Phase diagram of the Pb-NiSb system and properties of (NiSb)<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> solid solutions

The phase diagram of the Pb-NiSb system is presented. The system is pseudobinary, with a limited series of NiSb-based solid solutions: ≃1 mol % Pb at 300 K. In the temperature range ≃520–670 K, the system contains un unstable compound, Ni₃Pb₂Sb₃. At 1320 K, a monotectic transformation occurs (≃15–71 mol % NiSb). Electrical and thermal conductivity measurements reveal an additional contribution to the lattice thermal resistivity of the (NiSb)_{1 − x} Pb _x solid solutions and show that electrons and phonons in these materials are scattered elastically.     

Gas dynamic analysis of the performance of diffuser augmented wind turbine

A diffuser augmented wind turbine (DAWT) is considered an important application of the advanced concepts to improve the attractiveness of wind energy. The present paper aims to find a theoretical demonstration of DAWT by using theoretical analysis, mathematical models, assumptions, estimations and maximization of power coefficients and augmentation ratios, in addition to computer programs for calculations and drawings. The final results show that the maximum power coefficient (Cpd ₀) and augmentation ratio (R _b-) relative to Betz — are directly proportional to pressure recovery factor(Cr), turbine factor (Ct), and maximum velocity ratio(No), but inversely proportional to overall recovery factor (Co) of diffuser. The power coefficient(Cpd ₀ ) of DAWT reaches 1.5 at C₀ ≃ -0.5,No ≃ 1.0 andCr ≃ 0.5, but the augmentation ratio(R _b ) reaches 6.0 at C₀ ≃ -0.5,Cr ≃ 0.9, and reaches 7.0 atNo ≃ 1.0 and Ct ≃ 1.0, which gives a good application for DAWT systems.     

Electrical properties of (K0.5Na0.5)1? x Ag x NbO3 lead-free piezoelectric ceramics

(K_0.5Na_0.5)_1−x Ag _x NbO₃ lead-free piezoelectric ceramics have been fabricated by an ordinary ceramic technique. The results of XRD reveal that Ag⁺ diffuses into the K_0.5Na_0.5NbO₃ lattices to form a new solid solution with an orthorhombic perovskite structure and the solubility of Ag⁺ into A-sites of K_0.5Na_0.5NbO₃ is about 0.20. The ceramics can be well-sintered at 1,100–1,110 °C. The partial substitution of Ag⁺ for A-site ion (K_0.5Na_0.5)⁺ decreases slightly both paraelectric cubic-ferroelectric tetragonal (T _C) and ferroelectric tetragonal-ferroelectric orthorhombic phase transition temperatures (T _O−T). The ferroelectricity of the ceramics becomes weak at high Ag⁺ concentration. The ceramic with x = 0.10 possesses optimum electrical properties: d ₃₃ = 135 pC/N, k _P = 0.43, k _t = 0.46, ε _r = 470, tanδ = 3.39%, and T _C = 394 °C.     

Microstructures and thermoelectric properties of p-type pseudo-binary AgxBi0.5Sb1.5−xTe3 (x = 0.05–0.4) alloys prepared by cold pressing

The p-type pseudo-binary Ag_xBi_0.5Sb_1.5−xTe₃ (x = 0.05–0.4) alloys were prepared by cold pressing. The thermal conductivities (κ) were calculated from the values of heat capacities, densities and thermal diffusivities measured, and range approximately from 0.66 to 0.56 (W K^− 1 m^− 1) for the Ag_xBi_0.5Sb_1.5−xTe₃ alloy with molar fraction x being 0.4. Combining with the electrical properties obtained in the previous study, the maximum dimensionless figure of merit ZT of 1.1 was obtained at the temperature of 558 K.     

Anisotropy of Superconducting Single Crystal SmFeAsO0.8F0.2 Studied by Torque Magnetometry

Single crystals of the oxypnictide superconductor SmFeAsO_0.8F_0.2 with T _c≃45(1) K were investigated by torque magnetometry. The crystals of mass ≤0.1 μg were grown by a high-pressure cubic anvil technique. The use of a high-sensitive piezoresistive torque sensor made it possible to study the anisotropic magnetic properties of these tiny crystals. The anisotropy parameter γ was found to be field independent, but varies strongly with temperature ranging from γ≃8 at T≲T _c to γ≃23 at T≃0.4T _c. This unusual behavior of γ signals unconventional superconductivity.      

