Browsing by Author "Charifi, Z."

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Ab Initio Investigations of the Structural, Electronic, Magnetic and Mechanical Properties of Crx (X = As, Sb, Se, and Te) Transition Metal Pnictides and Chalcogenides
(Iop Publishing Ltd, 2019) Charifi, Z.; Guendouz, D. J.; Baaziz, H.; Soyalp, F.; Hamad, B.
The structural, electronic, magnetic, and mechanical properties of CrX (X = As, Sb, Se and Te) transition metal pnictides and chalcogenides were investigated using ab initio density functional theory using the local density approximation and generalized gradient approximation. Under ambient conditions, CrAs and CrTe are stable in the orthorhombic MnP (MP)-type antiferromagnetic (AFM) and hexagonal NiAs (NA) (FM) structures, respectively, whereas CrSb and CrSe have NA-type (AFM) structure. The half-metallic behavior was predicted for the zinc blende (ZB) and wurtzite (WZ) structures of CrAs, the zinc blende (ZB)-type of CrSb and CrSe compounds and the zinc blende (ZB) and rock salt (RS) structures of CrTe. However, the remaining structures are found to exhibit a metallic behavior. The highest total magnetic moment of 4 mu(B) was predicted for the RS and ZB (FM) structures of CrTe. The investigated CrX compounds were found to be mechanically stable at ambient pressure. The high value of B/G ratio indicates that CrSb (NA) is a ductile material, whereas CrAs (MP), CrSe and CrTe (NA) are brittle due to the lower B/G value.
A Dft Study of the Electronic and Magnetic Properties of Fe2mnsi1-Xgex Alloys
(Elsevier, 2012) Hamad, B.; Charifi, Z.; Baaziz, H.; Soyalp, F.
We performed density functional theory (DFT) calculations to study the structural, electronic and magnetic properties of Fe2MnSi1-xGex alloys (x=0, 0.25, 0.50, 0.75, and 1.00). The lattice constant is found to increase linearly as a function of Ge concentration with a decrease in the formation energy. The total magnetic moment is found to be 3 mu(B) for all alloys with the most contribution from Mn local magnetic moments. Iron atoms, however, exhibit much smaller spin moments about 10% of the bulk value. It seems that due to the proximity of Fe, magnetic moments have been induced on the sp atoms, which couple antiferromagnetically with Fe and Mn spin moments. Although, the band gap remains almost constant (0.5 eV), the spin-flip gap decreases as a function of x. (C) 2012 Elsevier B.V. All rights reserved.
Effect of Octahedral Cation on Electronic, Magnetic and Optic Properties of Cox2o4 (X = Cr, Mn and Fe) Spinel Compound
(Taylor & Francis Ltd, 2022) Hetache, N.; Charifi, Z.; Ghellab, T.; Baaziz, H.; Soyalp, F.
The magnetic, structural and optical properties of CoX2O4 (X = Cr, Mn and Fe) spinels are calculated using GGA + U approximation. The effect of the octahedral cation X on the properties of these spinels are analyzed. In order to better understand the electronic aspect of these compounds we studied the issue between the relative forces of the exchange effect and the crystal field effect through a complete analysis of the densities of electronic states. Obtaining the correct ground state is only possible if the electron-electron interactions between magnetic cations are introduced. When the X cations are changed, the crystalline structure changes totally from cubic normal spinel for CoFe2O4 to tetragonal normal spinel one for CoMn2O4 to inverse spinel for CoCr2O4. The electronic properties of our spinels are significantly different, an increase in the band gap from Fe to Mn to Cr compounds is obtained. Magnetic exchange interactions are strongly affected by sub-lattices occupation in the inverse phase of CoFe2O4 and significant structural distortion of the CoMn2O4 compound. The analysis of structural parameters and electronic structures plays a role on the trends of magnetic exchange interactions. We have noticed that the iron states in CoFe2O4 are extremely localised making this spinel very different from the X cation states in the other two spinels. So the variation in X cations allows us to confirm the trend in the properties of CoX2O4. The prediction of optical properties is possible and it allowed us to calculate different optical parameters. We have noticed that epsilon(1)(0) decreases with increasing band gap.
Electronic Structure, Phase Stability, Vibrational and Thermodynamic Properties of the Ternary Nowotny-Juza Materials Limgsb and Liznsb
(Elsevier Science Bv, 2017) Guendouz, Dj.; Charifi, Z.; Baaziz, H.; Soyalp, F.; Ugur, G.; Ugur, S.
