Synthesis and single crystal X‐ray structure of the tetragonal tungsten bronze Pb0.91K1.72Li1.46Nb5O15

Crystals of Pb_0.91K_1.72Li_1.46Nb₅O₁₅, belonging to tetragonal tungsten bronze materials, were grown by the slow cooling technique, and characterized by means of single crystal X‐ray diffraction: the structure was solved in the P4bm tetragonal space group, with the following unit cell parameters: a = 12.548(5), c = 4.042(5) Å, V = 636.4(9) ų. The three‐dimensional framework can be described as a layered structure down crystallographic axis c, with arrays of NbO₆ octahedra, whose corner sharing makes up the formation of tunnels filled up by Li, Pb and K displaying complex cation‐oxygen coordinations. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Light‐induced self‐defocusing property in tetragonal tungsten bronze crystals

In open‐circuit boundary conditions, tetragonal tungsten bronze (CSBN75) crystals are settled on one of arms of Michelson's interferometer in such a way that even minor perturbation of the penetrated beam can be enlarged and observed through the Michelson's interferometer rings. The experimental results shows that CSBN75 (Δn < 0) are self‐defocusing photorefractive crystals. In this paper, qualitative and quantitative discussion on the light‐induced change in the index of refraction is given. The self‐defocusing character in CSBN75 suggests that it is possible to observe the dark spatial solitons with this crystal in further investigation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth of ZrW2O8 and its optical and mechanical characterization

ZrW₂O₈ is known for its isotropic negative thermal expansion over a wide of range of temperature from ?272 to 777 °C. However, ZrW₂O₈ melts incongruently at 1257 °C and is stable only over a short temperature interval between 1105 and 1257 °C. This makes the growth of single crystals a formidable challenge. In order to study the intrinsic properties of this compound, a repeatable, viable single crystal growth strategy is required. Here we report a simple, self-seeding, self-fluxing single crystal growth process which resulted in single crystals of ZrW₂O₈ up to about 4 mm in size. Grown crystals were characterized by X-ray diffraction (XRD), Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. Mechanical properties of the crystals were studied using nanoindentation.     

K2.6Nb11.6O30: a novel tetragonal bronze structure

K_2.6Nb_11.6O₃₀, Mr = 1659.33 g mol^–1, crystallizes in the tetragonal system, space group P4/mbm, Z = 1. The lattice parameters are a = 12.549(3) Å, c = 3.978(2) Å, V = 626.4(4) ų, D _x _{x} = 4.398 g cm^–3. The crystal structure was solved and refined from 413 independent reflections, obtained by X-ray diffraction on a single crystal. The final R index and weighted R _w index are 0.0500 and 0.1178, respectively. The three-dimensional network of K_2.6Nb_11.6O₃₀ is similar to that of tetragonal tungsten bronze with K and Nb partially occupying the interstitial pentagonal and trigonal sites. The most interest of this structure is the planar pentagonal coordination of Nb atoms.     

Ba2TiSi2O8晶体的生长及包裹物缺陷分析

采用提拉法生长了Ba2TiSi2O8 (BST)晶体,并采用SEM和EDS等手段对晶体内部包裹物缺陷进行了分析.发现多晶原料中的Na,K,C1杂质元素的存在是导致晶体内部产生包裹物缺陷的主要诱因,采用低的生长速率和较快的晶体转速有利于获得高质量BTS单晶.另外,本论文还对晶体的硬度和透过光谱进行了测试与分析.     

Low-temperature growth of tetragonal tungsten nanowire arrays on tungsten substrate using Ni solid catalysts

Tetragonal tungsten nanowire arrays were successfully fabricated on tungsten substrate using Ni catalysts by chemical vapor deposition (CVD) at 950 °C. The synthesized tungsten nanowires grew along [100] direction, with a high aspect ratio more than 50 and sharp tips. The Ni catalyst was found to be located at the wire's bottom and assisted the nucleation of the tungsten nanowire. Samples were characterized in detail by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) technologies. Based on the analysis of the experimental results, the possible formation mechanism of nanowires was proposed as well.     

Crystal growth and characterization of Rb0.3K0.7TiOPO4

Single crystal growth and characterization of Rb_0.3K_0.7TiOPO₄ are reported. After improving the technological procedures of crystal growth, high-quality large single crystals were obtained. The refractive indices, pyroelectric coefficient, dielectric, piezoelectric, elastic, thermoelastic and elastooptic constants, SHG efficiency and damage threshold were measured.     

