Analysis of 3He Crystal Images Using a Computer-Generated Wire-Frame

Facetted crystals of bcc ³He have been observed with optical techniques in magnetic fields up to 9 T. Two-dimensional projections of the 3D crystals are obtained with a CCD camera. To analyze the growth rate of the various facets an interactive computer program is developed, which allows the user to analyze pictures made of crystals showing facets that have the 110-, 100- or 112-orientation. The working principles of this program are described and a picture taken from a ³He single crystal is analyzed as an example.PACS numbers: 67.80 −s, 81.10 Aj     

First Observation of the Critical Size of Facets on 3He Crystals near 1 mK

We have been able to obtain the step free energies of the basic (110) and (100) facets on ³He crystals near 1 mK by using a new method in which the critical radius of facets is measured on slowly melting crystals. The critical radius is obtained by tracking optically the moment that the facet collapses. Our findings confirm that at such low temperatures the liquid–solid interface of ³He is indeed strongly coupled to the crystal lattice, as was suggested in our previous studies.     

Observations on Faceting of 3He Crystals at T=0.55 mK

We report on our recent observations on growing ³ He crystals in which altogether eleven different types of facets were found. The crystals were imaged with a novel low-temperature Fabry-Pérot interferometer. Intensity based analysis methods combined with a phase shift technique were used to identify the observed facets.     

Crystal morphology of ternary compound (Cr,Fe)5Si3 obtained by in situ chemical vapour deposition

Ternary compound crystals of (Cr, Fe)₅Si₃ were obtained on a quartz substrate by the in situ CVD process using in situ reaction of the stainless steel 410 powder, Si₂Cl₆ and hydrogen, and its crystal morphology was examined in some detail. Crystals with various interesting morphologies, such as spiral, conical, rose-like, seaweed-like, globefish-like, etc., were obtained. The most commonly observed growth habits of the crystals were spiral, conical and seaweed-like crystals.     

Morphology and Growth Kinetics of 3He Crystals Below 1 mK

The shapes as well as the growth and melting properties of bcc-³He single crystals have been investigated with a low temperature Fabry-Pérot interferometer. Eleven types of facets were clearly identified during slow crystal growth at the temperature of 0.55 mK, where the solid is in the antiferromagnetically ordered u2d2 phase. The growth rates of the individual facets have been measured and the results indicate significant growth anisotropy. The observed linear dependence of the growth velocity on the driving force shows that facets grow due to the presence of screw dislocations, while the step velocity is limited by the spin wave velocity due to the strong interaction of the moving step with magnons in the solid. The measured growth rates of the facets and the assumed growth mechanism gave us the unique opportunity to obtain the step free energies for ten different types of facets observed during a single growth sequence. The dependence of the free energy of the step on the step height is compared with predictions of the weak- and strong-coupling models. Our results suggest that ³He crystals have rather strong coupling of the liquid/solid interface to the crystal lattice and that the step-step interactions are of elastic origin.     

Growing high-quality Bi12SiO20 crystals of large diameter (85 mm)

Conditions that ensure reproducible growth of ??110??-oriented perfect Bi₁₂SiO₂₀ (BSO) crystals by the low-thermal-gradient Czochralski technique, whereby the entire crystallization front is occupied by the (110) crystal face, have been determined with the aid of numerical simulations. Using the established regime, BSO crystals have been obtained with a diameter of 85 mm, a length of 200 mm, and a mass of 10 kg. The density of dislocations in the crystals does not exceed 10 cm^?2, and the refractive index inhomogeneity is below 10^?3.     

Single-crystal K x (Zn y Ti8−y )O16 priderites: growth and characterization

Single crystals of K _x (Zn _y T_8–y O₁₆ priderites have been grown from a melt of K₂O-MoO₃ using the flux-zone technique. High-purity crystals > 10 mm in length were obtained, with no indication of twinning. Lattice parameters of a=1.0162(8) nm and c=0.2971(7) nm were obtained from X-ray diffraction measurements. Habit planes were identified from scanning electron microscope images. X-ray photoelectron spectroscopy confirmed the titanium oxidation state as +4. High-temperature complex impedance spectroscopy between 300 and 820 K was used to electrically characterize the crystals. This indicated that the materials had a low d.c. conductivity and a conductivity of 1.68×10^–3 S cm^–1 at 100 kHz.     

