ZnSe红外窗口材料的性能及其制备

ZnSe是一种优秀的红外窗口材料,得到广泛的关注.在本文叙述了ZnSe红外窗口材料的光学特性和力学特性,以及详细地描述ZnSe体单晶熔体法、气相法、溶液法和固相再结晶制备技术及其影响因素.     

溶胶-凝胶法制备不同锌硅比硅酸锌陶瓷

本文采用溶胶-凝胶法制备不同锌硅比的Zn2SiO4陶瓷。红外光谱分析发现其溶胶-凝胶化过程主要依赖于原料中正硅酸乙酯的水解和聚合。研究发现,随着锌硅比从1.6增加到2.0时,粉体的烧结温度在增加。XRD结果表明当锌硅比小于1.9时,陶瓷主晶相是Zn2SiO4,同时存在有少量的SiO2相,大于和等于1.9时出现了ZnO相。微波介电性能的研究结果表明,随着锌硅比的增加,介电常数略有增加;品质因子先增加后减小。当锌硅比等于1.8时,陶瓷的品质因子达到123000,其介电常数为6.5。     

新型有机热释电晶体——酒石酸铵系列晶体研究

本文从晶体结构对称性的观点出发,寻找新型有机热释电晶体材料,选取了具有P21空间群结构的酒石酸铵系列晶体作为研究对象,用水溶液缓慢降温法生长了酒石酸铵及其掺质酒石酸铵晶体,掺质分别为尿素、溴化铵和甘氨酸,研究了晶体生长形态并作了比较.测定了酒石酸铵系列晶体的红外光谱、晶胞参数和主要热释电性能.发现酒石酸铵系列晶体的热释电性能,其品质因子具有与TGS晶体相同的数量级.     

非线性晶体应用于中长波红外固体激光器的研究进展

中波红外3～5μm波段以及长波红外8～12 μm波段的激光处于大气传输窗口,在激光成像、环境监测、激光雷达、激光医疗、化学遥感和红外对抗等领域有着非常广阔的应用前景.基于非线性光学晶体,采用光学非线性频率变换技术在实现中长波红外固体激光输出方面具有明显的技术优势.该方法激光器结构简单,且晶体本身并不参与能量交换,因而没有量子亏损,从而产热很少.同时具有单色性好、宽调谐、高功率等优点.本文针对常用以及新型非线性光学晶体,对其应用于中长波红外固体激光器的研究进展做了详细的总结.     

高温高速流场条件下蓝宝石材料对红外成像影响分析

蓝宝石是一种性能优良的红外窗口材料,文章结合某高速飞行器应用要求设计了高温高速流场条件下蓝宝石对红外成像影响试验,分析了蓝宝石对红外成像影响结果,提出了对各种影响的校正方法,为高速飞行器红外成像制导技术应用研究提供了技术基础.     

掺质TGS系列晶体生长与性能研究

采用水溶液缓慢降温法生长了掺质为乳酸、异丙醇胺、L-丝氨酸、1,2-丙二胺、1,3-丙二胺TGS系列晶体,研究了晶体生长形态,测定了晶胞参数、红外光谱和热释电性能.实验结果表明,所有掺质均已进入晶体,晶体生长形态和热释电性能随着掺质种类不同而发生不同的变化.掺L-丝氨酸TGS晶体的品质因子大于纯TGS晶体.     

CVD方法生长平面和曲面块状多晶硫化锌

采用化学气相沉积方法成功地生长出硫化锌多晶红外光学材料.加工后的成品多晶硫化锌尺寸为直径150mm,厚度为6mm;既有曲面的整流罩,又有平面窗口,蒸镀多层防反膜.由于采用了自制的活性硫化氢为原料,以及较好的工艺生长条件,生长的硫化锌红外光学材料长波透射比达到理论值75;.镀多层防反膜以后,中、长红外波段透过率均有所提高,但镀膜技术还有待改进.文中对硫化锌的透过曲线进行了分析与比较,结果表明我们生长的硫化锌杂质较少,是红外透过率高的原因.文中还测试了硫化锌的其它主要性能.     

8～12μm长波红外材料ZnS多晶的制备

真空热压烧结法是最经济、高效地制备ZnS多晶的方法之一.ZnS多晶的红外透过率是衡量材料品质的重要参数.本文运用TEM、XRD和化学分析方法,研究了原料粉末特性和热压工艺参数对热压ZnS多晶红外透过率的影响,并确定了合理的热压工艺参数.运用该方法制备的ZnS多晶6mm厚的试样,8～12μm波段平均红外透过率为66.7;.     

