arXiv subjects

Mimoun El Marssi

Publications and source records attributed to Mimoun El Marssi.

31 records · Page 2Linked to original sources

arXiv2020

Structural, dielectric, electrocaloric, and energy storage properties of lead free Ba$_{0.975}$La$_{0.017}$(ZrxTi$_{0.95-x}$)Sn$_{0.05}$O$_3$ (x = 0.05; 0.20) ceramics

A-site deficient Ba$_{0.975}$La$_{0.017}$(ZrxTi$_{0.95-x}$)Sn$_{0.05}$O$_3$ (x = 0.05; 0.20) ceramics (BLaZ100xTS) were synthesized using the solid-state reaction. The microstructural study revealed a high density and low porosity in the studied ceramics. Besides, grain size lower than 1.5 micrometer was observed in the studied compounds, which is due to the incorporation of the rare earth element (lanthanum). X-ray diffraction and Raman studies revealed that BLaZ5TS and BLaZ20TS crystallize in a perovskite-type structure with tetragonal and cubic symmetry, respectively. The dielectric study showed a normal ferroelectric-paraelectric phase transition for BLaZ5TS while a diffuse phase transition is noticed for BLaZ20TS sample. The energy-storage density and the associated energy efficiency were determined from the P-E loops versus temperature and the calculated values are comparable with results obtained on BCZT systems. Furthermore, the adiabatic temperature change (Delta)T was calculated through the indirect method and a relatively high value of (Delta)T/(Delta)E = 0.2 10-6 K m/V is obtained in BLaZ5TS system. The simultaneous presence of energy storage property and electrocaloric responsivity makes this system a promising environmentally friendly candidate for application in electronic devices.

cond-mat.mtrl-sci↗

arXiv2020

Rare-earth effect on the physical properties of Na$_{0.5}$Bi$_{0.5}$TiO$_3$ system: A Density Functional Theory investigation

Na$_{0.5}$(Bi$_3$/4RE$_{1/4}$)$_{0.5}$TiO$_3$ (RENBT, RE = Nd, Gd, Dy, and Ho) compounds were investigated in the framework of first-principles calculations using the full potential linearized augmented plane wave (FP-LAPW) method based on the spin-polarized density functional theory implemented in the WIEN2k code. Combined charge density distribution and Ti K-edge x-ray absorption spectra revealed that the RENBT compositions with high polarization values were accompanied by a higher TiO$_6$ distortion, DyNBT, and NdNBT compounds. The effect of the rare-earth elements on the polarization were confirmed experimentally with the collection of the hysteresis loops. The investigation of the electronic properties of the compounds highlighted the emergence of a magnetization owing to the 4f orbital effect of the rare-earth elements. Besides, the investigation of the chemical ordering showed a short-range chemical ordering for the pure composition and an increased A-site disorder for dysprosium doped NBT system. The increased disorder may speak for increased relaxor properties in the RE doped compositions.

cond-mat.mtrl-sci↗

arXiv2020

Complex impedance and Raman spectroscopy of Na$_{0.5}$(Bi$_{1-x}$Dy$_x$)$_{0.5}$TiO$_3$ ceramics

In this work structural refinement, complex impedance spectroscopy, and Raman spectroscopy have been investigated on Na$_{0.5}$(Bi$_{1-x}$Dy$_x$)$_{0.5}$TiO$_3$ (xDyNBT) ceramic systems. The pure NBT, 2DyNBT and 5DyNBT compounds crystallize in a rhombohedral structure while the 15DyNBT composition crystallizes in an orthorhombic Pnma structure. We reported that dysprosium addition affects the phase transition temperatures as well as the dielectric losses. The electrical transport at high temperatures was investigated using the CIS over a wide frequency range. The studied samples showed a non-Debye type process, with a short-range relaxation for the pure NBT and a coexistence of both localized and long-range relaxations of charge carriers for the 2DyNBT and 5DyNBT compounds. For the high concentration, 15DyNBT, a short-range relaxation is observed. Moreover, using a brick-layer model we discuss the resistance and capacitance of the different contributors (grain and grain boundaries) in our samples. High temperature Raman spectroscopy investigation was performed in order to follow the temperature evolution of the structural transformations on ferroelectric compounds. Anomalies in the temperature evolution of the vibrational modes are seen to correlate well with the temperature transitions observed from dielectric measurements.

