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Karoui K.,University of Sfax | Rhaiem A.B.,University of Sfax | Jomni F.,Campus Universities | Moneger J.L.,CNRS Le Mans Institute of Molecules and Materials | And 2 more authors.
Journal of Molecular Structure | Year: 2013

The X-ray powder diffraction patterns show that at room temperature [N(CH3)4]2ZnCl2Br2 crystallizes in the orthorhombic system with Pnma space group. Three endothermic peaks at T1 = 251 K, T2 = 276 K and T3 = 283 K are observed by differential scanning calorimetry technique. In order to characterize these transitions, Raman spectra have been recorded in the wide temperature range (between 170 and 400 K) and the frequency range related to the internal and external vibrations of the cations and anions (3200-20 cm -1). The evolution of Raman spectra against temperature shows that the compound is homogeneous, and singularities occur in the vicinity of 283 K and especially at 251 K. The second goal of the present work was to obtain the Tc temperature transition using the dielectric measurements at different temperatures. Measurements of the dielectric constant ε', ε'' and tan δ at several temperatures showed that this compound becomes ferroelectric below 257 K. The impedance spectra and the complex modulus show double relaxation peaks in the paraelectric phase, which suggests the presence of grains and grain boundaries in this sample. © 2013 Elsevier B.V. All rights reserved. Source


Rouahi A.,CNRS Grenoble Electrical Engineering Lab | Rouahi A.,Campus Universities | Kahouli A.,CNRS Grenoble Electrical Engineering Lab | Kahouli A.,Campus Universities | And 7 more authors.
Journal of Physics D: Applied Physics | Year: 2013

The influence of phases and phase's boundaries of TiO2 and Ta2O5 in the dielectric and electric response of TiTaO (100 nm thick) elaborated by RF magnetron sputtering was highlighted by complex impedance spectroscopy. Dielectric and electric modulus properties were studied over a wide frequency range (0.1-105 Hz) and at various temperatures (-160 to 120 °C). The diagram of Argand (ε″ versus ε′) shows the contribution of phases, phases' boundaries and conductivity effect on the electric response of TiTaO thin films. Moreover, the resistance of the material decreases when the temperature increases, thus the material exhibits a negative temperature coefficient of resistance. The electric modulus plot indicates the presence of two peaks of relaxation. The first relaxation process appears at low temperature with activation energy of about 0.22 eV and it is related to the first ionization energy of oxygen vacancies. The second relaxation process appears at high temperature with activation energy of about 0.44 eV. This second peak is attributed to the Maxwell-Wagner-Sillars relaxation. The plots of the complex dielectric modulus and the impedance as a function of frequency allow concluding to a localized relaxation due to the long-range conductivity in the TiTaO film. © 2013 IOP Publishing Ltd. Source


Zermani M.A.,National Engineering School of Tunis | Feki E.,Campus Universities | Mami A.,Campus Universities
2012 20th Mediterranean Conference on Control and Automation, MED 2012 - Conference Proceedings | Year: 2012

This study presents multivariable control strategies for humidity and temperature for neonate incubator. This process is TITO system (Two Input Two Output). Identification process of incubator is the first step for design and implementation controller. An experiment method is proposed to determine the transfer function matrix, which decouples the TITO system into four independent loops. Discrete-time system transfer matrix parameters were estimated in real time by the least-squares method. Secondly we take into account couplings between outputs and we consider a decoupling controller to eliminate the strong interaction. After that we develop a generalized predictive decoupled control. At last the simulation results demonstrate the effectiveness of this proposed strategy. © 2012 IEEE. Source


Rouahi A.,CNRS Grenoble Electrical Engineering Lab | Rouahi A.,Campus Universities | Kahouli A.,CNRS Grenoble Electrical Engineering Lab | Kahouli A.,Campus Universities | And 3 more authors.
Journal of Alloys and Compounds | Year: 2012

Polycrystalline Ba 0.7Sr 0.3TiO 3 thin film with Pt/BST/Pt/TiO 2/SiO 2 structure was prepared by ion beam sputtering. The film was post annealed at 700 °C. The dielectric and electric modulus properties were studied by impedance spectroscopy over a wide frequency range [0.1-10 5 Hz] at different temperatures [175-350 °C]. The Nyquist plots (Z″ vs. Z′) show the contribution of both grain and grain boundaries at higher temperature on the electric response of BST thin films. Moreover, the resistance of grains decreases with the rise in temperature and the material exhibits a negative temperature coefficient of resistance. The electric modulus plot indicates the non-Debye type of dielectric relaxation. The values of the activation energy computed from both plots of Z″ and M″ are 0.86 eV and 0.81 eV respectively, which reveals that the species responsible for conduction are the same. The scaling behavior of M″/M″max shows the temperature independent nature of relaxation time. The plot of normalized complex dielectric modulus and impedance as a function of frequency exhibits both short and long-range conduction in the film. © 2012 Elsevier B.V. All rights reserved. Source


Rouahi A.,CNRS Grenoble Electrical Engineering Lab | Rouahi A.,Campus Universities | Kahouli A.,CNRS Grenoble Electrical Engineering Lab | Kahouli A.,Campus Universities | And 4 more authors.
Applied Physics A: Materials Science and Processing | Year: 2012

Dielectric measurements have been performed on ion beam sputtering (IBS) barium strontium titanate Ba0.7Sr0.3TiO3 thin films at annealing temperatures 470 and 700 °C using impedance spectroscopy. The effect of the annealing temperature upon the electrical properties of the films is also investigated using capacitance-voltage techniques. Increasing annealing temperature suggested the increases of density and grain size, whereas the density of the trapped oxygen vacancy may be decreasing with increasing annealing temperature. The barrier height (Ea) of the oxygen vacancy decreases with increasing annealing temperature. The C-V characteristics were investigated in relation to the annealing temperature to identify the anomalous capacitance in the MIM configuration films. Among all measurement temperatures, it was observed that the data fit well by the "LGD" model. The interfacial effect and its dependence of morphology structure have been studied, and the results are discussed. © Springer-Verlag Berlin Heidelberg 2012. Source

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