Application of diffusion couple technique for the determination of the Ti‐Bi‐Sn phase diagram

The system Ti‐Bi‐Sn has been investigated by solid/liquid diffusion couples at 500, 600, 700 and 800°C. A non‐negligible solubility of Sn into solid Bi is found. Diffusion layers of the recently revealed ternary compound Ti₃BiSn have been observed, thus its existence has been confirmed. Data about the homogeneity ranges of the binary end‐system compounds have been obtained. The assessed growth constants of the diffusion layers are comprised in the interval 10^‐12 –10^‐14 m².s^‐1. The phases participating in the hypothetical ternary eutectic reaction, probably are: (Bi), (Sn), Liquid and Ti₂Sn₃. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Diffusion couple studies of the Ti‐Bi‐Zn system

The system Ti‐Bi‐Zn has been investigated using diffusion couples consisting of solid Ti and liquid (Bi+Zn) phase. The diffusion paths at 400, 500, 700 and 800 °C have been traced by means of electron microprobe analyses. The growth constants of the diffusion layers are roughly assessed. The phase diagram data obtained in this investigation are compared with previous studies of equilibrated alloys. The existence of the ternary compound TiBiZn has been confirmed. The formation of another phase with approximate formulae Ti₄Bi₃Zn to Ti₉Bi₇Zn₄ has been observed at high temperatures. The latter compound as well as the ternary extension of the Ti_XBi_Y (X ≈ 5, Y ≈ 6) phase react easily with air. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Contribution to the tin‐rich region of the Sn‐Zn‐Ti system

The tin‐rich region of the system Sn‐Zn‐Ti system has been studied by diffusion couples, differential scanning calorimetry and electron microprobe analyses. Ternary eutectic reaction occurs at 193.7°C near to the binary tin‐zinc eutectic point and titanium content less than 0.9 at.% Ti. Three ternary compounds with approximate formulae: Ti₈Sn₅Zn₂ to Ti₅Sn₃Zn, TiSn₄Zn₅ and Ti₂Sn₄Zn₃ have been observed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Wet‐chemical synthesis and characterization of NiBi nano‐ and micro‐particles

Preparation and characterization of NiBi nano‐ and micro‐particles are presented. Firstly, predetermined compositions were obtained by simultaneous precipitation from solutions of Bi(NO₃)₃ and Ni(NO₃)₂. The precipitates were heated under oxygen flow and in air, and thereafter reduced to metals under hydrogen flow at 673 K. Correlation between the predetermined and the actual compositions of the products was found. Characterization of the precipitates was carried out employing X‐ray diffraction, scanning and transmission electron microscopy. Nickel‐bismuth intermetallic phase (NiBi) particles with nano‐ and micro‐dimensions were observed in the samples after reduction. The other possible Ni–Bi intermediate phase (NiBi₃) did not form at these conditions although its presence was expected according to the phase diagram. This finding might be useful for the implementation of Bi‐based solders where the growth of the compound NiBi₃ in the solder joints must be prevented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Notes on some supposed transitions of the phase NiBi

X‐Ray, DSC and magnetic susceptibility measurements were performed with NiBi specimens in the interval from room temperature to 700 K. The hypothesis of solid‐state transitions in this phase was not confirmed. Thermal and magnetic effects are observed, but they are due to the existence of small amount of phases others than NiBi (i.e. unreacted Ni and Bi). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High‐strength bimodal ultrafine Ti‐based alloys with enhanced ductility

Bulk Ti₆₅Fe₃₅ and (Ti₆₅Fe₃₅)_96.15‐xSn_3.85Nb_x (x = 0, 3, 5 and 7 at.%) alloys were prepared by cold crucible levitation melting, and tested in compression at room temperature. The Sn and Nb modified hypereutectic Ti‐Fe alloys exhibited improved mechanical properties under compression. (Ti₆₅Fe₃₅)_93.15Sn_3.85Nb₃ alloy displayed an ultimate compressive strength of 2.7 GPa and a compressive plastic strain of 15%. Electron microscope observations revealed Ti‐Fe(Sn,Nb) alloys having a bimodal microstructure with micrometer‐scale primary TiFe dendrites distributed in an ultrafine eutectic (β‐Ti+TiFe) matrix. The orientation relationship of β‐Ti with TiFe phases is TiFe (011)[100] ∥ β‐Ti (011)[100]. The improved mechanical properties are attributed to the morphology of the phase constituents and the larger lattice mismatches between β‐Ti and TiFe phases due to the additions of Sn and Nb.     

