International Journal of Modern Physics B

We argue that the usual Hubbard's model produces only s-wave pairing functions and, even then, only at unphysically large values of the lumped parameter J≡4t²/U. It follows that a reliable theory of high-T_c superconductivity has to include additional features if it is to reproduce the d-wave gap. We test the effects of an alternating potential caused by a charge stripe, on the ground state of the Hubbard model in strong-coupling. If we "fine tune" we do find the d-waves. However, a better-formulated version of a three-band model yields a sturdier theory of pair formation in high-T_c superconductivity. The coupling constant g₁=t²/V factors out, hence it serves only to establish the unit of energy; the underlying Hamiltonian is universal. We outline the principal properties of this model, including the intimate relation between charge-density stripes and the d-wave pair function, its rejection of 45° stripes (checkerboard pattern), and other concerns.

In order to elucidate the type of trap distribution in borate glass we have analyzed a set of glow peaks around 110°C recorded with different doses of β-ray irradiation. The glow curves are subjected to the rigorous Computerized Glow Curve Deconvolution (CGCD) both in the framework of kinetic formalism and differential equation formalism to judge which type of trap distribution favors in borate glass. It is observed that the distribution of traps is exponential, which is also well supported by standard error analyses i.e. Figure Of Merit (FOM) and Chi-square (χ²) test.

A Quasi-lattice model of liquid binary mixtures has been used to establish a model for calculating some thermodynamic properties of compound forming ternary liquid alloys. The effect of varying Z on the concentration fluctuations was also investigated. Results obtained for limiting case of the model are presented and compared with that obtained by Bhatia and Singh for binary liquid alloys. A framework for calculating the Warren Cowley short range order for ternary liquid alloys as a function of Z is also formulated.

By considering a discrete isospectral problem [H.-X. Yang et al., Phys. Lett. A338, 117 (2005)], integrable positive and negative lattice equations are derived, from which the modified (2+1)-dimensional Toda lattice is obtained. The method of enlarging spectral problems to construct the integrable couplings for lattice soliton equations is extended to higher-dimensional systems. Illustrating by examples, the positive and negative integrable couplings of the resulting lattice hierarchy and three classes of integrable couplings of (2+1)-dimensional mToda lattice are discussed.

Multilayer transparent conducting zinc oxide films have been prepared on boro-silicate substrates by the commercially sol gel dip coating process. Each layer was fired at 550°C in a conventional furnace for 15 min. The final coatings were then tempered under a flux of forming gas (N₂/H₂) at 400°C for 2 h. The coatings were characterized by surface stylus profiling and optical spectroscopy (UV-NIR). Results show that (1) ZnO films with electrical resistivity of 6×10^-4 Ω·cm, free carrier mobility of approximately 77 cm²/V·s and free carrier density of approximately 6.14×10¹⁹cm^-3 are obtained for multilayers 310 nm and (2) the transmittance is approximately 60.4% and the reflectance is nearly 34.7% are obtained at a wavelength of 800 nm when the thickness of the ZnO multilayers is 310 nm. The crystal structure and grain orientation of ZnO films were determined by X-ray diffraction. SEM investigations revealed that the surface morphology of growing ZnO films on boro-silicate substrate is dominated by the smooth surface with a fine microstructure.

Single crystals of Na_0.495CoO₂ were obtained through a flux method followed by de-intercalation of sodium. The resistivity (ρ) and thermal stability were studied for the de-intercalated samples exposed to humid air. It was found that the de-intercalated Na_0.495CoO₂ crystal is vulnerable to water in the air, and a hydration process in which H₂O molecules fill oxygen vacancies in CoO₂ layers instead of being intercalated between CoO₂ layers is suggested to be responsible for the remarkable change in resistivity induced by water absorption. The Na_0.495CoO₂ sample shows a weak localization of carriers just below 200 K and Co³⁺–Co⁴⁺ charge ordering at about 40 K, lower than the corresponding charge ordering transition temperature reported in Na_0.5CoO₂. The lower charge ordering transition temperature might be caused by the slight deviation of Na content (x) from 0.5.

