Growth,thermal and optical properties of a new nonlinear optical crystal: ZnBi2B2O7

Single crystals of ZnBi₂B₂O₇ (ZBBO) have been successfully grown by the top-seeded growth method from a high-temperature melt. The crystal was colorless and transparent with size of 15×10×5 mm³. The orientation of ZBBO crystal has been discussed. The melting point, molar enthalpy of fusion, and molar entropy of fusion of the crystal were determined to be 964.02 K, 110680.36 J mol⁻¹, and 113.92 J K⁻¹ mol⁻¹, respectively. The transparency range of the crystal extends from 370 to 2100 nm.     

Floating-zone growth of large high-quality CoAl2O4 single crystals

We report the first successful floating-zone growth of high-quality CoAl₂O₄ single crystals with volume up to 1 cm³ free from inclusions and sub-grains. The neutron rocking curves of the CoAl₂O₄ crystal have the width of about 0.30 degree proving the excellent quality of the grown samples. X-ray synchrotron experiments show that crystals have spinel structure with the lattice constant a₀=8.09853(1) Å. Magnetization measurements give the effective magnetic moment μ_eff=4.63 μ_B per Co⁺² ion in a good agreement with previous measurements on ceramic samples.     

Float zone growth of Dy:GdVO4 single crystals for potential use in solid-state yellow lasers

Single crystals of dysprosium-doped gadolinium orthovanadate (Dy:GdVO₄) were successfully grown by the floating zone method and their fluorescence properties were investigated. The as-grown crystals did not contain any macroscopic defects such as cracks and inclusions for any Dy-concentration of up to 4 at%. Every crystal showed optical homogeneity under observation with a polarizing microscope; that is, no low-angle grain boundaries and growth striations were detected. In the visible region, two distinct fluorescence bands were observed around 480 and 575 nm, corresponding to ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions, respectively. The excitation spectrum for the emission of 573 nm indicates the possibility to use a commercially available laser diode of 450 nm as a pumping source for solid-state yellow laser.     

An electron microscopy study of the crystal growth of schwertmannite needles through oriented aggregation of goethite nanocrystals

The formation of the iron oxyhydroxide schwertmannite has been monitored by time-resolved transmission electron microscopy (TEM) studies. Schwertmannite aggregates are found to form initially as spherical agglomerates of ferrihydrite crystallites, which then begin to grow characteristic needles on their surfaces. High-resolution images of the needles show that they are initially comprised of aligned goethite nanocrystals, which subsequently coarsen to form crystallographically coherent needles of goethite. Thus, needle formation on schwertmannite aggregates can be considered as the first stage in the phase transformation from schwertmannite to goethite. The results of this study suggest that schwertmannite is not a distinct mineral phase, but may be a mixture of ferrihydrite and poorly crystalline goethite with a distinctive morphology directed by the presence of surface-adsorbed sulfate anions.     

Floating zone growth and compositional inhomogeneity study of La0.75Y0.05Sr0.2MnO3 single crystals

Single crystals of La_0.75Y_0.05Sr_0.2 MnO₃ have been grown by the floating zone technique. The yttrium distribution in the radial and axial directions in the crystals was studied for different growth rates. The sample grown at high rate showed inhomogeneity in the yttrium content in the growth direction, while the sample grown at relatively low rate was homogeneous in the growth direction, but demonstrated compositional separation between the Y-poor central part and Y-enriched peripheral part in the perpendicular plane. The compositional separation led to magnetic inhomogeneity.     

Synthesis and characterization of single-crystalline PrCO3OH dodecahedral microrods and its thermal conversion to Pr6O11

Single-crystalline PrCO₃OH dodecahedral microrods with an orthorhombic structure have been successfully synthesized by the hydrothermal method used urea as the precipitator. Pr₆O₁₁ dodecahedral microrods have been obtained by thermal conversion of PrCO₃OH dodecahedral microrods at 600 °C in air for 6 h. The as-synthesized products were characterized by X-ray powder diffraction, field-emission scanning electron microscope, transmission electron microscopy, high-resolution transmission electron microscopy, selected-area electron diffraction, X-ray photoelectron spectra, fourier transform infrared spectroscopy and thermogravimetry–differential thermal analysis. The effect of the reaction parameters on the morphology of the product has been investigated. The dodecahedral microrods with larger size and better crystallinity can be obtained under the higher reaction temperature. The possible formation mechanism of PrCO₃OH microrods was discussed.     