Determination of the phase diagram for the crystallization of L‐asparaginase II by a turbidity technique

Phase diagrams including the metastable zone width for the L‐asparaginase II from Escherichia coli with both PEG₆₀₀₀ and ethanol as a precipitant agent were determined, respectively. A turbidity technique giving results of nucleation and solubility limits in hours rather than in days was introduced. For the first time such data necessary for designing and controlling of crystallization processes of L‐asparaginase II are presented. Since the catalytical activity is an important parameter for L‐asparaginase II as an enzyme, a new type of phase diagram plotting the enzymatic activity as a function of temperature was established as well. Additionally, the crystalline L‐asparaginase II crystals with different shapes that formed in PEG₆₀₀₀ and ethanol, respectively, were also investigated by X‐ray Powder Diffraction (XRPD).     

Determination of the phase diagram for the crystallization of L‐asparaginase II by a turbidity technique ‐ part II. ‐MPD and crystallography studies‐

The phase diagram for the crystallization of L‐asparaginase II including the metastable zone width (MZW), in the presence of PEG₆₀₀₀ and ethanol, respectively, has been studied by an online turbidity technique out of the crystallization in solution (see part I of this work 1 ). Here this paper describes a further investigation on constructing a phase diagram including MZW for the crystallization of L‐asparaginase II with a different precipitant agent of 2‐methyl‐2, 4‐pentandiol (MPD). Along with the phase diagram, the single crystal X‐ray data were successfully collected at 100K from a crystal formed in the presence of 26% (v/v) MPD. The crystals indicate an orthorhombic form and belong to the space group of P2₁2₁2₁ with the unit cell parameters a = 93.9, b = 125.77, c = 151.75Å. The crystal diffracted up to a resolution of 2.88 Å.     

Flux growth and characterization of Ti‐ and Ni‐doped forsterite single crystals

Forsterite monocrystals doped with Ti and Ni were grown by the flux growth technique. A suitable mixture of flux (MoO₃, V₂O₅, Li₂CO₃) and nutrient was slowly cooled down to 750 °C from 1250 °C or 1350 °C. The crystals were then characterized by powder and single‐crystal X‐ray diffraction, scanning electron microscopy and differential scanning calorimetry (DSC). Variations observed in crystal size were attributed by both the varying experimental conditions in which they had been obtained, and to the amount of Ni substituted for Mg in the structure. High abundances of doped forsterite required a cooling rate of 1.8 K h^‐1. These synthetic, well‐characterized Ti and Ni doped forsterite crystals may have potential for exploitation in industrial fields. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Gas‐phase synthesis of Fe‐Bi metastable and dumbbell particles

Fe‐Bi nanoparticles were prepared in the gas‐phase by DC magnetron sputtering and in‐fight annealing. The morphological, structural and compositional properties were investigated by High‐resolution transmission electron microscopy, energy dispersive X‐ray spectroscopy and scanning transmission electron microscopy. High‐resolution microscopy studies show that primary particles produced without in‐flight annealing are spherical with a diameter of about 50 nm. Particles sintered at 773 K acquire a dumbbell structure with Fe‐FeO and Bi sections.     

Single‐crystal growth and characterization of mullite‐type orthorhombic Bi2M4O9 (M = Al3+, Ga3+, Fe3+)

Pure and homogeneous single crystals of orthorhombic mullite‐type Bi₂M₄O₉ (M = Al³⁺, Ga³⁺, Fe³⁺), and a mixed Bi₂Fe_1.7Ga_2.3O₉ crystal from an equimolar Ga/Fe composition were grown by the top seeded solution growth (TSSG) method. All these compounds melt incongruently in the range of about 800 and 1100 °C. In case of bismuth gallate and ferrate inclusion‐free crystals with dimensions up to several cubic centimeters can be grown. Limited solubility in Bi₂O₃ and the high steepness of the liquidus curve are the reasons for getting only small imperfect bismuth aluminate crystals. In contrast to ceramic materials preparation reported in literature, divalent calcium and strontium could not be incorporated into the mullite‐type structure during the melt growth process. Several fundamental physical properties like heat capacity, thermal expansion, heat conductivity, elastic constants, high‐pressure behavior and oxygen diffusivity were determined by different research groups using single‐crystalline samples from the as‐grown materials. Furthermore, the refractive indices of Bi₂Ga₄O₉ were measured in the range of 0.430 and 0.700 μm. Such as many other bismuth containing compounds the refractive indices of Bi₂Ga₄O₉ are larger than 2, and Bi₂Ga₄O₉ is an optic biaxial positive crystal. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

