近化学计量比铌酸锂晶体组分过冷与临界生长速率研究

本文在用双坩埚提拉法生长近化学计量比LiNbO3晶体的过程中观察到了组分过冷的实验数据,同时根据Tiller-Chalmers稳定性判据公式半定量计算了近化学计量比LiNbO3晶体临界生长速率的理论值,得到一般电阻加热双坩埚提拉法生长近化学计量比LiNbO3晶体的临界生长速率为0.1mm/h数量级.通过临界生长速率解释了一系列晶体生长的实验结果.提出了一些工艺措施来避免组分过冷,根据这些工艺获得了无包裹体的近化学计量比LiNbO3晶体.     

BGO熔体急冷自发结晶形貌

本文研究了BGO熔体在急冷的条件下自发结晶的显露形貌.在急冷的条件下,组成BGO的各个面族自由发育.{321}面族、{211}面族和{111}面族都是按[GeO4]4-四面体以顶角相连的化学键链生长发育的,生长速度快,优先显露,在熔体急冷时保留下来.表面形貌显露不完整的{100}面族是[GeO4]4-四面体以棱相连所对应的面族,生长速度较慢,尚未显露完全熔体就已冷却.从生长速度考虑,在实际生长晶体时以[321]、[211]、[111]方向生长可以获得较快的速度.     

水平定向结晶法生长大尺寸板状蓝宝石缺陷研究

采用水平定向结晶法(HDS)成功生长出了质量优异的板状蓝宝石晶体.利用光学显微镜,扫描电镜(SEM),并结合化学腐蚀法对生长出的蓝宝石晶体不同位置的样品进行宏观缺陷及微观位错形貌的观测和研究,分析了水平定向结晶法生长蓝宝石晶体的宏观缺陷类型和位错的形貌,探讨了该缺陷在晶体中的分布规律及其形成原因.实验结果发现晶体的宏观缺陷主要包括气泡和包裹体.并结合能谱(EDS)测试包裹体的成分,分析其形成的原因.结果表明块状或絮状的小尺寸包裹体主要是由于C,Si杂质聚集原料中的其它杂质形成;长条形或圆形的大尺寸包裹体是由于Al,O元素的化学计量比严重适配,造成固液界面局部组分过冷形成.结合化学腐蚀法,发现该晶体的位错形貌均为三角型腐蚀坑,并探讨了晶体中位错的形态.     

近化学计量比LiNbO3晶体各向畴形态的研究

本文对采用双坩埚提拉法生长的近化学计量比LiNbO3晶体沿其各向切块腐蚀后通过直接观察和在金相显微镜下观察,对其各个面的畴结构进行了分析.我们发现晶体a面上由于镜相对称不反映畴结构,b面和c面上的腐蚀形貌则完全显露而且按一定的方向整齐地排列,证明我们生长的SLN晶体是完全单畴结构的晶体.     

近化学计量比铌酸锂晶体组分测定与缺陷观察

采用助熔剂提拉法生长得到近化学计量比LiNbO3晶体.用多种方法测定了晶体组分,结果表明生长得到的晶体中[Li2O]含量为49.80;摩尔分数;对晶体缺陷的研究表明晶体质量有待提高,并分析了晶体中出现包裹物的原因.     

助熔剂提拉法生长化学计量比LiNbO3晶体

利用助熔剂提拉法,分别从掺入11mol;K2O的同成份LiNbO3熔体中和从掺入19mol;*!K2O的化学配比LiNbO3熔体中生长出高质量近化学计量比LiNbO3单晶.对这两种从不同配比熔体中生长的晶体进行光谱分析表明,与同成份比LiNbO3相比较,其紫外吸收边出现明显蓝移,OH红外吸收峰的位置和线宽也都有显著的变化.室温极化反转测试显示,两种晶体的矫顽场分别为4.4kV/mm和0.8kV/mm.根据所得测量结果,估计两种晶体中Li2O的含量分别为49.6mol;和49.9mol;.其中从掺19mol; K2O化学配比LiNbO3熔体中生长出的LiNbO3单晶的Li2O含量已非常接近50mol;的化学配比.进一步优化生长工艺,获得成份均匀、大尺寸化学计量比晶体的工作正在进行中.     

