Studies on the Synthesis, Growth and Characterization of ([Paranitrophenyl]Imino)Benzene NLO Crystal by Sankaranarayanan-Ramasamy Method

The study of imine-bridged organics has been the hot spot synthesis of second order nonlinear optical (SONLO) and photo-responsive materials in recent years. Herein we present a study of synthesis, growth, and characterization of ([paranitrophenyl]imino)benzene (PNPIB) NLO single crystal. The title compound was synthesized in one step by Schiff base formation. PNPIB single crystal of diameter of 40 mmand length 50 mmwas successfully grown by SR method using a seed as the nucleus. The growth rate formula is derived for the SR method. PNPIB single crystals of 10 mmdiameter and 60 mmheight have been grown at an average growth rate of 3 mmper day from the point seed in a glass crystallizer. Almost 100% stable crystal conversion efficiency was achieved. The as grown PNPIB crystals were characterized using single crystal X-ray diffraction (XRD), X-ray powder diffraction (XRPD), Fourier Transform Infrared (FTIR), Ultraviolet-Visible-Near Infrared (UV-Vis-NIR), 1H & 13C NMR spectral studies, dielectric measurement and NLO studies. Single crystal XRD analysis confirms that the grown ingot belongs to the space group of P2 of monoclinic system thus exhibiting noncentrosymmetric structure. The crystalline perfection was assessed by XRPD. The powder diffraction pattern of the grown crystal has been indexed. The presence of C=N bond with intramolecular hydrogen bonding and the protonation of ions were confirmed by FTIR analysis. The UV-Vis-NIR spectrum of the crystal shows that the crystal has a cut-off at 298 nm. The 1H & 13C NMR spectra confirm the molecular structure. The dielectric behaviour was measured in the frequency range 1 KHz - 10 KHz for the temperature range from 30℃ to 170℃. The slight decrease in dielectric constant has been observed as the frequency is increased and the dielectric loss is very low for the entire frequency range. The second harmonic generation (SHG) in the crystal was observed by Kurtz powder technique.

FEM simulations and experimental studies of the temperature field in a large diamond crystal growth cell

We investigate the temperature field variation in the growth region of a diamond crystal in a sealed cell during the whole process of crystal growth by using the temperature gradient method （TGM） at high pressure and high temperature （HPHT）. We employ both the finite element method （FEM） and in situ experiments. Simulation results show that the temperature in the center area of the growth cell continues to decrease during the process of large diamond crystal growth. These results are in good agreement with our experimental data, which demonstrates that the finite element model can successfully predict the temperature field variations in the growth cell. The FEM simulation will be useful to grow larger high-quality diamond crystal by using the TGM. Furthermore, this method will be helpful in designing better cells and improving the growth process of gem-quality diamond crystal.

Effect of 6H-SiC crystal growth shapes on thermo-elastic stress in the growing crystal

The effect of 6H-SiC crystal growth shapes on the thermo-elastic stress distribution in the growing crystal was systematically in- vestigated by using a finite element method. The thermo-elastic stress distribution in the crystal with a flat growth shape was more homoge- neous than that in the crystals with concave and convex growth shapes, and the value of thermo-elasticity in the crystal with a fiat growth shape was also smaller than that in the two other types of crystals. The maximum values of thermo-elastic stress appeared at interfaces be- tween the crystal and the graphite lid. If the lid was of the same properties as 6H-SiC, the thermo-elastic stress would decrease in two orders of magnitude. Thus, to grow 6H-SiC single crystals of high quality, a transition layer of SiC formed by deposition or reaction is suggested; meanwhile the thermal field in the growth chamber should be adjusted to maintain the crystals with fiat growth shapes.

3D anisotropy simulation of dendrites growth with phase field method

The anisotropy problem of 3D phase-field model was studied,and various degrees of anisotropy were simulated by numerical calculation method.The results show that with the change of interface anisotropy coefficients,from smooth transition to the appearance of angle,equilibrium crystals shape morphology has a critical value,and 3D critical value is 0.3.The growth of dendrites is stable and the interface is smooth when it is less than critical value;the interface is unstable,rolling edge appears and the growth is discontinuous when it is more than critical value.With the increase of anisotropy coefficients,the dendrites grow faster under the same condition.