Growth,structure, and superconducting properties of Bi2Sr2Ca2Cu3O10 and (Bi,Pb)2Sr2Ca2Cu3O10‐y crystals

Large and high‐quality single crystals of both Pb‐free and Pb‐doped high temperature superconducting compounds (Bi_1‐xPb_x)₂Sr₂Ca₂Cu₃O_10‐y (x = 0 and 0.3) were grown by means of a newly developed “Vapour‐Assisted Travelling Floating Zone” technique (VA‐TSFZ). This modified zone‐melting technique was realised in an image furnace and allowed for the first time to grow Pb‐doped crystals by compensating for the Pb losses occurring at high temperature. Crystals up to 3×2×0.1 mm³ were successfully grown. Post‐annealing under high pressure of O₂ (up to 10 MPa at T = 500°C) was undertaken to enhance T_c and improve the homogeneity of the crystals. Structural characterisation was performed by single‐crystal X‐ray diffraction (XRD) and the structure of the 3‐layer Bi‐based superconducting compound was refined for the first time. Structure refinement showed an incommensurate superlattice in the Pb‐free crystals. The space group is orthorhombic, A2aa, with cell parameters a = 27.105(4) Å, b = 5.4133(6) Å and c = 37.009(7) Å. Superconducting studies were carried out by A.C. and D.C. magnetic measurements. Very sharp superconducting transitions were obtained in both kinds of crystals (ΔT_c ≤ 1 K). In optimally doped Pb‐free crystals, critical temperatures up to 111 K were measured. Magnetic critical current densities of 2�10⁵ A/cm² were measured at T = 30 K and μ₀H = 0 T. A weak second peak in the magnetisation loops was observed in the temperature range 40‐50 K above which the vortex lattice becomes entangled. We have measured a portion of the irreversibility line (0.1‐5 Tesla) and fitted the expression for the melting of a vortex glass in a 2D fluctuation regime to the experimental data. Measurements of the lower critical field allowed to obtain the dependence of the penetration depth on temperature: the linear dependence of λ(T) for T < 30 K is consistent with d‐wave superconductivity in Bi‐2223. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Evaporation induced diameter control in fiber crystal growth by micro‐pulling‐down technique: Bi4Ge3O12

Diameter self‐control was established in Bi₄Ge₃O₁₂ fiber crystal growth by micro‐pulling‐down technique. In accordance with Bi₂O₃‐GeO₂ phase diagram, the diameter was controlled due to compensation of solidification with evaporation of volatile Bi₂O₃ self‐flux charged into the crucible with excess. The crucibles had capillary channels of 310 or 650 μm in outer diameter. The crystals up to 400 mm long and 50‐300 μm in diameter were grown at pulling‐down rates of 0.04‐1.00 mm/min. The melt composition and the pulling rate were generally only two parameters determining solidification rate. As a result, crystals with uniform (± 10%) diameter and aspect ratio up to 10⁴ were produced without automation of the process. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of CuInS2 single crystals from Sb2S3 and Bi2S3 solutions

The phase diagrams of the CuInS₂‐Sb₂S₃ and CuInS₂‐Bi₂S₃ systems were investigated using X‐ray powder diffraction and differential thermal analysis. Based on these results, the compositions for the growth of the CuInS₂ single crystals from CuInS₂‐Sb₂S₃ and CuInS₂‐Bi₂S₃ melts were selected and Bridgman crystal growth process was performed. The investigation of the obtained single crystals using X‐ray powder diffraction and optical absorption spectra indicates that the incorporation of the solvent atoms into the crystal lattice is absent. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Multi‐factors on photocatalytic properties of Y‐doped Bi2WO6 crystallites prepared by microwave‐hydrothermal method

Different contents of Y‐doped Bi₂WO₆ crystallites were synthesized by a microwave‐hydrothermal method. The photocatalytic properties with different contents of Y‐doped Bi₂WO₆ crystallites were studied. The Y‐doped Bi₂WO₆ crystallites were also characterized by XRD, EDX, SEM and UV‐vis DRS and the multi‐factors on photocatalytic properties of Y‐Doped Bi₂WO₆ crystallites were discussed. The results indicate that Y³⁺ replacing Bi³⁺ enters into the Bi₂WO₆ lattice, producing a degree of Bi₂WO₆ lattice distortion. It also has an impact on the crystallinity of Bi₂WO₆ and the band gap is from 2.49 eV to 2.71 eV. The photocatalytic results show that when the content of Y doping becomes 10%, the degradation rate of rhodamine B is above 90% after 40 min irradiation, which shows that doping the proper rare earth ions is conducive to the photocatalytic properties of Bi₂WO₆ crystallites.     

