The Synthesis of Fluorine Containing Phenyl Benzoates and Their Properties as Liquid Crystals

A new series of fluorine containing phenyl benzoates has been synthesized and the transition temperatures of these compounds have been determined. A series of 4-trifluoromethylphe 4nyl 4-n-alkybenzoates showed no liquid crystalline behaviour, but the 4-trifluoromethylphenyl 4-n-alkoxybenzoates series, with six carbons or more in alkoxy chain, was mesomorphic. The 4-cyanophenyl 4-perfluoroalkylbenzoates showed smectic liquid crystalline properties.     

Investigation of Optical Properties of YAlO3Pr3+ Single Crystals

Colour centers in YAlO₃:Pr³⁺ crystals originating under xenon lamp or y–radiation and oxidizing annealing are considered. The nature of colour centers under these treatments is similar in nominally pure and Pr³⁺ containing crystals but the intensity of induced absorption lines is higher in activated crystals which assumably is associated with valent transitions of Pr ions.     

Synthesis,Characterization and Mesomorphic Properties of New Rod-like Thiophene Based Liquid Crystals

Two new mesogenic homologous series of Schiff base esters, 2-[4-(4′-n-Alkoxy benzoyloxy) benzylidenamino] 3-cyno thiophine (Series-A) and Schiff base cinnamates, 2-[4-(4′-n-alkoxy cinnamoyloxy) benzylidenamino] 3-cyano thiophene (Series-B), comprising a thiophene moiety were synthesized. Structural elucidation was carried out using elemental analysis and spectroscopic techniques such as FT-IR, ¹H-NMR and ¹³C-NMR, and mass spectrometry. The mesomorphic properties and thermal stabilities of the title compounds were studied by using differential scanning calorimetry and optical polarizing microscopy. All the derivatives are mesomorphic in nature showing the nematic phase, and the higher members of Series-A show a smectic C phase whereas Series-B exhibits only the nematic mesophase. The mesomorphic properties of the present series are compared with other structurally related compounds.     

溴化铈晶体的生长与性能研究

采用改进的坩埚下降法生长出φ1.5"×1.5"的无宏观缺陷的溴化铈晶体毛坯.研究测试了溴化铈晶体的荧光光谱、紫外-可见透射光谱及光输出、能量分辨率、本底等闪烁性能.结果表明:在光致激发下,溴化铈晶体的发光主峰位于390 nm;其10 mm厚度样品在390nm处的光透过率为60;;φ1"×1"大小的样品在137Cs源的662 keV伽马射线作用下能量分辨率为4.26;,光输出相当于NaI(Tl)晶体的125;;溴化铈晶体中在0.005 Bq/g探测限下未检测到138La和227Ac元素,本底水平显著低于掺铈溴化镧晶体.     

水热法合成CsxWO3纳米棒及其红外吸收性能

Cs_xWO₃纳米棒因其优异的近红外吸收性能得到研究人员的广泛关注,但目前水热法合成Cs_xWO₃纳米棒存在易形成等轴状纳米颗粒,或合成温度高,需要后续处理等问题。本文以钨酸铵((NH₄)₆ W₇O₂₄·6H₂O)、氯化铯(CsCl)、盐酸(HCl)和油胺(C₁₈H₃₇N)为原料,在220 ℃水热反应24 h合成了直径和长度分别为10~20 nm和100~250 nm的Cs_0.2WO₃纳米棒。研究了溶剂、合成路径以及HCl对Cs_0.2WO₃纳米棒的物相和形貌的影响,探讨了Cs_0.2WO₃纳米棒的形成机理,测试了Cs_0.2WO₃纳米棒的红外吸收性能。结果表明:过少和过量的HCl不利于合成Cs_0.2WO₃,改变HCl和CsCl的加入顺序,降低(NH₄)₆ W₇O₂₄·6H₂O、CsCl和HCl间的反应速率,有助于合成Cs_0.2WO₃纳米棒,且Cs_0.2WO₃纳米棒的红外吸收性能优于等轴状纳米颗粒。     

InSeI单晶的制备及其结构与性能研究

利用化学气相传输法(CVT)制备了InSeI单晶。该晶体为黄色的针状物,晶体较脆。在室温下进行X射线衍射分析发现,其属于四方晶系,晶胞参数为a=b=1.864 3(5) nm,c=1.012 0(3) nm,V=3.517 2 nm³,空间群为I4₁/a。紫外可见光吸收光谱、光致发光光谱等结果显示该晶体的禁带宽度是2.48 eV,在一定波段光的激发下,InSeI单晶在600 nm左右有较宽的发射峰,表明该晶体的发光方式为缺陷态发光。介电温谱表明InSeI单晶在440 K时其四方相的结构发生了相变。     

