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 ? δ} (0.06 ≤ x ≤ 0.5) and La_{1.85 ? x} Sr_{0.15 + x} Cu_{1 ? x} Co _x O_{4 ? δ} (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 ${\text{Cu}}{\kern 1pt} - {\kern 1pt} {\text{O(1)}}$ stretching vibration mode (689 cm^?1). The softening of the ${\text{Cu}}{\kern 1pt} - {\kern 1pt} {\text{O(1)}}$ phonon vibration mode gives an index of the weakening of ${\text{Cu}}{\kern 1pt} - {\kern 1pt} {\text{O}}$ hybridization. The distortion of CuO₆ octahedron and the microstructural inhomogeneity induced by Co doping lead to the widening of the IR absorption peaks.     

The HREM study of precipitates in an Al−Zn−Mg alloy

A study of precipitate phases in an Al–Zn–Mg alloy in the T74 condition has been conducted by means of high resolution electron microscopy. It has been observed that G.P. zones, and phases exist simultaneously in the matrix. The G.P. zones are plate-like forming on (111) matrix plane. The phase has a hexagonal structure witha=0.496 nm,c=1.403 nm and the orientation relationship with the matrix is . A new orientation relationship between the phase and the matrix is found to be .     

Computations of Low-Energy Non-Icosahedral Structures of C6− 60

Abstract

Owing to the three-fold degeneracy of the LUMO in C₆₀, its hexa-anion is not subjected to Jahn-Teller distortions. In contrast to the accepted presumptions, however, computations at the MNDO, AMI, PM3, SAM1, HF/STO-3G, HF/3-21G, and HF/4-31G levels show that the completely relaxed, non-icosahedral cage of C^6? ₆₀is lower in energy. The computed energy gain varies between 60 and 150 kJ/mol and thus, it is consistently significant (the most sophisticated approach, HF/4-31G, yields 93 kJ/mol). The longest C-C bond in the relaxed structures is at most computed 0.05 Å longer compared to the 5/6 bond in the icosahedral C^6? ₆₀The symmetry of C^6? ₆₀is relaxed to D₂ A C_2v, isomer is discussed, too.     

Hydrothermal synthesis and magnetic properties of CoxFe1−x/CoyLazFe3−y−zO4 composites

A series of iron–cobalt alloy and cobalt–ferrite composites doped with La³⁺ (Co_xFe_1−x/Co_yLa_zFe_3−y−zO₄) in which the Fe–Co alloy has either a bcc or a fcc structure and the oxide is a spinel phase, have been synthesized by using the disproportionation of Fe (OH)₂ and the reduction of Co (II) by Fe⁰ in a concentrated and hot KOH solution. when x ≤ 0.1, the structures of the Fe_xCo_1−x alloy and cobalt–ferrite are fcc structure; and when x ≥ 0.25, the structures of the Fe_xCo_1−x alloy is bcc structure. The fcc structure of alloy is favored for [KOH] close to 9 N, Co(II)/Fe(II) ratios between 0.5 and 0.9 and short reaction time of synthesis. And the bcc structure of the alloy is favored for [KOH] close to 1 N, Co(II)/Fe(II) ratios between 0.1 and 0.5 and long reaction time of synthesis. A low [KOH] favors nucleation leading to octahedral of 1 μm. And [KOH] of 9–12 N favors particle growth. The metal occurs in square particles of 100–150 nm included within the spinel. Powder X-ray diffraction (XRD), thermal gravity analysis (TGA) and different thermal analysis (DTA), scanning electron microscope (SEM), transmission electron micrograph (TEM) and vibrating sample magnetometer (VSM) were employed characterize the crystallite sizes, structure, morphology and magnetic properties of the composites. And the effect of the Co(II)/Fe (II) ratio (0 ≤ Co/Fe ≤ 1), concentration of KOH, reaction time and substitution Fe³⁺ ions by La³⁺ ions on structure, magnetic properties of the composites were investigated.     