Vapour‐phase growth,purification and large‐area deposition of ZnO tetrapod nanostructures

Large‐yield zinc oxide (ZnO) nanosized tetrapods have been obtained by a standard vapour‐phase growth technique to which a few modifications have been added, such as the separation of the Zn source evaporation region from the Zn oxidation region inside the reactor setup. This modification allows to keep the growth conditions constant and continuous for a long time, thus favouring the obtainment of large amounts of ZnO tetrapod nanostructures. As some contaminations usually occur due to metallic Zn particles and/or different ZnO nanostructures, including not completely reacted ZnO_1‐x solid phases, they can be removed by a three‐step “purification” procedure as described in the article. Further to that, a deposition method from suitable liquid suspensions is also reported, which allows to produce homogeneous distributions of ZnO tetrapods on large substrate areas. The proposed procedures are expected to be particularly appropriate for a large production of samples for device use. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X‐ray diffraction analysis of powder and thin film of (Gd1‐x Yx)2O3 prepared by sol‐gel process

The mixed oxide (Gd_1‐xY_x)₂O₃ (0.0 ≤ x ≤ 1.0) were synthesized, as powder and thin film, by a sol‐gel process. X‐ray diffraction data were collected and crystal structure and microstructure analysis were performed using Rietveld refinement method. All samples were found to have the same crystal system and formed solid solutions over the whole range of x. The cationic distribution, Gd³⁺ and Y³⁺, over the two non‐equivalent sites 8b and 24d of the space group Ia3 is found to be random for all values of (x). The lattice parameter is found to vary linearly with the composition (x). Replacing Gd³⁺ and Y³⁺ by each other introduces a systemic decrease in the x‐coordinate of cation position (24d) and slight changes in the oxygen coordinates. Crystallite size and microstrain analysis is performed along different crystallographic directions and anisotropic changes are found with the composition parameter (x). The average crystallite size ranges from 75 to 149 nm and the r.m.s strain from 0.027 to 0.068 x10^‐2. Textured Gd_1.841Y_0.159O₃ (400) buffer layers, with a high degree of alignment in both out‐plane and in‐plan, are successfully grown on cube textured Ni (001) tape substrates by sol–gel dip coating process. The resulting buffer layers are crack‐free, pinhole‐free, dense and smooth. YbBa₂Cu₃O_7‐x (YbBCO) thin film could be (00l) epitaxially grown on the obtained buffer layer using sol–gel dipping technique. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Solidification behavior and microstructural evolution of the Cr‐Nb eutectic alloy

A series of microstructures including fully coupled eutectic, both α‐Cr and β‐Cr₂Nb primary dendrites embedded in eutectic and only β‐Cr₂Nb primary dendrites plus eutectic were observed in the arc‐melted Cr‐Cr₂Nb eutectic alloy. By employing EPMA analysis performed at the eutectic regions, the eutectic composition of the Cr‐Cr₂Nb system was indicated to contain less than 18 at.%Nb. Based on the solidification phase selection involving phase competitive nucleation and growth, the α‐Cr phase was predicted to be the primary nucleating phase and the β‐Cr₂Nb the primary growing phase. Under large undercooling conditions, the solidification process was controlled by nucleation, which led to the formation of α‐Cr primary particles. With the decrease in undercooling, the solidification process developed into growth controlling, which caused the occurrence of β‐Cr₂Nb primary phase since the actual solidification path of the alloy lay within the hypereutectic region. The explanation was confirmed by the experimental composition analysis.     

Voltage‐current characteristics of Bi‐2223 superconducting tape near Tc under γ irradiation

Voltage‐current characteristics at four different applied magnetic fields (7, 20, 30, and 40 mT) of Bi₂Sr₂Ca₂Cu₃O_x superconducting tape were measured in the temperature range from 100 to 115 K. They were also measured at zero magnetic field before and after γ irradiations up to 10 MRad at different temperatures just below the critical temperature. The data were fitted to a power law expression V = I ^β(T) in which the exponential parameter β under 20 mT field and after irradiation is found to fluctuate around three and then drops to unity near the critical temperature which may be interpreted as a sign of Kosterlitz‐Thouless transition. The electrical properties of the tape were found to be very sensitive to γ irradiation where most of the changes take place in low γ doses. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)