Sonochemical synthesis, characterization, and photocatalytic properties of Bi2−x Sb x WO6 nanorods

We report an efficient route for the sonochemical synthesis of Bi_2?x Sb _x WO₆ (x = 0, 0.01, 0.02, 0.05, 0.1, and 2) nanorods using bismuth nitrate/antimony chloride and sodium tungstate as precursors. The products obtained have been characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV–Vis diffuse reflectance spectroscopy. The photoactivities of all the samples for the Rhodamine-B (RhB) photodegradation were investigated systematically under UV and visible light irradiation. The results of the photocatalytic degradation of RhB in aqueous solution showed that 2–5 % antimony ion doping greatly improved the photocatalytic efficiency of sonochemically synthesized Bi₂WO₆ nanorods under both UV and visible radiation compared to its undoped counterpart. Among all the samples, the Sb₂WO₆ nanorods exhibited the highest photodegradation efficiency since 86 % of RhB could be photodegraded in 90 min under UV radiation. The stability of the photocatalysts was ascertained using FT-IR and Raman spectroscopy.     

Infrared laser-induced piezo-optics in Sb2Se3− x Te x –BaCl2–PbCl2 glass

IR-induced elasto(piezo)-optical (PO) triggering effects in complex chalcogenide glasses with general formula Sb₂Se_{3- x} Te _x ?BaCl₂–PbCl₂ (with x = 0.2, 0.8, 1.3) were found under the influence of a pulsed 190 ns CO₂ laser with wavelength 10.6 μm. It was shown that increasing x leads to an increase of the PO efficiency. This is caused by appearance of enhanced excited dipole moments due to variations of polarizability. Simultaneously variations of the PO versus pump–probe delay times in the nanosecond time range were explored. A substantial role of the electron–phonon subsystem in the observed IR-induced PO triggering is demonstrated. The investigations were done both for diagonal as well as off-diagonal PO tensor components.     

Pb1−x Bi x /Bi/Pb1−x Bi x Josephson junction

A superconductor/semimetal/superconductor (S/SM/S) Josephson junction has been developed. We have used an alloy of Pb_1–x Bi _x (0x 0.6) as the superconductor and Bi as the semimetal. By irradiating at X-band microwave of 10 GHz, Shapiro steps were observed for various bismuth barrier thicknesses inÅ and bismuth weight ratiosx. Finally, we obtained the empirical relationship for barrier thickness, below which microwaves could be detected for various bismuth weight ratiosx at the temperature of 4.2 K.     

Crystallization kinetics of bulk amorphous (Se65Te35)100−x Sb x

Kinetic studies of crystallization in (Se₆₅Te₃₅)_100–x Sb _x with 0x10 glasses, using the differential scanning calorimetry technique, were performed. Crystallization enthalpy data, H _c, were collected as a function of composition. The crystallization data were examined in terms of recent analyses developed for non-isothermal crystallization studies, to arrive at E _c. The results indicate bulk nucleation and crystallization with two- and three-dimensional growth, respectively, for the (Se₆₅Te₃₅)₉₈Sb₂ and (Se₆₅Te₃₅)₉₂Sb₈ glass composition.     

Structural and optical properties of Bi x Se1−x films

Bi _x Se_1–x thin films have been studied because of their structural and optical properties with a view to judging their suitability as the recording medium in phase-change type optical recording. Amorphous films deposited at room temperature were crystallized by thermal annealing. X-ray diffraction analysis and surface morphological studies are reported. A maximum reflectivity difference of 25% at =830 nm was obtained upon amorphous-to-crystalline transition. The optical constants calculated by the Newton-Raphson method using the experimental transmittance, reflectance and thickness data are reported.     

制备条件对Bi2Te3和Bi0.5Sb1.5Te3材料热电性能的影响

采用水热法制备Bi2Te3/Sb2Te3纳米粉体并热压制备块体热电材料.用X射线衍射分析产物的相结构和成分,扫描显微镜与透射电镜观察产物的形貌.测量试样从室温到700K的塞贝克系数与电导率.实验结果表明,使用水热法制备了Bi2Te3与Sb2Te3纳米粉体,经热压后部分氧化.热压温度对于块体试样热电性能影响显著.     

