High-Resolution X-ray Study of the Smectic A-Smectic B Phase Transition and the Smectic B Phase in Butyloxybenzylidene Octylaniline

We have carried out a high resolution X-ray study of the smectic phases of Butyloxybenzylidene Octylaniline. We find that the phase previously identified as Smectic-B in this material is crystalline with in-plane order extending over at least 1.4 μm. The in-plane Bragg peaks are accompanied by anomalously strong diffuse scattering that can be described by a form 1/(q ²⊥ + γ² q ² _z). Unless the elastic constant C₄₄ is more than an order of magnitude smaller than previously reported values of ～ 10⁸ ergs/cm³ the diffuse scattering can not be due to acoustic phonons. The crystalline-B to Smectic-A melting transition is strongly first order with no observable pre-transition effects on either side of the transition.     

Surface growth mechanisms and structural faulting in the growth of large single and spherulitic titanosilicate ETS-4 crystals

Morphological, surface and crystallographic analyses of titanosilicate ETS-4 products, with diverse habits ranging from spherulitic particles composed of submicron crystallites to large single crystals, are presented. Pole figures revealed that crystal surfaces with a-, b- and c- axes corresponded to 110, 010 and 001 directions, respectively. Thus, technologically important 8-membered ring pores and titania chains in ETS-4 run along the b-axis of single crystals and terminate at the smallest crystal face. Height of the spiral growth steps observed on 1 0 0 and 0 0 1 surfaces corresponded to the interplanar spacings associated with their crystallographic orientation, and is equivalent to the thickness of building units that form the ETS-4 framework. Data suggest that the more viscous synthesis mixtures, with a large driving force for growth, increased the two- and three-dimensional nucleation, while limiting the transport of nutrients to the growth surface. These conditions increase the tendency for stacking fault formation on 1 0 0 surfaces and small angle branching, which eventually results in spherulitic growth. The growth of high quality ETS-4 single crystals (from less viscous synthesis mixtures) occurred at lower surface nucleation rates. Data suggest that these high quality, large crystals grew due to one-dimensional nucleation at spiral hillocks, and indicate that under these conditions un-faulted growth is preferred.     

不同晶体结构Gd2(MoO4)3:Eu3+荧光粉的合成及其发光性能研究

采用溶胶凝胶-燃烧法,柠檬酸为络合剂合成出系列Gd₂(MoO₄)₃:Eu³⁺荧光粉.利用X射线衍射(XRD)、扫描电子显微镜(SEM)和荧光光谱对样品的结构、形貌和发光性能进行了研究.XRD分析表明:稀土离子与柠檬酸为1:0.5时,800℃热处理获得单斜结构的Gd₂(MoO₄)₃:Eu³⁺荧光粉.单斜结构的Gd₂(MoO₄)₃:Eu³⁺荧光粉到正交结构的Gd₂(MoO₄)₃:Eu³⁺荧光粉的转换可以通过改变稀土离子与柠檬酸摩尔比和热处理温度等合成条件实现.Gd₂(MoO₄)₃:Eu³⁺荧光粉的形貌受合成条件的影响.荧光光谱研究表明:Gd₂(MoO₄)₃:Eu³⁺荧光粉的主发射峰位于616 nm处来自于Eu³⁺的⁵D₀→⁷F₂电偶极跃迁.正交结构的Gd₂(MoO₄)₃:Eu³⁺荧光粉发射强度明显高于单斜结构的荧光粉.计算⁵D₀→⁷F₂与⁵D₀→⁷F₁跃迁发射的相对强度比值表明:正交结构的Gd₂(MoO₄)₃:Eu³⁺中Eu³⁺局域环境的对称性较高。     

Morphology of β-BaB2O4 (BBO) Crystals in Relation to its Structure and Growth Conditions

β-BaB₂O₄ (BBO) crystals with well-defined morphology have been grown from Na₂O solutions using the top seeded solution growth (TSSG) method. The crystal morphology in relation to its structure and growth conditions has been studied in detail on the basis of crystallography and crystal chemistry. It is found that the morphological characteristics are related to the orientations of structural unit (B₃O₆)^3— anion rings in the crystal. On the other hand, the growth parameters may greatly affect the appearance of faces of the crystal, but the crystals still generally take trigonal in outline and have a diagnostic character of point group 3m. The observed morphology is in disagreement with BFDH and PBC analyses and is explained from the incorporation of the growth units on the faces and facets. Since the incorporation rates of the growth units are different on different faces, the boule habits with well-defined morphology are formed.     

