Bulk single-crystal growth of ternary AlxGa1−xN from solution in gallium under high pressure

We have successfully grown bulk, single crystals of Al_xGa_1−xN with the Al content x ranging from 0.5 to 0.9. Samples were grown from Ga melt under high nitrogen pressure (up to 10 kbar) and at high temperature (up to 1800 °C) using a gas pressure system. The homogeneity and Al content of the crystals were investigated by X-ray diffraction and laser ablation mass spectrometry. On the basis of the high-pressure experiments, the corresponding pressure–temperature (p–T) phase diagram of Al–Ga–N was derived. The bandgap of the material was determined by the femtosecond two-photon absorption autocorrelation method and is equal to 5.81±0.01 eV for the Al_0.86Ga_0.14N crystals.     

Self-assembly of highly crystalline spherical BiVO4 in aqueous solutions

Spherical bismuth vanadate particles are self-assembled from aqueous Bi(NO₃)₃ and NH₄VO₃ solutions by adjusting pH and tuning the amount of surfactant sodium dodecyl sulfate (SDS) via facile hydrothermal method. The BiVO₄ samples were characterized by X-ray diffraction (XRD) and the peaks suited well with the pure phase monoclinic scheelite BiVO₄. Field emission scanning electron microscopy (SEM) showed the average size of the spherical particles was 5 μm and the assembling stages in the hydrothermal synthesis process were recorded. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) revealed the nanoparticles were single crystal. FT-IR spectroscopy test results demonstrated there was no SDS left in the samples. The mechanism of the self-assembling has also been proposed.     

Study on the growth and interfacial strain of CoFe2O4/BaTiO3 bilayer films

CoFe₂O₄/BaTiO₃ bilayer films were epitaxially deposited on SrTiO₃ substrates by laser molecular beam epitaxy (LMBE). The growth process of the bilayer films was in-situ monitored by reflection high-energy electron diffraction (RHEED). Sixty nanometer thick-BTO layer was firstly fabricated in a layer-by-layer growth mode with an atomic smooth surface. CFO films with a varying thickness ranging from 5 to 60 nm were subsequently deposited on BTO-coated STO substrates. The different growth behaviors of CFO films were observed due to the lattice mismatch strain. Between two short stages of the growth mode transforming, a long duration with Stransky and Krastonov growth mode was maintained. Strainfully relaxed CFO film in the island growth mode was finally formed. High-resolution X-ray diffraction (HRXRD) was used to further analyze the strain effect. It was found that the tensile stress imposed on BTO by CFO was strengthened with increasing the thickness of CFO films, which could lessen the distortion of BTO by counteracting the compressive stress caused by STO substrates. The strengthened tensile stress weakened the ferroelectric property of BTO films by reducing structural tetragonality, which was demonstrated by polarization-electric (P-E) measurement.     

Growth and characterization of KY(WO4)2 crystals

Single-crystal growth of KY(WO₄)₂ (KYW) by top-seeded solution growth technique has been investigated. The effects of seed orientation, temperature gradient experienced by the growing crystal and rate of crystallization on crystal quality are reported. The best results are obtained when the growth is seeded along the 0 1 0 direction. Minute deviations from this growth direction are found to be detrimental to crystal perfection. The differential thermal analysis shows that the amount of super-cooling required for dissolution and crystallization of KYW in the flux is only 5° and this promotes an easy formation of tiny crystallites in the solution. Consequently, the crystal rotation and the solution cooling rates are found to have pronounced effects on the growth of KYW crystal.     

Crystal growth and characterization of K2B4O11H8

Single crystals of K₂B₄O₁₁H₈, a non-centrosymmetric borate material, have been prepared by slow evaporation of water solution at room temperature. The crystals were colorless and transparent with smooth faces. The single-crystal X-ray diffraction analysis showed that K₂B₄O₁₁H₈ crystallized in the orthorhombic space group P2₁2₁2₁ with a=6.8556(6) Å, b=11.7787(12) Å, c=12.8949(14) Å, Z=4, R₁=0.0188, and wR₂=0.0464. The powder X-ray diffractometry (PXRD), infrared spectrum, transmittance spectrum, TG–DTA curves and second harmonic generation properties of title compound have been determined.     

