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Kamel Khirouni

Bio: Kamel Khirouni is an academic researcher from University of Gabès. The author has contributed to research in topics: Dielectric & Dielectric spectroscopy. The author has an hindex of 26, co-authored 213 publications receiving 2608 citations.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the dielectric properties of Ca0.85Er0.1Ti1−xCo4x/3O3 (CETCox) were systematically characterized.
Abstract: The dielectric properties of Ca0.85Er0.1Ti1−xCo4x/3O3 (CETCox) (x = 0.00, 0.05 and 0.10), prepared by a sol–gel method, were systematically characterized. The temperature and frequency dependence of the dielectric properties showed a major effect of the grain and grain boundary. The dielectric constant and dielectric loss of CETCox decreased sharply with increasing frequency. This is referred to as the Maxwell–Wagner type of polarization in accordance with Koop's theory. As a function of temperature, the dielectric loss and the real part of permittivity decreased with increasing frequency as well as Co rate. Indeed, a classical ferroelectric behavior was observed for x = 0.00. The non-ferroelectric state of the grain boundary and its correlation with structure, however, proved the existence of a relaxor behavior for x = 0.05 and 0.10. The complex electric modulus analysis M*(ω) confirmed that the relaxation process is thermally activated. The normalized imaginary part of the modulus indicated that the relaxation process is dominated by the short range movement of charge carriers.

247 citations

Journal ArticleDOI
TL;DR: From the temperature dependence of the average normalized change (ANC), it is deduce the temperature at which the available density of trapped charge states vanishes and the presence of electrical relaxation in materials is indicated.
Abstract: This study presents the electrical properties, complex impedance analysis and dielectrical behavior of La05Ca05−xAgxMnO3 manganites with compositions below the concentration limit of silver solubility in perovskites (0 ≤ x ≤ 02) Transport measurements indicate that all the samples have a semiconductor-like behavior The metal-semiconductor transition is not observed across the whole temperature range explored [80 K–700 K] At a specific temperature, a saturation region was marked in the σ (T) curves We obtained a maximum σdc value at ambient temperature with the introduction of 20% Ag content Two hopping models were applied to study the conduction mechanism We found that activation energy (Ea) related to ac-conductivity is lower than the Ea implicated in dc-conductivity Complex impedance analysis confirms the contribution of grain boundary to conductivity and permits the attribution of grain boundary capacitance evolution to the temperature dependence of the barrier layer width From the temperature dependence of the average normalized change (ANC), we deduce the temperature at which the available density of trapped charge states vanishes Such a temperature is close to the temperature at which the saturation region appears in σ(T) curves Moreover, complex impedance analysis (CIA) indicates the presence of electrical relaxation in materials It is noteworthy that relaxation species such as defects may be responsible for electrical conduction The dielectric behavior of La05Ca05−xAgxMnO3 manganites has a Debye-like relaxation with a sharp decrease in the real part of permittivity at a frequency where the imaginary part of permittivity (e′′) and tg δ plots versus frequency demonstrate a relaxation peak The Debye-like relaxation is explained by Maxwell–Wagner (MW) polarization Experimental results are found to be in good agreement with the Smit and Wijn theory

155 citations

Journal ArticleDOI
TL;DR: In this paper, the authors reported some physical properties of AgAlP2O7 compound obtained through the standard solid-state reaction technique and studied the electrical properties over a wide range of temperature (440-640 k) in the frequency range of 40-10MHz.
Abstract: In this paper, we report some physical properties of AgAlP2O7 compound obtained through the standard solid-state reaction technique. AgAlP2O7 has been studied by X-ray diffraction, Raman spectroscopy and impedance spectroscopy. The title compound crystallized at room temperature (T = 300 K) in the monoclinic system with P21/c space group. The electrical properties were studied over a wide range of temperature (440–640 K) in the frequency range of 40 Hz–10 MHz. Study of frequency dependence of AC conductivity suggests that the material obeys the Jonscher’s universal dynamic law. The conductivity is equal to 9.37 × 10−5 Ω cm−1 at 640 K, and it is thermally activated with activation energy of 0.76 eV. The variation of DC conductivity with temperature follows the Arrhenius behavior. The calculated values of s decreased with temperature. This behavior reveals that the conduction mechanism is correlated with barrier hopping. The binding energy W m and the hopping distance R ω were deduced.

