M. Megdiche

AC impedance analysis, equivalent circuit, and modulus behavior of NaFeP2O7 ceramic

II-NaFeP2O7 was prepared by conventional ceramic fabrication technique. Rietveld refinement, impedance properties, conductivity dispersion, electric modulus, and their scaling were carried out as a function of frequency and temperature. Thus, X-ray diffraction analysis indicates that the sample exhibits a single-phase nature with a monoclinic structure. In addition, analysis of Nyquist plots as well as modulus analysis revealed the contribution of two electrically active regions corresponding to bulk mechanism and distribution of grain boundaries. The near values of activation energies, obtained from the impedance and modulus spectra, confirm that the transport happens through an ion hopping mechanism, dominated by the motion of the Na+ ions in the framework of the investigated material resulting from intersecting tunnels or voids where Na+ is located.

Electrical, dielectric properties and study of AC electrical conduction mechanism of Li0.9□0.1NiV0.5P0.5O4

In this paper, we report the measurements of impedance spectroscopy for a new olivine-type lithium deficiency Li0.9□0.1NiV0.5P0.5O4 compound. It was synthesized by the conventional solid-state technique. All the X-ray diffraction peaks of the compound are indexed, and it is found that the sample is well crystallized in orthorhombic olivine structure belonging to the space group Pnma. Conductivity and dielectric analyses of the sample are carried out at different temperatures and frequencies using the complex impedance spectroscopy technique. The electrical conductivity of Li0.9□0.1NiV0.5P0.5O4 is higher than that of parent compound LiNiV0.5P0.5O4. Temperature dependence of the DC conductivity and modulus was found to obey the Arrhenius law. The obtained values of activation energy are different which confirms that transport in the title compound is not due to a simple hopping mechanism. To determine the conduction mechanism, the AC conductivity and its frequency exponent have been analysed in this work by a theoretical model based on quantum mechanical tunnelling: the non-overlapping small polaron tunnelling model.

Characterizations and morphology of sodium tungstate particles

A solid-state reaction technique was used to synthesize polycrystalline Na2WO4. Preliminary X-ray studies revealed that the compound has a cubic structure at room temperature. The formation of the compound has been confirmed by X-ray powder diffraction studies and Raman spectroscopy. Electrical and dielectric properties of the compound have been studied using complex impedance spectroscopy in the frequency range 209 Hz–1 MHz and temperature range 586–679 K. The impedance data were modellized by an equivalent circuit consisting of series of a combination of grains and grains boundary. We use complex electrical modulus M* at various temperatures to analyse dielectric data. The modulus plots are characterized by the presence of two relaxation peaks thermally activated. The morphologies and the average particle size of the resultant sodium tungstate sample were demonstrated by atomic force microscopy, scanning electron microscopy and transmission electron microscopy. The thicknesses and optical constants of the sample have been calculated using ellipsometric measurements in the range of 200–22 000 nm by means of new amorphous dispersion formula which is the objective of the present work. The results were obtained for Na2WO4 particles from experimental (EXP) and measured (FIT) data showed an excellent agreement. In addition, the energy gap of the Na2WO4 sample has been determined using ellipsometry and confirmed by spectrophotometry measurements.