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.     

Phase and morphology controllable synthesis of Sb2O3 microcrystals

A simple and facile solution route has been developed for phase and morphology controllable synthesis of antimony trioxide (Sb₂O₃) microcrystals. Orthorhombic phase and cubic phase Sb₂O₃ microcrystals have been selectively synthesized in high yield. The products were characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The as-obtained microcrystals exhibited a variety of morphologies and structures, such as microspindles, nanoplates, and octahedra. Several experimental parameters have been investigated to gain morphology control of Sb₂O₃ microcrystals. Based on the time-dependent experimental results, an aggregation, and recrystallization mechanism was proposed to describe the formation process of these novel microstructures.     

Synthesis and ammonia sensing property of Ag3CuS2 nanocages obtained from Cu7S4 18-facet hollow nanopolyhedra

Ag₃CuS₂ nanocages were successfully fabricated for the first time via a convenient ion-exchange route by Ag⁺ reacting with Cu₇S₄ 18-facet hollow nanopolyhedra. The average size and shell thickness of Ag₃CuS₂ nanocages were around 400 and 30 nm, respectively. Room-temperature response of Ag₃CuS₂ nanocages to ammonia was investigated by photoluminescence-type sensor. Sensing results suggested that these hollow-structured Ag₃CuS₂ exhibited better performances including higher sensitivity, shorter response and recovery time than their rod-shape counterparts. A possible hole trapping mechanism was proposed.     

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.     

Glasses and glass-ceramics in the oxyfluoride ternary system Pb(PO3)2-WO3-PbF2

Glasses were prepared by the melt-quenching method in the ternary system Pb(PO₃)₂-WO₃-PbF₂ and doped with Er³⁺ in order to prepare luminescent transparent glass-ceramics. This work focused on thermal and structural characterization of tungsten lead-phosphate glasses and crystallization study for preparing transparent glass-ceramics. Thermal properties such as thermal stability and crystallization behavior upon heating were investigated by DSC in function of PbF₂ content. For low PbF₂ concentrations, only one crystallization peak due to Pb₃(PO₄)₂ is observed whereas samples containing more than 15% of PbF₂ present another exothermic event at lower temperatures related with precipitation of PbF₂, Pb₂P₂O₇ and Pb₂OF₂. Structural investigations by Raman spectroscopy suggest that PbF₂ modifies the tungsten-phosphate network through the formation of P―F and P―O―Pb bonds but the average network connectivity remains almost constant. A crystallization study has been performed by DSC to investigate the dominant crystallization mechanisms in these glasses and it has been established that Pb₃(PO₄)₂ is nucleated on the surface whereas PbF₂, Pb₂P₂O₇ and Pb₂OF₂ crystallize dominantly from the glassy bulk. Transparent glass-ceramics containing nanosized PbF₂ crystallites were also prepared by suitable heat-treatment on the glass sample containing 20% of PbF₂ and Raman microscopy of these glass-ceramics supports the crystallization mechanisms determined by DSC.     

Physical properties of self-flux and WO3-containing solutions useful for growing type III KGd(PO3)4 single crystals

Density, surface tension and dynamic viscosity of self-flux and WO₃-containing solutions useful for growing type III KGd(PO₃)₄ single crystals have been measured at temperature near the saturation temperature. The thermal behavior of these physical properties has also been studied. Solutions containing WO₃ show a higher density than self-flux solutions and the density decreases linearly when the temperature increases, in the two cases. Near the saturation temperature, self-flux solutions present a surface tension slightly lower than that of WO₃-containing solutions. The dynamic viscosity of WO₃-containing solutions is slightly lower than that of self-flux solutions when this property was measured at the same temperature. We observed that, in WO₃-containing solutions, the saturation temperature is lower than in self-flux solutions. Thus, at the growth temperatures, the two solutions present dynamic viscosities only slightly different, so we expect that the introduction of WO₃ up to 10 mol% in the growth solution does not represent any important improvement in its hydrodynamics and this small change does not compensate for the possibility of introduction of tungsten impurities in the crystal structure affecting the physical properties expected for these crystals. Taking into account the values measured for these physical properties, we choose the initial conditions for growing type III KGd(PO₃)₄ single crystals from self-flux solutions.     