Estimation of growth rate in unidirectionally solidified multicrystalline silicon by the growth-induced striation method

Multicrystalline silicon was grown by unidirectional solidification method using the accelerated crucible rotation technique. The application of the accelerated crucible rotation technique in unidirectional solidification method induced growth striations across the axial direction of the grown crystal. This striation pattern was observed from carbon concentration distribution, obtained by using Fourier transform infrared spectroscopy. The generated striation pattern was found to be weak and discontinuous. Some striations were absent, probably due to back melting, caused during each crucible rotation. From the growth striations and applied time period in crucible rotation, the growth rate was estimated by using Fourier transformation analysis.     

一族Nd:YxGd1-xVO4混晶性质比较及其调Q性能研究

Czoehralski法成功生长了一系列不同Cd／Y的低掺杂Nd：YxGd1-xVO4混晶，并对它们的一些基本性质进行了比较，发现随着Gd含量的增加，晶体晶胞a，c轴常数呈线性增长，故YVO4和GdVO4晶体可以实现无限互溶。少量Gd掺杂可使混晶晶体比热和荧光寿命增大，并有效地增强了其荧光强度。我们对该晶体的低功率泵浦下的Cr^4 ：YAG调Q激光性能也进行了研究，发现Nd：YxGd1-xVO4混晶具有良好调Q性能。     

Investigations on the effect of InSb and InAsSb step-graded buffer layers in InAs0.5Sb0.5 epilayers grown on GaAs (0 0 1)

We report the structural and electrical properties of InAsSb epilayers grown on GaAs (0 0 1) substrates with mid-alloy composition of 0.5. InSb buffer layer and InAs_xSb_1−x step-graded (SG) buffer layer have been used to relax lattice mismatch between the epilayer and substrate. A decrease in the full-width at half-maximum (FWHM) of the epilayer is observed with increasing the thickness of the InSb buffer layer. The surface morphology of the epilayer is found to change from 3D island growth to 2D growth and the electron mobility of the sample is increased from 5.2×10³ to 1.1×10⁴ cm²/V s by increasing the thickness of the SG layers. These results suggest that high crystalline quality and electron mobility of the InAs_0.5Sb_0.5 alloy can be achieved by the growth of thick SG InAsSb buffer layer accompanied with a thick InSb buffer layer. We have confirmed the improvement in the structural and electrical properties of the InAs_0.5Sb_0.5 epilayer by quantitative analysis of the epilayer having a 2.09 μm thick InSb buffer layer and 0.6 μm thickness of each SG layers.     

Epitaxial growth of the CoFe2O4 film on SrTiO3 and its characterization

Cobalt ferrite (CoFe₂O₄) thin film is epitaxially grown on (0 0 1) SrTiO₃ (STO) by laser molecular beam epitaxy (LMBE). The growth modes of CoFe₂O₄ (CFO) film are found to be sensitive to laser repetition, the transitions from layer-by-layer mode to Stranski–Krastanov (SK) mode and then to island mode occur at the laser repetition of 3 and 5 Hz at 700 °C, respectively. The X-ray diffraction (XRD) results show that the CFO film on (0 0 1) SrTiO₃ is compressively strained by the underlying substrate and exhibits high crystallinity with a full-width at half-maximum of 0.86°. Microstructural studies indicate that the as-deposited CFO film is c-oriented island structure with rough surface morphology and the magnetic measurements reveal that the compressive strained CoFe₂O₄ film exhibits an enhanced out-of-plane magnetization (190 emu/cm³) with a large coercivity (3.8 kOe).     

Crystal growth of the quasi-one dimensional spin-magnet LiCuVO4

The phase relationships in the Li–Cu–V–O and Li–Cu–V–O–Cl systems were investigated and the phase diagrams determined. Based on these diagrams single crystals of the low-dimensional spin compound LiCuVO₄ with maximal dimensions up to 12×3×3 mm³ were grown from a solution of LiCuVO₄ in a LiVO₃ or a LiVO₃–LiCl melt. The stoichiometry of the grown crystals is discussed.