Abdelaziz Ammar
University of Bordeaux
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Featured researches published by Abdelaziz Ammar.
Journal of Physics and Chemistry of Solids | 1987
Jean-Pierre Doumerc; Abdelaziz Ammar; Aree Wichainchai; M. Pouchard; Paul Hagenmuller
Resume The CuCo0.5Ti0.5O2, CuNi0.5Ti0.5O2 and CuNi0.5Sn0.5O2 quaternary oxides have been prepared using direct solid state reaction. AgNi0.5Ti0.5O2 and CuScO2 have been obtained only by exchange reaction. They exhibit a 3R-delafossite type structure. For CuCo0.5Ti0.5O2, a 2H-polytype is also observed. The lattice constant variation with the size of the cation occupying the B-site is similar for both mixed (AB0.5′B0.5″O2) and simple ABO2 delafossites. The evolution with the size of B-site cations of the BO6 or (B′, B″)O6 octahedron D3d-deformation is explained by that of the covalency of the σ(B-O) bonds. No evidence of a B′ B″ ordering has been detected in the materials.
Materials Research Bulletin | 1986
Jean-Pierre Doumerc; Aree Wichainchai; Abdelaziz Ammar; M. Pouchard; Paul Hagenmuller
Abstract Magnetic properties of ABO 2 (A = Cu, Ag, Pd and B = Cr, Fe) delafossite-type compounds are investigated on the base of a 2D-Heisenberg model using the expansion series method proposed for reciprocal magnetic susceptibility by Rushbrooke and Wood. Exchange integrals have been determined and their evolution correlated to the variation of the Cr 3+ Cr 3+ distance as the A cation varies. 3D-long range ordering which takes place at low temperature has been tentatively determined from the thermal variation of the susceptibility. The investigation leads to the conclusion that interlayer B 3+ B 3+ interactions which occurs through (CuO 2 ) 3− groups are relatively strong in spite of the important structural anisotropy. Magnetic behavior of CuAlO 2 , CuCoO 2 and AgCoO 2 have also been determined and discussed.
Solid State Sciences | 2002
M. Pouchard; Christian Cros; Paul Hagenmuller; Edouard Reny; Abdelaziz Ammar; Michel Ménétrier; Jean-Marc Bassat
Low sodium content silicides discovered by some of us in the sixties are compared to some analogous families of materials. As endofullerenes constituted by the smallest Si 20 ,S i 24 and Si28 clusters, they are polymerized in 3D-structures of face sharing polyhedra, giving rise to clathrate-like structures (similar to those of the gas and liquid hydrates). Several physical properties (conductivity, 23 Na and 29 Si NMR, EPR) show that the electronic transfer from sodium to the silicon host is rather low and appears only gradually with rising Na-content as a consequence of Na 3s and Si 3s-3p orbital mixing which gives rise to an antibonding band. Silicon clathrates differ from the homologous germanium and tin compounds characterized by a large number of defects in the host structure which leads to stronger ionization of the alkali atoms and to the formation of some Ge − anions within Zintl–Klemm-type phases. 2002 Editions scientifiques et medicales
Journal of Physics and Chemistry of Solids | 1988
J.M. Dance; A. Wichainchai; P. Dordor; E. Marquestaut; Jean-Pierre Doumerc; Abdelaziz Ammar
Abstract EPR measurements on CuAl0.99Cr0.001O2 have allowed the determination of the zero field splitting (D = 0.330 cm−1). An interpretation of the exchange narrowing of EPR linewidth has been given based on the Anderson and Weiss model leading to a value of 1.8 for the C0-constant in the expression for the exchange field: H e = C 0 ( Jg −1 β)[S(S + 1)] 1 2 . From these results and previous data a D-value be proposed for AgCrO2 (0.307cm−1), and compared to those for CuAlO2 and CuCrO2. The variation is correlated with the degree of trigonal distortion of the Cr3+ octahedral site based on structural data. The thermal variation of the linewidth for AgCrO2 and CuCrO2 confirms the existence of 3D-long range antiferromagnetic ordering at temperatures close to those determined from static susceptibility measurements.
Materials Research Bulletin | 1992
Jean-Pierre Doumerc; Michel Pouchard; P. Hagenmuller; M Elazhari; Abdelaziz Ammar; M. Elaatmani
Abstract In the delafossite-type AMO 2 (A= Cu, Ag) oxides, the ionic radius of the trivalent element M may vary between 0,54 and 1,03 A. However, the formation of solid solutions of formula CuM′ 1−x M″ x O 2 is possible only if the ionic radius difference is not too large. Such a situation occurs for M′= La 3+ and M″= Y 3+ , but not for M″= Ga 3+ . On the other hand, unsuccessful attempts to prepare binary delafossites with A= Cu and M= Ni or Tl as well as other general considerations show that redox equilibria and electronic structure play a major part in the stability of these materials.
Solid State Sciences | 2004
Abdelaziz Ammar; Christian Cros; M. Pouchard; Nicolas Jaussaud; Jean-Marc Bassat; Gérard Villeneuve; Mathieu Duttine; Michel Ménétrier; Edouard Reny
Solid State Sciences | 2003
Nicolas Jaussaud; M. Pouchard; Graziella Goglio; Christian Cros; Abdelaziz Ammar; F. Weill; P. Gravereau
Journal of Alloys and Compounds | 2004
Khadija El Ataoui; Jean-Pierre Doumerc; Abdelaziz Ammar; L. Fournes; Alain Wattiaux; Jean-Claude Grenier; Michel Pouchard
Solid State Sciences | 2003
Khadija El Ataoui; Jean-Pierre Doumerc; Abdelaziz Ammar; P. Gravereau; L. Fournes; Alain Wattiaux; Michel Pouchard
Solid State Sciences | 2005
Khadija El Ataoui; Jean-Pierre Doumerc; Abdelaziz Ammar; Jean-Claude Grenier; L. Fournes; Alain Wattiaux; Michel Pouchard