Microstructure and Physical Properties of Bi1.9+<Emphasis Type="Italic">x</Emphasis>Sr1.7−<Emphasis Type="Italic">x</Emphasis>La0.4CuO6 System

The crystal microstructure, superconductivity, and normal state transport properties of Bi_1.9+xSr_1.7?xLa_0.4CuO_6+δ(0 ≤ x ≤ 0.4) system were investigated by means of electron diffraction (ED), resistivity, and TEP. Analyses of the experimental results indicate that with the increase of Bi content, the incommensurate modulation wavelength decreases and the distortion of CuO₆ octahedron enhances. Increasing Bi content decreases the carrier concentration rapidly, and induces an MI transition. The destruction of superconductivity mainly derives from two aspects: the enhancement of structural distortion due to the introduction of more Bi and the variation of the carrier concentration of the system.     

Phonon Vibration and Conduction of La2 ? xSrxCuO4 ? δ and La1.85 ? xSr0.15 + xCu1 ? xCoxO4 ? δ

Polycrystalline samples La_{2 – x} Sr _x CuO_{4 –} (0.06 x 0.5) and La_{1.85 – x} Sr_{0.15 + x} Cu_{1 – x} Co _x O_{4 –} (0 x 1) were synthesized by a conventional solid state reaction method. The structure, phonon vibration, and conduction were investigated by means of XRD, infrared (IR) spectra, and resistance. It is found that the increase of itinerant hole carriers could mask the in-plane stretching vibration mode (689 cm^–1). The softening of the phonon vibration mode gives an index of the weakening of hybridization. The distortion of CuO₆ octahedron and the microstructural inhomogeneity induced by Co doping lead to the widening of the IR absorption peaks.     

The Transport Properties of Bi-Riched Bi2Sr2CuO6+δ Single Crystal

As-grown superconducting Bi-riched Bi₂Sr₂CuO₆₊ single crystals have been grown by the traveling solvent floating zone technique. The superconducting transition temperature T _c was about 6 K and the room temperature resistivity was about 2×10^–3 Ohm-cm. Transport properties, such as resistivity, magnetoresistance and Hall effect were measured from overdoped to underdoped samples annealed in inert atmosphere at 650°C. The transition temperature can be raised to 12 K after post annealing. The Hall measurement shows that the hole carrier density decrease after annealing. The temperature dependence of Hall angle is T ^1.5, not quadratic as observed for most high-T _c superconducting oxides such as YBa₂Cu₃O₇. The variation of onset T _c with different external magnetic field is very different from high-T _c superconductors. The in-plane conductivity shows the dependence of ln T and can be explained by weak localization theory.     

Microstructure and Tensile Properties of Spray-deposited IC6 Alloy

The microstructure and mechanical properties of a Ni3Al based Ni-Al-Mo superalloy-IC6 which possesses low impurity content and high density by spray deposition technique have been studied.The results indicate that the IC6 alloy has good tensile strength and elongation both at room and intermediate temperatures     

Impurity Resonance States in Bi2Sr1.6La0.4CuO6+δ

Using scanning tunneling spectroscopy (STS) at 4.2?K, we observed impurity resonance in single crystals of Zn doped Bi₂Sr_1.6La_0.4CuO_6+?? (T _C =28?K) (Bi2201). Many impurity resonances characterized by the peak structure near E _F were observed. We found that the number of the resonances was less than that of the doped impurities (0.45?% determined by inductively coupled plasma optical emission spectrometry). The resonance peaks were observed only in the region having smaller gap less than ??_cut??26?meV. This ??_cut was about half of that reported in Bi₂Sr₂CaCu₂O_8+?? .     

XRD and PES Studies of the Bi2Sr2Ca1?xPrxCu2O8+δ System

The Bi₂Sr₂CaCu₂O₈₊ system samples doped with Pr on Ca sites were synthesized. Resistivity measurements, x-ray powder diffraction, and photoemission experiments were performed. The experiment results show that Pr ions entered the lattice and chemical environment plays a major role in the shift of core-level spectra and valence-band spectra.     

Effect of ZrO2 Addition on Microstructure, Transport and Magnetic Properties of Bi2Sr2CaCu2O8+δ System

The influence of zirconium (Zr) addition to the Bi₂Sr₂CaCu₂O_8+δ (Bi2212) system on its phase formation, microstructure, transport, and magnetic properties is investigated. Samples have been characterized by means of X-ray diffraction analysis (XRD), scanning electron microscopy equipped with energy dispersive of X-ray analysis (SEM/EDX), and resistivity versus temperature measurement. The results show an increase of the critical temperature of superconductive transition T _c for x=0.01 and in all the samples containing Zr the Bi2212 phase is the majority. SEM observations show whiskers grains randomly distributed and microstructural change due to the addition of Zr. Resistivity measurement show that the temperature of the onset of transition T _c increases by 9 K for x=0.005, 0.02, and 5 K for x=0.01 of ZrO₂. An improvement of the normal state conductivity is obtained for the lowest content of Zr (x=0.005). In the normal state, all the samples exhibit a metallic behavior except the sample with x=0.01, which exhibit a semiconductor character.     