Nucleation time-lag from nucleation and growth experiments in deeply undercooled glass-forming liquids

A new approach is proposed to explain the strong difference between the induction periods (nucleation time-lags) obtained from nucleation rate measurements and from crystal growth experiments for lithium silicate glasses; and their similar magnitude for a Na₂O · 2CaO · 3SiO₂ glass. For these two glass families, the time-lags for nucleation estimated from crystal growth kinetics were compared with those directly obtained from nucleation experiments. A theoretical analysis was performed employing analytical solutions of the Frenkel-Zeldovich equation. In such analysis, the frequently assumed condition of size-independence of the thermodynamic properties of the crystallites was used. Provided this assumption is correct, time-lag data obtained in the two above mentioned ways should coincide. Consequently the significant difference between the values of nucleation time-lag for lithium silicate glasses from nucleation and growth data gives a strong indirect evidence for the deviation of the properties of critical nuclei from the respective parameters characterizing the state of the newly evolving macrophase. For Na₂O · 2CaO · 3SiO₂ glass at intermediate stages of crystallization we show that the average composition of the growing crystals is close to that of the near-critical nuclei. The fact that the nucleation and growth rates of this soda-lime-silica glass refer to the same phase provides an explanation for the similarity of the induction periods estimated from nucleation and growth experiments.     

Crystal growth and characterization of two-leg spin ladder compounds: Sr14Cu24O41 and Sr2Ca12Cu24O41

Single crystals of Sr_14−xCa_xCu₂₄O₄₁ (x=0 and 12) are grown by the travelling solvent floating zone technique using an image furnace. The grown crystals are characterized for their single crystallinity by the X-ray and Neutron Laue method. The magnetic susceptibility measurements in Sr₁₄Cu₂₄O₄₁ show considerable anisotropy along the main crystallographic axes. Low-temperature specific heat measurement and DC susceptibility measurement in Ca-doped crystal showed antiferromagnetic ordering at 2.8 K at ambient pressure. High-pressure AC susceptibility measurement on Ca-doped crystal showed a sharp superconducting transition at 2 K under 40 kbars. T_c onset reached a maximum value of 9.9 K at 54 kbars. The bulk superconductivity of the sample is confirmed by the high-pressure AC calorimetry with T_c max=9.4 K and T_N=5 K at 56 kbars.     

Growth aspects of barium oxalate monohydrate single crystals in gel medium

Single crystals of barium oxalate monohydrate (BaC₂O₄.H₂O, BOM) were grown in pure form by controlled diffusion of Ba²⁺ using the gel technique at different temperatures. Starting from aqueous Ba²⁺ chloride (BaCl₂) and acetic acid (C₂H₂O₄) in gel, this method offers a low‐cost and an easiest alternative to other preparation methods for the production of barium oxalate bulky single crystals. The optimal conditions for the growth of BOM crystals in silica gel were found by investigating different growth parameters such as gel pH, gel aging and crystallization temperature. Irrespective of all such crystallization environments, growth rate of the crystals were initially less and then exhibited supersaturation effect leading to non‐linearity. Gel aging and temperature has profound effect on nucleation density that resulted less number of crystals of maximum size in the gel matrix. Perfect single crystals were grown on gels of higher pH. The macropore morphology and porosity was controlled by changing age of the gel. It has been found that temperature has a fabulous effect in controlling the nucleation density by altering the supersaturation conditions for the formation of critical nuclei. The entire growth kinetics informed that the grown crystals were derived by the one dimensional diffusion controlled process. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Misoriented domain formation in 6H-SiC single crystal

6H-SiC single crystals were grown by the physical vapor transport (PVT) technique. Misoriented domains (MDs) were observed in as-grown crystals. Raman spectra and X-ray diffraction indicated that the MDs are 4H polytype with either (1 0 1¯ 2) or (1 0 1¯ 6) growth plane. Formation probability of MDs increased continuously as the thermal insulator had been repeatedly used. Simulations based on heat transfer demonstrated that the changes of the temperature and the temperature axial gradient at the center of the growth front were responsible for the phenomenon. The formation mechanism was put forward in terms of atomic structure of various crystal planes.     

