Studies of Structural, Dielectric and Electrical Characteristics of Complex Perovskite: Pb(Co1/3Mn1/3W1/3)O3

A lead-based multiferroic, Pb(Co1/3Mn1/3W1/3)O3, was synthesized by using a high-temperature solid-state reaction technique. Based on X-ray structural analysis, an orthorhombic crystal structure has been suggested for the material. The scanning electron microscopy (SEM) image exhibits a morphology with and uniform grains distribution. A detailed study of variation of dielectric parameters with frequency and temperature exhibits that Pb(Co1/3Mn1/3W1/3)O3 undergoes multiple phase transitions; first transition (Tc1) appeared at 436K (ferroelastic to ferroelectric) whereas second transition ( Tc2) appeared at 504K ( ferroelectric to paraelectric). Since the peaks of dielectric constant are broader and diffused, a diffusivity parameter (γ) has been estimated to the amount of disordering in the material structure.The contribution of grain,grain boundaries and electrode effect in electrical conduction mechanisim can be understood by frequency-temperature dependence of resistive characterestics using CIS spectroscopy (complex impedance spectroscopy). Impedance or Nyquist plots were modeled with an equivalent circuit having capacitance, resistance and related parameters. Studies of transport properties, ac conductivity, electrical modulus and magneto-electric (ME) effect of the materialis reported in this communication.

Computation of Melting Dissipative Magnetohydrodynamic Nanofluid Bioconvection with Second-order Slip and Variable Thermophysical Properties

This paper studies the combined effects of viscous dissipation, first and second-order slip and variable transport properties on phase-change hydromagnetic bio-nanofluid convection flow from a stretching sheet. Nanoscale materials possess a much larger surface to volume ratio than bulk materials, significantly modifying their thermodynamic and thermal properties and substantially lowering the melting point. Gyrotactic non-magnetic micro-organisms are present in the nanofluid. The transport properties are assumed to be dependent on concentration and temperature. Via appropriate similarity variables, the governing equation with boundary conditions are converted to nonlinear ordinary differential equations and are solved using the BVP4C subroutine in the symbolic software MATLAB. The non-dimensional boundary value features a melting (phase change) parameter, temperature-dependent thermal conductive parameter, first as well as second-order slip parameters, mass diffusivity parameter, Schmidt number, microorganism diffusivity parameter, bioconvection Schmidt number, magnetic body force parameter, Brownian motion and thermophoresis parameters. Extensive computations are visualized for the influence of these parameters. The present simulation is of relevance in the fabrication of bio-nanomaterials for bio-inspired fuel cells.

Dielectric and Raman studies of Ba0.06(Na1/2Bi1/2)0.94TiO3–NaNbO3 ceramics

In this work the X-ray diffraction, scanning electron microscopy, Raman and dielectric studies of lead free perovskite (1 – x)Ba0.06(Na1/2Bi1/2)0.94TiO3–xNaNbO3 (0 ⩽ x ⩽ 1.0) ceramics, prepared using a standard solid state reaction method, were investigated. X-ray diffraction studies of all the ceramics suggested the formation of single phase with crystal structure transforming from rhombohedral-tetragonal to orthorhombic symmetry with the increase in NaNbO3 content. Raman spectra also confirmed the formation of solid solution without any new phase. Dielectric studies showed that the phase transition is of diffusive character and diffusivity parameter decreases with increasing NaNbO3 content. The compositional fluctuation was considered to be the main cause of diffusivity.

Anticollocated Backstepping Observer Design for a Class of Coupled Reaction-Diffusion PDEs

The state observation problem is tackled for a system ofncoupled reaction-diffusion PDEs, possessing the same diffusivity parameter and equipped with boundary sensing devices. Particularly, a backstepping-based observer is designed and the exponential stability of the error system is proven with an arbitrarily fast convergence rate. The transformation kernel matrix is derived in the explicit form by using the method of successive approximations, thereby yielding the observer gains in the explicit form, too. Simulation results support the effectiveness of the suggested design.