Résumé: Because of their technological interest in electronics, optoelectronics, sensor technology, and spectroscopic photon counting X-ray photodiode, the AlxIn1-xP alloys have been studied extensively. The ground state structure, mechanical, electronic, optical, and thermodynamic properties for the ternary alloys AlxIn1-xP in the cubic structure are presented. The theoretical calculations are performed using the generalized gradient approximation (GGA) and the semilocal modified Becke-Johnson (mBJ). Although the mBJ (GGA) energy band gap varies nonlinearly with Al concentration, the obtained values agree well with the available experimental data. Interestingly, it is found that at 83% Al, a transition from direct to indirect gap occurs because the binary compounds InP and AlP compounds have a direct band gap ( ) and an indirect band gap ( ), respectively. The thermodynamic study reveals that AlxIn1-xP alloys are stable at high temperature, with the existence of a solid solution for all compositions. Furthermore, at the critical composition xc=0.55, the value of the direct band gap varies in the narrow range 2.429 - 2.413 eV, corresponding to the wavelengths 514 - 513 nm. Consequently, this range of energy band gap recommends the ternary AlxIn1-xP alloys for optoelectronic device applications, such as solar cells or photovoltaic.

Résumé: Using the first principal study, we present and discus the structural, electronic and magnetic properties of an ordered double perovskite Ba2FeMoO6 in the cubic (Fm-3m) and tetragonal (I4/mmm) symmetries. The phase stability for ferromagnetic and paramagnetic states, has been treated by applying the generalized gradient approximation (GGA-08). Moreover, the calculated lattice parameters are found to be in good agreement with experimental data. For understanding the electronic properties in the studies Ba2FeMoO6, band structure, total and partial density of states have also been performed and discussed thoroughly. On the other hand, the Monte Carlo simulations were used to study the magnetic properties of Ba2FeMoO6. The Curie temperature was established. The magnetic changes entropy and relative cooling power were deduced. Finally, the magnetic hysteresis cycle was given. The tunability of TC and magnetocaloric properties, the reversible magnetocaloric effect, and the simple fabrication of the samples investigated here suggest a new research area for the development more promising magnetic coolers.

Résumé: We determined the structural, mechanical, electronic and magnetic properties of the Co2VGa Heusler alloy by employing the FP-LAPW method and Monte Carlo simulation. The structural stability studies were performed by calculating the total energies in nonmagnetic (NM), ferromagnetic (FM) and (AFM) states in both F43m (n.216) and Fm3m (n. 225) phases for different volumes around the equilibrium cell volume. The first principles calculations results revealed that the Co2VGa has a stable ferromagnetic (FM) state in the Fm3m (n. 225) phase. The calculated lattice parameter is found to be in a good agreement with the theoretical data, whereas the bulk modulus exhibits a significantly high magnitude placing Co2VGa Heusler alloy in the range of hard materials. Purposely, the elastic parameters (C11, C12, and C44) and their derivatives have been then directly calculated. The investigated energy band structure shows that the Co2VGa is half metallic in the minority spins direction with a small band gap equal to 0.20 eV (WC-GGA), 0.14 eV (GGA-PBEsol) and 0.53 eV (mbj-GGA)exchange-correlation potential. In addition, total magnetic moments MT(μB), stiffness constant of the spin wave (D) and the Curie temperature TC(K) are also calculated. In other hand, the magnetic and magnetocaloric effect of this material are studied using the results obtained by FP-LAPW method. The transition temperature, magnetic entropy change and relative cooling power are calculated.

Résumé: Pure ZnO and ZnO–Bi2O3 nanocomposites with 5 wt% and 10 wt% of Bi2O3 content were synthesized using the co-precipitation method. Optical properties such as refractive index (n), extinction coefficient (k), bandgap (Eg), and Urbach energies, as well as the band structure, were determined by modeling the experimental transmittance and reflectance UV–Vis spectra. The deduced bandgap and Urbach energies for pure ZnO (3.758 eV) increase with the increase of the doping degree of Bi2O3 in ZnO–Bi2O3 nanocomposite films. X-ray diffraction and scanning electron microscopy (SEM) was used to study the structural and morphological properties of these nanocomposite films. Pure ZnO and nanocomposites with Bi2O3 exhibit crystalline domains with wurtzite hexagonal structures, and as the doping degree of Bi2O3 increases, the crystallite size decreases. Based on SEM micrographs, the ZnO nanoparticles (NPs) structure shows the presence of aggregation. Moreover, Bi2O3 NPs in the nanocomposite film led to the further aggregation in the form of large rods. The elemental and chemical properties of the nanocomposites were investigated using infrared and energy-dispersive X-ray spectroscopy. The charge transfer process in the studied system is between ZnO and Bi2O3 conduction bands. Density-functional theory (DFT) calculations were performed for ZnO, Bi2O3, and ZnO-Bi2O3 compounds to investigate structural, optical, and electronic properties, being in agreement with the experimental results.

Résumé: The La0.7Sr0.3Mn0.95Fe0.05O3 sample has been prepared by solid-state method. The crystallographic analysis demonstrates that the sample crystallizes with the P n m a space group in the orthorhombic structure. For the morphologic study, the size counting garnered from SEM images, the value of the average grain size is DSEM = 140 nm. A phenomenological model is used in present research work to explain the magnetocaloric effect. Using the measurements of magnetization, the magnetocaloric properties are estimated under different external magnetic fields based on this model. Additionally, based on the modified Bean–Rodbell model, we theoretically studied the magnetocaloric properties of the elaborated material with consideration of the magnetic disorder effect.