掺杂LiNbO3晶体的生长缺陷与其体全息存储性能的研究

本文叙述了利用侵蚀法研究掺杂LiNbO3的晶体缺陷,并讨论了晶体缺陷的形成机理以及其与体全息存储性能的关系.通过实验发现了常温下侵蚀铌酸锂晶体的规律,并利用侵蚀法观测到铌酸锂晶体样品表面呈三角锥状的位错侵蚀坑.测量了晶体样品的散射噪声,从中找出了晶体缺陷与存储图像质量关系.并发现掺Zn的Fe:LiNbO3晶体其晶体缺陷减少,晶体体全息存储性能有了明显提高.     

双掺杂铌酸锂晶体的生长及其光折变性质

采用提拉法以固液同成分配比(Li2CO3/Nb2O5＝48.6/51.4)生长了Fe掺杂及(Zn,Fe)、(Mg,Fe)和(Ce,Fe)双掺杂LiNbO3(LN)单晶.Ce:Fe:LiNbO3晶体的质量,指数增益系数和衍射效率皆高于Fe:LiNbO3晶体.所测得(Zn,Fe):LN、(Ce,Fe):LN、(Mg,Fe):LN和Fe:LiNbO3晶体的抗光致散射能力分别为8.2×103,3.2×102,8.3×102和1.2×102W/cm3;在488nm光进行的光折变实验中还原处理后的(Ce,Fe):LiNbO3晶体具有最高的二波耦合增益系数,为40.2cm-1,其全息衍射效率可达82.2%;实验结果表明(Zn,Fe):LiNbO3和(Mg,Fe):LiNbO3具有抗光散射能力强,响应时间短的特点,而(Ce,Fe):LiNbO3的增益系数和衍射效率均为最高,明显优于Fe:LiNbO3晶体.     

Material Properties of Ferroelectric Liquid Crystals and Their Relevance for Applications and Devices

Recent developments in understanding structural and material properties of ferroelectric liquid crystals are reviewed with emphasis on their relevance for electro-optic effects and device applications.

In only a few years the material situation has changed from one characterized by an almost complete lack of technically useful materials to one, not yet adapted to technical needs, but beginning to offer interesting, commercially available ferroelectric mixtures. The present device limitations can, however, be tracked down, not so much to the principal non-availability of materials as to the lack of understanding of which material properties are desirable and needed, in particular to permit simple and efficient matrix addressing. Thus we have centered our discussion to properties of prime importance for device dynamics in this review, which also contains a general discussion of material properties based on the molecular structure, as well as an assessment of the present industrial development.     

Hydrothermal Synthesis and Characterization of VSZ-3 Zeolite Crystals

Zeolite crystals (named here VSZ-3) synthesized at 350°C by hydrothermal method are illustrated and described. These crystals are shown to be analcime type zeolites. It is established that their size is the largest among the zeolite crystals ever reported, and are stable upto 1000°C. The VSZ-3 crystals are prismatic pyramidal and needle-like. They are characterized by X-rays, SEM, TGA, DTA and IR. Their chemical composition is shown to be 5.95 SiO₂ ṁ Al₂O₃ ṁ 0.91 Na₂O ṁ 0.17 H₂O. Mechanism of growth of these crystals is explained.     

Sb掺杂钨酸铅晶体中Sb的分布与闪烁特性研究

研究了Bridgman法生长的Sb掺杂钨酸铅(PWO)晶体中Sb的分布和闪烁特性.晶体中Sb含量的测定表明,Sb在PWO晶体中的分凝系数约为0.63.由于Sb掺杂可以补偿PWO晶体的组分缺失而降低其中空位和一些色心的浓度,与未掺杂晶体相比较,Sb掺杂晶体具有更好的光学透过率和更高的发光强度.而且,在富氧气氛下退火后,Sb掺杂晶体的发光谱特征变化较小,仍能保持较高的快慢分量比.     