Phase diagram and thermoelectric properties of Ag3−x Sb1+x Te4 system

In order to obtain better thermoelectric performance in the composition domain should be stabilized, the phase diagram of the Ag_3–x Sb_1+x Te₄ system by varying the Ag:Sb ratio. The phase diagram is investigated using the differential thermal analysis and the powder X-ray diffraction techniques. The Seebeck coefficient and the electrical resistivity of the grown bulk crystals of the system are also measured. The phase diagram of the Ag_3–x Sb_1+x Te₄ system indicates that a mixed phase of AgSbTe₂ and Ag₂Te, which is expected to show higher thermoelectric performance, exists in a wide temperature range between 600 and 830 K at a composition of Ag_2.2Sb_1.8Te₄. The maximum of Seebeck coefficient for AgSbTe₂ (x = 1) is 0.73 mV/K at about 680 K. The thermoelectric performance is lowered by the compositional deviation from Ag:Sb:Te = 1:1:2.     

Mobility of Electrons at Liquid Helium Surface under Overheating

Mobility of surface electrons (SE) on liquid helium at low temperatures (T≃0.52 K) is studied as a function of the driving electric field E _∥ in the range 1–25 mV/cm. The experimental conditions correspond approximately to effective electron temperatures T _e ≃1–12 K. The measurements are performed for SE with the surface electron density n _s =1.46×10⁸ cm⁻² at different holding electric fields E _⊥ =200–1400 V/cm. The mobility is observed to be an increasing function of the driving field. The function depends strongly on the holding electric field applied. The experimental results are in reasonable agreement with theoretical curves calculated using the force-balance equation method expressing the mobility in terms of the dynamical structure factor of SE.     

Pb5Ge3O11 ferroelectric films prepared by a modified sol—gel method

Single-crystal Pb₅Ge₃O₁₁ films 5–105 μm thick, adhering well to platinum substrates, were prepared by pyrolysis of metalorganic precursors in combination with in situ sol-gel processing. The best films consisted of densely packed crystallites ranging in size from 200 to 300 μm, with hexagonal habits. A welldefined ferroelectric transition was revealed at 170–180°C. The typical parameters of the films are ɛ₂₀ = 30–40, tan δ ≃0.02, ɛ_max ≃200, P_s = 3.2 μC/cm²,E _c = 16 kV/cm, and ρ = 10⁸-10⁹ Ω cm, in agreement (except for ɛ_max) with those of lead germanate crystals     

Phase equilibria in the systems AgInSe<Subscript>2</Subscript>-HgIn<Subscript>2</Subscript>Se<Subscript>4</Subscript> and AgInSe<Subscript>2</Subscript>-HgSe

The equilibrium phase diagrams along the AgInSe₂-HgIn₂Se₄ and AgInSe₂-HgSe joins of the ternary system Ag₂Se-HgSe-In₂Se₃ have been constructed using X-ray diffraction and differential thermal analysis. Both joins are pseudobinary, with eutectic phase diagrams (type V in Roseboom’s classification). The eutectics are located at ≃30 mol % HgIn₂Se₄ (melting point of 1000 K) and ≃54 mol % HgSe (993 K), respectively. Both systems have considerable terminal solid-solution ranges.     

Thermal expansion of silico-phosphate glasses with small additions of Fe2O3: EPR and dilatometric studies

Electron paramagnetic resonance (EPR) and dilatometric measurements in phosphosilicate glass have been made in order to elucidate an anomalous trend of the linear thermal expansion coefficientβ when Fe₂O₃ was added to the composition. The g≃2 and g_eff≃4.27 EPR lines were attributed, respectively, to undistorted and octahedrally coordinated Fe³⁺ ions, and to Fe³⁺ ions in low symmetry (rhombic) sites. The Fe³⁺ ion distribution in the network at different temperatures has been explained by a model of chemical insertion and it has been proved that the Fe³⁺ ions have two kinds of role as network modifiers. A relationship has also been found betweenβ and the amounts of Fe₂O₃ added in the range 0 to 12 wt %. It is with deep regret that we note the death of Professor G. L. Del Nero.     

Heating of a current filament and formation of constrictions in a pulsed vacuum discharge

It is shown that a rapid current rise in a pulsed vacuum discharge is accompanied by enhanced compression of the current filament by its self-induced magnetic field. As a result, a constriction forms at a distance L≃1 mm from the cathode and the electron temperature increases to 10²–10³ eV at currents of order 1 kA. This behavior explains the observed increase in the degree of ion charge and the appearance of x-rays as the current pulse length decreases. The criterion for a rapid rise is the condition τ<L/V≃10⁻²⁷ s, where τ is the characteristic current amplification time and V≃10⁶ is the velocity of the cathode plasma. Pis’ma Zh. Tekh. Fiz. 24, 50–56 (September 26, 1998)     

Glass transition and fragility of telluro-vanadate glasses containing antimony oxide

The activation energy (ΔH ^*) of the glass transition and the heating-rate dependence of the glass transition temperature (T _g) of V₂O₅–Sb₂O₃–TeO₂ glasses were determined using differential scanning calorimetry technique. Non-isothermal measurements were performed at different heating rates φ (=3, 6, 9, 10, 13 K/min). The heating rate dependence of T _g was used to investigate the applicability of different theoretical models describing the glass transition. The application of Moynihan and Kissinger et al. models to the present data led to different values of (ΔH ^*) at each different heating-rate regions. This behavior was attributed to the strong heating rate dependence of the activation energy of the process. The fragility parameter (m = ΔH ^*/RT _g) were ≲90, suggesting that these glasses may be classified as strong glasses. The viscosity, η, calculated at a few selected temperatures near the glass transition region increased with increasing Sb₂O₃ content at any given temperature, which is also expected. Also the compositional dependence of T _g and ΔH ^* was investigated.     