Structure and Crystal Growth of Li_2Zn_2(MoO_4)_3

Single crystal of Li2Zn2（MoO4）3 has been grown from a flux of Li2MoO4 by the top-seeded solution-growth method, and its stnicture was refined by the Rietveld method. It belongs to the orthorhombic system, space group Pnma with a = 5.1114, b = 10.4906 and c = 17.6172A. Good agreement between the experimental and calculated profile （Rp = 6.69%, Rwp = 9.73% and Rexp = 6.58%） was reached.

Application of the Method of Characteristics to Population Balance Models Considering Growth and Nucleation Phenomena

The population balance modeling is regarded as a universally accepted mathematical framework for dynamic simulation of various particulate processes, such as crystallization, granulation and polymerization. This article is concerned with the application of the method of characteristics (MOC) for solving population balance models describing batch crystallization process. The growth and nucleation are considered as dominant phenomena, while the breakage and aggregation are neglected. The numerical solutions of such PBEs require high order accuracy due to the occurrence of steep moving fronts and narrow peaks in the solutions. The MOC has been found to be a very effective technique for resolving sharp discontinuities. Different case studies are carried out to analyze the accuracy of proposed algorithm. For validation, the results of MOC are compared with the available analytical solutions and the results of finite volume schemes. The results of MOC were found to be in good agreement with analytical solutions and superior than those obtained by finite volume schemes.

Optical Spectroscopic Properties of Yb^(3+)-Doped MgMoO_4 Crystal Grown by the TSSG Method

This paper reports the growth and spectral assessments of Yb^（3＋） ion doped MgMoO_4（Yb^（3＋）：MgMoO_4） crystal grown by the TSSG method. Polarized spectral properties of Yb^（3＋）：MgMoO_4 crystal, including absorption and emission cross-sections, absorption FWHM and fluorescence lifetime, have been investigated. The laser performance parameters bmin, Isat and Iminhave also been evaluated. All the investigated results show the Yb^（3＋）-doped MgMoO_4 crystal is expected as a promising candidate for ultrashort pulse and tunable lasers.

The Growth and the Optical, Mechanical, Dielectric and Photoconductivity Properties of a New Nonlinear Optical Crystal—L-Phenylalanine-4-nitrophenol NLO Single Crystal

Nonlinear optical single crystals of L-phenylalanine-4-nitrophenol have been grown by the slow evaporation method. The grown crystal was subjected to the single crystal X-ray diffraction analysis, to confirm that it belongs to the monoclinic crystal structure, with space group P21. The optical transmission study reveals the transparency of the crystal in the entire visible region and the cut off wave length has been found to be 320 nm. The optical band gap is found to be 3.87 eV. The transmittance of the L-phenylalanine-4-nitrophenol crystal has been used to calculate the refractive index (n), the extinction coefficient (K) and the real (εr) and imaginary (εi) components of the dielectric constant. The mechanical behaviour of the grown crystals was studied using Vicker’s microhardness tester. The dielectric constant and dielectric loss of L-phenylalanine-4-nitrophenol are measured in the frequency range of 50 Hz to 5 MHz at different temperatures. The photoconductivity study confirms the negative photoconductive nature of the sample.

Growth, Structural, Spectral and Optical Studies on Pure and L-Alanine Mixed Bisthiourea Cadmium Bromide (LABTCB) Crystals

Pure bisthiourea cadmium bromide (BTCB) and 1 mole % L-alanine mixed bisthiourea cadmium bromide (LABTCB) single crystals have been grown by slow evaporation method. The grown crystals have been characterized by single crystal XRD analysis, powder XRD analysis, FTIR analysis, UV-Vis-NIR analysis and SHG studies. XRD analysis confirms the crystalline nature of the materials. The addition of L-alanine changes the crystal structure from orthorhombic to tetragonal. The presence of various functional groups present in the pure BTCB and LABTCB crystals have been confirmed by FTIR analysis. The UV-Vis-NIR spectrum shows the transmission characteristics of the crystals. The SHG study depicts the nonlinear optical efficiency of the crystals.

Crystal and electronic structure of a quasi-two-dimensional semiconductor Mg_(3)Si_(2)Te_(6)

We report the synthesis and characterization of a Si-based ternary semiconductor Mg_(3)Si_(2)Te_(6),which exhibits a quasitwo-dimensional structure,where the trigonal Mg_(3)Si_(2)Te_(6)layers are separated by Mg ions.Ultraviolet-visible absorption spectroscopy and density functional theory calculations were performed to investigate the electronic structure.The experimentally determined direct band gap is 1.39 eV,consistent with the value of the density function theory calculations.Our results reveal that Mg_(3)Si_(2)Te_(6)is a direct gap semiconductor,which is a potential candidate for near-infrared optoelectronic devices.