129 citations

Journal ArticleDOI
TL;DR: In this paper, the authors synthesized a Cu-doped ZnO (CZO) nanoparticles material using a sol-gel method with different doping concentrations of Cu (0, 2, 3 and 4
Abstract: In the current study, we synthesized a Cu-doped ZnO (CZO) nanoparticles material using a sol-gel method with different doping concentrations of Cu (0, 2, 3 and 4 at.%). The control of the Cu concentration on structural, electrical and optical properties of CZO nanoparticles was investigated in detail. The XRD analysis of the CZO nanoparticles reveals the formation of ZnO hexagonal wurtzite structure for all samples which confirm the incorporation of Cu2+ ions into the ZnO lattice by substitution. Furthermore, CZO nanoparticles showed a small red shift of absorption band with the incorporation of Cu from 0 to 4 at.%; i.e. a decreased band gap value from 3.34 eV to 3.27 eV with increasing of Cu doping content. The frequency dispersion of the electric conductivity were studied using the Jonscher universal power law, according to relation σ(ω) = σDC + A ωs(T). Alternative current conductivity increases with increasing Cu content in spite of the decrease the activation energy with copper loading. It was found that the conductivity reached its maximum value for critical Cu concentration of 3 at.%. The frequency relaxation phenomenon was also investigated and all results were discussed in term of the copper doping concentration.

114 citations

Journal ArticleDOI
TL;DR: In this article, the annealing effect on the structural, elastic, thermodynamic, optical, magnetic, and electric properties of Ni0.6Zn0.4Fe1.5O4 (NZFAO) nanoparticles was presented.
Abstract: This article presents the annealing effect on the structural, elastic, thermodynamic, optical, magnetic, and electric properties of Ni0.6Zn0.4Fe1.5Al0.5O4 (NZFAO) nanoparticles (NPs). The samples were successfully synthesized by the sol–gel method followed by annealing of the as-synthesized at 600, 800, 900, 1050, and 1200 °C. This approach yielded the formation of a highly crystalline structure with crystallite size ranging from 17 nm to 40 nm. X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques, as well as energy disperse spectroscopy (EDS), Fourier transform infrared (FTIR) and Raman spectroscopy, were used in order to determine the structural and morphological properties of the prepared samples. Rietveld XRD refinement reveals that Ni–Zn–Al ferrite nanoparticles crystallize in inverse cubic (Fdm) spinel structure. Using FTIR spectra, the elastic and thermodynamic properties were estimated. It was observed that the particle size had a pronounced effect on elastic and thermodynamic properties. Magnetic measurements were performed up to 700 K. The prepared ferrite samples present the highest Curie temperature, which decreases with increasing particle size and which is consistent with finite-size scaling. The thickness of the surface shell of about 1 nm was estimated from size-dependent magnetization measurements using the core–shell model. Besides, spin resonance, magnetostriction, temperature coefficient of resistance (TCR), and electrical resistivity properties have been scientifically studied and appear to be different according to their size. The optical properties of synthesized NZFAO nanoparticles were investigated, and the differences caused by the particle sizes are discussed on the basis of the phonon confinement effect. This effect was also inspected by the Raman analysis. Tuning of the physical properties suggests that the Ni–Zn–Al ferrite samples may be promising for multifunctional diverse applications.

109 citations


Cited by
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16 Mar 1993
TL;DR: Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure as discussed by the authors.
Abstract: Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.