Structural, mechanical, hardness indentation measurements of Sn65−x Ag25Sb10Cu x solder alloys rapidly solidified from melt at cooling rate 1.1×105 K s−1

Structural, mechanical properties, and hardness indentation measurements of Sn_65–x Ag₂₅Sb₁₀Cu _x (x=0, 0.5, 1.0, 1.5, 2.0, and 2.5 wt %) solder alloys have been studied and analyzed. The alloy exhibits mechanical properties superior to those in both the Sn–Ag₂₅ binary and Sn–Ag₂₅Sb₁₀ ternary solder alloys. The addition of small amounts of Cu is found to refine the effective grain size, while retaining the uniform distribution of Ag₃Sn, SnSb, and Cu₁₀Sn₃ precipitates in the solidification microstructure, thus significantly improving the ductility and strength.     

Heterovalent substitution of group IV and V diamagnetic ions in the ferromagnetic spinel CuCr2S4

Heterovalent substitution of As⁵⁺, Sb⁵⁺, V⁵⁺, and Sn⁴⁺ diamagnetic ions in CuCr₂S₄ was studied. The results show that, similar to other 3d¹⁰ diamagnetic ions, the As⁵⁺ ions occupy only tetrahedral interstices in the close packing of sulfur ions, while the Sb⁵⁺ and Sn⁴⁺ 4d¹⁰ ions, as well as the Sc³⁺, Ti⁴⁺, and V⁵⁺ 3d⁰ ions occupy only octahedral sites. A new compound of composition Cu₃AsCr₈S₁₆ was synthesized and characterized. It crystallizes in an orthorhombic (sp. gr.Pmm2) spinel-derived structure containing ordered Cu and As ions in tetrahedral sites(a = 13.942 ± 0.004 Å,b = 6.878 ± 0.002 Å,c = 19.692 ± 0.006 Å, Z = 4, V = 1888.43 ± 0.92 Å). The CuCr_1.5Sb_0.5S₄ spinel phase is found to crystallize in sp. gr.Fd3m (a = 10.009 ± 0.002 Å,u = 0.3815 ± 0.0004 Å) with partial ordering on octahedral sites.     

Specific heat and enthalpy of lattice disordering of LaF3 superionic crystals

Specific heat (C _p ) data obtained near the phase transition of LaF₃ are used to estimate the activation enthalpy for anion disordering, H _d. At the critical point T _c = 263 K, the concentration of disordered fluoride ions is n _c = 2.86 × 10²⁰ g⁻¹. In the dielectric phase of LaF₃ (T < T _c), H _d is 0.24–0.26 eV. In the superionic phase (T ≥ T _c), where the concentration of disordered fluoride ions exceeds n _c, the enthalpy of disordering drops to H _d ≃ 0.04 eV.     

Complex impedance and admittance of a silver-conducting glass

From the analysis of complex impedance and admittance data of (Agl)₇₅(Ag₄P₂O₇)₂₅ glass, an Ag⁺-ion conductor, it was revealed that the sample can be approximated by a seriesRC ₁ circuit at high temperature, with the capacitorC ₁ arising from the charge-carrier depleted region near the anode which develops as conduction proceeds, and by a parallelRC ₂ circuit at low temperature, with the capacitorC ₂ arising from the saturated value for ionic polarization of, say, the silver-iodine pairs as well as from the relaxation effect of the Ag⁺ ions for conduction. TheC ₁ andC ₂ values were found to be almost temperature-independent at peak frequencies of the distorted semicircles in respective complex planes, with the ratioC ₁/C ₂ as large as 10⁴.     