硅酸钛钡高温压电晶体及其传感器件研究进展

压电材料作为重要的功能材料,由其制备的结构健康检测器件已被广泛应用于国民经济的诸多领域。随着现代工业技术特别是航空航天、核电能源和智能制造等的发展,各类高温工况环境对压电材料的性能提出了更高的要求,因此研制综合性能优异的高温压电材料并将其应用到具有更高服役温度的传感器件中受到了研究者的广泛关注。硅酸钛钡(Ba_(2)TiSi_(2)O_(8),BTS)晶体具有较高的电阻率、较低的介电损耗和优良的压电性能,是一种具有良好应用前景的高温压电单晶材料。本文主要介绍了BTS晶体的提拉法生长制备工艺、单晶电弹性能表征、材料相变调控以及采用该晶体为核心元件研制的声表面波传感器和高温振动传感器的研究进展,最后对新型高温压电晶体及其传感器件的研发进行了总结和展望。

中长波Cr^(2+)/Fe^(2+)∶CdSe激光晶体生长及元件制备

本文采用自主研发的双温区真空石墨加热单晶炉,通过钼坩埚密封布里奇曼法成功生长出了Cr^(2+)∶CdSe晶体和Fe^(2+)∶CdSe晶体,晶体尺寸达Φ51 mm×110 mm。Cr^(2+)∶CdSe晶体和Fe^(2+)∶CdSe晶体分别在1400~2400 nm和2500~5200 nm波段存在明显的吸收,同时,Cr^(2+)∶CdSe晶体和Fe^(2+)∶CdSe晶体在7~15μm波段透过率均接近CdSe晶体透过极限(~70%),换算吸收系数约为0.005 cm^(-1)。采用钼坩埚密封布里奇曼法制备的Cr^(2+)/Fe^(2+)∶CdSe晶体具有过渡金属离子掺杂浓度可控、掺杂均匀、晶体品质高等优点,可同时作为中波红外激光晶体和长波红外非线性光学晶体材料。

Ga-N熔体热力学性质及钠助熔剂法制备GaN单晶的研究进展

作为第三代半导体的关键材料之一,Ⅲ族氮化物在过去几十年中因其应用于光电子和微电子器件而得到了广泛的研究,如发光二极管(LED)、激光二极管(LD)和高电子迁移率晶体管(HEMT)。Na助熔剂法已成为生长高质量GaN晶体的重要技术之一。综述和讨论了Na助熔剂法GaN结晶的发展历程与最新技术,包括Ga-N的结晶热力学性质、熔体结构、助熔剂选择、单点籽晶技术、多点籽晶技术、孔隙与位错控制、形貌演化与生长条件优化等。最后,对比其他体GaN技术,展望了Na助熔剂法的挑战与机遇。

CsPbBr_(3)晶体生长及变温霍尔效应研究

以定向凝固法提纯的CsPbBr_(3)多晶为原料,采用垂直布里奇曼法生长出尺寸为∅30 mm×70 mm的CsPbBr_(3)单晶。采用ICP-OES对提纯后的多晶测试表明,提纯后的CsPbBr_(3)多晶中杂质含量减少了28.7%。经XRD和EDS对切割得到的晶片分析发现,晶片的晶面方向属{210}晶面族,晶体中Cs、Pb、Br_(3)种元素分布均匀,原子百分含量符合化学计量比。采用傅里叶红外光谱仪和紫外-可见分光光度计对晶体的透过率测试显示,生长晶体在500~4000 cm^(-1)波数范围内的红外透过率超过75%,紫外短波截止边为552 nm,拟合计算出对应的禁带宽度为2.246 eV。选取7个不同温度点对CsPbBr_(3)单晶进行变温霍尔效应测试发现,生长晶体为P型导电,在250~300 K和300~350 K之间晶体中主要的载流子散射机制分别为声学波散射和电离杂质散射,在150~250 K温度范围内,更符合多种散射机构共同作用的散射机制。进一步拟合载流子浓度p与1/T的关系,计算获得晶体中杂质电离能ΔE_(A)=0.3042 eV。

冰晶生长对冷冻水产品品质影响及新型冷冻方式研究进展

冷冻技术在水产品保鲜方面应用广泛,但水产品在冻结过程中受冰晶形成、晶体生长与冰晶重结晶的影响,易造成细胞结构的破损,导致水产品品质下降。为深入分析冰晶生长与水产品品质变化间的关系,该文总结了冰晶生长对水产品的蛋白质变性、脂肪氧化、持水力、质构及感官特性影响,综述了物理场辅助冻结及添加抗冻剂、重结晶抑制剂等减小冰晶尺寸的新方法,为控制冰晶生长及提高冷冻水产品品质提供了理论参考。

