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Guelma, Algeria

Boufelfel A.,University du 08 Mai 45
International Journal of Hydrogen Energy | Year: 2016

Using ab initio calculations, I fully describe the electronic, magnetic and elastic properties of mono equi-atomic multilayer of L10 FePd and FePdH where H belongs to one of the two layers or to both. I found that the magnetic polarization of palladium in FePd is almost annihilated when hydrogen is present in both atomic layers. On the other hand the reduction of Fe moment is hydrogen proximity dependant. From phonons calculations of the frequencies at the center of the Brillouin zone Γ(0; 0,0), I found an anomaly when hydrogen is only present in the palladium layer. Moreover, this late structure its calculated elastic constants did not follow the trend of variation present in the rest of studied structures. Also, from macroscopic bulk and shear elastic moduli its calculated anisotropies, point to considerable elastic anisotropies. My intuitive explanation, based on the electronic population of the 4d↑↓ and 3 d↑↓ orbitals of Pd and Fe respectively, is these values are a consequence of critical phase transition of Pd from magnetic to non magnetic state. Copyright © 2016 Hydrogen Energy Publications, LLC.

Haireche S.,Blida University | Boumeddiene A.,Blida University | Guittoum A.,Center de Recherche Nucleaire de Draria | El Hdiy A.,University of Reims Champagne Ardenne | Boufelfel A.,University du 08 Mai 45
Materials Chemistry and Physics | Year: 2013

We have prepared solid thin film samples of SnO2:Sb in different ratios using atmospheric pressure chemical vapour deposition technique APCVD. The chemical composition was determined with Rutherford Backscattering Spectroscopy (RBS) within an error of 1%. X-ray diffraction was used to study the influence of Sb concentration on the lattice parameters and preferred orientations. We have found that sample of concentration 4% showed a (200) preferred orientation. The AFM and SEM images showed that the surface roughness of our samples was influenced by the doping concentrations. The lowest electrical surface resistance was 8.0 Ω □-1 for a 3% concentration sample. We found that the contribution to the metallic state is influenced by oxygen vacancy and Sb doping. Also, the sample of good electrical conductive property has an optical gap of 3.60 eV band at room temperature. © 2013 Elsevier B.V. All rights reserved.

Boufelfel A.,University du 08 Mai 45
Journal of Magnetism and Magnetic Materials | Year: 2013

I report calculations of the electronic structure of α-NaFeO 2-type form layered LiFeO2 in the general gradient approximation (GGA) and GGA+U with two popular correlation exchange flavors (PBE and BLYP). I self-consistently calculated the coulomb repulsion U for the Fe atom in this compound and found, using PBE+U (6.04 eV) model, agreement between my description of the magnetic structure and experimental results. Also, I classify α-NaFeO2-type rhombohedral structure LiFeO2 as a p-d chargetransfer semiconductor and the partially and totally Li removed compounds of this structure as metallic where electrons around the Fermi level are those of O2p orbitals. © 2013 Elsevier B.V. All rights reserved.

Maghnaoui A.,University du 08 Mai 45 | Boufelfel A.,University du 08 Mai 45
Journal of Magnetism and Magnetic Materials | Year: 2012

We calculated, using spin polarized density functional theory, the electronic properties of zigzag (10,0) and armchair (6,6) semiconductor silicon carbide nanotubes (SiCNTs) doped once at the time with boron, nitrogen, and oxygen. We have looked at the two possible scenarios where the guest atom X (B, N, O), replaces the silicon X Si, or the carbon atom X C, in the unit cell. We found that in the case of one atom B @ SiCNT replacing a carbon atom position annotated by B C exhibits a magnetic moment of 1 μ B/cell in both zigzag and armchair nanotubes. Also, B replacing Si, (B Si), induce a magnetic moment of 0.46 μ B/cell in the zigzag (10,0) but no magnetic moment in armchair (6,6). For N substitution; (N C) and (N Si) each case induce a magnetic moment of 1 μ B/cell in armchair (6,6), while N Si give rise to 0.75 μ B/cell in zigzag (10,0) and no magnetic moment for N C. In contrast the case of O C and O Si did not produce any net magnetic moment in both zigzag and armchair geometries. © 2012 Elsevier B.V. All rights reserved.

Zanat K.,University du 08 Mai 45 | Boufelfel A.,University du 08 Mai 45
Journal of Magnetism and Magnetic Materials | Year: 2012

We have studied the interlayer exchange coupling (IEC) in Co/Os n/Co in trilayer geometry using the quantum well (QW) model, RKKY theory in the framework of ab-initio total energy calculation. Also we have used the phase accumulation model (PAM) to describe the thickness dependence of QW states energies. We predict the presence of a short period oscillation in Os with 3.54 ML in addition to the long one of 7 ML which has been measured experimentally. Our results of PAM relate the oscillation periods of 6.29 ML and 3.69 ML to Γ(k| |=0) and M(k| |≠0) direction, respectively. On the other hand, using our calculated Fermi surface including spinorbit coupling of bulk Os we identified the two periods as the spanning vectors at Γ-centered nested electron surfaces e 9, 6.86 ML for long period, and inner hole ellipsoid h 7, 3.80 ML for short period. These periods are very comparable to those periods of 6.8 ML and 3.7 ML obtained by RKKY-fitting of the IEC. The principal behavior of the IEC found experimentally is reproduced by the theory. We have found in our calculations of IEC in the multilayer geometry Co m/Os n a shift of the AF coupling peaks when we varied the thickness of the FM layers which might be interpreted as due to QW interactions. © 2011 Elsevier B.V. All rights reserved.

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