准同型相界组分PMNT弛豫铁电单晶的畴结构与极化特性

采用坩埚下降法生长了具有准同型相界(MPB)组分的65Pb(Mg1/3Nb2/3)O3-35PbTiO3 (PMNT65/35)弛豫铁电单晶.用偏光显微镜研究了(001)、(110)和(111)三个结晶学取向的铁电畴结构,观察到明暗交替的变化.通过对极化前后电畴形状的比较,分析了极化前后铁电畴形态的变化原因.晶片极化条件为:600 V/mm 的电场并保持10～15 min.研究了极化介质不同对极化后晶片压电性能的影响.     

LB膜模板诱导晶体取向生长

LB膜作为模板可诱导晶体取向成核和外延生长,生成的晶体材料具有独特的微观结构和优异的物理化学性能.这种方法对于生物矿化现象的研究以及新颖材料合成策略的设计等方面具有重要的启示意义.本文从LB膜诱导晶体取向生长的机理及利用等方面综述了该领域研究的最新进展.     

CVD-ZnS胞状生长现象对材料结构与性能的影响

采用化学气相沉积法(CVD)制备大尺寸ZnS晶体(CVD-ZnS),利用扫描电子显微镜、透射电子显微镜、X射线衍射分析对CVD-ZnS内部的胞状结构进行表征,表明胞状生长现象能改变CVD-ZnS材料内部的晶粒生长方向、分布方式,但对材料内部的物相、元素分布并未造成显著影响;通过对胞状物密集区的光学均匀性检测,分别为2.71×10-5和2.85×10-5,均方根值分别为6.46×10-6和4.98×10-6,正常区域的样品光学均匀性为9.53×10-6,均方根值为1.51 ×10-6,表明胞状物的存在会降低CVD-ZnS材料的光学均匀性;采用三点弯曲法测试材料弯曲强度,四组弯曲强度数据表明CVD-ZnS正常区的弯曲强度明显高于CVD-ZnS胞状物密集区.     

BNBT无铅压电陶瓷晶粒定向生长

采用固相合成法制备了0.94(Na1/2 Bi1/2)TiO3-0.06BaTiO3(BNBT)陶瓷粉体,用传统压电陶瓷工艺制备了无铅压电陶瓷,研究了烧结工艺对其径向收缩率和相对密度的影响.结果表明:随着保温时间的增加,径向收缩率和相对密度都出现了极大值.将陶瓷粉体与分散剂均匀混合制成高固相含量的浆料,以SrTiO3(100)单晶基片做模板,通过流延法制备了晶粒定向生长模型材料,初步探讨了热处理工艺对晶粒定向生长习性的影响.结果表明,随着保温时间的增加,晶体生长层厚度增加,生长层致密度增大.     

铽镓石榴石单晶的生长、表征及其挥发机理研究

使用预先烧结好的多晶原料,在一定比例的N2和CO2混合气氛下,采用提拉法生长出了高质量的铽镓石榴石(TGG)单晶.采用XRD、ICP和热力学计算进行分析,结果表明,晶体生长过程中的挥发机制为Tb3Ga5O12的分解,分解产物为Tb3 GaO6,Ga2O和O2.CO2被Ga2O还原产生O2,抑制了Tb3Ga5O12的分解.TGG单晶的化学分子式存在Tb富集或Ga缺失,为Tb3Ga4.4～4.5O11.1～11.3非化学计量比相.将晶体毛坯加工成φ2.8 mm×10.7 mm的晶棒,消光比测试结果表明镀增透膜后消光比平均可提高18.8 dB.     

氨气浓度对碳纳米管生长影响的研究

利用等离子体增强化学气相沉积系统,用CH4、NH3和H2为反应气体,在沉积有100nm厚Ta过渡层和60nm厚NiFe催化剂层的Si衬底上制备了碳纳米管,并用扫描电子显微镜研究了它们的生长和结构.结果表明当氨气浓度为20;、40;和60;时,碳纳米管的平均长度分别为3.88μm、4.52μm和6.79μm,而其平均直径变化不大,均在240nm左右.最后,分析讨论了氨气浓度对碳纳米管生长和结构的影响.     