Structural and electrical properties of layered tetradymite-like compounds in the GeTe—Bi2Te3 and GeTe—Sb2Te3 systems

Analysis of the available crystallographic data shows that the GeTe-Bi₂Te₃ and GeTe-Sb₂Te₃ pseudobinary systems contain a wide variety of many-layered, long-period compounds belonging to the nGeTe · mBi₂Te₃ and nGeTe · mSb₂Te₃ homologous series. The Hall coefficient, thermoelectric power, and electrical conductivity of some of these compounds were measured over a wide temperature range. The temperature-dependent carrier mobility data suggest that both acoustic phonons and point defects contribute to the scattering of charge carriers. The lattice thermal conductivity of the many-layered, long-period compounds studied, κ_ph = 6–8 mW/(cm K), is notably lower than that of the constituent tellurides     

Effect of Te Doping on the Structure and Superconductivity of K x Fe2−y Se2−z Te z Single Crystals

We report the structure, transport, and magnetic properties of K _x Fe_2?y Se_2?z Te _z single crystals grown by optical floating zone technique. The phase separation phenomena were observed in the Te-doped samples. With increasing Te doping level, the c-axis lattice parameter expands for both insulating/semiconducting and superconducting phases while the superconducting transition temperature (T _c) decreases and eventually vanishes at z = 0.51. The critical current density was estimated to be 10³–10⁴ A/cm² for the all doped samples. The upper critical field and anisotropic superconducting ratio increase with Te doping. We compared the results of critical current density J _c, upper critical field μ ₀ H _c2 and apparent thermally activated energy U ₀ for the samples with z = 0, 0.09, and 0.16. The influence of Te doping on the vortex pinning and the implication of U ₀ versus μ ₀ H is discussed.     

放电等离子烧结制备的Bi2Te3／Sb2Te3复合材料的热电性能

研究了用低温湿化学法和水热法制备纳米级的Bi2Te3和sb挪e3颗粒，并通过透射电镜观察其微观形貌。Bi2Te3粉末的微观形貌为直径在30-50n之间的片状小颗粒，而sb2Te3颗粒的微观形貌为薄带状，直径约为70nm，长度则为从150-300nm不等，并对其晶体的形核和长大机理进行了讨论。认为，纳米小颗粒状的Bi2Te3晶体可能是通过“表面形核和侧向生长”形成的产物，而薄带状的sb2Te3晶体可能是在Te块解体形成的条带状碎屑基础上形成的。用放电等离子烧结法（spark plasma sintering）制备不同比例的Bi2Te3／Sb2Te3块状复合材料，测量并比较了其热电性能。通过改变Bi2Te3的量，可以提高复合材料的电性能。成分不同的层片间的散射，能更有效地降低块体材料的热导率。在500K的温度下，Bi2Te3和sb2Te3以摩尔比为1：1复合烧结的试样的热导率低达0．7W／（m·K）。进一步优化Bi2Te3和sb2Te3的复合比例，其热电性能可能会有进一步的提高。     

Room-temperature multiferroic properties and magnetoelectric coupling in Bi4−x Sm x Ti3−x Co x O12−δ ceramics

We present the structural, dielectric, ferroelectric, magnetic and magnetoelectric studies of lead free; single phase Bi_4?x Sm _x Ti_3?x Co _x O_12?δ (0 ≤ x ≤ 0.07) ceramics, synthesized using a standard solid-state reaction technique. Raman spectroscopy analysis reveals the relaxation of distortion in TiO₆ octahedron. Field emission scanning electron microscopy confirmed the growth of plate-like grains. It is observed that with the substitution of Sm³⁺ and Co³⁺ ions the dielectric constant, loss tangent and ferroelectric transition temperature decreases. Electrical dc resistivity, remnant polarization and magnetization increases with increasing Sm³⁺ and Co³⁺ contents. The magnetoelectric coupling co-efficient, α = 0.65 mV cm^?1 Oe^?1 is realized for Bi_4?x Sm _x Ti_3?x Co _x O_12?δ (x = 0.07) ceramic sample. Our results clearly demonstrate the lead free, multiferroic nature of Sm/Co-substituted Bi₄Ti₃O₁₂, which may find useful application in designing cost-effective electromagnetic devices.     

The mechanisms of yield and plastic flow in HgTe and Cd x Hg1−x Te

Single crystals of HgTe and Cd _x Hg_1–x (0.18<x<0.30), oriented for single slip, have been deformed in four-point bending at strain rates 10^–4 sec^–1 and temperatures from –11 to +84° C for HgTe, and 20 to 195° C for Cd _x Hg_1–x Te. At the lowest temperatures, the stress-strain curve exhibits a sharp yield relaxation and subsequent zero work hardening regime, as commonly observed for other semiconductors. Experiments show that the yielding mechanism is that proposed by Johnston and Gilman for LiF. Possible explanations for the post-yield zero work hardening phenomenon are discussed. The influence of composition, temperature and strain rate on the stress-strain behaviour are reported. At 20° C, the upper and lower yield stresses ( _uy and _1y ) increase with increasingx in qualitative agreement with our earlier hardness results. For Cd_0.2Hg_0.8Te, _1y varies with temperature,T, at a strain rate of 10^–4 sec^–1, according to _1y exp (Q/kT) whereQ is 0.16 eV. For HgTe the comparable value is 0.11 eV. Atx=0.25 and constant temperature, _1y depends on strain rate as _1y ^1/n wheren is 4. The stress level for deformation of Cd_0.2Hg_0.8Te at 10^–4 sec^–1 and 20° C is 2–3 kg mm^–2, comparable with that for InSb at 300° C or Si at 1000° C. Strain rate cycling tests on Cd _x Hg_1–x Te give values of activation volumeV* around 10b³ at 20° C, independent of plastic strain (up to 2–3%), suggesting that deformation in these alloys is controlled by the Peierls mechanism, as observed in other II–VI compounds.     