Effect of Zn, Ni and Fe Impurities on Bi2Sr1.6La0.4CuO6+��

We measured the change of T _c with the doping of the magnetic and nonmagnetic impurity in Bi₂Sr_1.6La_0.4CuO_6+?? (Bi2201). The reduction of T _c is about 20% in samples with Zn (1.1%), Ni (1.0%), and Fe (1.2%), and a slight difference was observed among these samples. We also observed the resonance peak at the Zn-impurity site by scanning tunneling spectroscopy at 4.2 K. The observed resonance peak showed the four-fold symmetry, and appeared at approximately ?1.5 meV.     

Microstructure and Mechanical Properties of TiAl-based Alloy

Two phases gamma titanium aluminide alloy,Ti-46.5Al-2.5V-1Cr.was investigated to characterizemicrostructures and to define the microstructure/mechanical property relationship.Many kinds ofmicrostructure of gamma and α_2 phases were obtained by heat treatments in the α+γ,α_2+γ and αfields.The effects of microstructure on tensile properties,fracture toughness and J-R resistancecurve at room temperature,were systematically studied.The experimental results showed that themicrostructure had a strong effect on mechanical properties,The duplex microstructure produced byheat treatment at 1250℃×4 h with controlled cooling resulted in the highest ductility of 4.8% tensileelongation,low fracture toughness and crack growth resistance.The fully lamellar microstructureproduced by heat treatment in the α field having large grain sizes resulted in the highest fracturetoughness but the lowest ductility.     

Out-of-Plane Negative Magnetoresistance of Bi2Sr1.6La0.4CuO6+δ Single Crystals in the Underdoped Region

In order to investigate a relationship between the carrier concentration and negative magnetoresistance in the underdoped region, we have performed out-of-plane electrical resistivity measurements for underdoped Bi ₂ Sr _1.6 La _0.4 CuO ₆₊ single crystals. Giant negative magnetoresistance has been observed in the most abundant carrier sample with = 0.12 in our experiment. The negative magnetoresistance reduces with decreasing carrier concentration.     

Substitution Effect of Sn for Cu in the Bi2Sr2CaCu2?xSnxO8+δ System

The Bi₂Sr₂CaCu₂O₈₊ system samples doped with Sn on Cu sites were synthesized. Resistivity temperature dependence, X-ray powder diffraction and photoemission experiments have been performed. Suppression of superconductivity in the Sn-doped Bi₂Sr₂CaCu₂O₈₊ system has been observed. X-ray photoemission measurements show that Sn ion enters the lattice. Our results reveal that Sn ions are mostly in bivalent states.     

Mechanical Properties of Bi1.6Pb0.4Sr1.8Ba0.2Ca2Cu3?x Ni x O10+δ Superconducting System

Samples of Bi_1.6Pb_0.4Sr_1.8Ba_0.2Ca₂Cu_3?x Ni _x O_10+?? were prepared by solid-state reaction methods. Mechanical properties (Vickers microhardness, Young modulus, yield strength, fracture toughness and surface energy) by Vickers microhardness measurements have been carried out to examine the effects of Ni substitution. The results showed a deterioration of the mechanical properties with the enhancement of Ni content.     

Magnetic and transport properties of Mn3+xGa1?xN compounds

Mn_3+x Ga_1−x N compounds with x = 0.0 and 0.1 were prepared by re-sintering Mn₂N_0.86, Ga bulk and Mn powders. These compounds are deduced to be the N-deficiency ones. In Mn₃GaN, a step-like magnetic transition, from frustrated antiferromagnetism to paramagnetism with increasing temperature, occurs at 370 K, while the same magnetic transition of Mn_3.1Ga_0.9N is far above 380 K. The enhanced magnetization of Mn₃GaN at low temperatures is ascribed to the fast lowering of antiferromagnetism. The electrical resistivity of Mn₃GaN exhibits a typically metallic conducting behavior with a positive magnetoresistance of 4–7%.     

