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First-principle investigations of structural and electronic properties of TMAl (TM = Fe, Co, and Ni) transition metal aluminides

100%

Bendouma D. , Allel M. , Mustapha I. B. , Miloud B. , Abdelkader T.

tom Vol. 33, No. 2

251--258

In the present work, we have investigated the structural and electronic properties of TMAl (TM = Fe, Co, and Ni) transition metal aluminides in the B2 structure, using first-principle calculations of the density functional theory (DFT) based on the linearized augmented plane wave method (FP-LAPW) as implemented in the WIEN2k code, in which the energy of exchange and correlation are treated by the generalized gradient approximation (GGA), proposed in 1996 by Perdew, Burke and Ernzerhof (PBE). The ground state properties have been calculated and compared with other calculations, and the electronic structures of all FeAl, CoAl, and NiAl compounds exhibited a metallic behavior. It was depicted that the density of states is characterized by the large hybridization between the s-p (Al) and 3d (Fe, Co, and Ni) states, which creates the pseudogap in the region of anti-bonding states. Moreover, the band structures of FeAl, CoAl, and NiAl are similar to each other and the difference between them is in the energy level of each band relative to the Fermi level.

FP-LMTO study of structural, electronic, thermodynamic and optical properties of Mg x Cd1−x Se alloys

86%

Bensaid D. , Ameri M. , El H. M. D. , Azaz Y. , Bendouma D. , Al-Douri Y. , Ameri I.

Materials Science Poland

2014

tom Vol. 32, No. 4

719--728

Structural, electronic and optical properties of MgxCd1−xSe (0 6 x 6 1) are calculated for the first time using density functional theory. Our results show that these properties are strongly dependent on molar fraction of particular components – x. The bond between Cd and Se is partially covalent and the covalent nature of the bond decreases as the concentration of Mg increases from 0 % to 100 %. It is found that MgxCd1−xSe has a direct band gap in the entire range of x and the band gap of the alloy increases from 0.43 to 2.46 eV with the increase in Mg concentration. Frequency dependent dielectric constants ε1(ω),ε2(ω) refractive index n(ω) are also calculated and discussed in detail. The peak value of refractive indices shifts to higher energy regions with the increase in Mg. The larger value of the extraordinary refractive index confirms that the material is a positive birefringence crystal. The present comprehensive theoretical study of the optoelectronic properties of the material predicts that it can be effectively used in optoelectronic applications in the wide range of spectra: IR, visible and UV. In addition, we have also predicted the heat capacities (CV ), the entropy (S), the internal energy (U) and the Helmholtz free energy (F) of MgxCd1−xSe ternary alloys.