Manoun B.,Laboratoire Of Physico Chimie Des Materiaux |
Igartua J.M.,Polytechnic University of Valencia |
Lazor P.,Uppsala University
Journal of Molecular Structure | Year: 2010
In this paper, we report on high temperature Raman spectroscopy studies (up to 550 °C) of the phase transitions in Sr2BWO6 (B = Ni, Mg) double perovskite oxides. For both compounds, the transition from the tetragonal (I4/m) phase to the cubic (Fm-3m) phase is accompanied by considerable changes in the temperature dependence of the modes. To better view this phase transition, the FWHM temperature dependence of the most intense modes were studied; by this study, we have obtained a sensitive guide to the onset of the phase transition. A large increase of the FWHM with increasing temperature is observed for all modes in the spectrum, clear transitional effects were observed: the width behaves in a linear way as a function of temperature; when the temperature reached around 300 °C, a drop in the width of this mode was observed; thus, showing the phase transition occurrence for both compounds. This drop is much more illustrated in Ni-containing compound than in Sr2MgWO6. © 2010 Elsevier B.V. All rights reserved.
Sadik N.,Unite de Chimie Analytique et science de LEnvironnement |
Sabbar E.,Laboratoire Of Physico Chimie Des Materiaux |
Mountadar M.,Unite de Chimie Analytique et science de LEnvironnement
Physical and Chemical News | Year: 2010
The main aim of this study was the synthesis of the Layered Double Hydroxides (LDH) also called "Anionic Clays" starting from salted natural water (sea water). According to this method, the contribution f divalent Metal, to prepare the Layered Double Hydroxides (LDH), is done quite simply starting from alted natural water. The HDL prepared according to this method will be noted LDHmf the influence of the parameters on the synthesis of the Layered Double Hydroxides (LDH) starting from sea water was carried out to know the pH, the reports/ratios molar Mg/Al and the influence of the reports molar CO32-/Al3+on the crystallinity of HDLm. The product obtained was characterized by various echniques: the diffraction of X-rays on powder, the Infra-red spectroscopy, thermogravimetric analysis and chemical analysis. The results obtained show well the presence of a phase well crystallized hydrotalcite [Mg-Al-CO3] with the appearance of a secondary phase: CaCO3. This new method of anion synthesis of clays was the national patent object No27 223 .
Cherif K.,CNRS Condensed Matter Physics Laboratory |
Belkahla A.,CNRS Condensed Matter Physics Laboratory |
Dhahri A.,Laboratoire Of Physico Chimie Des Materiaux |
Dhahri J.,CNRS Condensed Matter Physics Laboratory
Journal of Superconductivity and Novel Magnetism | Year: 2015
In this paper, we study the structural and electrical properties of the perovskite manganite La0.7Ba0.2 Ca0.1Mn1−xCrxO3, synthesized by the solid-state reaction method. The Rietveld refinement of X-ray diffraction data indicates that there is no structural change owing to Cr substitution in La0.7Ba0.2Ca0.1Mn1−xCrxO3 (0 ≤ x ≤ 0.15). The conductivity of all samples was measured as a function of frequency in the range between 40 and 106 Hz and a temperature ranging from 160 to 300 K. The ac conductance spectrum is found to obey the Jonscher universal power law: Gac = Gdc+Aωn. The variation of the conductivity exponent (n) with temperature confirms the presence of hopping in the conduction process. According to dc conductance study, electronic conduction is found to be dominated by thermally activated hopping. The Cr content affects the activation energy (Ea). Its values decrease from Ea = 72 meV for x = 0 to Ea = 34 meV for x = 0.15. © Springer Science+Business Media New York 2015.
Mustapha Bouhent M.,Laboratoire Of Physico Chimie Des Materiaux |
Mustapha Bouhent M.,University Blaise Pascal |
Derriche Z.,Laboratoire Of Physico Chimie Des Materiaux |
Denoyel R.,CNRS Chemistry Laboratory |
And 2 more authors.
Journal of Solid State Chemistry | Year: 2011
[Mg1-x Alx(OH)2][(NO3) x, nH2O] Layered Double Hydroxide (LDH) sorbents with variable Mg/Al molar (R=(1-x)/x) ratios were investigated for adsorption of azo dye, orange II (OII) at various pH and temperature conditions. Mg 2AlNO3 displays the highest adsorption capacity with 3.611 mmol of OII per gram of Mg2AlNO3 at 40 °C. Adsorption isotherms have been fitted using the Langmuir model and free energy of adsorption (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) were calculated. The experimental values for ΔG° in temperature range between 10 and 40 °C were found to be negative indicating that a spontaneous process occurred. Positive calculated enthalpy values, characteristic of an endothermic process were found. Characterization of solids (PXRD, FTIR, UVvis, TGA/DTA, adsorption isotherm BET analysis, SEM and Zetametry) before and after adsorption showed that adsorption proceeds in two steps. First, adsorption occurs at the LDH surface, followed by intercalation via anion exchange. © 2011 Elsevier Inc. All rights reserved.
Azdouz M.,Laboratoire Of Physico Chimie Des Materiaux |
Azdouz M.,Laboratoire des ressources naturelles et environnement |
Manoun B.,Laboratoire Of Physico Chimie Des Materiaux |
Essehli R.,Ecole des Mines de Nantes |
And 5 more authors.
Journal of Alloys and Compounds | Year: 2010
The new solid solution series Ba3-xSrx(VO4)2 (0 ≤ x ≤3) has been synthesized and studied by a combination of X-ray powder diffraction and Raman vibrational spectroscopy. This continuous solid solution crystallise in the hexagonal system with R over(3, ̄) m space group. The structure has been determined at room temperature from X-ray diffraction by the Rietveld method analysis. It is formed by a 3D network of (Ba/Sr)(1)(VO4)2 4- layers linked into a crystal network by (Ba/Sr)2+ (2) cations. The vibrational spectra of this crystalline orthovanadate solid solution series are interpreted by means of factor group analysis in terms of space group R over(3, ̄) m (D3 d 5). Assignments of the V-O vibrational stretching and bending modes, as well as some of the external modes, have been made. While all the modes show a monotonous shift as a function of the composition x, a break in the curves of intensities, full width at half maximum and band areas as a function of x is observed and attributed to the statistical distribution of Ba and Sr ions in the same crystallographic sites. © 2010 Elsevier B.V. All rights reserved.