高温相偏硼酸钡(α-BaB2O4)晶体的缺陷行为分析

运用同步辐射X射线白光形貌研究了α-BaB2O4晶体内部的完整性,并分析了α-BaB2O4晶体的缺陷行为及缺陷形成原因.在(001)面发现生长扇界和亚晶界,而在(100)面和(120)面分别观察到了位错、位错簇以及针状包裹体.使用双晶衍射实验发现在(001)面有生长条纹,这些生长条纹呈环形,该条纹与熔体中温度波动而导致的生长速率波动有关.运用白光形貌拍摄到高清晰的劳埃斑,表明晶体为三方结构.     

下降法生长的GdCOB晶体中的包裹物

本文通过对GdCOB晶体进行了光学显微观察;结合电子探针微区分析手段,讨论了Bridgman法生长所得GdCOB晶体中几类不同性质的包裹物.这些包裹物主要为富钙的固相包裹物,组分过冷形成的熔体包裹,以及气泡包裹.并分析了它们的组成和成因.     

高温相偏硼酸钡（α—BaB2O4）晶体的缺陷钎为分析

运用同步辐射X射线白光形貌研究了α-BaB2O4晶体内部的完整性,并分析了α-BaB2O4晶体的缺陷行为及缺陷形成原因。在（001）面发现生长扇界和亚晶界，而在（100）面和（120）面分别观察了位错，位错簇以及针状包裹体。使用双晶衍射实验发现在（001）面有生长条纹，这些生长条纹呈环形，该条纹与熔体中温度波动而导致的生长速度波动有关。运用白光形貌拍摄到高清晰的劳埃斑，表明晶体为三方结构。     

近化学计量组分掺铒铌酸锂的制备及性能测试

通过气相输运平衡技术,严格控制生长条件和气氛,制备了化学组分均匀、光学质量优异的近化学计量组分Er:LiNbO3晶体.通过对吸收边、喇曼谱及红外OH-吸收谱的测量,发现吸收边"蓝移";OH-吸收带显著减弱;Er:LiNbO3晶体中的E模(152cm-1)和A1模(632cm-1)的线宽也明显变窄.这些特征都证实了得到的Er:LiNbO3晶体已接近于化学计量组分,经过计算,其Li+含量达到49.7mol;.     

氧化锌晶体的研究进展

基于ZnO的紫外激光器的实现掀起了对于传统的纤锌矿结构的半导体ZnO材料的新的研究热潮.ZnO以其优良的综合性能将成为下一代光电子材料,因此对ZnO单晶的研究有重要的理论和实践意义.目前生长ZnO的方法有助熔剂法、水热法、气相法和坩埚下降法等等,但所生长的ZnO单晶的尺寸和质量都有待于提高.     

热屏间距对泡生法蓝宝石单晶生长影响研究

太空、军事和科研等高科技领域的持续发展极大促进了对蓝宝石晶体的需求,泡生法是蓝宝石晶体的主要制造方法之一;热场结构对所得蓝宝石晶体的质量具有重要影响.本文对采用泡生法工艺制造蓝宝石单晶过程中,具有内置7层氧化锆外置8层钼金属的新型热屏结构间距进行研究.通过数值模拟考察热屏间距对单晶炉功率、固-液界面形状和晶体热应力的影响确定了合理的热场结构;并与试验生产结果进行对比验证.结果表明:热屏间距增大使得单晶炉功率明显提升,并引起固-液界面凸度增大;而蓝宝石晶体热应力出现减小.综合考察三个影响因素的影响,最后确定热屏间距为5 mm时单晶炉能耗较低,可用于制造高质量的蓝宝石晶体.     

Growth and characterization of semi organic nonlinear optical LHPCL crystals

The growth of single crystals of L‐histidinium perchlorate (LHPCL), a semi organic nonlinear optical material with dimension upto 5 × 6 × 2.5 mm³ is reported. Good optical quality single crystals were grown from aqueous solution by slow solvent evaporation technique. The grown crystals were characterized by single crystal X‐ray diffraction (XRD), FT‐IR and optical transmission studies. Thermal studies confirm that LHPCL has a fairly high thermal stability (272°C) when compared with other members of histidine family. The scanning electron microscopy (SEM) provides information on the quality of the samples and grain distribution over the surface of the sample. The dielectric constant and dielectric loss of the compound were measured at different frequencies, and also at varying temperatures and the results of these experiments are discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High pressure solution growth of GaN

An internally heated pressure vessel was used to study the decomposition reaction of GaN at temperatures above 900°C and the phase equilibria in the system Ga-N₂. As a consequence of these studies we have undertaken the crystal growth of GaN free crystals and epitaxial layers on sapphire by a VLS process. We have succeeded in the synthesis of high quality epitaxial layers showing the terrace structure typical of LPE. As a function of the growth conditions both n and p type gallium nitride were obtained, the latter only in polycrystalline form.     