Synthesis,characterization and growing mechanism of monodisperse Fe3O4 microspheres

Monodisperse Fe₃O₄ microspheres assembled by a number of nanosize tetrahedron subunits have been selectively synthesized through the hydrothermal process. The synthesized Fe₃O₄ microspheres have good dispersibility. The subunits made up of microspheres were uniform in size and like-tetrahedron in shape. The average diameter of each Fe₃O₄ microsphere is about 50–55 μm. The length of each edge of tetrahedron is about 100 nm. A series of experiments had been carried out to investigate the effect of reductant, precipitator and reaction time on the formation of Fe₃O₄ microsphere and tetrahedron subunits. The results show that ascorbic acid as reductant and urea as precipitator supplied a relatively steady environment during the synthesis process and led to the formations of Fe₃O₄ tetrahedron subunit and monodisperse Fe₃O₄ microspheres. As the reaction time increased from 3 to 24 h, the Fe₃O₄ microspheres tended towards dispersion and becoming large in size from 10–20 to 50–55 μm, and the subunits formed Fe₃O₄ microspheres that varied from spheroid to tetrahedron and from a small nanoparticle (20–30 nm) to a large one (90–110 nm). A reasonable explanation for the formations of the Fe₃O₄ microsphere and the tetrahedron subunit was proposed through Ostwald ripening and the attachment growth mechanism, respectively.     

Structure and dynamics of liquid Al1−xSix alloys by ab initio molecular dynamics simulations

First-principles molecular dynamics (MD) simulations are performed to study the structure and dynamics of liquid Al_1−xSi_x (x = 0.0, 0.12, 0.2, 0.4, 0.6, 0.8) at the temperature of 1573 K. The composition dependence of static structure factors, pair correlation functions, and diffusion constants are investigated. We found that the structure of the liquid Al_1−xSi_x alloys is strongly dependent on the composition. From our simulation and analysis, we can see that although liquid Al_1−xSi_x is metallic, there are some degrees of covalent tetrahedral short-range order in the liquid. The degree of tetrahedral short-range order increases linearly as the Si concentration in the liquid increased. The diffusion coefficients of both Al and Si atoms in liquid Al_1−xSi_x alloys at 1573 K are not very sensitive to the composition.     

Compositional analysis of a polymer-induced liquid-precursor (PILP) amorphous CaCO3 phase

Amorphous calcium carbonate (ACC) has been of keen interest in the biomimetics field because of recent evidence which suggests it plays an important role in biomineralization. In this report, an in vitro model system is used to examine the composition of an amorphous phase generated by polyanionic process-directing agents, such as the sodium salt of polyaspartic acid (Pasp), which is considered a simple mimic to the proteins associated with calcific biominerals. This additive leads to the formation of a highly hydrated, amorphous mineral precursor to calcium carbonate (CaCO₃), referred to as a polymer-induced liquid-precursor (PILP) phase. The precursor phase was collected by centrifugation, and the quantity of precursor phase and the water content were determined. It was found that Pasp promotes and stabilizes the amorphous precursor, which has a composition that steadily changes with time as the polymer and water are excluded. Elemental analysis was used to investigate the role of the polymer in influencing the calcium/carbonate ratio, the water content, and the amount of precursor phase. Raman and ATR-FTIR spectroscopy were used to compare the compositions of the precursor phases generated with different polymeric concentrations. The role of Pasp in generating and stabilizing the ACC precursor phase is discussed.     