火焰热解法生长定向碳纳米管

本文研究了火焰热解法的碳纳米管制备实验(催化剂为Fe/Mo/Al2O3),发现在火焰热解法条件下碳纳米管阵列可在火焰热解腔中定向生长,产物较为整齐,碳管形态较好.本课题组之前在电场作用下采用Fe(CO)5为催化剂,在V型体火焰中亦可制得碳纳米管阵列,对比两者发现热解腔内制得阵列碳纳米管长度较长,定向性更优;而电场作用下的V型体火焰中制得阵列中的碳纳米管较直.进而,在火焰热解法制备中施加电场,发现随电压增加,碳纳米管阵列更直,碳管长度和产量明显增长.     

大尺寸优质TGG晶体的自动提拉法生长

采用液相法合成原料,通过自动提拉法在铱坩埚中成功地生长出直径为35 ～40 mm,长度为40 ～ 50 mm的大尺寸优质TGG晶体.该晶体外观笔直,内部光滑透明,没有螺旋纹,没有界面反转.经氦氖激光器检测证明该晶体具有无散射、无核心、不开裂的优点,经X射线粉末衍射证明晶体和底料均为TGG相,没有其它物相产生,且光学性能方面吸收值低,损伤阈值高.     

静电场对V型火焰法中碳纳米管定向生长的影响

针对V型火焰实验系统的特点,考察了在种不同的静电场引入方式,以及在5V、30V和150V三种偏置电压下碳纳米管的定向生长情况.对实验结果进行了SEM、TEM表征,验证了静电场对碳纳米管定向生长的诱导作用,同时发现在一定范围内,随着偏置电压的增人,碳纳米管的准直性生长越明显.     

连续铸造铜单晶的晶体取向与竞争生长

本文采用自制单晶连铸设备和X射线衍射方法研究连铸铜单晶的晶体取向与竞争生长.结果表明,在晶体演化过程中逐渐淘汰的晶面为(311)、(200)和(111),最后单晶生长的晶面为(200),连铸铜单晶的晶体生长方向为[100],晶体取向[100]与晶轴的偏离度小于10°.单晶生长时固液界面向熔体呈凸出形状,这有利于晶体生长过程中的竞争和淘汰.还发现了连铸铜单晶取向在一定范围内,并不是唯一取向的单晶.     

Monte Carlo Simulation Algorithms of Grain Growth in Polycrystalline Materials

In the paper we present a variety of Monte Carlo algorithms, that can be employed to simulate the grain growth in polycrystalline materials during sintering. The simulation algorithms of monophase or two‐phase structure, on both the square and triangular distribution of lattice points, possibly with the second phase particles being either of static or dynamic nature, are described. The paper deals with oriented and anisotropic grain growth as well. A considerable number of input parameters in the simulation procedure makes it possible to set up a large amount of combinations of conditions under which we want to simulate the sintering process.     

Reducing Inversion Twinning in Single Crystal Growth of GaPO4

Gallium orthophosphate (GaPO₄) single crystals were grown by the reverse temperature gradient method from phosphoric acid solutions under hydrothermal conditions. Twins after (110) were studied by etching faces having been cut perpendicular to one of the twofold axes. Based on the determination of the twin boundary position as well as on the knowledge of the growth rates of different crystallographic forms, a few faces have been chosen to be quite promising for growing high‐quality GaPO₄ single crystals if they are offered at the referring seed crystal. From the characterization of the grown crystals conditions have been found, which may lead to the reduction of the inversion twin number during the growth process.     