超薄异质结太阳能电池理论模拟计算及分析

采用AFORS-HET软件对超薄异质结太阳能电池的窗口层、本征层的掺杂浓度、厚度、带隙等参数进行了数值模拟和优化,结合实际具体分析了每个参数对超薄异质结电池性能的影响规律,且得出了最佳的优化参数。模拟结果表明:对于衬底厚度仅为80 μm的超薄异质结太阳能电池,随着窗口层厚度的增加,电池性能整体呈现下降的趋势,通过结合实际,得出窗口层的最佳厚度范围是5～9 nm;随着窗口层掺杂浓度的增加,电池性能整体呈现先增加后趋于恒定的趋势,窗口层理论上的最佳掺杂浓度范围为7×10¹⁹～8×10¹⁹;窗口层的带隙宽度对电池的开路电压和效率影响较大,对填充因子和短路电流有较小的影响,窗口层的最优带隙范围为1.85～2.0 eV。随着本征层厚度的增加,电池的填充因子FF和效率E_ff呈现先增加后减小的趋势,短路电流逐渐减小,而开路电压基本不变,本征层的最佳厚度是5～10 nm;当本征层的光学带隙小于1.8 eV时,对电池性能影响较小,当大于1.8 eV,电池性能急剧下降,因此本征层的最佳带隙范围是1.6～1.8 eV。     

硫属卤化物红外二阶非线性光学晶体材料的研究进展

对二阶红外非线性光学晶体材料的研究是当前激光及非线性光学领域研究的重点、难点和热点之一.由于满足应用需求的材料比较缺乏,很有必要从源头上探索潜在的新型红外非线性光学晶体材料.硫属化合物和卤化物是红外非线性光学晶体新材料探索的主要体系,前者一般表现出大的倍频效应和宽的红外窗口,后者则多具有大的光学带隙,即高的抗激光损伤阈值.结合两者的优势,有望获得综合非线性光学性能优异的新材料.在此背景下,本文综述了近期硫属卤化物红外非线性光学晶体材料的研究现状,包括含S8单元的卤化物、包盐硫属卤化物和钡基硫属卤化物.这些硫属卤化物的粉末样品大都表现出优异的非线性光学性能.最后,本文讨论了该方向未来研究的机会和重点.     

Bandstruktur und thermoelektrische Eigenschaften von Wismut-Antimon-Legierungen

The authors investigate the influence of the electronic band structure on the thermoelectrical properties of Bi_xSb_1–x-alloys (0 ≦ (1–x) ≦ 1). For alloys with a high figure of merit the differential thermoelectric power and the ratio σ/k (σ: electrical conductivity, k: thermal conductivity) give an equal share to the increase of the figure of merit (in relation to pure bismuth). It become evident that the descrease of ratios of mobility for free carriers with different sign is overcompensated by means of modifications of the partial Seebeck coefficients. This is a result of changes in the electronic band structure and in the position of the Fermi level in an m-band-model with m > 2, impairing the electrical conductivity and the thermal conductivity in different wise.     

Synthesis of lead telluride particles by thermal decomposition method for thermoelectric applications

The lead telluride fine crystalline particles were synthesized using thermal decomposition and chemical interaction of lead acetate and tellurium powder mixture in reducing atmosphere (H₂). For the process control, thermal gravimetry (TG), the different‐scanning calorimetry (DSC), X‐ray diffraction (XRD), electronic microscopy (SEM) and measurements of the specific surface of particles were used. Additionally the influence of gas phases on the decomposition kinetics, crystal structure, size, specific surface of the particles and the physical properties were analyzed. Seebeck coefficient values increased with decreasing synthesis temperature and increasing specific surfaces of the powder. The presented method of preparing lead telluride polydisperse particles is developed to create nano‐structured thermoelectric materials with high figure of merit.     

Sr掺杂对Ca3Co4O9基材料热电性能的影响

采用溶胶-凝胶法,结合常压烧结工艺制备了Ca3-xSrxCo4O9(x=0～0.5)热电陶瓷材料,并对材料的热电性能进行了测试。结果表明,Sr掺杂对Ca3Co4O9基材料的热电性能有较大影响。随着掺杂量的增加,电导率逐渐增大,Seebeck系数略有减小。Sr掺杂能显著降低热导率,而且随着掺杂量的增加,热导率的下降幅度逐渐增大。Sr掺杂显著改善Ca3Co4O9材料的热电性能,当掺杂量为0.5时获得最佳热电性能,573 K时Z值达1.07×10-4 K-1。     

Synthesis of PbTe‐SnTe particles by thermal decomposition of salts to create nano‐structured thermoelectric materials

Micro‐ and nanocrystalline particles of Pb‐Sn‐Te mixed crystals were synthesized using thermal decomposition and chemical interaction of lead acetate, tin oxalate and tellurium powder mixture in H₂ atmosphere. For the process parameter optimization data of thermal gravimetry (TG), X‐ray diffraction (XRD), electronic microscopy (TEM, SEM) and measurements of the specific surface of particles were used. Additionally the influence of gas phases on the decomposition kinetics, crystal structure, size, specific surface of the particles, gains composition and the physical properties were analyzed. Seebeck coefficient values increased and conductivity decreased with decreasing tin concentration. The presented method for preparing PbTe‐SnTe polydisperse particles is developed to create nano‐structured thermoelectric materials with high figure of merit. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modification of pyroelectric crystal TGS using thermodynamic theory