High-resolution electron microscopy of solution-grown crystals of poly (p-phenylene sulphide)

Crystals of poly (p-phenylene sulphide) were obtained from an-chloronaphthalene solution. The chain axis (the crystalc-axis) was usually normal to the support-film. For these crystals, high-resolution electron microscopic images were taken as the projection of the molecular chains on theab plane along the chain axis. Occasionally it was observed that crystals took different orientations on the support-film for undefined reasons. From such orientations, the high-resolution image of a crystal rotated by 28.7° around thea-axis from the usual orientation, was also obtained.     

Crystal growth of bulk and cored fibre of 4-(N,N-dimethylamino)-3-acetamidonitrobenzene (DAN)

Large crystals of 4-(N,N-dimethylamino)-3-acetamidonitrobenzene (DAN) were grown from solutions by lowering the temperature; and bulk and cored fibre DAN crystals were grown by the Bridgman-Stockbarger (BS) method. The growth conditions and factors which affect the crystal quality were investigated.     

Growth,first-principles simulations and near-infrared optical properties of rare earth (Nd3+, Er3+)-doped CeF3 crystals for laser applications

Nd³⁺:CeF₃ and Er³⁺:CeF₃ crystals with different doping concentrations were successfully grown by the Bridgman method. The physicochemical parameters, such as crystal structure and phonon vibration energy were obtained by XRD and Raman tests. The results show that rare earth (Nd³⁺ or Er³⁺) does not change the hexagonal phase structure of the crystal, and the doping of rare earth ions does not change the maximum phonon frequency. The measured results are 388 and 392 cm^??1, respectively, which are similar to CeF₃ single crystal and half of common oxide crystal. According to the first principle, the difference charge density of the two crystals can be intuitively obtained. The calculated band gap values of the two crystals are 2.91 and 4.37 eV, respectively, which are similar to the results of absorption spectrum measurement. The NIR luminescence performance of Nd³⁺:CeF₃ crystal was tested by 808 nm pump. When the doping concentration reached 2 at%, the emission intensity was the strongest at 1064 nm (⁴F_3/2→⁴I_11/2). The luminescence properties of Er³⁺:CeF₃ crystal at 1550 nm (⁴I_13/2→⁴I_15/2) were tested by 980 nm pump. The emission intensity keeps the highest when the doping concentration reaches 3 at%. The concentration quenching and the dipole-dipole interaction in crystals are studied using energy transfer theory, and the J-O strength parameters of crystals are calculated. The results show that Nd³⁺:CeF₃ and Er³⁺:CeF₃ crystals have excellent properties and excellent near-infrared luminescence performance, which has great potential in laser applications.

     

Structural,thermal, dielectric,nonlinear optical properties and DFT investigations of a novel material 2-(6-chloropyridin-3-yl)-N'-(2,3-dihydro-1,4-benzodioxin-6-ylmethylidene)acetohydrazide for optoelectronic applications

A new organic nonlinear optical (NLO) material 2-(6-chloropyridin-3-yl)-N'-(2,3-dihydro-1,4-benzodioxin-6-ylmethylidene)acetohydrazide (CDA) has been synthesized by reflux method. Single crystals were grown by slow evaporation technique and the crystal structure was elucidated by single crystal X-ray diffraction method. Density functional theory (DFT) calculations at B3LYP/6–31+?+?G(d, p) basis set was used to predict the molecular geometry and were carried out further to comprehend the electronic structure, vibrational spectra, natural bonding orbitals (NBO), frontier molecular orbitals (FMO) and molecular electrostatic potential (MEP). An optical transparency at the cut-off wavelength of 355 nm was determined by UV–Vis–NIR spectroscopy. Thermal behavior of CDA was studied by TGA/DTA analysis. The dielectric constant (ε), dielectric loss (tan δ) and AC conductivity as a function of frequency and temperature was studied. Second Harmonic Generation (SHG) efficiency of the CDA was determined using Kurtz and Perry powder technique and was 0.5 times greater than that of the KDP crystal. The third-order nonlinear optical properties were investigated in solution by Z-scan technique using a continuous wave (CW) DPSS laser at the wavelength of 532 nm. The title compound exhibited significant two-photon absorption (β?=?2.228?×?10–4 cm W^?1), nonlinear refraction (n₂?=?1.095?×?10–8 cm² W^?1) and optical limiting (OL threshold?=?2.511?×?103 W cm^?2) under the CW regime. The nonlinear optical parameters were calculated using time-dependent Hartree–Fock (TDHF) method. The overall obtained results suggested that the studied CDA molecule could be a potential NLO material for frequency generator, optical limiters and optical switching applications.