Growth and characterization of a new langasite‐type single crystal Sr3NbAl1.5Ga1.5Si2O14

Single crystals of Sr₃NbAl_1.5Ga_1.5Si₂O₁₄ (SNAGS) with langasite structure have been successfully grown by Czochralski method. The X‐ray diffraction (XRD) verified that the as‐grown crystal was isostructural with A₃BC₃D₂O₁₄ structure and the lattice parameters were calculated as follows: a = 8.242 Å, c = 5.041 Å, V = 296.6 ų. The piezoelectric coefficient d₁₁ was 5.7pC/N, which was 2.47 times of α‐quartz (d₁₁=2.31pC/N). The electric resistivity was up to 3.04×10⁶ Ωcm at 700 °C for X‐cut sample. In addition, the transmission spectrum of the SNAGS crystal showed that it had a high transmittance (>80%) in the range of 350‐800 nm and exceeded 90% above 520 nm. These results suggest that the SNAGS crystals have potential applications in high‐temperature piezoelectric sensors and optical techniques. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Studies on the growth and defects of La3Ga5SiO14 (LGS) crystals

New and high quality piezoelectric crystals La₃Ga₅SiO₁₄ (LGS) grown by the Czochralski method in a Platinum or Iridium crucible are reported in this paper. The growth defects in the LGS crystals were investigated by Transmission electron microscopy (TEM). It was found that cracks, inclusions, grain boundary and thermal stress in the LGS crystals. Their formation mechanisms and the method of eliminating these defects are discussed. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of Gallium Orthophosphate Single Crystals under Hydrothermal Conditions

Gallium orthophosphate (GaPO₄) single crystals have been grown from phosphoric acid solutions under hydrothermal conditions. The crystals have been studied in terms of twinning because of the strong effect of this structural defect on the piezoelectric properties. The growth rates of individual faces have been compared to each other by considering the dipyramidal habit of the grown crystals.     

氧分压对化学气相沉积法合成ZnO纳米结构形貌的影响

本文利用化学气相沉积(CVD)法在镀有Au(10 nm)膜的单晶Si(100)上制备了ZnO薄膜,并研究了不同的氧分压对ZnO形貌的影响.借助扫描电镜(SEM)、X射线衍射仪(XRD)和透射电子显微镜(TEM)对样品的形貌、结晶质量和晶体生长取向进行了表征.结果表明:当O2分压较小的时候,O2只能与Zn团簇的某些界面发生反应并逐渐结晶生成层状的ZnO微米团簇.当 O2分压较大的时候,ZnO通过二次生长形成由微米柱阵列和表面无序纳米线构成的分层复合结构,并且表面纳米线的密度随着氧分压的增加而增加.高分辨透射电镜(HRTEM)和选取电子衍射(SAED)分析表明,单根纳米线是沿[001]方向生长的ZnO单晶.     

间硝基苯胺晶体的定向生长及光学性能研究

采用过冷熔体定向约束生长方法生长了尺寸约为30×15×8 mm3的块状间硝基苯胺晶体,并对生长晶体的光学均匀性、光学透过率、二次谐波转换效率以及激光损伤阈值等性能进行了测试.结果表明:生长的间硝基苯胺晶体在500～1150 nm波段内的光学透过率均在92;以上;最高二次谐波转换效率达到69.6;;单点激光脉冲损伤阈值分别为19.8 GW/cm2(输入光波为1064 nm)和45.3 GW/cm2(输入光波为532 nm).采用过冷熔体定向约束生长的间硝基苯胺晶体适合用作Nd: YAG激光的二次倍频器件,也适于作500～1150 nm波段的光学调制器件.     

金刚石单晶高温高压合成中氮对硫的影响

为了研究在金刚石大单晶生长过程中氮对硫的影响,在6.5 GPa高压条件下采用温度梯度法分别研究了两种不同合成体系中金刚石的合成.利用傅里叶显微红外光谱(FTIR)仪对所合成的金刚石进行了测试,测试结果表明:晶体中(a)中不含有氮,晶体中(b)中氮的浓度为280 ppm.此外,对所合成的样品进行了X射线光电子能谱测试,测试结果表明:在Ib型金刚石中有硫元素存在,而硫未进入到IIa型金刚石中.因此,金刚石中氮的存在对金刚石中硫的进入有促进作用.