The series mean spherical approximation (SMSA) for the hard sphere–Yukawa (HSYK) fluid is applied to C₆₀. The energy and range parameters of HSYK potential have been reduced to one parameter by forcing the q→0 limit of the Fourier transform of the potential to be identical to that of the empirical potential of C₆₀. The new equation of state (EOS) allows us to investigate the liquid–vapor coexistence curve and calculate the thermodynamic properties of liquid C₆₀. The comparisons with computer simulation results suggest the importance of treating the attractive tail of the potential accurately. The estimated critical parameters T_c=1984.8 K, ρ_c=0.464 nm^-3 and P_c=36.3 bar, which are in good agreement with NVT-Monte Carlo computer simulation predictions. The results are discussed by making reference to previous studies.

In this work, effect of thickness of the liquid crystalline layer on the morphologic, thermotropic and thermodynamical properties of the nematic–isotropic liquid and isotropic liquid–nematic phase transitions in Shiff based liquid crystals has been investigated.

The shift of temperatures of the nematic–isotropic liquid and isotropic liquid–nematic phase transitions to the lower temperatures and the widening of linear and temperature widths of the heterophase regions of these phase transitions by the increase in the thickness of liquid crystalline layer have been found.

The effect of thickness of liquid crystalline layer on morphologic, thermotropic and thermodynamical properties of liquid crystals under investigations is connected with change of interaction energy between liquid crystalline molecules and reference surfaces.

The ESR spectra of amorphous thin films of mixed oxides In₂O₃–SnO₂ system is presented. An initial increase in the intensity of ESR signal at g=1.994, and decrease in the intensity of the signal at g=1.98 with an increase in Sn content in In₂O₃ lattice is caused by the Sn atom substitution of In atom, giving out one extra electron. The decrease in the intensity of ESR signal at g=1.994 and an increase in the intensity of the signals at g=1.98 above the critical Sn content (10 mol% SnO₂) is caused by the defects formed by Sn atoms, which act as carrier traps rather than as electron donors. The increase in the intensity of ESR signal at g=1.89 with the increase in Sn content in mixed oxides In₂O₃–SnO₂ system is caused by the increase in the concentration of oxygen vacancies, which are generated in the In₂O₃ and SnO₂ lattices by thermal evaporation. The increase in the intensity of ESR signals at g=1.994, g=1.98 and g=1.89 with the increase in thickness is caused by the bulk properties of the films. The increase in the intensity of ESR signals at g=1.994, g=1.98 and g=1.89 with the increase in substrate temperatures is due to the increase in the concentration of oxygen vacancies, which are generated at higher substrate temperatures and to the diffusion of Sn atoms from interstitial locations into the In cation sites, which result in higher electron concentration. The decrease in the intensity of ESR signals at g=1.994, g=1.98 and g=1.89 with an increase in annealing temperature is attributed to the rearrangement of the atoms and to the removal of voids, which causes a decrease in the number of unsatisfied bonds and formation of indium and tin species of lower valence states. The new oxidation states, the In²⁺ and the Sn²⁺, formed due to the annealing of the samples can be attributed to the internal electron transfer from oxygen 2p to the In5s and Sn5s levels, both in In₂O₃ and SnO₂.

The dielectric constant of lead-based ferroelectric ceramics in three different systems, i.e. BT-PZT, PMN-PT and PMN-PZT, was measured under uniaxial compressive pre-stress to investigate the contributions of different domain-phenomena. The dielectric constant was observed at room temperature under the compressive pre-stress up to 15 MPa, 22 MPa and 5 MPa for BT-PZT, PMN-PT and PMN-PZT, respectively, using a homebuilt uniaxial compressometer. Dielectric constant of the BT-PZT ceramics increased significantly with increasing applied stress. Larger changes in the dielectric constant with the applied stress were observed in the PZT-rich compositions. However, for PMN-PT and PMN-PZT ceramic systems, changes in the dielectric constant with the stress were found to depend significantly on the ceramic compositions. The experimental results could be explained by both intrinsic and extrinsic domain-related mechanisms involving domain wall motions, as well as the de-aging phenomenon from the application of the compressive pre-stress. Roles of different types of domains, i.e. micro-domains and nano-domains, were also discussed.