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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] A Monte Carlo model was developed to study the ferroelectric and energy storage properties of PbZr1−xTixO3 (PZT). The proposed model aims to calculate the exchange coupling constants in ferroelectric PbZr1−xTixO3 thin films system, useful for Monte Carlo simulation within metropolis algorithm. Thus, the effect of temperature on the ferroelectric properties of the PZT thin films, such as, hysteresis loops, polarization and coercive field were investigated. Moreover, the phase diagram as a function of x values of Ti in PbZr1−xTixO3 was studied. The obtained P-E hysteresis loops permitted to predicte the energy storage properties of the studied system. A maximum of the recoverable energy density of 13.93 J cm−3 was obtained with the energy density efficiency of 79% for x = 0. The obtained results are in good agreement with the reported experimental data for the same material. (paper)
[en] We discuss the fundamental transparent conducting properties of halogens doped SnO2 rutile systems include the structural, electronic structure, optical and electrical properties. Within this study, we employ the first-principles calculation of the full potential linearized augmented plane wave (FP-LAPW) method based on the density function theory and semiclassical Boltzmann equations. It is found that the halogens substitutional doping cause an expansion of SnO2 lattice constants and low thermodynamic perturbation. The dopants act as shallow donors by creating impurity states at the bottom of the conduction band that lead to blue-shift in the optical transparency. Moreover, the electrical conductivity of SnO2 Rutile is significantly improving by halogens doping. In fact, these results could stimulate the future experimental works for elaborating new generations of the transparent conducting oxides in an optimal way.
[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] The double perovskite Sr2CrReO6 has very important characteristics for spintronic applications. It is a ferrimagnetic material distinguished by its high Curie temperature Tc≈635 K. We made this statistical study to further reveal the different ways in which this compound can behave with respect to interaction couplings and crystal fields prevailing in the system. We used as approximation an effective field theory (EFT) without correlation in the context of the Ising model. Thus we report different phase diagrams, firstly in relation to the exchange couplings present in the model adopted, and secondly in relation to the crystal fields of Cr and Re. We compare the results found by this method with those found by other statistical methods. Several phase transitions are detected and reentrant phenomenon was observed. - Highlights: • Phase diagram of double perovskite Sr2CrReO6 has been investigated • The phase diagrams depend on the exchange couplings and the crystal fields • Reentrant phenomenon has been observed