The growth and properties of (Sbx Bi1–x)2Te3 crystals

Abstract

Vertical Bridgman systems with programmable temperature control are used to grow (Sb_xBi_1:x)₂Te₃ crystals. High purity Bi, Sb and Te are used as sources and the diameter of 1.1 cm, little soft bulk crystals of (Sb_xBi_1–x)₂ Te₃ can be obtained. Scanning electron microscope (SEM) and electron probe microanalysis (EPMA) are used to analyze the micro‐structure and the compositions of the crystal. From the X‐ray diffraction patterns it appears that the grown crystal is single crystal or directive polycrystal. If the uniformity of the source solution and grown temperature are under control, then the high quality of single crystals can be obtained. The dependence of crystal structure and the thermoelectric characteristics on the changed compositions of grown crystals are discussed. The optimum composition for the thermoelectric properties is Sb_1.00 Bi_1.04Te_2.96. When the DC current, 3A, is applied to the Sb_1.00 Bi_1.04 Te_2.96 crystal with suitable electrodes, the temperature difference (△T) between two sides of the crystal can be as high as 60°C. It is 2 times larger than that ever obtained by Sb₂Te₃ crystal. It appeared that the grown (Sb_xBi_1‐x)₂Te₃ crystals have the potential on the fabrication of thermoelectric devices and electronic cooling system.     

Structural and optical properties of Cd x Zn(1 − x)Te thin films

Seven Cd _x Zn_{(1 ? x} Te solid solutions with x = 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 were synthesized by fusing stoichiometric amounts of CdTe and ZnTe constituents in silica tubes. Each composition was used in the preparation of a group of thin films of different thicknesses. Structural investigation of the obtained films indicates they have a polycrystalline structure with predominant diffraction lines corresponding to (111) (220) and (311) reflecting planes, which can be attributed to the characteristics of growth with the (111) plane. The optical constants (the refractive index n, the absorption index k, and the absorption coefficient α) of Cd _x Zn_{(1 \s -x)} Te thin films were determined in the spectral range 500–2000 nm. At certain wavelengths it was found that the refractive index, n, increases with increasing molar fraction, x. It was also found that plots of α² (hv) and α^1/2 (hv) yield straight lines, corresponding to direct and indirect allowed transitions respectively obeying the following two equations: $$\begin{gathered} E_g^d = 1.583 + 0.277x + 0.197x^2 \hfill \\ E_g^{ind} = 1.281 + 0.111x + 0.302x^2 \hfill \\ \end{gathered}$$      

Static bismuth disorder in Bi2−x(CrTa)O7−y

The crystal structure of the pyrochlore Bi_2−x(CrTa)O_7−y has been refined by the Rietveld method from powder neutron and synchrotron X-ray diffraction data. Using the ideal pyrochlore structural model, anomalously high atomic displacement parameters (APD), which could not be satisfactorily explained with anisotropic ADP, of both Bi and O′ sites were observed. The structure was successfully refined with a model that incorporated static displacive disorder of both the Bi and O′ atoms. Using this model physically reasonable ADP parameters for both the Bi and O′ atoms, and improvement in the various measure of fit were obtained. The underbonding of the Bi atoms, observed in ideal pyrochlore model, but removed in the disordered structure, is believed to be the main driving force for this disorder.     

Composition dependence of some thermo-physical properties of multi-component Se78−x Te20Sn2Bi x (0 ≤ x ≤ 6) chalcogenide glasses

New multi-component glassy materials with composition of Se_78?x Te₂₀Sn₂Bi _x (0 ≤ x ≤ 6) have been synthesized by well-known melt quenching technique. The as-prepared glasses have been characterized by applying an advanced transient plane source technique to study their thermal transport properties (effective thermal conductivity, diffusivity, specific heat per unit volume) at room temperature. Density measurements have been done to correlate the obtained results. Using the experimental data of density measurements, the basic physical parameters, such as mean atomic volume, compactness, average coordination number etc., are evaluated for the synthesized glasses and the results are discussed as a function of glass composition. We have also determined the phonon mean free path (τ) using the experimental value of effective thermal diffusivity. The composition dependence of the thermal transport properties of aforesaid glassy system has also been discussed.     