A comprehensive study of structure, phase stability, electronic, vibrational and thermodynamic properties of LiMgSb and LiZnSb compounds is performed by carrying out First-principles calculations within densityfunctional theory using the full potential linearized augmented plane wave (FP-LAPW) combined with the pseudo-potential method. The generalized-gradient approximation (GGA) and the local density approximation (LDA) are chosen for the exchange-correlation energy. The Engel-Vosko (EV-GGA) formalism and mBJ approach are applied for the electronic properties. By exchanging the position of the atoms in the cubic structure, three phases (alpha, beta, gamma) are composed. Under ambient conditions, LiMgSb is stable in the cubic a structure however LiZnSb in the wurtzite one. At high pressure, these compounds undergo a structural phase transition from the cubic alpha to cubic gamma phase for LiMgSb and from the wurtzite to cubic gamma phase for LiZnSb, and the transition pressures were calculated. The quasi-harmonic Debye model, in which the phononic effects are predicted, is applied to the investigate of the thermodynamic properties. The temperature effect on the volume V(T), bulk modulus, B(T), thermal expansion coefficient alpha(T), specific heats (C-V and C-p) and Debye temperatures Theta(D), in different pressure and temperature range from 0 to 1000 K are investigated. Our results are in good agreement with previous theoretical calculations and the available experimental data. The band structure, density of states (DOS), and phonon dispersion curves have been obtained and analyzed.
Electronic, Optical, and Thermoelectric Properties of Vacancy-Ordered Double Perovskite K2snx6 (X = Cl, Br, I) From First-Principle Calculations
(Institute of Physics, 2024) Zikem, A.; Baaziz, H.; Ghellab, T.; Charifi, Z.; Soyalp, F.
The present study explores the structural, optoelectronic, and thermoelectric properties of potassium tin halide vacancy-ordered double perovskites K2SnX6 (X = Cl, Br, and I) in their stable monoclinic phase. Our study uses first-principles calculations based on density functional theory (DFT). Electronic band structures reveal direct band gaps for K2SnCl6 and K2SnBr6, while K2SnI6 exhibits an indirect band gap. Theoretical computations utilising the modified Becke-Johnson potential (mBJ-GGA) demonstrate that the optical band gaps of K2SnCl6, K2SnBr6, and K2SnI6 decrease in the following order: 2.581 eV, 1.707 eV, and 4.126 eV, respectively. These values render the materials suitable for photovoltaic applications. Analysis of dielectric functions, absorption coefficients, and refractive indices demonstrates their potential as light-absorbing materials. We evaluate the thermoelectric properties, including electronic and lattice thermal conductivities, Seebeck coefficients, and power factors, which lead to favorable thermoelectric performance. The maximum figure of merit (ZT) values of 0.58, 0.69, and 0.50 are achieved for K2SnCl6, K2SnBr6, and K2SnI6, respectively, at 500 K. These findings highlight the potential of these materials for applications in solar cells and thermoelectric devices, emphasising their effectiveness at elevated temperatures. © 2024 IOP Publishing Ltd.
First Principles Study of Hydrogen Storage Material Nabh4 and Lialh4 Compounds: Electronic Structure and Optical Properties
(Iop Publishing Ltd, 2016) Ghellab, T.; Charifi, Z.; Baaziz, H.; Ugur, S.; Ugur, G.; Soyalp, F.
A comprehensive study of structure, phase stability, optical and electronic properties of LiAlH4 and NaBH4 light-metal hydrides is presented. The calculations are carried out. within density functional theory using the full potential linear augmented plane wave method. The exchange-correlation potential is treated within the local density approximation. and the generalized gradient approximation (GGA) to calculate the total energy. Furthermore, the Engel-Vosko GGA. approach is employed to compute. electronic and optical properties such as reflectivity spectra. The phases a, beta and gamma of LiAlH4 and NaBH4 hydrides are investigated, the phase transition from the beta to the. high-pressure gamma phase is determined for NaBH4. and is accompanied by a 1% volume decrease. For LiAlH4, no phase transition is detected. The materials under consideration are classified as wide band gap compounds. From the analysis of the structures at different phases, it is deduced that the hydrides show strong covalent interaction between B (Al) and H in the [BH4](-) ([AlH4](-)) anions and ionic bonding character between [BH4](-) and Na+ for NaBH4, and [AlH4](-) and Li+ for LiAlH4. The complex dielectric function, absorption coefficient and the reflectivity spectra are also computed and analyzed in different phases.
Investigation of Electronic Structure and Thermodynamic Properties of Quaternary Li-Containing Chalcogenide Diamond-Like Semiconductors
(Iop Publishing Ltd, 2016) Berarma, K.; Charifi, Z.; Soyalp, F.; Baaziz, H.; Ugur, G.; Ugur, S.