Growth and Optical Properties of Doped LiTaO3 Single Crystals

Single crystals of lithium tantalate (LiTaO₃) doped with Pr, Nd + Yb and Tm were grown by the Czochralski method. A thermal system with 50 mm diameter iridium crucible and two different afterheaters (active and passive) was checked with respect to temperature distribution in a pulling region. The obtained crystals were up to 20 mm in diameter and up 50 mm in length. Crystals were poled, and the Curie temperature was determined for specimens cut of from different parts of single crystals. The polarized absorption spectra, time resolved emission spectra and emission lifetime of Pr³⁺ doped LiTaO₃ crystals were measured. An intense emission from the ³P₀ level was observed. Optical properties of the Yb³⁺ ions excited by energy transfer from Nd3+ ions have been researched for LiTaO₃:Nd, Yb crystals.     

KCaCl3:Ce晶体的生长及发光性能

采用坩埚下降法生长出不同摩尔分数Ce³⁺(1%、2%、4%、6%、8%)掺杂的KCaCl₃:Ce单晶。晶体属于正交晶系,晶胞参数为a=0.756 0 nm,b=1.048 2 nm,c=0.726 6 nm。热重分析仪测得熔点为740 ℃,透过率测试显示晶体在可见光波段均具有较好光学透过率。对晶体的光致发光光谱、光致衰减时间、X射线激发发射光谱、透过率等光学性能进行了表征。光致发光光谱显示KCaCl₃:Ce晶体在358 nm和378 nm波长左右有宽的发射峰,符合Ce³⁺的5d₁→²F_5/2和5d₁→²F_7/2能级跃迁,通过拟合,KCaCl₃:Ce晶体的衰减时间在30 ns左右。晶体在X射线激发下均表现出优异的X射线发光性能。     

LaFeO3单晶生长及其性能研究

以La2O3和Fe2O3粉体为原料,在1400℃,烧结24 h制备出了LaFeO3多晶料棒,采用浮区法生长出LaFeO3单晶。晶体沿(100)晶向生长,晶体的(100)晶面单晶摇摆曲线的半高宽为26″,证实其单晶化程度很高;在298～773 K温度范围内测试了晶体热学性能,晶体比热变化范围为0.58～0.76 J/g.K,热扩散系数变化范围为3.47～0.85 mm2/s,热导率变化范围为13.10～4.21 W/(m.K);研究退火工艺对晶体近红外透过率的影响,在700℃,48h退火可以明显提高透过率达到65%。     

6-n-Alkoxy-3-Pyridinecarboxaldehydes: New Intermediates to Liquid Crystals. Properties of Some Derivatives

The synthesis of new intermediates to liquid crystals, a series of 6-n-alkoxy-3-pyridinecarboxaldehydes is described. The mesomorphic properties of their precursors, the 6-n-alkoxy-3-pyridinecarboxylic acids are reported. Some derivatives of the carboxaldehydes, the 6,6′-di-n-alkoxy-3,3′-dipyridylmethylenehydrazines and the 6′,6”- di-n-n-alkoxy-3′,3”-dipyridylmethylene-l,4-phenylenediamines, are described and their mesomorphic properties reported. The 1,4-phenylenediamine derivatives show greater mesomorphic stability than the azines, most of the azines being non-mesomorphic while the 1,4-phenylenediamine derivatives show smectic polymorphism with wide mesophase ranges.     

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.     

Semiconducting Properties of TI2Te3 Single Crystals

Electrical conductivity and Hall effect measurements were performed on single crystals of TI₂Te₃ to have the general semiconducting behaviour of this compound. The measurements were done at the temperature range 160–350 K. All crystals were found to be of p-type conductivity. The values of the Hall coefficient and the electrical conductivity at room temperature were 1.59 × 10³ cm³/coul and 3.2 × 10⁻² ω⁻¹ cm⁻¹, respectively. The hole concentration at the same temperature was driven as 39.31 × 10¹¹ cm⁻³. The energy gap was found to be 0.7 eV where the depth of impurity centers was 0.45 eV. The temperature dependence of the mobility is discussed.     

Growth and Optical Properties of LiNbO3: MgO Single Crystals

The technological procedure of the manufacturing of the LiNbO₃^˙ single crystals doped with 5 mol.% MgO is described in this paper. The results of the investigation of the crystal optical properties, ESR spectra and optical homogeneity are presented. The refractive index dispersion in 300–700 nm region and their temperature dependencies in 20–500 °C range are measured. The dispersion curve is approximated by the two oscillator Sellmeier formula. The data on the LiNbO₃: MgO crystal optical resistance are presented.