Growth and characterization of L‐histidine hydrochloride monohydrate single crystals

Good optical quality single crystal of L‐histidine hydrochloride monohydrate (LHC) a novel semi organic NLO material was grown by slow solvent evaporation technique. The crystal was characterized by X‐ray diffractometry (XRD), Fourier Transform Infra‐red (FTIR), UV‐Vis‐NIR, TGA, DTA, microhardness and solubility studies. The SHG efficiency is found to be higher than that of KDP crystal. The dielectric constant and dielectric loss of the crystal was studied as function of frequency and the results are discussed. Photoconductivity studies were also carried out which reveals the positive photoconducting properties of the sample. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

水热法KTP晶体生长与宏观缺陷研究

本文报道了水热法KTP晶体的生长工艺及晶体生长形态,系统研究了水热法KTP晶体的宏观缺陷,其宏观缺陷主要为添晶、生长脊线、裂隙和包裹体.提出了晶体生长工艺的改进措施,如提高原材料和试剂的纯度、调整籽晶的悬挂方式、减少籽晶的尺寸等,都可以减少晶体的宏观缺陷,提高晶体的质量.//(011)切向的籽晶生长的晶体质量较高,且能很好地应用于激光器件中.     

Enhancement of stability of growth,structural and NLO properties of KDP crystals due to additive along with seed rotation

Potassium Acetate (CH₃COOK) and Potassium Citrate (K₃C₆H₅O₇) as new additives were added into the potassium dihydrogen phosphate (KDP) solutions in different molar ratios. The metastable zone width and induction period with and without these additives were determined and compared. Dielectric measurements on pure and doped KDP crystals at various temperatures ranging from 313 to 423 K were carried out by the conventional parallel plate capacitor method which results low dielectric constant value dielectrics in doped crystals. The high resolution XRD studies show that CH₃COOK doped KDP crystal and K₃C₆H₅O₇ doped KDP crystal do not contain any internal structural grain boundaries and indicates that the crystalline perfection is very good. Moreover, the addition of these potassium additives improves the quality of the crystal and yields highly transparent crystals with well defined features. The effect of additives on the growth, nucleation kinetics, structural, NLO and optical properties has been investigated. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A novel way of modifying the thermal gradient in Vertical Bridgman‐Stockbarger Technique and studies on its effect on the growth of benzophenone single crystals

In order to grow benzophenone single crystal, an organic nonlinear optical material, a cost‐effective Vertical Bridgman‐Stockbarger system has been designed and fabricated by employing a two‐zone, transparent furnace made out of immiscible liquids. Transparent, optical quality benzophenone single crystals were successfully grown as a result of a suitable thermal gradient achieved by means of introducing an intermediate liquid in between the two immiscible liquids. The effect of change in the volume of the intermediate liquid thereby the thermal gradient on the growth parameters was analyzed. The quality of the grown single crystal was justified using X‐ray powder diffraction analysis, FTIR, TG‐DTA and optical transmission studies. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

中红外非线性光学晶体的研究进展

本文综述了几种重要的中红外非线性光学晶体的研究进展,分别详细介绍了各自的结构特点、非线性性能以及他们在频率变换方面的重要应用.提出了在中红外非线性光学晶体生长中遇到的困难,并探讨了解决问题的途径.认为生长性能优异、足够尺寸的红外非线性光学晶体具有非常重要的应用价值,并对中红外非线性光学晶体的研究进行了展望.     

导模法生长高质量氧化镓单晶的研究

使用导模法生长了宽度25 mm,长度100 mm的氧化镓(β-Ga2O3)单晶.晶体外观完整、无色、无开裂,粉末XRD测试证明所获得的晶体为β相,晶体摇摆曲线半峰宽为93.6",峰形对称,说明晶体质量良好.测试了未掺杂晶体的紫外透过光谱,并推算了晶体的禁带宽度为4.77 eV.此外,还重点讨论了晶体放肩时的工艺参数对晶体质量的影响.