Ba3(VO4)2晶体的生长和拉曼性质的研究

采用提拉法生长了尺寸为φ22mm×50 mm的Ba3(VO4):晶体.室温下测试了Ba3(VO4)2晶体不同激发配置下自发拉曼散射光谱.另外测试了该晶体在532 nm、25 ps脉冲下的受激拉曼散射,观察到3阶斯托克斯线(625.5 am)和1阶反斯托克斯线(506.8 nm),并估算了Ba3(VO4)2晶体的稳态拉曼增益系数.     

Crystal structure and resistivity characteristics of new tantalum bronze K6Ta6.5O15 + x F6 + y

The structure of K₆Ta_6.5O_{15 + x} F_{6 + y} (I) with partly reduced tantalum has been determined by the methods of X-ray diffraction analysis (SYNTEX P1 diffractometer, λMoK _α radiation, 808 independent reflections): sp. gr. P 6/m, a = 13.118(4), c = 3.862(1) Å, R _F = 0.0292. The resistivity of metal-like crystals I is almost independent of temperature in the temperature range T = 4–300 K. The physical properties studied allow one to relate the crystals to the group of tantalum bronzes. The structure of compound I is compared with that of the well-known crystals of the transparent dielectric K₆Ta_6.5O_14.5F_9.5 (Ia) containing only pentavalent tantalum not belonging to the group of bronzes. The I and Ia structures have the same basic frameworks but different distributions of additional Ta atoms located along the channel axes and different degrees of delocalization as well as the numbers and degrees of delocalization of the surrounding anions. The relation between these structural features and the resistivity characteristics of the two compounds is also discussed.     

新型钨青铜型晶体Ca0.28Ba0.72Nb2O6的生长研究

研究了Ca0.28Ba0.72Nb2O6 (CBN-28)多晶料的制备和单晶的生长,用提拉法成功生长出CBN-28单晶.从X射线粉末衍射数据计算了CBN-28晶体的晶胞参数,并对其粉末衍射图各衍射峰进行了指标化.CBN晶体属四方晶系4mm点群.晶胞参数为a=1.2432(±2)nm,c=0.3957(±1)nm.采用浮力法测得其平均密度为5.372g/cm3,测得其莫式硬度为7,并通过测量CBN-28的介电性质,确定其居里点为260℃.     

Electrical Conductivity and Thermal Dehydration Studies of Mixed Single Crystals of BaCu(C2O4)2 · 6 H2O,Ba1–xCuxC2O4 · 4 H2O and Ba1–2x(NH4)2xC2O4 · 4 H2O

The measurement of electrical conductivity for the investigation of the number of water molecules present in the mixed crystals of barium copper oxalate and barium ammonium oxalate lattice have been carried out in the temperature range 30 to 450 °C. The dehydration temperature and the number of water molecules removed out of the structure at a particular temperature is estimated from the sharp increase in conductivity at these points. The almost steep increase of conductivity is attributed to the increase in the number of mobile charge carriers H⁺ and OH^– ions generated from the escaping water molecules. The study of electrical conductivity in association with the thermal behaviour has been used to understand the mechanism of conduction.     

Cao.28Ba0.72Nb2O6单晶的光学常数及吸收特性

山大晶体所采用提拉法生长出新晶体铌酸钙钡.本文通过分光光度计和椭偏光谱仪分别测得室温下铌酸钙钡的透射率和折射率随波长的变化关系.透射率光谱显示该晶体在波长大于380nm的可见光谱区是透明的.色散关系表明此材料的双折射较大,在短波区域寻常光及非常光的折射率之差约为0.12.此外,由透射率曲线计算了可见光范围内铌酸钙钡的吸收系数.从而得到吸收系数的平方根与光子能量的函数关系曲线.通过对该曲线的研究,发现铌酸钙钡晶体吸收边以下对应的跃迁为间接跃迁,计算出间接跃迁的禁带宽度Eg以及声子能量Ep.     

