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El Yakoubi E.Y.,University Ibn Zohr | Nafidi A.,University Ibn Zohr | Morghi R.,University Ibn Zohr | Braigue M.,University Ibn Zohr | And 5 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2011

We report here on the preparation, X-ray diffraction with Rietveld refinement, resistivity and AC magnetic susceptibility measurements of (Y 1-xEux)(SrBa)Cu3O6.94. Each sample was subject to two types of heat treatment: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. For each x, the [AO] treatment increases the orthorhombicity ε (for 0 ≤ x ≤ 1 ), Tc(for x ≥ 0.45) and by 6 K to 87 Kfor x= 1[AO], and the distance d[Cu(1)- Sr/Ba] (decrease Tc) for x < 0.4 and decrease it (increase Tc) for x < 0.4. In the normal state, the [AO] treatment reduced the linear resistivity parameters indicating a diminution of the interaction of carrier charges with phonons. There was a remarkable improvement in the shielding effect S (amplitude of X'(T)) in the case of the samples [AO] at all T < Tc and for any applied field for x > 0.5. For each x and heat treatment, S(x) decreases when Hdc and the temperature increase. Remarkable correlations were observed. A combination of several factors such as decrease in d[Cu(1) - (Sr/Ba)]; increase in cationic and chain oxygen ordering; Psh and in-phase purity for the [AO] samples may account for the observed data. © 2010 IEEE.


Yakoubi E.Y.E.,University Ibn Zohr | Nafidi A.,University Ibn Zohr | Braigue M.,University Ibn Zohr | Morghi R.,University Ibn Zohr | And 8 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2011

We report here on the preparation, resistivity, AC magnetic susceptibility measurements and effect of heat treatments in (Yi1-xSm x)(SrBa)Cu306+z. Each sample was subject to two type of heat treatment: oxygen annealing [O] and argon annealing lbllowed by oxygen annealing [AO]. An enhancement of Tc[A0] was observed for x ≥ 0.4. In the normal state, the [AO] treatment reduced the linear resistivity parameters indicating a diminution of the interaction of carrier charges with phonons. Tc(X) and Tc(ρ = 0) were in good agreement. An enhancement of the AC irreversibility line H(t = Tp/T c)was observed due to [AO] treatment for x > 0.5 indicating an improvement in the pinning properties. The data were analysed with the relation H = K'(l - t)n. Remarkable correlations were observed between δTc(x) = TC[AO] - Tc[O] and δK'(x); and between Tc), d[Cu(2) - Y/Sm] (x) distance and the number p sh(x) of holes by Cu(2) - O2 superconducting planes. A combination of several factors such as decrease in d[Cu(1) - (Sr/Ba)] for x > 0.4; increase in cationic and chain oxygen ordering; Psh and in-phase purity for the [AO] samples may account for the observed data. © 2010 IEEE.


Cherif A.,Ferhat Abbas University Setif | Cherif A.,INSA Lyon | Meddad M.,Ferhat Abbas University Setif | Meddad M.,INSA Lyon | And 6 more authors.
Optical and Quantum Electronics | Year: 2014

The piezoelectric transformers reach densities of power more significant than their magnetic counterparts. However, one of the principal factors limiting the density of power is the acceptable maximum deformation by material constituting the transformer. The heating of the piezoelectric transformers is mainly of mechanical origin. This heating generates a degradation of the characteristics which in its turn generates an additional heating being able to lead to a phenomenon of thermal avalanche. In this work, two nonlinear methods [synchronized switch harvesting on inductor (SSHI) and SSHI-max] have been explored to improve the performance of the Rosen transformer basing on the tension generated by the secondary so as to increase the capacity of mechanic-electric conversion. The simulation results show that SSHI and SSHI-max techniques significantly increase the capacity of mechanic-electric conversion of inserts stuck on a vibrating structure and consequently, the power recovered in electric form. The comparative results of voltage gain, efficiency and the transmitted power of the transformer, before and after SSHI-max and SSHI control are given. These ones indicated that the two nonlinear techniques are promising as applications to improve the performances of the piezo-transformers. © 2013 Springer Science+Business Media New York.


Morghi R.,Laboratory of Condensed Matter Physics | Nafidi A.,Laboratory of Condensed Matter Physics | Aboulkassim A.,Laboratory of Condensed Matter Physics | Khallouq K.,Laboratory of Condensed Matter Physics | And 7 more authors.
Journal of Optoelectronics and Advanced Materials | Year: 2013

Polycrystalline samples (Y1-xEux)SrBaCu3O6+z have been synthesized by solid state reaction method with two distinguished heat treatment. The irreversibility line and flux pinning proprieties (pinning force density) has been investigated by AC susceptibility measurements. The experimental data for irreversibility line fit well with the power law relation: H=(1-T/Tc)n. Results show that the effect of annealing under argon flux leads to an enhancement of irreversibility line and an increase of pinning density force for high applied magnetic field which is justified by the improvement of crystallographic quality and the intergranular coupling of the samples heated under argon flux [AO].

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