Reduction of grown-in dislocation density in Ge Czochralski-grown from the B2O3-partially-covered melt

Germanium (Ge) single crystals with an extremely low density of grown-in dislocations were grown by the Czochralski (CZ) technique with boron oxide (B₂O₃) liquid. Because attachment of particles floating on the melt surface to a growing Ge crystal leads to generation of dislocations during the growth, partial covering of the Ge melt surface with B₂O₃ liquid was attempted. Such attachment of particles was drastically suppressed or the particles were caught by the introduction of B₂O₃ liquid, and a particle-free Ge melt was realized in the central region of the melt surface. Ge single crystals were successfully grown from such melt, the grown-in dislocation density being 0–1×10³ cm⁻², which was remarkably lower than that in Ge crystals grown by a conventional CZ technique. The contaminations by B and O atoms of the grown crystal detected by SIMS analysis were very low. These Ge crystals have the potential for application to be applied as high-quality, dislocation-free substrates of GaAs solar cells for various usages including in space.     

The character of FeMn-1# powder catalyst and its influence on the synthesis of diamond

In this paper industrial diamond crystal was synthesized using FeMn-1# powder catalyst in China-type cubic high-pressure apparatus at 5.7 GPa and 1400–1600 °C. The growth feature of diamond in the graphite–FeMn-1# system was researched. Optical microscope observation showed that all the diamond crystals were light yellow octahedral with grain size of 0.3–0.5 mm. There are also plenty of bubbles in the crystals. By SEM, we can see that the surface of diamond is smooth and the crystal is intact. Mössbauer spectrum was used to detect the impurity in the diamonds.     

Properties of gallium- and aluminum-doped bulk ZnO obtained from single-crystals grown by liquid phase epitaxy

Bulk properties of gallium (Ga)- and aluminum (Al)-doped zinc oxide (ZnO) were studied using bulky single-crystalline thick films grown by liquid phase epitaxy (LPE). The highest possible dopant concentration was 1×10¹⁹ cm^–3 for LPE growth at around 800 °C. The electron concentration was nearly same to the Ga and Al concentrations. The donor binding energy decreased to nearly zero with an increase in dopant concentration, and electron mobility of the sample with relatively high dopant concentration (1×10¹⁹ cm^–3) was more than 60 cm² V^–1 s^–1 at room temperature. The LPE technique is a potential solution for the production of ZnO for optical applications because the well-defined excitonic luminescence could be seen from the LPE-grown-doped single-crystals.     

Initial transient in Zn-doped InSb grown in microgravity

Three Zn-doped InSb crystals were directionally solidified under microgravity conditions at the International Space Station (ISS) Alpha. The distribution of the Zn was measured using SIMS. A short diffusion-controlled transient, typical for systems with k >1 was demonstrated. Static pressure of ∼4000 N/m² was imposed on the melt, to prevent bubble formation and de-wetting. Still, partial de-wetting has occurred in one experiment, and apparently has disturbed the diffusive transport of Zn in the melt.     

Control of multi-zone resistive heater in low temperature gradient BGO Czochralski growth with a weighing feedback,based on the global dynamic heat transfer model

The global heat transfer in a crystallization setup has been optimized to develop a strategy of control over a three-zone heater in the BGO Czochralski process, in order to provide invariable thermal conditions near the solid–liquid interface in the stage of a constant-diameter crystal growth. The functional related to the exactness of the heat balance condition at the crystallization front, i.e., the Stefan problem, was chosen as the target function. The optimization yielded unexpected results. The temperature of the lower heater should be lowered, relative to that of the middle heater, with increasing crystal length, whereas the temperature of the upper heater is to be raised. These recommendations were incorporated into a dynamic model of the oxide Czochralski process with a weighing control and into the control loop of the temperature regulators of a crystallization setup. A comparison of results of the time-dependent simulation with the real growth process confirmed that the new control strategy minimizes the deviation of the solid–liquid interface from the prescribed one, significantly decreases variations of interface shape during the process, and enables growth of high-quality crystals.     