Preparation and characterization of in1−xGaxAsyP1−y epilayers by liquid-phase epitaxy

In_1–x Ga _x As _y P_1–y epilayers with three different solid compositions of ln_0.73Ga_0.27As_0.60P_1.40, In_0.59Ga_0.41As_0.87P_0.13 and ln_0.53Ga_0.47As were grown on (1 0 0) InP substrate at 623° C by the step cooling technique of liquid-phase epitaxy. From the optical transmission measurements, the corresponding wavelengths of the InGaAsP epilayers were 1.30, 1.55 and 1.69 m, respectively, which are in good agreement with those obtained from the calculations using Vegard's law. The full widths at half maximum of the photoluminescent spectra at 14 K of these layers were as low as 18.6, 22.5 and 7.9meV, respectively. The electron mobility of the InGaAsP epilayers is a function of the solid composition with the ln_0.53Ga_0.47As epilayer having the highest electron mobility. The mobility and concentration of this layer are 8,873cm²V^–1 sec^–1, 9.7×10¹⁵cm^–3 and 22,900 cm²V^–1 sec^–1, 8.5×10¹⁵cm^–3 at 300 and 77 K, respectively. The compensation ratio is between 2 and 5.     

Nonstoichiometry and physical properties of the perovskite BaxLa1−xFeO3−y system

A series of samples in the Ba _x La_1–x FeO_3–y system (x=0.00, 0.25, 0.50, 0.75, and 1.00) have been prepared at 1200°C under an atmospheric air pressure. The solid solutions of the system were analysed from the X-ray diffraction spectra and thermal analyses. X-ray diffraction studies assigned the compositions of the x=0.00 and 1.00 to the orthorhombic system and the compositions of the x=0.25, 0.50, and 0.75 to the cubic system. The reduced lattice volume increased with the x value in the system. The mole ratios of the Fe⁴⁺ ion in the solid solutions, or values, were determined by Mohr salt analyses and the non-stoichiometric chemical formulae of the system were formulated from the x, , and y values. From the results of the Mössbauer spectroscopy, the coordination and the magnetic property of the iron ion have been discussed. The electrical conductivities were measured as a function of temperature under atmospheric air pressure. The activation energy was minimum at the composition of x=0.50. The conduction mechanism can be explained by the hopping model between the mixed valences of the Fe³⁺ and Fe⁴⁺ ions.     

Dielectric properties of the system Ba1−xLaxTi1−xCo x O3

The dielectric behaviour of compositions withx=0.01, 0.05, 0.10 and 0.20 in the system Ba_1–x La _x Ti-_1-x Co _x O₃ was studied in the temperature range 300–473 K. The compositions withx = 0.01 and 0.05 show a diffuse ferroelectric-paraelectric phase transition, while other compositions do not show this transition in this temperature range. The frequency dependence of dielectric constant and dielectric loss in the samples withx0.05 indicates that spacecharge polarization contributes significantly to their observed dielectric parameters.     

Superconducting Density of States from the Magnetic Penetration Depth of Electron-Doped Cuprates La2−x Ce x CuO4−y and Pr2−x Ce x CuO4−y

From measurements of the magnetic penetration depth, (T), from 1.6 K to T _c in films of electron-doped cuprates La_2–x Ce _x CuO_4–y and Pr_2–x Ce _x CuO_4–y we obtain the normalized density of states, N _s(E) at T=0 by using a simple model. In this framework, the flat behavior of ^–2(T) at low T implies N _s(E) is small, possibly gapped, at low energies. The upward curvature in ^–2(T) near T _c seen in overdoped films implies that superfluid comes from an anomalously small energy band within about 3k _B T _c of the Fermi surface.     

