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An attempt has been made to explore theoretically the anisotropic properties of penetration depth of optimally doped iron pnictide superconductors in the presence of magnetic field reported by Tanatar et al. (2009). In doing so, the modified Phenomenological Ginzburg Landau (GL) theory applicable to two band superconducting systems by Purohit et al. (2016) is used here. The analysis and calculated values of anisotropic ratio of penetration depth found to be 2.24 which is very close to the experimental value of 2.1 to 2.6 as reported earlier. [ABSTRACT FROM AUTHOR]

Trigonometric Fourier approximation and Lipchitz class of function had been introduced by Zygmund and McFadden respectively. Dealing with degree of approximation of conjugate series of a Fourier series of a function of Lipchitz class Misra et al. have established certain theorems. Extending their results, in this paper a theorem on trigonometric approximation of conjugate series of Fourier series of a function f ∊W (LP, ξ(t) by product summability (E,s)(N, pn, qn) has been established. [ABSTRACT FROM AUTHOR]

Structural, Dielectric and Conduction behavior of Lanthanum modified Strontium Bismuth Titanate (SrBi4-xLaxTi4O15) (SBLT) ceramic were investigated. X-ray diffraction (XRD) analysis at room temperature of the prepared materials confirmed the formation of the compounds with orthorhombic crystal system. Lanthanum-doping results decrease in transition temperature. The ac conductivity (σ ac) and tangent loss of SBLT samples decreased compare to the SBT, which can be explained in terms of decrease of oxygen vacancy concentration. [ABSTRACT FROM AUTHOR]

We analyse the effect of uniform electric field on the low temperature multisubband electron mobility in an InGaAs/InAlAs double quantum well structure in which the side barriers are delta-doped with layers of Si. The electric field, which is perpendicular to the interface plane of the structure, alters the subband energy levels and wave functions which in turn leads to a change in the subband mobility. We consider ionized-impurity scattering, alloy disorder scattering and interface roughness scattering and analyse the changes in them due to the applied electric field mediated by the intersubband interactions. We show that application of the field transforms a system from double subband occupancy to single subband occupancy thereby suppressing the intersubband interaction which in turn enhances the mobility. We also change the well width to study its effect on mobility as a function of the applied electric field, which yields interesting results. [ABSTRACT FROM AUTHOR]

The polycrystalline sample of LiSr2Nb5O15 (LSN) was prepared by a high temperature solid-state reaction technique. Studies of structural and microstructural characterizations were performed by X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. X-ray studies reveal that the material has an orthorhombic structure at room temperature. Dielectric properties were measured over a wide range of temperature (28-500 °C) and frequency (102-106 Hz). Conductivity of the material increases with rise in temperature. [ABSTRACT FROM AUTHOR]

A new tungsten bronze ceramic sample Na2Pb2Nd2W2Ti4Ta4O30 was prepared by a high-temperature solid-state reaction technique. X-ray diffraction studies of the compound showed the formation of single-phase orthorhombic crystal structure at room temperature. Surface morphology of the compound was studied by scanning electron microscope (SEM). Study of dielectric properties ([variant_greek_epsilon]r, tanδ) of the compound at different frequencies (1, 10, 100 kHz and 1 MHz) in a wide temperature range (300-700 K) shows ferroelectric phase transition of diffused type at 400K. [ABSTRACT FROM AUTHOR]

This article reports a systematic study of doping effects on the structural and electrical properties of layer structured strontium bismuth titanate ceramic. In this study monophasic SrBi4Ti4-xZrxO15 with x=0.00, 0.05, 0.10, 0.15, 0.20, 0.25 ceramics were synthesized from the solid-state reaction route. X-ray diffraction analysis shows that the Zr-modified SBT ceramics have a pure four-layer Aurivillius phase structure. Dielectric properties revealed that the diffuseness of phase transition increases where as corresponding permittivity value decrease with increasing Zr content. Piezoelectric properties of SBTZ ceramics were improved by the modification of Zirconium ion. Moreover, the reason behind for improvement of piezoelectric properties of modified SBTZ ceramics was also discussed. [ABSTRACT FROM AUTHOR]

The composites of BiFeO3-PbTiO3 (BF-PT) and BiFeO3-PbZrO3 (BF-PZ) were prepared by mixed oxide method. Room temperature X-ray diffraction data confirms the rhombohedral and tetragonal crystal structure respectively. Dielectric constant of BF-PZ is found to give high value compared to BF-PT and hence, there is an increase value of ac conductivity for the former. Both the composites show negative temperature coefficient of resistance (NTCR) behavior. The activation energies of BF-PT and BF-PZ are found to be 0.35 eV and 0.53 eV respectively. The d33 coefficients are found to be 2.0 and 2.1 pC/N for BF-PT and BF-PZ respectively. [ABSTRACT FROM AUTHOR]

