International Journal of Modern Physics B

The thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA) of the as-deposited and electrochemically oxidized Hg₁Ba₂Ca₁Cu₂O_6+δ(Hg-1212) samples were carried out in air, flowing oxygen and nitrogen environment in order to estimate the thermal decomposition temperature and hence to maintain the annealing temperature and atmosphere. After annealing, electrochemically synthesized films showed an increase in T_c from 104.7 K to 119 K and J_c values from 1.43×10³ to 4.3×10³A/cm². Electrochemically oxidized Hg-1212 films in under-, optimally- and over-doped states were irradiated with a Red He–Ne laser (2mW) and the T_c was found to increase from 104.7 K to 106 K and J_c from 1.43×10³ to 1.89×10³A/cm². The effects of annealing and photo-irradiation on structural, microstructural and superconducting properties of electrochemically synthesized Hg-1212 films were investigated and discussed in detail in this paper.

The complex arrangements of atoms near grain boundaries are difficult to understand theoretically. We propose a phenomenological (Ginzburg–Landau-like) description of crystalline phases based on symmetries and some fairly general stability arguments. This method allows a very detailed description of defects at the lattice scale with virtually no tunning parameters, unlike the usual phase-field methods. The model equations are directly inspired from those used in a very different physical context, namely, the formation of periodic patterns in systems out-of-equilibrium (e.g. Rayleigh–Bénard convection, Turing patterns). We apply the formalism to the study of symmetric tilt boundaries. Our results are in quantitative agreement with those predicted by a recent crystallographic theory of grain boundaries based on a geometrical quasicrystal-like construction. These results suggest that frustration and competition effects near a defect in crystalline arrangements have some universal features, of interest in solids or other periodic phases.

The optical properties of metal-free phtalocyanine (H₂Pc) in thin film form is investigated. X-ray diffractograms of the (H₂Pc) powder show that it has a α-polycrystalline form with a monoclinic structure. The thermal evaporation of (H₂Pc) powder leads to α-polycrystalline films, oriented preferentially to the (001) plane. After annealing at 623 K for two hours, a mixture of α- and β-phases is formed on an amorphous background. The optical properties of (H₂Pc) thin films have been studied using spectrophotometeric measurements of transmittance and reflectance in the range 200–2200 nm for a different film thickness. The refractive index and the absorption index show independence on the film thickness. The refractive index shows anomalous dispersion in the region of the fundamental absorption edge. The absorption measurements show the characteristic splitting of the Q-band and ΔQ is obtained as 0.22 eV. The absorption coefficient in the absorption region reveals indirect transitions. The fundamental and the onset energy gap are determined as 2.74 eV and 1.55 eV, respectively.

We propose an operator Hamiltonian (a ring of identically coupled harmonic oscillators) to describe the linear lattice chain with Born–von Karmann boundary condition. We apply the method of "invariant eigen-operator" to study this Hamiltonian and derive its invariant eigen-operator. The vibrational spectrum is thus obtained. This approach seems concise and direct and can be extended to tackle other Hamiltonian models.

The ground state properties and the structural phase transformation of tin dioxide (SnO₂) have been investigated using first principle full potential-linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). We used local density approximation (LDA) and the generalized gradient approximation (GGA), which are based on exchange-correlation energy optimization, to optimize the internal parameters by relaxing the atomic positions in the force directions and to calculate the total energy. For band structure calculations, we utilized both the Engel-Vosko's generalized gradient approximation (EVGGA), which optimizes the exchange-correlation potential, and also GGA. From the obtained band structures, the electron (hole) valance and conduction effective masses are deduced. For compressed volumes SnO₂ is shown to undergo two structural phase transitions with increasing pressure from the rutile- to the CaCl₂-type phase at 12.4 GPa and to a cubic phase, space group at 22.1 GPa. The calculated total energy allowed us to investigate several structural properties, in particular, the equilibrium lattice constants, bulk modulus, cohesive energy, interatomic distances and the angles between different atomic bonds. In addition, we discuss the bonding parameter in term of charge density, which show the localization of charge around the anion side.

Electrorheological (ER) fluids are a kind of smart materials whose rheological properties can be rapidly changed by applied electric fields. Many potential industrial applications of ER technology have been proposed. In order to formulate better ER fluids and design ER devices, it is important to predict the yield stress of ER fluids based on the ER fluids components and the operating conditions. This paper proposes a new method for predicting the yield stress of ER fluids with neural network (NN). A multilayer perceptron with a single hidden layer of neurons is used to model the ER effect. The data for training and test were produced from the simulation of previous proposed mathematical models. The Levernberg–Marquardt back propagation algorithm was selected for fast learning. The results show the neural network model can well approximate the previous theoretical model, and the predicted outputs of NN agree nearly with the theoretical model values under the same input, all of which demonstrate that it is possible to generate a robust NN model for rapidly predicting the yield stress of ER fluids under different input parameters.

We describe the fractal solid by a special continuous medium model. We propose to describe the fractal solid by a fractional continuous medium model, where all characteristics and fields are defined everywhere in the volume but they follow some generalized equations which are derived by using fractional integrals of fractional order. The order of fractional integral can be equal to the fractal mass dimension of the solid. Fractional integrals are considered as an approximation of integrals on fractals. We suggest the approach to compute the moments of inertia for fractal solids. The dynamics of fractal solids are described by the usual Euler's equations. The possible experimental test of continuous medium model for fractal solids is considered.

Magnetic properties of Bi³⁺-doped La_0.67-xBi_xCa_0.33MnO₃(x = 0, 0.05, 0.1, 0.2) are investigated. Using the mean-field and ferromagnetic spin-wave theory at low temperatures, total exchange integrals and Curie temperatures are calculated in the range 0≤x≤0.2. Calculated values of T_c are in good agreement with those obtained by magnetic measurements. In addition, the total exchange integral decrease with Bi³⁺ shows the existence of canted ferromagnetic order in the samples, as observed in experimental results.

The self-diffusion coefficient of the cyclohexane in some polybutadiene solutions was measured by NMR pulse magnetic field gradient method. The experimental data were analyzed on the basis of the free volume theory. A specific algorithm for analyze was proposed. Preliminary investigation indicates a deviation from the WLF theory for these solutions.

The current induced local spin polarization due to weak Rashba spin-orbit coupling in narrow strip is studied. In the presence of longitudinal charge current, local spin polarizations appear in the sample. The spin polarization perpendicular to the plane has opposite sign near the two edges. The in-plane spin polarization in the direction perpendicular to the sample edges also appears, but does not change sign across the sample. From our scaling analysis based on increasing the strip width, the out-of-plane spin polarization is important mainly in a system of mesoscopic size, and thus appears not to be associated with the spin-Hall effect in bulk samples.