Numerical description for the recalescence of bulk-undercooled Cu70Ni30 alloy

Assuming thermal balance and solute conservation, a numerical model has been proposed to describe the recalescence behavior of bulk-undercooled Cu–Ni melts. Applying a finite-difference scheme, the transformed solid fraction upon recalescence is given as a function of the liquid temperature, while the average liquid concentration can be tracked by calculation of the liquid/solid (L/S) Gibbs energy difference, in combination with a dendrite growth model. Accordingly, a transition from non-equilibrium to equilibrium process has been described from the evolution of L/S Gibbs energy difference. Applying the present model, the experimentally observed maximum recalescence temperature can be well predicted.     

Crystallization behavior of (GeS2)0.1(Sb2S3)0.9 glass

The crystal growth kinetics of antimony trisulfide in (GeS₂)_0.1(Sb₂S₃)_0.9 glass has been studied by microscopy and DSC. The linear crystal growth kinetics has been confirmed in the temperature range 492 ? T ? 515 K (E_G = 405 ± 7 kJ mol⁻¹). The applicability of standard growth models has been assessed. From the crystal growth rate corrected for viscosity plotted as a function of undercooling it has been found that the most probable mechanism is interface controlled 2D nucleated growth. The non-isothermal DSC data, corresponding to the bulk sample, can be described by the Johnson-Mehl-Avrami equation.     

Growth and characterization of Nd:CLNGG crystal

The disordered laser crystal neodymium-doped calcium lithium niobium gallium garnet (Nd:CLNGG) was successfully grown by the Czochralski method. Its thermal properties, including the average linear thermal expansion coefficient, thermal diffusion coefficient, specific heat, and thermal conductivity were measured, and continuous-wave (CW) laser performance at 1.06 μm was demonstrated. The maximum power of 1.48 W was achieved with corresponding optical conversion efficiency of 12.4% and slope efficiency of 16.2%.     

Growth of large-sized Ce:Y3Al5O12 (Ce:YAG) scintillation crystal by the temperature gradient technique (TGT)

In this work, Ce:YAG crystal with the size of ?4 in was successfully grown by the TGT method. The optical and scintillation properties of as-grown Ce:YAG crystals were investigated. Three obvious absorption bands at 223, 340 and 460 nm and two weak color-center absorption bands at 296 and 370 nm are observed in as-grown Ce:YAG crystal. Fluorescence with an emission peak at 398 nm is observed due to the color centers, and absorption bands of the color centers can be eliminated by annealing in O₂ or H₂ atmosphere at 1673 K for 24 h. Yellow-green fluorescence centered at 530 nm is found when the crystal was excited at 460 nm and the 530 nm excitation spectrum shows two peaks at 340 and 460 nm. X-ray fluorescence spectrum of as-grown crystal shows three emission peaks at 300, 360 and 530 nm. An average light output of 1360 phe/MeV and a single exponential decay with the decay time constant of 62.97 ns are found in as-grown Ce:YAG crystal.     

Templated cocrystallization of cholesterol and phytosterols from microemulsions

A major cause of cardiovascular disease is high cholesterol (CH) levels in the blood, a potential solution to which is the intake of phytosterols (PS) known as CH-reducing agents. One mechanism proposed for PS activity is the mutual cocrystallization of CH and PS from dietary mixed micelles (DMM), a process that removes excess CH from the transporting micelles. In this study, microemulsions (MEs) were used both as a model system for cocrystallization mimicking DMM and as a possible alternative pathway, based on the competitive solubilization of CH and PS, to reduce solubilized CH transport levels from the ME. The effects of different CH/PS ratios, aqueous dilution, and lecithin-based MEs on sterol crystallization were studied. The precipitated crystals from the ME-loaded system with PS alone and from that loaded with 1:1 or 1:3 CH/PS mixtures were significantly influenced by ME microstructure and by dilution with aqueous phase (X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC) results). No new polymorphic structures were detected apart from the corresponding sterol hydrates. Mixed crystal morphology and the habit of the precipitated sterols were strongly affected by the CH/PS ratio and the structures of the diluted ME. As the amount of PS in the mixture increased or as the ME aqueous dilution proceeded, precipitated crystal shape became more needle-like. The mixed sterols seemed to be forming eutectic solids.