Effect of 20% Cr-doping on structural and electrical properties of La0.67Ca0.33MnO3 perovskite

Effect of 20% Cr-doping on structural and electrical properties of La0.67Ca0.33MnO3 perovskite
Abstract

Structural and electrical properties of La0.67Ca0.33Mn1-xCrxO3 (x = 0 and 0.2) manganites are studied in this work. The samples were prepared using Pechini sol-gel method at 1173 K. Rietveld analysis of X-ray diffraction (XRD) patterns shows the formation of pure crystalline phase with orthorhombic Pnma structure with a decrease of the unit cell volume and crystalline domain size when increasing Cr-content. Electrical properties of the samples have been investigated using complex impedance analysis in 180 320 K temperature range with varying frequency between 40 and 10(6) Hz. For both samples, frequency dependence of imaginary part of impedance (Z '') shows the existence of relaxation phenomenon. The impedance study using Nyquist representation revealed the appearance of semicircle arcs and an equivalent circuit of the type of R-1 (R-2//Z(CPE)) has been proposed to explain the impedance results. The conductance curves were analyzed by Jonscher power law and the deduced activation energy values are close to those calculated from relaxation time indicating that relaxation process and conductivity have the same origin. (C) 2016 Elsevier B.V. All rights reserved.

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published in: 2017-02-19 13:46:14

Effect of trivalent rare earth doping on magnetic and magnetocaloric properties of La-0.47(Y,Eu)(0.2)Pb0.33MnO3 manganites

Effect of trivalent rare earth doping on magnetic and magnetocaloric properties of La-0.47(Y,Eu)(0.2)Pb0.33MnO3 manganites
Abstract

The La(0.47)Ln(0.2)Pb(0.33)MnO(3) (Ln=Eu and Y) polycrystalline has been synthesized using the solid state reaction method at high temperature. The X-ray diffraction shows that the materials crystallized in the orthorhombic structure. Magnetization measurements versus temperature in a magnetic applied field of 0.05 T show that all our samples exhibit a paramagnetic-ferromagnetic transition with decreasing temperature. The value of the Curie temperatures are 275 K and 264 K for Ln=Eu and Y, respectively. The magnetic entropy change reaches a peak (-Delta S-m(max)) also decreases from 3.31 J/kg. K for Ln=Eu to 2.97 J/kg. K for Ln=Y, and the corresponding values of relative cooling power (RCP) reach 243.25 and 178.88 J/kg, under a magnetic field of 5 T. The results suggest that those polycrystalline could be useful for magnetic refrigeration in a broad temperature range.

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published in: 2017-02-19 13:43:24

Structural and complex impedance spectroscopic studies of Ni0.5Mg0.3Cu0.2Fe2O4 ferrite nanoparticle

Structural and complex impedance spectroscopic studies of Ni0.5Mg0.3Cu0.2Fe2O4 ferrite nanoparticle
Abstract

Spinel ferrite having composition Ni0.5Mg0.3Cu0.2Fe2O4 was prepared by the sol-gel technique at 1473 K. The X-ray diffraction results indicate that the ferrite sample has a cubic spinel-type structure with Fd (3) over barm space group. The electrical properties of the studied sample using complex impedance spectroscopy technique have been investigated in the frequency range 10(2)-10(7) Hz and in the temperature range 300-500 K. The total conductivity curves for sample are found to obey Jonscher power law (sigma(omega) = sigma(dc) A omega(n)) with an increase in the frequency exponent (n) as temperature increases. The activation energy deduced from the analysis of the conductivity curves matches very well with the value estimated from the relaxation time, indicating that relaxation process and electrical conductivity are attributed to the same defect. 

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published in: 2017-02-19 13:42:04

Parameter Identification of a Sandwich Beam Using Numerical-Based Inhomogeneous Wave Correlation Method

Parameter Identification of a Sandwich Beam Using Numerical-Based Inhomogeneous Wave Correlation Method
Abstract

To achieve low calculation-cost structural identification process, a numerical-based Inhomogeneous Wave Correlation (IWC) method is proposed in this paper as an extension to the experiment-based IWC. It consists, in a wave propagation framework also called wavenumber space (k-space), on identifying the propagation parameters such as the wavenumber and the spatial damping from the Frequency Response Functions (FRFs)computed using numerical simulations. The proposed method is applied to a sandwich beam with honeycomb cores in flexural vibration. Compared to its implementation based on experimentally-measured FRFs, the proposed numerical-based IWC proves to be an efficient tool for more inner structural parameter identification in wide frequency band with respect to the Mc Daniel method considered as reference.

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published in: 2017-02-19 13:39:27

Structural, dielectric and complex impedance properties of T0.6Co0.4Fe2O4 (T=Ni, Mg) ferrite nanoparticles prepared by sol gel method

Structural, dielectric and complex impedance properties of T0.6Co0.4Fe2O4 (T=Ni, Mg) ferrite nanoparticles prepared by sol gel method
Abstract

Spinel ferrites T0.6Co0.4Fe2O4 (T= Ni, Mg) were prepared by Pechini sol-gel technique at 1323 K. The X-ray diffraction results indicate that the ferrite samples have a cubic spinel type structure with Fd (3) over barm space group. FTIR showed two absorption bands (v(1) and v(2)) that are attributed to the stretching vibration of tetrahedral and octahedral sites. The electrical properties of the studied samples using complex impedance spectroscopy technique have been investigated in the frequency range 40 Hz - 10(7) Hz and in the temperature range 200 - 420 K. The total conductivity curves for samples are found to obey Jonscher power law sigma(omega) =sigma(dc) A omega(n) with an increase of the frequency exponent (n) as temperature increases. The effect of frequency, temperature and composition on dielectric constant (epsilon') and dielectric loss (tan delta) has been discussed in terms of hopping of charge carriers between Fe2 and Fe3 ions. Activation energy has been estimated from both temperature dependent of de conductivity and relaxation time data, which indicates that same kinds of charge carriers are governing both the processes. Nyquist plots of impedance show semicircle arcs for samples and an electrical equivalent circuit of the type of R-g (R-gb//Z(CPE)) has been proposed to explain the impedance results.

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published in: 2017-02-19 13:37:06

Multi-modal vibration energy harvesting approach based on nonlinear oscillator arrays under magnetic levitation

Multi-modal vibration energy harvesting approach based on nonlinear oscillator arrays under magnetic levitation

 Issam ABED, Najib KACEM, Noureddine BOUHADDI, Mohamed Lamjed BOUAZIZI, « Multi-modal vibration energy harvesting approach based on nonlinear oscillator arrays under magnetic levitation ». Smart Materials and Structures, Volume: 25, Issue: 2 ,N° 025018,  2016.

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published in: 2016-10-15 23:11:12