氨热法GaN单晶生长的位错密度演变研究

氮化镓单晶具有高击穿电压、直接带隙、高饱和电子漂移速率、良好的化学稳定性等特性,在光电子器件和大功率电子器件中有广泛的应用。然而异质外延氮化镓会产生高位错密度,限制了氮化镓基器件的性能发挥。本研究以HVPE-GaN为籽晶,采用氨热法生长了氮化镓单晶,利用扫描电子显微镜(SEM),光学显微镜和湿法腐蚀研究了氨热法氮化镓单晶籽晶区至侧向生长区的位错演变。研究结果表明,侧向生长区的氮化镓单晶位错密度明显低于籽晶区,侧向生长超过25μm后,位错密度降低2个数量级。

溶液法生长大尺寸CsCu_(2)I_(3)钙钛矿单晶及其光学性能研究

近年来,铜基钙钛矿因其出色的稳定性和环境友好性在发光和闪烁等领域受到了广泛关注。然而,目前对CsCu_(2)I_(3)晶体材料的研究主要集中在0维和1维领域,这限制了人们对材料本征性质和各向异性的深入理解,也限制了其在闪烁体中的实际应用。本文通过溶液降温法开展了CsCu_(2)I_(3)体块单晶的生长工艺研究,成功得到了长度达5 mm的高质量CsCu_(2)I_(3)单晶,该晶体无色透明、棱角分明、显露面完整。XRD测试结果表明,CsCu_(2)I_(3)晶体在经过6个月后依然保持了良好的稳定性;吸收光谱显示该晶体在310 nm波段具有明显的吸收峰,计算得到其禁带宽度为3.42 eV,表明CsCu_(2)I_(3)晶体属于宽禁带半导体;发射光谱显示该晶体发射波长位于580 nm处,半峰全宽为75 nm,绘制CIE色度图得到其发光色度坐标为(0.47,0.50),位于黄光区域,属于暖白色调(色温3000 K),这与该晶体在紫外灯照射下发出黄色荧光的现象一致;CsCu_(2)I_(3)晶体的荧光寿命测得为51.6和215.5 ns。

基于溶液法制备卤化铅钙钛矿的直接型辐射探测器研究进展

X射线和γ射线探测在医学成像、安防检查、国土安全、无损检测等各个领域得到广泛应用,钙钛矿材料具有高辐射吸收系数、高载流子迁移率-寿命乘积、特殊的缺陷容忍特性而成为辐射探测器件优异的候选材料。溶液法在制备钙钛矿材料方面具有显著的优势,溶液法的成本较低,能在低温或环境条件下制备,更易推行工业化生产,是未来优化材料体系,制备高质量、大尺寸晶体材料的关键技术。本文从溶液法制备卤化铅钙钛矿材料的角度出发,分析晶体生长及材料组成对辐射探测性能的影响,重点介绍从优化晶体生长质量和器件结构设计等方面提升辐射探测性能,最后总结钙钛矿材料在辐射探测领域面临的挑战,并展望了未来研究的发展方向,期望为钙钛矿材料在辐射探测领域走向工业化提供参考。

含镓石榴石系列大晶格常数磁光衬底单晶研究进展

近年来,光通信技术与集成电子器件飞速发展,以稀土铁石榴石(RIG)为代表的磁光薄膜被视为应用于近红外通信窗口最具潜力的磁光材料。为了尽量减小磁光薄膜在制备过程中相关性能受到的影响,衬底材料的选择成为关键。制备RIG磁光薄膜通常采用Si类及石榴石氧化物类作为衬底材料。RIG磁光薄膜的晶格常数一般在12.4左右,含镓类石榴石氧化物单晶衬底基片与其晶格常数相近,具有大晶格常数特性,是其合适的衬底材料之一。但是,由于原料氧化镓高温易挥发,使含镓类石榴石单晶制备成为一直以来关注和讨论的热点。深入研究含镓类石榴石衬底单晶有望促进新一代磁光器件的发展。本文综述了在含镓类石榴石系列单晶中,氧化物磁光衬底单晶的研究进展,总结了本团队在该类晶体生长、晶体结构、关键参数等方面的研究工作,展望了该类晶体的研究发展趋势。