semiconductors. For the specific conductivity of nucleic acid chains, estimates provide a conductivity of one to two orders of magnitude lower than in graphite.     

Features of transformations in REE-containing systems of nitrate precursors in preparatory processes of formation of multifunctional oxide materials

Abstract

The complex study provides a reliable idea of ??the trends in the joint behavior of structural components in the water-salt systems of nitrate precursors of REE, alkaline, alkaline earth metals in the preparatory stages of the processes of forming multicomponent oxide polyfunctional materials on their basis with thermal activation. Stages of such transformations are revealed; The regularities of complex and phase formation in systems and factors influencing them are determined; A number of physicochemical properties of the intermediate phases formed - coordination lanthanides nitrates: their composition, types of compounds, atomic-crystalline structure, regularities of transformations during heat treatment were studied.     

Growth and characterization of semicarbazone of cyclohexanone

A new organic single crystal of semicarbazone of cyclohexanone (SCCH) has been synthesized and grown as a bulk single crystal by low temperature solution growth technique for the first time in the literature. The grown crystal has been confirmed by X‐ray diffraction and proton nuclear magnetic resonance spectral analyses and also characterized by FT‐ir and FT‐Raman studies. Thermal properties of the grown crystals were studied by thermogravimetric and differential thermal analyses. Optical transmittance was studied by ultraviolet‐visible spectrum and the second harmonic generation property was tested by using Q switched Nd: YAG laser as a source. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of density of states on optical properties of GaSe thin film

A systematic investigation on the effect of substrate temperature on the structure, optical absorption and density of states of vacuum evaporated gallium monoselenide (GaSe) thin films is reported. The X‐ray diffraction analysis shows an occurrence of amorphous to polycrystalline transformation in the films deposited at higher‐temperature substrates (573K). The compositional analysis is made with Auger Electron Spectroscopy (AES). The thickness of the film (175nm) is measured by a multiple beam interferometery. Optical characteristics of the GaSe sample have been analyzed using spectrophotometer in the photon energy range of 1.0 ‐ 4 eV. The absorption mechanism has been recognized and the allowed indirect as well as forbidden direct transitions have been found. As‐deposited films show two indirect and allowed transitions due to spin‐orbit splitting of the valence band, as reported here for the first time. Low field conduction have enabled us to determine the density of states in amorphous and poly‐GaSe films. The amorphous and polycrystalline GaSe thin films have localized states density values of N (E_F) = 1.686 × 10¹⁷ cm^‐3 eV^‐1 and 1.257 × 10¹⁵ cm^‐3 eV^‐1 respectively. The experimental results are interpreted in terms of variations in the density of localized states due to progressive decrease of the unsaturated bonds during deposition. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

电子显微分析在表征纳米晶体化学组分中的应用

纳米材料的化学组分及含量影响其光、电、声、热、磁等物理性能,电子显微分析是表征纳米晶体化学组分的重要方法之一.本文综述了X-射线能谱(EDS)、X-射线波谱(WDS)、电子能量损失谱(EELS)和选区电子衍射(SAED)等现代电子显微分析技术在表征纳米晶体化学组分、形貌、尺寸和结构等方面的应用及其研究进展,并比较了这些分析方法存在的差异,提出了其应用中存在的不足及今后的研发方向.