Investigation of structural,electrical and tribological properties of duplex surface treated and aged Cu−Cr−Zr alloy

In this study, Cu−Cr−Zr alloy specimens were first subjected to aging heat treatment at 500 °C for two different durations (2 hours and 4 hours). Three different coating processes (silver, silver/copper duplex, and copper/silver duplex) were applied to the aged specimens using the physical vapor deposition method. Tensile test, microhardness measurement, wear test, electrical conductivity measurement and structural analysis (x-ray diffraction and scanning electron microscope) were applied to the specimens. After the aging processes, the highest hardness and strength values of the Cu−Cr−Zr alloy were obtained in the specimens that were aged at 500 °C for 4 hours. When the wear resistance and electrical conductivity of the coated specimens were examined, it was determined that the specimens with duplex surface treatment performed better.     

Raman scattering of magnetic excitations in Y1−x Prx Ba2Cu3−yAlyO7−δ single crystals

Magnetic excitations and their role for the superconductivity in cuprate superconductors have been widely discussed in the literature. Here, we present a study of Y_1–x Pr_x Ba₂Cu_3–yAl_yO_7– single crystals using Raman spectroscopy in an energy range of 50 – 10000 cm^–1 Raman shift. The high energy range is dominated by a two-magnon scattering process at 3J, where J is the superexchange energy. In the Pr-123 single crystal, we find J = 720 cm^–1, a damping of the one-magnon states = 200 cm^–1, and a resonance energy of 2.79_eV for the two-magnon excitation. The two-magnon peak shows a continuous increase of the one-magnon damping with decreasing x and a nearly constant J across the phase transition to the superconductor. Especially, we find a weak two-magnon peak for a superconductor with a T_c = 86 K.     

Critical Behavior of 2 − Ions in Argon Gas

We measured the drift mobility of ₂ ^– ions in argon gas close to the critical point for (1.005 < T/T _c < 1.04) above T _c 150.7 K in the density range (0.025 <N/N _c< 1.733) around the bulk critical density N _c = 8.08 atoms . nm^–3. The density-normalized zero-field mobility ₀ N of the ions shows a deep minimum as a function of the gas density N as T T _c ⁺ This anomalous reduction of ₀ N occurs at a density N _m 0.76N _c. We believe that this behavior is due to the strong electrostriction exerted by the ion on the highly compressible gas. By introducing suitable contributions to the effective ion radius R due to the large gas compressibility and taking into account short-range local density and viscosity augmentation due to electrostriction, the hydrodynamic Stokes formula ₀ = e/6R, where is the gas viscosity, is in good agreement with the experimental data.     

Effect of longitudinal−torsional vibration in ultrasonic-assisted drilling

In general, drilling of aeronautical materials is faced with some difficulties. To improve this process, a variety of methods have been presented by researchers. One of these methods is ultrasonic-assisted drilling (UAD). In this study, performance of longitudinal?torsional (L-T) vibration in UAD of Al 7075-T6 with HSS tool is investigated. Accordingly, a vibration tool with ability of producing L-T vibration was designed. After modal analysis and achievement of desired resonance frequency, it was fabricated and some experimental tests were conducted. A dynamometer with six degrees of freedom was utilized to measure torque and thrust force during the cutting process. As a result, it was revealed that this kind of vibration significantly reduces cutting forces compared with the conventional drilling (CD). Furthermore, this reduction was clarified by investigation of generated chips and tool rake angle. Moreover, effect of ultrasonic vibration on drill skidding and surface quality has been studied.     

The effect of indium on porcelain bonding between porcelain and Au−Pd−In alloy

The effect of small In additions on oxide structure and porcelain adherence to Au–Pd alloys was studied. In was oxidized internally as In₂O₃. No uniform external oxide layer could be seen. Small In addition (1 at %) did not have any detectable effect on porcelain adherence (12 MPa), whereas higher In concentration (5 at %) caused significant increase in bond strength (26 MPa). This increase was probably a result of higher In₂O₃ concentration at the surface.     

Investigation of structural,luminescence, and anti-bacterial properties of novel Zn1−xEuxAl2−yO4Sry phosphor

Journal of Materials Science: Materials in Electronics - In this research work, we synthesized novel zinc aluminate (Zn1?xEuxAl2?yO4Sry) sky bluish phosphors at 500&nbsp;°C via...