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[en] Magnetic, electronic and structural properties of titanium dioxide material with different structural defects are studied using the first-principles ab-initio calculations and the Korringa–Kohn–Rostoker method (KKR) combined with the coherent potential approximation (CPA) method in connection with the local density approximation (LDA). We investigated all structural defects in rutile TiO_2 such as Titanium interstitial (Ti_i), Titanium anti-sites (Ti_o), Titanium vacancies (V_T_i), Oxygen interstitial (O_i), Oxygen anti-sites (O_T_i) and oxygen vacancies (V_o). Mechanisms of hybridization and interaction between magnetic atoms are investigated. The transition temperature is computed using the Mean Field Approximation (MFA).Magnetic stability energy of ferromagnetic and disordered local moment states is calculated to determine the most stable state. Titanium anti-sites have a half-metallic aspect. We also studied the change type caused by structural defects in this material. - Highlights: • Green function technique is used to study disordered systems. • We used DFT to study electronic structure of TiO_2 perturbed by defects. • TiO_2 with titanium antisite defect posesses a magnetic behavior. • The transition temperature is computed using the Mean Field Approximation.
[en] First-principles density functional theory calculations were carried out to study the structural, electronic, optical and electrical properties of fluorine-doped zinc oxide in detail. Fluorine substitutions of the oxygen sites create shallow donors derived mainly from the orbital 2p of fluorine. Additionally, the calculated optical properties reveal that the energy band gap gradually expands when increasing the fluorine doping level, which leads to a blue-shift in the optical transparency. More interestingly, the electrical conductivity is significantly enhanced after fluorine doping. (paper)
[en] In the last few years there has been a growing interest in the double perovskite (DP) Sr_2CrReO_6, as a magnetic material used in spintronics, due to its high Curie temperature (T_C=610 K). Antisite disorder is a defect that affects the spin polarization and the Curie temperature of all PDs. We conducted this work by Monte Carlo simulation to study the effect of the antisite disorder on this compound for two cases: Cr-excess expressed by Sr_2Cr_1_+_xRe_1_−_xO_6 and Re-excess expressed by Sr_2Cr_1_−_xRe_1_+_xO_6. This simulation has transformed the concept of the antisite conceived as defect, into a tool to explain the role of transition metals, namely Cr and Re, in the stability and the magnetic performance of the compound Sr_2CrReO_6. This simulation allows positioning the Cr as a key element in determining the high Curie temperature and the ferromagnetic stability. The effect of crystal field of Re in the disordered sublattice regarding the disorder rates was also explored. - Highlights: • Monte Carlo simulation was performed to study the antisite defect in Sr_2CrReO_6. • Effect of the rates of Cr and Re was explored by studying the antisite defect. • Cr is the key element in determining the high TC and the ferromagnetic stability. • The effect of crystal field of Re regarding the disorder rates was also explored.
[en] In this paper, we theoretically and experimentally investigated the structural, electronic, optical and magnetic properties of Cobalt doped ZnO. We used the the SPRAY Pyrolysis technique on preheated substrate glass. Samples were characterized using x-ray Diffraction. Optical parameters such as the optical band gap energy (Eg), the refractive index (n), the dielectric constants (ϵr, ϵi) and the optical conductivity (σ) as a function of photon energy have been investigated. As main result, 2% Co doping leads to improve the optical and optoelectronic properties of ZnO with a higher refractive index, optical conductivity and absorption near infrared region. Furthermore, we investigated the doping concentration effect on the magnetic and structural properties by first principal calculations and found a promising phase change temperature which is higher than room temperature. (paper)
[en] Fe3+ doped ZnO was elaborated using spray pyrolysis deposition technique with different concentrations of the doping element then characterized by the x-ray diffraction for the structural characterizations of our samples. We investigated optical properties using Uv-Vis spectrophotometer in the wavelength range of 200–880 nm and also magnetic properties by first principal density functional theory electronic structure calculations to estimate the sample magnetic properties and the Curie temperature. The change in the physical parameters and its relation with the measured optical band gap were investigated in detail to understand the cause and to improve the optical and magnetic properties. The measured optical absorption spectra and band gap values are in agreement with the Ferromagnetic stability of the magnetic dopants charge states. The magnetic interaction was explained by the Zener p-d double exchange. The optimized structure was confirmed using the first-principle stability calculations. (paper)