924 citations

01 Jan 2013
TL;DR: In this article, the authors discuss p-type ZnO materials: theory, growth, properties and devices, comprehensively, and summarize the growth techniques for p- type ZnOs.
Abstract: Abstract In the past 10 years, ZnO as a semiconductor has attracted considerable attention due to its unique properties, such as high electron mobility, wide and direct band gap and large exciton binding energy. ZnO has been considered a promising material for optoelectronic device applications, and the fabrications of high quality p-type ZnO and p–n junction are the key steps to realize these applications. However, the reliable p-type doping of the material remains a major challenge because of the self-compensation from native donor defects (V O and Zn i ) and/or hydrogen incorporation. Considerable efforts have been made to obtain p-type ZnO by doping different elements with various techniques. Remarkable progresses have been achieved, both theoretically and experimentally. In this paper, we discuss p-type ZnO materials: theory, growth, properties and devices, comprehensively. We first discuss the native defects in ZnO. Among the native defects in ZnO, V Zn and O i act as acceptors. We then present the theory of p-type doping in ZnO, and summarize the growth techniques for p-type ZnO and the properties of p-type ZnO materials. Theoretically, the principles of selection of p-type dopant, codoping method and X Zn –2V Zn acceptor model are introduced. Experimentally, besides the intrinsic p-type ZnO grown at O-rich ambient, p-type ZnO (MgZnO) materials have been prepared by various techniques using Group-I, IV and V elements. We pay a special attention to the band gap of p-type ZnO by band-gap engineering and room temperature ferromagnetism observed in p-type ZnO. Finally, we summarize the devices based on p-type ZnO materials.

308 citations

01 Jan 1996
TL;DR: Ahn et al. as discussed by the authors studied the effect of Fe doping on the Mn site in the ferromagnetic and antiferromagnetic phases of (Formula presented) and found that conduction and ferromagnetism were consistently suppressed by Fe doping.
Abstract: Author(s): Ahn, KH; Wu, XW; Liu, K; Chien, CL | Abstract: The effect of Fe doping (l20%) on the Mn site in the ferromagnetic ((Formula presented)) and the antiferromagnetic ((Formula presented)) phases of (Formula presented) has been studied. The same ionic radii of (Formula presented) and (Formula presented) cause no structure change in either series, yet conduction and ferromagnetism have been consistently suppressed by Fe doping. Colossal magnetoresistance has been shifted to lower temperatures, and in some cases enhanced by Fe doping. Doping with Fe bypasses the usually dominant lattice effects, but depopulates the hopping electrons and thus weakens the double exchange. © 1996 The American Physical Society.

273 citations

Journal ArticleDOI
TL;DR: In this paper, the dielectric properties of Ca0.85Er0.1Ti1−xCo4x/3O3 (CETCox) were systematically characterized.
Abstract: The dielectric properties of Ca0.85Er0.1Ti1−xCo4x/3O3 (CETCox) (x = 0.00, 0.05 and 0.10), prepared by a sol–gel method, were systematically characterized. The temperature and frequency dependence of the dielectric properties showed a major effect of the grain and grain boundary. The dielectric constant and dielectric loss of CETCox decreased sharply with increasing frequency. This is referred to as the Maxwell–Wagner type of polarization in accordance with Koop's theory. As a function of temperature, the dielectric loss and the real part of permittivity decreased with increasing frequency as well as Co rate. Indeed, a classical ferroelectric behavior was observed for x = 0.00. The non-ferroelectric state of the grain boundary and its correlation with structure, however, proved the existence of a relaxor behavior for x = 0.05 and 0.10. The complex electric modulus analysis M*(ω) confirmed that the relaxation process is thermally activated. The normalized imaginary part of the modulus indicated that the relaxation process is dominated by the short range movement of charge carriers.

247 citations

Journal ArticleDOI
15 May 2019-Joule
TL;DR: In this paper, a computational framework was employed to evaluate and screen polyanionic materials as cathode coatings, focusing on their phase stability, electrochemical and chemical stability, and ionic conductivity.

233 citations