Physical and Dielectric Properties of Some Nonionic Surfactants

Fatty acid esters have been prepared by reacting the acid C18 with polyethylene glycols having varying numbers of Oxythylene units (4~88 units) by the direct eSterification reaction method.Surface and interfacial tensions are studied at various experimental conditions, including, concentration, temperature, and chemical constitution of the surfactants. Critical micelle concentrations (CMC), surface excess Г and residual area occupied by each surface active agent molecule A have been calculated using Gibb's equation. CMC values range from 10 to 55x10-5 mole/L for all studied agents, while the residual area occupied by each molecule varies from 0.6 to 1.5 nm2. Variation of CMC of some of these agents with temperature have been also examined and data obtained are used to calculate the heat of micellization △Hm and the entropy change during micellization △Sm. Values of △Hm varies from 14.63 kJ/mole to 2.717 kJ/mole depending on the chemical constitution of the agent under consideration. The apparent dipole moments μ of three surfactants were measured following the Headstrand's method. Values of μ are 3.24, 3.14 and 3.02 D for stearates. oleates. and linoleates adducts with polyethylene glycol (1000).     

Microstructure and Mechanical Properties of Dy-α-sialon/Nano-size SiC Composites

The composite of Dy-α-sialon/10 wt pct nano-size SiC particles has been prepared from precursor powders of Si3N4, AIN, Al2O3, Dy2O3 and nano-size β-SiC. The hardness, toughness and bending strength of the composite at ambient temperature are a little higher than those of Dy-α-sialon.while the bending strength is maintained up to 1000℃ and about 2 times more than that of Dy-α-sialon at the same temperature. The fracture surfaces show that the grain size of the composite is smaller than that of Dy-α-sialon, and both Of them have predominately transgranular mode of fracture. It is believed that the decrease of the bending strength of Dy-α-sialon at elevated temperature is caused by the viscous flow of the grain boundary phase, while the addition of nanosize SiC particles effectively increases the viscosity of the grain boundary phase and therefore prevents the strength loss of Dy-α-sialon/nano-size SiC composites at elevated temperature     

Mechanical Properties and Microstructure of Diamond–SiC Nanocomposites

A bulk composite material close in hardness to diamond was fabricated from nanocrystalline diamond and SiC. The mechanical properties and microstructure of the composite were studied. Young's modulus of the composite is found to be notably lower than the one following from the additivity rule, which is attributable to the influence of structural defects present in the interfacial zone between SiC and diamond. SiC consists of nanometer-scale grains near the interface and submicron grains in the pores.     

Structure and Diamagnetic Properties of (Pb0.6SnyCu0.4 ? y)Sr2(Y1 ? xCax)Cu2Oz

The effect of Sn doping in (Pb_0.6Sn _y Cu_{0.4 – y} )Sr₂(Y_{1 – x} Ca _x )Cu₂O _z with 0 y 0.3 and 0 x 0.7 was investigated. It was established that a nearly pure 1212 phase can be obtained at 0 y 0.1 and 0 x 0.3. The obtained XRD patterns as well as the results of the EDX and ICP-AES analyses showed that Sn substitution is possible in the (Pb,Cu)-1212 phase. Superconductivity was observed at 0.4 x 0.7. The onset of the diamagnetic transitions varied from 10 to 30 K. The influence of the strong Pb deficiency on the superconducting properties of the samples was discussed.     

Electron Spectroscopy of Single-Layer (n = 1) Bi2Sr2?xLaxCuO6+δ Crystals at Optimal Doping

On single crystals of the single-layer (n = 1) high-T _c superconductor Bi₂Sr_2–x La _x CuO₆₊ at optimal doping (x = 0.4), the electron spectroscopies x-ray absorption (XAS) and high-resolution angle-resolved photoemission (ARPES) were performed. The XAS gives the intensity of the so-called prepeak of the O 1s line what is due to the unoccupied part of the Zhang–Rice (ZR) singlet band. For ARPES, the advantages of single-layer material are the absence of bilayer effects and the possibility to study the electronic properties of the normal state at a sample temperature where the thermal broadening is extremely small (<10 meV). The controlled variation of the polarization vector of the synchrotron radiation made it possible to resolve a distinct fine-structure of the occupied part of the ZR singlet band at the Fermi level. These observations have enormous consequences for line shape analyses and the determination of pseudogaps, and thus the mechanism of high-T _c superconductivity.     

Systematic Evolution of the Magnetotransport Properties of Bi2Sr2−x La x CuO6 with Carrier Concentration

We report that it is possible to obtain a series of high-quality crystals of Bi ₂ Sr _2–x La _x CuO ₆ , of which the transport properties have been believed to be dirtier than those of other cuprates. In our crystals, the normal-state transport properties display behaviors which are in good accord with other cuprates; for example, in the underdoped region the in-plane resistivity _ab shows the pseudogap feature and in the overdoped region the T dependence of _ab changes to T ⁿ with n>1. The characteristic temperatures of the pseudo-gap deduced from the resistivity and the Hall coefficient data are presented.