     

Crystal Structure of Rb[UO2(SO4)F]

Single crystal of Rb[UO₂(SO₄)F] (I) was studied by X-ray diffraction [rhombic system, space group Pca2 ₁, Z = 12, unit cell parameters: a = 25.393(3), b = 6.735(1), c = 11.496(3) Å]. The main structural units of crystals of I are [UO₂(SO₄)F]^- layers belonging to the crystallochemical group AT³M² (A = UO₂ ^{2 +}) of uranyl complexes and combined into three-dimensional framework by electrostatic interactions involving interlayer rubidium ions.     

Effects of packaging SrI2(Eu) scintillator crystals

Recent renewed emphasis placed on gamma-ray detectors for national security purposes has motivated researchers to identify and develop new scintillator materials capable of high energy resolution and growable to large sizes. We have discovered that SrI₂(Eu) has many desirable properties for gamma-ray detection and spectroscopy, including high light yield of ∼90,000 photons/MeV and excellent light yield proportionality. We have measured <2.7% FWHM at 662 keV with small detectors (<1 cm³) in direct contact with a photomultiplier tube, and ∼3% resolution at 662 keV is obtained for 1 in.³ crystals. Due to the hygroscopic nature of SrI₂(Eu), similar to NaI(Tl), proper packaging is required for field use. This work describes a systematic study performed to determine the key factors in the packaging process to optimize performance. These factors include proper polishing of the surface, the geometry of the crystal, reflector materials and windows. A technique based on use of a collimated ¹³⁷Cs source was developed to examine light collection uniformity. Employing this technique, we found that when the crystal is packaged properly, the variation in the pulse height at 662 keV from events near the bottom of the crystal compared to those near the top of the crystal could be reduced to <1%. This paper describes the design and engineering of our detector package in order to improve energy resolution of 1 in.³-scale SrI₂(Eu) crystals.     

Facetting and optical perfection in Czochralski grown garnets and ruby

Studies of ruby (Al₂O₃/Cr³⁺) and rare-earth aluminium garnet single crystals, in particular the mixed garnets formed between Y₃Al₅O₁₂ (YAG) and Dy₃Al₅O₁₂ (DyAG), have shown that the formation of facets on the solid/liquid interface, which give rise to a strained central core within the crystals, is dependent upon the shape of the solid/liquid interface. Development of the strained and facetted core can be prevented by modifying the growth conditions to produce a flat solid/liquid interface and as a result the optical perfection of the crystals is greatly improved. Certain crystals, e.g. DyAG, grow naturally with aflat interface, and in the present work this has been shown to be due to the optical absorption characteristics of this material. In other materials, e.g. YAG and ruby, the interface shape can be controlled by the rate at which the growing crystal is rotated. The changes in temperature gradient produced in a YAG melt by changes of crystal rotation rate have been measured, and their effect upon crystal perfection is described.     

Tetramethylammonium Neptunium(IV) Isothiocyanate [N(CH3)4]4[Np(NCS)8]

A new Np(IV) complex, [N(CH₃)₄]₄[Np(NCS)₈], was prepared. Its crystal structure was determined, and the absorption spectra in the IR and near IR ranges were measured. Crystal data: a = 27.280(6), b = 12.288(3), c = 13.493(3) Å, space group Pna2₁, Z = 4, V = 4523(2) A³, R = 0.044, wR(F ²) = 0.091. The crystal structure of the compound consists of [Np(NCS)₈]^{4 -} anions and N(CH₃)₄ ⁺ cations. The coordination polyhedron of the Np atom is a distorted tetragonal antiprism formed by the nitrogen atoms of eight NCS^- ions.     

Structural,optical, electrical properties of new hybrid organic–inorganic NLO single crystal: bis(1H-benzotriazole) hexaaqua-zinc bis(sulfate) tetrahydrate (BZS)