On the Crystal Structure of Tribarium Gallate (Ba3Ga2O6)

Single crystals of tribarium gallate (Ba₃Ga₂O₆) have been synthesized from a melt with composition 70 mol.% BaO and 30 mol.% Ga₂O₃ in the temperature range between 1200 °C and 1400 °C. The compound adopts space group Pa with a = 16.746(9) Å and Z = 24 formula units per unit cell. The refinement of the atomic parameters resulted in a residual of R1 = 0.040 (wR2 = 0.102) for 1157 observed reflections (I>2 σ (I)). Ba₃Ga₂O₆ belongs to the group of cyclo‐gallates and is closely related to K₄SrGe₃O₉. Main building element are isolated, highly puckered, twelve‐membered rings build by [GaO₄]‐tetrahedra. Charge balance is achieved by incorporation of Ba ions in the voids between the rings. The coordination number of the alkaline earth atoms is six, eight and nine, respectively.     

Point defects in barium-sodium niobate (Ba2NaNb5O15) crystals

The paper deals with studies of the nature and the kinetics of point defect formation and dissociation in barium-sodium niobate single crystals as a result of vacuum heat treatement and ionizing Co⁶⁰ γ-radiation.     

Crystal growth and dislocation arrangement of Czochralski alexandrite (BeAl2O4:Cr) single crystals

The [001] oriented alexandrite (BeAl₂O₄:Cr) single crystals have been grown by the Czochralski pulling technique. The X-ray topographic investigation indicates that the grown-in dislocations mainly originate from the seed and propagate along the path normal or nearly perpendicular to the growth interface. The dislocation density and arrangement is closely related to the quality of the seed crystal.     

Crystal Growth and Basic Characterisation of the Bismuth Borate Bi2B8O15

Top‐seeded growth of Bi₂B₈O₁₅ from a stoichiometric melt is reported. Crystals have been grown with dimensions of up to 24 × 12 × 5 mm³ . Bi₂B₈O₁₅ shows twin domains at room temperature; their origin was investigated by methods of thermal analysis. The domains were found to result from a sluggish phase transition that occurs in a broad temperature range (ΔT ≈ 20 K) around ∼390 K. Unit cell parameters at room temperature were determined: a = 4.3140(6) Å, b = 22.148(2) Å, c = 6.4695(6) Å, β = 105.46(1)° , possible space group P2₁ (no.4), the non‐centrosymmetry was proved using powder SHG.     

大尺寸MgAl2O4晶体的提拉法生长研究

铝酸镁(MgAl2O4)晶体的性能优良,具有高熔点、高硬度、高强度,在紫外、红外、可见光波段具有良好的透过性,广泛应用于军事、科研、新材料等领域.本文详细介绍了采用下称重,CZ法(Czochralski)生长大尺寸(φ58mm)MgAl2O4单晶的工艺条件,并对影响晶体质量的主要因素进行了分析,讨论,给出了解决晶体质量问题的手段和有效途径.     

Crystal growth and characterization of PbI2‐AgI binary system

The crystals of the binary system PbI₂‐AgI (PIAI) were obtained by heating the mixture of individual PbI₂ (PI) and AgI (AI) placed at 30° angle in the horizontal tubular furnace of variable temperature zone. The crystals were characterized by powder XRD, TG/DTA, FT‐IR and SEM. The 3.37% weight loss in the sample after heating at 853 K is due to the presence of water molecules absorbed (3446 cm^–1) by the crystals during sintering and cooling process. The cell parameters of the crystal were determined using the powder X‐ray data. The PbI₂‐AgI crystallizes in monoclinic system a = 10.799 (±0.009), b = 7.492 (±0.004), c = 6.929(±0.004) Å and α = 90°, β = 108.04(±0.073) γ = 90°, V = 533.18 ų. The electrical conductivity measurements of the crystals showed a sudden change in the current value at the temperature range 385–393 K. The activation energy before and after the drift was found to be 0.49 and 0.35 eV respectively. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrooptical coefficients and temperature and pressure derivatives of the elastic constants of tetragonal Li2B4O7

New values for the following properties of tetragonal Li₂B₄O₇ are reported: dielectric, electrostrictive, electrooptic, elastic, thermoelastic and piezoelastic constants, coefficients of thermal expansion and indices of refraction. These values are considered to be of superior precision compared to earlier published data. Most elastic constants possess positive temperature derivatives. This anomalous behaviour is not reflected in the pressure derivatives. The electrooptic effects are not large enough to compete with other materials used for technical applications.