Crystal structure and anisotropy of iodine-intercalated Bi2Sr2Ca n−1Cu n O x

The electronic state and structural configuration of the intercalated iodine species in stage-1, I-Bi₂Sr₂Ca _n?1Cu _n O _x (n = l, 2), have been studied through polarization-resolved Raman and¹²⁹I Mössbauer spectroscopy. The polarization dependence of the Raman spectra and the Mössbauer measurement confirmed the dominant species to be triiodide ions, I ₃ ^? , with alignment of these linear molecules either along thea- orb-axis in the host crystals. Transport measurements such as thermoelectric power and Hall coefficient clearly indicated that hole carriers are doped into the CuO₂ planes upon intercalation, by whichT _c of the host superconductor is changed. Furthermore, based on resistivity measurements in a magnetic field, we suggest that the iodine intercalation leads to a decrease of the anisotropy both in normal and superconducting states, suppressing the extremely two-dimensional character of the Bi₂Sr₂Ca _n?1Cu _n O _x systems.     

Fabrication and characterization of compositionally graded Bi1−x Gd x FeO3 thin films

An undoped BiFeO₃ thin film, Gd doped Bi_0.95Gd_0.05FeO₃ thin film with a constant composition, Gd up-graded doped Bi_1?x Gd _x FeO₃ and Gd down-graded doped Bi_1?x Gd _x FeO₃ thin films were successfully grown on Pt (111)/Ti/SiO₂/Si (100) substrates using a sol-gel and spin coating technique. The crystal structure, ferroelectric and dielectric characteristics as well as the leakage currents of these samples were thoroughly investigated. The XRD (X-Ray Diffraction) patterns indicate that all these thin films consist of solely perovskite phase with polycrystalline structure. No other secondary phases have been detected. Clear polarization-electric field (P-E) hysteresis loops of all these thin films demonstrate that the incorporation of Gd³⁺ into the Bi site of BFO thin film have enhanced the ferroelectric performance of pure BiFeO₃ thin film, and the Gd down-graded doped Bi_1?x Gd _x FeO₃ thin film has the best ferroelectric properties. Compared to other thin films, the optimal ferroelectric behavior of the Gd down-graded doped Bi_1?x Gd _x FeO₃ thin film results from its large dielectric constant, low dissipation factor and low leakage current.     

Kinetic studies of the glass transition in (Se65Te35)100−x Sb x by differential scanning calorimetry

Calorimetric studies of chalcogenide glasses, (Se₆₅T₃₅)_100–x Sb _x , obtained by ice-water quenching, were performed by a non-isothermal method. An X-ray diffraction study, as a function of temperature, was carried out, with samples of different compositions. The activation energy for relaxation time, was determined from the heating-rate dependence of values of the glass transition temperature, as a function of x. A maximum in E _t versus antimony concentration occurs at 1–2 at%. ¹²¹Sb Mössbauer results confirm the formation of Sb₂Se₃, by crystallization.     

Ion Beam Analysis and Physical Properties Measurements of (Tl0.8Hg0.2−x Sb x )Ba2Ca2Cu3O9−δ

The superconducting phase (Tl_0.8 Hg_0.2−x Sb _x ) Ba₂Ca₂Cu₃O_9−δ , with 0.0 ≤x≤0.2, was characterized by means of X-ray powder diffraction (XRD), scanning electron microscope (SEM), proton induced X-ray emission (PIXE), Rutherford backscattering spectrometry (RBS), electrical resistivity (ρ) and transport critical current density (J _ct). The tetragonal structure of (Tl, Hg)-1223 remains unchanged with antimony-substitution, whereas the lattice parameters were changed. The actual elemental-content of Tl, Hg, Sb, Ba, Ca and Cu, determined from PIXE, were very close to those of the nominal elemental-content. The oxygen-stoichiometry of the prepared samples was determined by non-Rutherford backscattering cross section at 3 MeV H⁺. A little increase in the oxygen stoichiometry was observed as Sb-content increased. The superconducting transition temperature T _c, determined from electrical resistivity, increased from 124.8 K to 131.5 K as x increased from 0.0 to 0.1 and then it decreased with the further increase in x. The same behavior is obtained for J _ct vs. x. This indicates that the optimal Sb-substitution in (Tl, Hg)-1223 is at about x=0.1.     

Thermodynamic properties of Ca1 − x Er x F2 + x and Ca1 − x Yb x F2 + x heterovalent solid solutions

The heat capacity of single crystals of the Ca_{1 ? x} Er _x F_{2 + x} (x = 0.05, 0.10) and Ca_0.95Yb_0.05F_2.05 fluorite solid solutions was determined by adiabatic calorimetry in the temperature range 55–300 K. The results were used to obtain temperature dependences of the Debye characteristic temperature, entropy, and enthalpy for the solid solutions.