0.5BiGdxFe1-xO3-0.5PbTiO3 with x=0.05, 0.10, 0.15, 0.20 composite was prepared by mixed oxide method. Structural characterization was performed by X-ray diffraction and studied that the materials show tetragonal structure at room temperature for all concentration of Gd. Studies of dielectric properties (er and tand) of the above compound at different frequencies in a wide range of temperature (25°-500°C) with an impedance analyser revealed that the dielectric constant increases with increase in Gd concentration as well temperature and the compound do not have any dielectric anomaly in the studied frequency and temperature range. [ABSTRACT FROM AUTHOR]

Representing the heavy fermion systems by the Periodic Anderson Model (PAM), we have used Zubarev technique to study the temperature dependence of resistivity. The resistivity calculated shows the general features experimentally observed in these materials. Further, we have shown how the strength of hybridization as well as the position of the f-level affects the electrical resistivity and Kondo temperature of these systems. [ABSTRACT FROM AUTHOR]

Here, we have studied theoretically the temperature dependence of magnetic susceptibility of some heavy fermion (HF) superconductors through Fulde model. It is observed that, the calculated magnetic susceptibility show correct behaviour as a function of temperature with existing experimental results for some U-based and Ce-based HF superconductors. The extrapolated Kondo temperature for UPt3 found to give nearly the same value as observed experimentally by Frings et al (1983). [ABSTRACT FROM AUTHOR]

Here, we have analyzed the electron-phonon interaction in the Periodic Anderson Model (PAM) to describe the temperature dependence of resistivity in some heavy fermion (HF) systems for finite wave vector (q ) and for finite temperature (T). Since the resistivity is related to the imaginary part of the electron self energy, the expression for the same is evaluated through double time temperature dependant Green function technique of the Zubarev type. The effect of different system parameters namely the position of 4f level, E0 and the electron - phonon coupling strengths on resistivity have been studied. The results obtained give satisfactory explanations to the experimental observations. [ABSTRACT FROM AUTHOR]

The high temperature superconductors in the mixed state rounding superconducting transition temperature have been explained by using anisotropic London theory as well as GL-equation. Due to strong overlapping of vortices at higher fields the super electron density varies in space and London theory fails to explain. For lower critical field with in London limit and temperature close to transition, GL-approach with phenomenological mass tensor can be approximated for studying mixed state behavior. Expressing bare penetration depth λ into effective penetration depth λeff such as λeff2 = λ2/f2 = λ2/1-b;f = 1-b and b = ba/Bc2, the high field behavior can be observed using 3D-anisotropic London theory by incorporating vortex overlapping. FeAs superconductors have distinguishing macroscopic properties such as an enormous upper critical field with low superconducting anisotropy and that leads the investigation of topology in the microscopic length scale. Particularly, the variation of specific heat as well as entropy in SmFeAsO0.8F0.15 has been verified by the GL-theory in London limit with vortex overlapping correction and found satisfactory result with the experimental findings. [ABSTRACT FROM AUTHOR]

A theoretical explanation is provided to understand the effect of impurity on the electron-phonon interaction in some alloyed Heavy Fermion (HF) systems in the normal state on the basis of Periodic Anderson Model (PAM). Two different mechanisms of the electron-phonon interaction, namely, the usual interaction between the Phonons with both the f-electrons as well as with the hybridization of conduction and f-electrons are considered. It is assumed that the impurities perturb the host crystal because of the difference in mass, the change in nearest neighbor force constant and the local modification of the electron-phonon interaction. The phonon self-energy due to these perturbations is calculated to the lowest order of the impurity concentration. The phonon response functions are evaluated for all wave vector q and temperature T in the mean field approximation. To avoid complications numerical evaluations are made for long wave length in the static limit. The influence of impurity mass parameter on other system parameters like position of f-level, the effective coupling strength on calculated phonon frequency is studied. [ABSTRACT FROM AUTHOR]

Sonochemical synthesis of ZnO and ZnO doped with boron has been carried out in a conventional sonicator and the presence of boron has been confirmed from ICP-OES measurement. PXRD indicates the formation of hexagonal wurzite structure of ZnO with larger crystallite size in the doped samples. TEM studies show the formation of tetrapod like structures for ZnO: B samples which is not seen in ZnO as prepared. The evolution of tetrapods has been explained on the base of impurity adsorption and carbo-thermal reduction taking place during the process of sonication. [ABSTRACT FROM AUTHOR]