Influence of silver doping on the physical properties of Mg ferrites

The physical properties of silver substituted magnesium ferrite MgAg_xFe_2−x O₄ (0.0 ≤ x ≤1) have been studied as a function of silver ion concentration. The samples were prepared using the flash combustion technique. The effect of Ag content on microstructure and magnetic properties has been studied. X-ray diffraction (XRD) analysis reveals the spinel structure besides metallic silver particle at all concentrations. The decrease in the lattice constant with increasing Ag up to the critical concentration (x = 0.2) was discussed. The close agreement of the theoretical and experimental lattice constant ratio from XRD pattern supports the occupancy of silver on the tetrahedral sites. The morphological features were studied using scanning electron microscope. The magnetic susceptibility, Curie temperature (T _C), and effective magnetic moment (μ _eff) were decreased with compositional parameter. The DC electrical conductivity of the investigated samples was measured and the results indicated the increase in conductivity with increasing Ag content from 5.6 × 10⁴ at x = 0 to 12.6 × 10⁴Ω⁻¹ cm⁻¹ at x = 1. The transition from the ferrimagnetic to paramagnetic state is accompanied by an increase in the thermo EMF. Ag–Mg ferrite shows p-type conductivity at all concentrations of Ag particles where the creation of lattice vacancies is due to presence of Ag⁺ ions gives rise to the p-type conductivity.     

Synthesis and structural characterization of Eu(III)-doped Zn7Sb2O12

In addition to the lanthanide series elements, Europium is one of the chemical elements of greatest interest for the development of species with oxidation state +3 (III), which leads to interesting electronic transitions. In a general sense, their emission spectrum lines are narrow and sensitive to effects of the ligand field around metallic ions. This property allows the use of Eu(III) as a structural probe. In this work, samples of semiconductor Zn₇Sb₂O₁₂ and of solid solutions based on isoelectronically Eu(III)-doped Zn₇Sb₂O₁₂ with stoichiometry Zn_7−3x Eu_2x Sb₂O₁₂ were prepared. Both Zn₇Sb₂O₁₂ and Zn_7−3x Eu_2x Sb₂O₁₂ were synthesized via a chemical route using Pechini’s method and characterized by Fourier transform infrared absorption vibrational spectroscopy (FTIR) and photoluminescence spectroscopy. In order to perform further spectral analyses, each spectrum was adjusted using a set of Gaussian functions. The FTIR spectrum analysis showed a slight band shift of the vibration mode assigned to the Sb–O bonding ascribed to the [SbO₆] octahedron vibration. The theoretical fitting of the luminescence curves showed a broadening of the most intense emission peaks related to the transition Eu(III) ⁵D₀ → ⁷F₂. As a whole, the results suggest that a less symmetric Eu(III) site occupation in inverse spinel structure may occur in sites close to the antimony octahedron, involving, however, non-substitutional site occupation.     

Preparation, characterization and conductivity studies of Li3?2xAl2?xSbx(PO4)3

New NASICON type materials of composition, Li_3−2x Al_2−x Sb _x (PO₄)₃ (x = 0·6 to 1·4), have been prepared and characterized by powder XRD and IR. D.C. conductivities were measured in the temperature range 300–573 K by a two-probe method. Impedance studies were carried out in the frequency region 10²−10⁶ Hz as a function of temperature (300–573 K). An Arrhenius behaviour is observed for all compositions by d.c. conductivity and the Cole-Cole plots obtained from impedance data do not show any spikes on the lower frequency side indicating negligible electrode effects. A maximum conductivity of 4·5 × 10⁻⁶ S cm⁻¹ at 573 K was obtained for x = 0·8 of the Li_3−2x Al_2−x Sb _x (PO₄)₃ system.     

Tantalum influence on electrical properties of lead-free (K0.4425Na0.52Li0.0375)(Nb0.93?xTaxSb0.07) O3 piezoelectric ceramics

Lead-free (K_0.4425Na_0.52Li_0.0375)(Nb_0.93−x Sb_0.07Ta _x )O₃ (abbreviated as KNLNST _x ) piezoelectric ceramics with x = 0.045–0.075 have been prepared by an ordinary sintering technique with sintering temperature at 1,120 °C. The results of X-ray diffraction reveal that Ta⁵⁺ has diffused into the perovskite lattice to form a solid solution. The grain growth of the ceramics was inhibited by substituting Ta⁵⁺ for Nb⁵⁺. It has been shown that the substitution of Ta decreases Curie temperature T _C and orthorhombic-tetragonal phase transition temperature T _O-T. Besides, the dependence of the ceramics with different Ta content on the dielectric, piezoelectric and ferroelectric properties has been investigated. The results indicate that Ta substitution provides “soft” piezoelectric characteristics, owing to improvements in d ₃₃, k _p and ε _r and a decease in Q _m. For the ceramics with x = 0.06, the piezoelectric coefficient d ₃₃ becomes maximum at a value of 270 pC/N, while the other electrical properties remain reasonably high: dielectric constant ε _r = 1,577, planar mode electromechanical coupling factors k _p = 0.4, Curie temperature T _C = 252 °C and the remanent polarization P _r = 16.03 μC/cm². These results show that (K, Na, Li) (Nb, Sb)O₃ ceramics with small amount of Ta (x <8 mol%) are good lead-free piezoelectric ceramic.