Compositional dependence of the optical properties of amorphous Sb2Se3−xSx thin films

Thin films of Sb₂Se_3−xS_x solid solutions (x = 0, 1, 2, and 3) were deposited by thermal evaporation of presynthesized materials on glass substrates held at room temperature. The films compositions were confirmed by using energy dispersive analysis of X-rays (EDAX). X-ray diffraction studies revealed that all the as-deposited films as well as those annealed at T_a < 423 K have amorphous phase. The optical constants (n, k) and the thickness (t) of the films were determined from optical transmittance data, in the spectral range 500-2500 nm, using the Swanepoel method. The dispersion parameters were determined from the analysis of the refractive index. An analysis of the optical absorption spectra revealed an Urbach’s tail in the low absorption region, while in the high absorption region an indirect band gap characterizes the films with different compositions. It was found that the optical band gap energy increases quadratically as the S content increases.     

Growth, refined structural and spectroscopic characteristics of Tm-doped NaGd(WO4)2 single crystals

The details of Tm³⁺-doped NaGd(WO₄)₂ single-crystal growth are discussed, the results of precise investigations of its structural and spectroscopic characteristics, as well as the analysis of cross-relaxation process of Tm³⁺ ions (³H₄→³F₄, ³H₆→³F₄) in this crystal are presented. Based on the Judd–Ofelt theory, three intensity parameters, spontaneous emission probabilities, fluorescence branching ratios and fluorescence quantum efficiency from ³H₄ and ³F₄ levels were refined.     

Growth of NaBi(WO4)2 crystal by modified-Bridgman method

NaBi(WO₄)₂ (NBW) crystals have been grown for the first time by modified-Bridgman method. Influences of some factors on the crystal growth process are discussed. X-ray powder diffraction experiments show that the unit cell parameters of NBW crystal are a=b=0.5284 nm, c=1.1517 nm, and V=0.3215 nm³. The differential thermal analysis shows that the NBW crystal melts at 923°C.     

Sodium tracer diffusion in glasses of the type (CaO·Al2O3)x(2 SiO2)1−x

Tracer diffusion coefficients of the radioactive isotope Na-22 were measured in glasses of the type (CaO·Al₂O₃)_x(2 SiO₂)_1−x to study the diffusion of sodium as a function of glass composition, x, temperature and initial water content. The diffusion of Na-22 in glasses diffusion-annealed in dry air can always be well described by a single tracer diffusion coefficient, but sometimes not in samples annealed in common air. It was found that the sodium tracer diffusion coefficient decreases by about six orders of magnitude when the glass composition x changes from 0 to 0.75 at 800 °C. The temperature dependence of the diffusion of sodium seems to decrease as the silica content increases. Variations of the initial water content in some of the glasses investigated did not very significantly influence the rate of the tracer diffusion of sodium.     

Preparation of Sb2S3 nanomaterials with different morphologies via a refluxing approach

Single-crystalline antimony trisulfide (Sb₂S₃) nanomaterials with flower-like and rod-like morphologies were successfully synthesized under refluxing conditions by the reaction of antimony trichloride (SbCl₃) and thiourea with PEG400 and OP-10 as the surfactants. X-ray diffraction (XRD) indicates that the obtained sample is orthorhombic-phase Sb₂S₃ with calculated lattice parameters a=1.124 nm, b=1.134 nm and c=0.382 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that the flower-like Sb₂S₃ is 9–10 μm in size, which is composed of thin leaves with thickness of 0.05–0.2 μm, width of 0.8–2.2 μm and length of 2.5–3 μm, and the rod-like Sb₂S₃ is 45–360 nm in diameter and 0.7–4 μm in length, respectively. UV–Vis analysis indicates that the band gap of Sb₂S₃ nanorods is 1.52 eV, suitable for photovoltaic conversion. A possible mechanism of formation was proposed. The effects of reaction time and surfactants on the growth of nanomaterials with different morphologies were also investigated.     

NaBi（WO4）2晶体生长工艺研究

采用提拉法(Cz法)生长了45×40mm大尺寸钨酸铋钠(NaBi(WO4)2,简称NBW)晶体,探讨了工艺参数和晶体开裂间的关系,并根据Brice模型,讨论了晶体中的热应力、热应变和晶体尺寸、温度梯度、提拉速度、晶体转速之间的关系,设计了生长NBW的最佳工艺条件液面上下10mm内温差为0.8℃/mm,拉速2～4mm/h,转速12～18r/min,冷却速率25℃/h.