Using first-principles calculations based on density functional theory, the structural, electronic and thermodynamic properties of Li2CdGeS4 and Li2CdSnS4 compounds are investigated. We confirmed that both Li2CdGeS4 and Li2CdSnS4 are diamond-like semiconductors of the wurtzstannite structure type based on that of diamond in terms of tetrahedra volume. All the tetrahedra are almost regular with major distortion from the ideal occurring in the LiS4 tetrahedron, with values for S-Li-S ranging. from 105.69 degrees to 112.84 degrees in the Li2CdGeS4 compound. Furthermore, the Cd-S bond possesses a stronger covalent bonding strength than the Li/Ge-S bonds. In addition, the inter-distances in Li2CdSnS4 show a larger spread than the distances in the Li2CdGeS4 compound. The electronic structures have been calculated to understand the bonding mechanism in quaternary Li-containing chalcogenide diamond-like semiconductors. Our results show that Li2CdGeS4 and Li2CdSnS4 are semiconductors with a direct band gap of 2.79 and 2.42 eV and exhibit mixed ionic-covalent bonding. It is also noted that replacing Ge by Sn leads to a decrease in the band gap; this behavior is explained in terms of bond lengths and electronegativity differences between atoms. Optical properties, including the dielectric function, reflectivity, and absorption coefficient, each as a function of photon energy are calculated and show an optical anisotropy for Li2CdGeS4 and Li2CdSnS4. The static dielectric constant epsilon(1)(0) and static refractive index n(0) decrease when Ge is replaced by Sn. The influence of pressures and temperatures on the thermodynamic properties like the specific heat at constant volume C-v, and at constant pressure C-p, the Debye temperature Theta(D), the entropy S and the Gruneisen parameter gamma have been predicted at enlarged pressure and temperature ranges. The principal aspect from the obtained results is the close similarity of both compounds.
The Study of Structural, Electronic and Thermoelectric Properties of Ca1-Xybxzn2sb2 (X=0, 0.25, 0.5, 0.75, 1) Zintl Compounds
(World Scientific Publ Co Pte Ltd, 2021) Mili, I; Latelli, H.; Ghellab, T.; Charifi, Z.; Baaziz, H.; Soyalp, F.
Based on the electronic structure, the physical properties of Ca1-xYbxZn2Sb2 (x = 0, 0.25, 0.5, 0.75, 1) Zintl compounds are studied. The transport properties can be significantly changed by varying the composition x. The materials under study are more metallic with increasing x and behaves like a semiconductor when x decreases. It is found that CaZn2Sb2 exhibits a larger thermopower magnitude (S = 241 mu V/K at T = 700 K) and the Seebeck coefficient decreases as x increases. The calculated figure of merit factor of YbZn2Sb2 is found to be low, this is explained by the fact that its structure is very compact and its bandgap is small which lead to high electrical and thermal conductivity due to high carrier concentration (n = 1:25.10(20) cm(-3) at T = 300 K). On other hand a narrow-gap (0:46 eV for CaZn2Sb2), provides a balance between a high Seebeck coefficient and low electronic thermal conductivity, with a slight increase in the carrier concentration when the temperature increases (3:87.10(19) cm(-3) at 600 K). As a consequence, CaZn2Sb2 compound is predicted to have good performance for thermoelectric applications. The electrical (sigma) and the thermal (K) conductivity for CaZn2Sb2 compound in both directions (along x and z-axes) are calculated. It is obtained that (sigma(xx)) is 120% of (sigma(zz)) at high-temperature, whereas S-zz Seebeck coefficient was higher than S-xx especially at T = 300 K (S-zz = 246 mu V/K; S-xx = 213 mu V/K). The large value of S-zz showed that the transport is dominated by zz-axis.
Theoretical Investigations of Co2mn1-Xcrxsn and Co2mnsn1-Ysiy Pseudo-Ternary Alloys: First Principles Calculations
(Elsevier Science Bv, 2015) Charifi, Z.; Hamad, B.; Baaziz, H.; Soyalp, F.
The electronic and magnetic properties of Co2Mn1-xCrxSn and Co2MnSn1-ySiy alloys are investigated using density functional theory (OFT) within a full-potential linearized augmented-plane-wave (FPLAPW) method. Amongst the systems under investigation, Co2MnSn1-ySiy alloys show half metallicity with 100% spin polarization at the Fermi level, however Co2Mn1-xCrxSn are found to be pseudo-half metals with Few minority states at the Fermi level and high spin polarization. The substitution of Si with Sn keeps the magnetic moment constant in Co2MnSn1-ySiy alloys, whereas the substitution of Mn with Cr decreases the magnetic moment and degrade the half-metallicity in Co2Mn1-xCrxSn alloys. The Curie temperature is calculated and it is found to be about 928 K for all Co2MnSn1-ySiy alloys, whereas it decreases linearly with x for Co2Mn1-xCrxSn alloys. The lattices constants, bulk modulii, energy gaps, polarization ratio and density of states are calculated and their variation versus x or y are discussed. (C) 2015 Elsevier B.V. All rights reserved.