cond-mat.mtrl-sci↗

arXiv2020

Enhanced magnetization in the multiferroic nanocomposites Bi$_{0.9}$Gd$_{0.1}$Fe$_{0.9}$Mn$_{0.05}$X$_{0.05}$O$_3$ (X= Cr, Co) thin films

In this work we elaborated and characterized nanocomposite thin films using a preselected multiferroic matrix Bi$_{0.9}$Gd$_{0.1}$Fe$_{0.9}$Mn$_{0.1}$O$_3$ (BGFMO) in the aim to enhance their basic ferroelectric and magnetic properties. The local ferroelectric character of these nanocomposites thin films was investigated by piezoresponse force microscopy (PFM). Switching behavior for ferroelectric domains was probed by locally manipulating domains. The magnetic investigation showed that the incorporation of transition metal elements in the BGFMO matrix brings out interesting increase in the macroscopic magnetisation at room temperature. Moreover, a spin glass type behavior is observed in M(T) curves for the studied thin films.

cond-mat.mtrl-sci↗

arXiv2020

Structural, Dielectric and Ferroelectric Properties of Lead-free BCZT Ceramics Elaborated by Low-temperature Hydrothermal Processing

Lead-free Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) ceramics have demonstrated excellent dielectric, ferroelectric and piezoelectric properties in comparison to lead-based materials. The synthesis of pure and crystalline BCZT nanopowders at low temperatures of 25, 80 and 160 C was reported previously by using a sol-gel method followed by a hydrothermal route. In this study, the structural, dielectric and ferroelectric properties of sintered BCZT ceramics at 1250 °C for 10h were investigated. XRD measurements revealed the presence of a single perovskite phase at room temperature with the coexistence of the orthorhombic and tetragonal symmetries. The increase of grain size and the ceramic density in BCZT ceramics result in an enhancement of the dielectric and ferroelectric properties of BCZT ceramics. More interestingly, the synthesis temperature of BCZT powders with high dielectric and ferroelectric properties could be decreased to a low temperature of 160 °C, which is about 1200 °C lower when compared with solid-state reaction and 840 °C lower when compared with sol-gel methods. The BCZT ceramics elaborated at 160 °C revealed excellent electrical properties. Hence, the use of low-temperature hydrothermal processing can be encouraging for the synthesis of lead-free ceramics with high dielectric and ferroelectric properties.

cond-mat.mtrl-sci↗

arXiv2020

Electrical and structural properties of pure and dysprosium doped $Na_{0.5}Bi_{0.5}TiO_{3}$ system: DFT and Monte Carlo simulation

The chemical ordering, electrical, optical, and magnetic properties of $Na_{0.5}Bi_{0.5}TiO_{3}$ (NBT) and 25$\%$ dysprosium doped NBT (DyNBT) were investigated in the framework of first-principles calculations using the full potential linearized augmented plane wave (FP-LAPW) method based on spin-polarized density functional theory implemented in the WIEN2k code. We demonstrated that NBT structure is stable in the 001 A-site configuration, while DyNBT presents an A-site disorder perceived by the minimal energy difference between the different A-site configurations. A significant magnetic moment of $5μB$ emerges in DyNBT system, while NBT is known to be non-magnetic. Dysprosium in NBT matrix seems to form an ionic bonding with oxygen atoms whereas Bi-O forms covalent bonding which is responsible for the decrease of the polarization value from 42.3 $μC/cm^{2}$ for NBT to 22.08 $μC/cm^{2}$ for the doped compound. In the second part, the transition temperature and the hysteresis loops of $Na_{0.5}(Bi_{1-x}Dy_{x})_{0.5}TiO_{3}$ system x = 0 - $25\%$ were investigated using the Monte Carlo simulation. We observed a decrease in the transition temperature as a function of dysprosium introduction. We pointed out from the hysteresis loops, an apparent decrease of the coercive field together with the remanent polarization as a function of doping and also as a function of temperature. Our proposed model was seen to approach the values of experimental studies.