A new hybrid organic–inorganic nonlinear (NLO) single crystal, Bis(1H-benzotriazole) hexaaqua-zinc bis(sulfate) tetrahydrate (BZS), has been successfully synthesized and the single crystals were grown by slow evaporation solution growth technique (SESG) using Millipore water as a solvent. The structure of the BZS crystal was solved and refined by single-crystal X-ray diffraction and demonstrates that the grown crystals belong to a triclinic system with the space group P-1. The asymmetric part of the titled compound contains isolated organic cation (C₆H₆N₃)₂, metallic cation [Zn(H₂O)₆]²⁺, sulfate anion (SO₄)^2? and free H₂O molecules. The interplay between the wide number of intermolecular interaction such as O–H···O, N–H···O, C–H···O and π–π stacking interactions were discussed. The optical transmittance spectrum shows that the crystal is excellent transmittance in the entire Vis–NIR region with the cutoff wavelength at 345 nm. The presences of expected functional groups were identified by Fourier transform infrared spectroscopy. The dielectric measurements were carried out at different temperature in the frequency range 100 Hz–5MHz. Furthermore, the studies of its third-order NLO properties using a Z-scan technique demonstrate that the BZS crystal possesses a strong reverse saturable absorption (RSA) and the self-focusing (SF) nature with large second order hyperpolarizability (γ?=?6.24?×?10^?34 esu). All the results indicate that BZS crystal might be the potential candidate for the third-order NLO applications.     

Feasibility study on Czochralski (Cz) growth of 3-methoxy 4-hydroxy benzaldehyde (MHBA) single crystals for nonlinear optical applications

Reported large nonlinear optical coefficients such as d₂₂ = 23.8d₃₆^KDP, d₂₁ = 13.5d₃₆^KDP, d₂₃ = 29.1d₃₆^KDP, d₂₅ = 12.8d₃₆^KDP of 3-methoxy 4-hydroxy benzaldehyde (MHBA) attract research on its bulk crystal growth for device application. The X-ray rocking and X-ray topographic studies of Cz-grown organic monoclinic crystals invariably reveal closely aligned sub-crystals which made melt growth difficult. In this context, the single crystal growth of MHBA by Czochralski pulling technique has been successfully demonstrated for the first time in the literature. Comparison study of obtained X-ray powder diffraction data with the literature confirmed the monoclinic structure. High-resolution X-ray diffraction (HRXRD) study confirms the better crystalline perfection of the grown crystal in comparison to that of solution-grown crystals and revealed the optimization of the growth process along [211¯] direction. TG, DTA and optical transmission studies carried out on the grown crystal exhibit its thermal and optical properties for SHG application.     

The elimination of defects in Czochralski grown lithium niobate

A method is described for growing large LiNbO₃ single crystals from the melt, completely free of low-angle grain boundaries. This crystalline perfection was achieved by eliminating localized cellular structures, which were introduced by thermal supercooling due to faceted growth. These defects were distributed only near the developed (012)_h and (0 –1 –2)_h planes when the growth of these planes as facets could be reduced rapidly in the conical part of the boule. Low-angle grain boundaries along the z-axis and polygonization of dislocations were induced by the stresses around the cellular structure. Voids and a corrugated interface have also been observed as a cell-boundary groove trail. The observation of cellular structures indicated that their formation was strongly dependent on growth in the radial direction and the pulled rate. Furthermore, to eliminate these structures, it was found most effective to keep the crystal growth rate, G, at less than 10 mm h^–1.     

Effect of cobalt (Co<Superscript>2+</Superscript>) concentration on structural,optical, thermal and mechanical properties of potassium acid phthalate (KAP) crystals

Single crystals of pure and Co²⁺ (0.2, 0.4 and 0.6 mol%) doped KAP crystals were grown by low temperature slow evaporation method. The grown crystals were subjected to various characterization techniques such as X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), UV–visible spectroscopy and Second Harmonic Generation studies. The XRD profile confirms that Co²⁺ ions incorporated into the KAP crystal lattice. The existence of functional groups in the grown crystals have been studied by FTIR analysis. Optical transmission is decreased when doping Co²⁺ concentration increase. After melting point, no decomposition is found in the pure crystal. Vickers micro hardness studies revealed that the doped crystals possess very high hardness values. The dielectric constant, dielectric loss and thermal stability values have been measured as a function of frequency and temperature respectively for the doped crystals.     

具有高活性(001)晶面的TiO2纳米方块的制备及光催化性能

采用水热法制备了尺寸为70~100 nm, 具有高活性(001)晶面的锐钛矿相TiO₂纳米方块, 利用FE-SEM、TEM、XRD和UV-Vis DRS等手段对催化剂结构和光吸收性能进行分析, 同时考察了水热反应温度和溶液pH对TiO₂形貌和(001)晶面暴露率的影响。以酸性红染料为目标污染物, 对催化剂的光催化活性进行研究。实验结果表明, 合成TiO₂纳米方块的最佳条件为水热温度180℃、溶液pH=4~5。(001)晶面的光催化活性优于(101)晶面, 具有33%(001)晶面暴露率的TiO₂纳米方块的光催化活性是普通TiO₂的1.6倍。