Based on the Devonshire thermodynamic theory, the relationship λ/χ = Ps/C can be regarded as a method to increase the pyroelectric material figure of merit of ferroelectric crystals. Several modified TGS crystals doped with urea or co-doped with urea and other dopants have been grown. The effect of the urea dopant on crystal growth and pyroelectric properties was investigated. The pyroelectric figures of merit M (λ/ε) of the doped TGS crystals are obviously higher than those of pure TGS. Furthermore, the variations of λ/χ and Ps/C as a function of temperature for these doped TGS single crystals were measured, and analyzed according to the Devonshire thermodynamic model.     

Diffuse scattering and chemical short range order in binary metallic glasses

X-ray and neutron scattering from binary metallic glasses is discussed in the context of the Bhatia-Thornton equations for the structure factor. For neutrons a generalised form of the Bhatia-Thornton equation must be used when there are different isotopes present. By making a distinction between correlated and uncorrelated scattering centres an expression can be derived which shows clearly the different contributions to the total scattered intensity. Information about the relative visibility of the alloy components can be obtained from this expression and a figure of merit or degree of contrast between the species defined, which is helpful in understanding results of experiments performed to date.     

Polymer Composite Based on DAST Submicron Crystals: Technology and Properties

We propose a new nonlinear optical material, a polymeric nanocomposite based on DAST submicron crystals (trans-4’-(dimethylamino)-N-methyl-4-stilbazolium tosylate). The method and the preparation conditions for films based on a mixture of polymer solutions and a DAST powder are studied. Polymer matrices of various types, solvent ratio for the pair DAST/polymer, and electrical poling conditions are investigated. Absorption and luminescence spectra and the second harmonic generation have confirmed the creation of red-form DAST nanocrystals in polymer films. The figure of merit for a resulting polymer film is approximately 400 times higher than that for LiNbO₃ at a wavelength of 1.32 microns.     

Nanocrystalline transparent SnO2‐ZnO films fabricated at lower substrate temperature using a low‐cost and simplified spray technique

Nanocrystalline and transparent conducting SnO₂‐ ZnO films were fabricated by employing an inexpensive, simplified spray technique using a perfume atomizer at relatively low substrate temperature (360±5 °C) compared with conventional spray method. The structural studies reveal that the SnO₂‐ZnO films are polycrystalline in nature with preferential orientation along the (101) plane. The dislocation density is very low (1.48×10¹⁵lines/m²), indicating the good crystallinity of the films. The crystallite size of the films was found to be in the range of 26–34 nm. The optical transmittance in the visible range and the optical band gap are 85% and 3.6 eV respectively. The sheet resistance increases from 8.74 kΩ/□ to 32.4 kΩ/□ as the zinc concentration increases from 0 to 40 at.%. The films were found to have desirable figure of merit (1.63×10^–2 (Ω/□)^–1), low temperature coefficient of resistance (–1.191/K) and good thermal stability. This simplified spray technique may be considered as a promising alternative to conventional spray for the massive production of economic SnO₂ ‐ ZnO films for solar cells, sensors and opto‐electronic applications. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determination and correlation of heavy atom positions in the derivatives used in the X-ray analysis of ribonuclease A at 2.5 Å resolution

The analysis of four heavy atom derivatives of ribonuclease A is described leading to isomorphous phasing at 2.5 resolution. Differences in the characteristics of the derivatives are discussed with respect to the determination of their heavy atom parameters and the correlation of sites between derivatives to produce a self consistent set. The criteria used to ensure consistency are described. In the final phase analysis using refined heavy atom parameters the least squaresR factors of the derivatives were .124, .143, .101, and .067 respectively, and the mean figure of merit for the 3444 observed reflexions was 0.66.In recognition of C. H. Carlisle's pioneering work in this field.     

Li_(0.067)Na_(0.933)Tb(MoO_4)_2磁光晶体的生长与磁光性能

采用Czochralski法生长了Li_(0.067)Na_(0.933)Tb(MoO_4)_2晶体,并测试了Li~+在NaTb(MoO_4)_2晶体中的有效分凝系数.由粉末X射线衍射数据计算了晶体的晶胞参数.室温下,采用消光法测试了Li_(0.063)Na_(0.933)Tb(MoO_4)_2晶体在532 nm、633 nm和1064 nm处的费尔德常数,分别为-293.6 rad·m~(-1)·T~(-1)、-200.5 rad·m~(-1)·T~(-1)和-68.6 rad·m~(-1)·T~(-1),与纯NaTb(MoO_4)_2相比,其费尔德常数均有所增加.结果表明,在1064 nm处Li_(0.067)Na_(0.933)Tb(MoO_4)_2晶体有较高的磁光优值.