cond-mat.mtrl-sci↗

arXiv2019

Magnetic properties of a new cobalt hydrogen vanadate with a dumortierite-like structure: Co13.5(OH)6(H0.5VO3.5)2(VO4)6

The magnetic properties of a novel cobalt-based hydrogen vanadate, Co13.5(OH)6(H0.5VO3.5)2(VO4)6, are reported. This new magnetic material was synthesized in single-crystal form using a conventional hydrothermal method. Its crystal structure was determined from single-crystal X-ray diffraction data and was also characterized by scanning electron microscopy. Its crystal framework has a dumortierite-like structure consisting of large hexagonal and trigonal channels; the large hexagonal channels contain one-dimensional chains of face-sharing CoO6 octahedra linked to the framework by rings of VO4 tetrahedra, while the trigonal channels are occupied by chains of disordered V2O4 pyramidal groups. The magnetic properties of this material were investigated by DC magnetic measurements, which indicate the occurrence of antiferromagnetic interactions.

cond-mat.mtrl-sci↗

arXiv2019

A novel alluaudite-type vanadate, Na2Zn2Fe(VO4)3: Synthesis, crystal structure, characterization and magnetic properties

A novel alluaudite type vanadate has been successfully synthesized in its single crystal and polycrystalline forms. Its crystal structure was determined by means of X ray diffraction measurements. This new vanadate crystallizes in monoclinic system. The crystal structure of this vanadate displays an open transition metals based framework enclosing two kind of tunnels where the sodium cations are located. Moreover, the purity of the obtained powder was confirmed by X ray powder diffraction analysis. Furthermore, this new vanadate was characterized by scanning electron microscopy, Infrared spectroscopy and by magnetic measurements. The magnetic susceptibility showed the antiferromagnetic behavior of this vanadate with negatve Curie- Weiss temperature consistently with the expected magnetic interactions between iron cations.

cond-mat.mtrl-sci↗

arXiv2019

Unconventional Spin-Glass-Like State in AgCo2V3O10, the Novel Magnetically Frustrated Material

Single crystals of a new silver and-cobalt based vanadate AgCo2V3O10 were grown from a melted mixture. The crystal structure determination reveals that this new vanadate crystallizes in triclinic system with space group P-1. The structure of the titled compound is constructed from CoO6octahedra and VO4 tetrahedra sharing edges and vertices leading to an open three-dimensional framework delimiting tunnels along [001], where the Ag cations are located. The bands observed in Raman spectrum were assigned to corresponding vibrations of the VO4 groups. DC and AC magnetization (susceptibility) measurements revealed the spin-glass (SG) -type transition below a frequency-independent temperature Tf(H) that is nearly independent on the applied magnetic field. Magnetic field H> 10 kOe induces the spin glass antiferromagnet. These observations brings AgCo2V3O10 into the class of geometrically frustrated magnetic systems.

cond-mat.mtrl-sci↗

arXiv2019

Structural, electrical and energy storage properties of BaO Na2O Nb2O5 WO3 P2O5 glass ceramics system

Ferroelectric glass-ceramics are promising composite materials with dual properties, of high dielectric permittivity and high dielectric breakdown strength. In this context, new phosphate glass-ceramics 2BaO-0.5Na2O 2.5[(1-x)Nb2O5 xWO3]-1P2O5 (x=0, 0.1, 0.2, 0.3 and 0.4) designated as B0, B1, B2, B3, B4 respectively, were prepared by the controlled crystallization technology and then crystallized at high temperature of 760 °C for 10 hours. Subsequently, the obtained glass-ceramics were studied by Differential Scanning Calorimetry (DSC), X-ray powder diffraction (XRD), Raman, impedance spectroscopy, and the P-E hysteresis loops. All of these techniques allowed the identification of Ba2Na4W2Nb8O30 phase with tungsten bronze structure embedded in the glassy matrix. The density of glass-ceramics was found to increase with increasing tungsten content to reach a maximum at x =0.3 and then decreases. Dielectric and conductivity parameters were found to be governed by the presence of oxygen vacancies. Room temperature energy storage property which depends on the composition X, was performed using P-E hysteresis loops of the glass-ceramics. The optimum discharge density was obtained for B3 with an energy efficiency of 73.77%.

cond-mat.mtrl-sci↗

arXiv2019

Direct electrocaloric, structural, dielectric, and electric properties of lead-free ferroelectric material Ba0.9Sr0.1Ti1-xSnxO3 synthesized by semi-wet method

By using the semi-wet synthesis method, lead-free ferroelectric materials Ba0.9Sr0.1Ti1-xSnxO3 with x = 0, 0.02, 0.05, and 0.10 (abbreviated as BSTS) were prepared and their structural, electric and electrocaloric properties were investigated. The X-ray diffraction (XRD) patterns show that the samples calcined at 950°C have well crystallized into perovskite structure suggesting the substitution of Ti4+ by Sn4+ in BST lattice. With increasing content of Sn, the enhancement of the dielectric permittivity was observed for (0<x<0.05) and the ferroelectric transition temperature (TC) was found to shift towards the room temperature (TC = 20°C for x = 0.10). Direct measurements of the electrocaloric effect (ECE) were performed on all samples by using the highresolution calorimeter. It is found that Ba0.9Sr0.1Ti0.95Sn0.05O3 exhibits a high ECE temperature change of DTEC = 0.188 K at an applied electric field of only 7 kV/cm. Impedance spectrum analysis of all the samples performed in the temperature range of 300-360°C reveals the existence of two relaxation contributions related to the grain and grain boundaries that are well separated in frequency. Activation energies of conduction and relaxation processes were deduced for both contributions in order to determine the conduction mechanism of the studied compositions.

cond-mat.mtrl-sci↗

arXiv2019

Phase transitions, energy storage performances and electrocaloric effect of the lead-free Ba0.85Ca0.15Zr0.10Ti0.90O3 ceramic relaxor

Lead-free Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) ceramic exhibits excellent dielectric, ferroelectric and piezoelectric properties at the Morphotropic Phase Boundary (MPB). Previously, we demonstrated that the use of the anionic surfactant Sodium Dodecyl Sulfate (SDS, NaC12H25SO4) could enhance the dielectric properties of BCZT ceramic using surfactant-assisted solvothermal processing [1]. In the present study, structural, dielectric, ferroelectric properties, as well as electrocaloric effect and energy storage performances of this BCZT ceramic were thoroughly investigated. X-ray diffraction (XRD) measurements revealed the presence of single perovskite phase at room temperature with the coexistence of orthorhombic and tetragonal symmetries. In-situ Raman spectroscopy results confirmed the existence of all phase transitions from rhombohedral through orthorhombic and tetragonal to cubic symmetries when the temperature varies as reported in undoped-BaTiO3. Evolution of energy storage performances with temperature have been investigated. BCZT ceramic exhibits a high energy storage efficiency of ~80% at 120 °C. In addition, the electrocaloric responsivity was found to be 0.164.10-6 K.m/V at 360 K.

cond-mat.mtrl-sci↗

arXiv2019

Influence of temperature and wavelength on the switchable photovoltaic response of a BiFe0.95Mn0.05O3 thin film

Photovoltaic (PV) response of epitaxial BiFe0.95Mn0.05O3 thin film grown by pulsed laser deposition has been investigated on a broad range of temperature. Wavelength dependent photovoltaic effect shows the contribution of in gap level states most likely connected to the manganese doping on the B-site of the perovskite unit cells and presence of defects (Bi and O vacancies). The temperature dependent response of the PV response rules out electromigration and/or Schottky barriers as dominant mechanisms. This is corroborated with the observed switchable photovoltaic effect that can be explained either by the depolarizing field or bulk photovoltaic effect. In addition the PV response shows strong correlation with the low temperature polaronic like conduction mechanism and high open circuit voltage (2.5V) is detected in the investigated vertical capacitive geometry.

cond-mat.mtrl-sci↗