Publications (9)19.05 Total impact

Article: Structural, electronic and optical properties of LiBeP in its normal and high pressure phases
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ABSTRACT: An investigation into the structural stabilities, electronic and optical properties of LiBeP under high pressure was conducted using the allelectron density functional theory within the local density approximation. Our results show that the sequence of the pressure induced phase transition of LiBeP is the Cu2Sb–type structure (P4/nmm), the MgSrSi–type structure (Pnma) and the LiGaGe–type structure (P63mc). The first transition (P4/nmm to Pnma) takes place at 2.95 GPa and the second (Pnma to P63mc) at 6.65 GPa. In the three phases, the bandgap is indirect and the valence band maximum is at the zone center. With increasing pressure LiBeP in the LiGaGe structure becomes a direct gap semiconductor at 19.75 GPa. The assignments of the structures in the optical spectra and the band structure transitions are discussed. The mean value of the optical dielectric constant for the Cu2Sb phase is smaller than that for the MgSrSi and the LiGaGe ones. This compound has a positive uniaxial anisotropy in the LiGaGe sstructure. The absorption coefficient along the z direction, αzzαzz, for the MgSrSi structure is higher than that in the other two structures in the visible regime.  [Show abstract] [Hide abstract]
ABSTRACT: Using density–functional perturbation theory, we have investigated the lattice dynamics of SrX (X=S, Se and Te) and their pressure dependence in both B1 (NaCl structure) and B2 (CsCl structure) phases. Static calculations predict the B1–B2 transition to occur at 17.7, 13.6 and 12.3GPa for SrS, SrSe and SrTe respectively. The inclusion of zeropoint vibrations lowers these values. The splitting varies little with pressure. The results compare well with available experiments. We have also used the calculated dispersions in conjunction with quasiharmonic approximation to predict temperature and pressure dependence of various quantities such as the thermal expansion coefficient, the bulk modulus and the heat capacity. Our results for the thermal expansion coefficient show that it decreases with pressure and does not show any negative behaviour. The predicted transition pressure decreases with temperature.  [Show abstract] [Hide abstract]
ABSTRACT: We have investigated the structural, elastic and electronic properties of Li2ZnGe in both C1b and L21 phases. The calculation are carried out by means of the full potential linearized augmented plane wave method within the density functional theory. The exchange and correlation effects have been treated using the local density and the generalized gradient approximations. The total energy minimizations give structural parameters in good agreement with available experimental data and show that C1b is the most stable and energetically favorable phase of this compound. The bulk modulus values indicate that the L21 phase is softer than the C1b one. The calculated elastic constants within the LDA show that the studied phases satisfy the stability criteria and the C1b phase is more stable. However, the GGA approximation predicts that L21 is not stable. The elastic moduli and the Debye temperature of polycrystalline samples are also calculated.Band structure calculation shows that C1b phase exhibits a semiconducting behavior with a narrow indirect gap. The conduction band valleys follow the X–L–Γ ordering of increasing energy. The L21 is found to be metallic. The valence charge density analysis show that the bonding in the C1b phase is partially covalent and partially ionic.  [Show abstract] [Hide abstract]
ABSTRACT: We have studied the vibrational properties of the filled tetrahedral semiconductor LiMgAs and its binary analog AlAs by using the planewave pseudopotential method within density functional theory. The calculated lattice constants for the studied compounds are in good agreement with previous theoretical and experimental results. The phonon dispersion curves and phonon density of states are calculated by using density functional perturbation theory. The sound speeds in different directions are quantitatively similar in LiMgAs and AlAs. The assignment of the zone center modes to the relative motion of the atoms shows that the lower optic modes are due to the Mg–As pair vibrations, while for the upper ones the Li–Mg pair dominates, which is attributed to the smaller Mg atom mass. The longitudinal interatomic force constant of Mg–As is about 66% higher than that of Li–As, showing the relatively high covalency of the former bond.  [Show abstract] [Hide abstract]
ABSTRACT: We have studied the dynamical properties of the filled tetrahedral compounds LiCdP and LiCdAs and the binary analogs InP and InAs by employing the planewave pseudopotential method within density functional theory. The calculated lattice constants for these compounds are consistent with other local density approximation calculations and they reproduce the trend encountered in the experimental data. The phonon dispersion curves and density of states are calculated by using density functional perturbation theory. The high frequency optic modes in LiCdP and LiCdAs are assigned to Li–P and Li–As pairs, respectively. The splitting of the LO and TO branches at Γ point for each pair suggests that the Li–P and Li–As bonds have high ionicity. The force constants of Cd–P and Cd–As are about 56% and 59% higher than those of Li–P and Li–As, respectively, showing the relatively high covalency of the former bonds.  [Show abstract] [Hide abstract]
ABSTRACT: We report on first principles studies of the electronic properties of the filled tetrahedral compound LiCdP and zinc–blende InP, using the full potential linearized augmented plane wave method within the local density approximation. The total energy calculations show that the α phase (Li+ near the anion) to be more stable than the β one (Li+ near the cation) for the LiCdP. The conduction band valleys follow the Γ–L–X ordering of increasing energy for βLiCdP and InP, and the Γ–X–L one for α–LiCdP. The conduction band modifications are discussed and found to obey the interstitial insertion rule except for the Γ state of βLiCdP. The valence charge density analysis shows that the Cd–P bond is covalent whereas the Li–P and the Li–Cd ones in α and β phases, respectively, are ionic.  [Show abstract] [Hide abstract]
ABSTRACT: We have investigated the structural and elastic properties of the Nowotny–Juza filled tetrahedral compounds LiCdX (X = N, P, As) by using the fullpotential linearized augmented plane wave method within the local density approximation. The αphase for the studied materials, which is energetically favourable than the β one, is softer than the binary analogous compounds; InN, InP and InAs. The calculated sound speeds are quantitatively similar for the ternaries and their binary analogous compounds. These results are confirmed by the data obtained from the phonon spectra for LiCdP and LiCdAs, using the plane wave pseudopotential method.  [Show abstract] [Hide abstract]
ABSTRACT: First principles calculations, by means of the full potential linearized augmented plane wave method within the local density approximation, were carried out for the pressure dependence of the electronic and optical properties of the filled tetrahedral compounds LiZnN, LiZnP and LiZnAs. The first order band gap pressure coefficient aΓ–Γ in LiZnN is larger than the corresponding one in GaN, while it is smaller in LiZnP and LiZnAs compared to the one in GaP and GaAs, respectively. The aΓ–L value in the ternaries is greater than the corresponding one in the binaries. The structures in the optical spectra shift towards higher energies when the pressure increases. The static dielectric function decreases with pressure.  [Show abstract] [Hide abstract]
ABSTRACT: First principles calculations, by means of the fullpotential linearized augmented plane wave method within the local density approximation, were carried out for the electronic and optical properties of the filled tetrahedral compounds LiMgN, LiMgP and LiMgAs. The bandgap trend in the ternaries is found to be similar to the one encountered in the zincblende AlX. The assignment of the structures in the optical spectra and band structure transitions are investigated in detail. The predicted values of the dielectric constants for LiMgN, LiMgP and LiMgAs are close to those of the binary compounds AlN, AlP and AlAs.
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72  Citations  
19.05  Total Impact Points  
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Institutions

20062014

Université 8 mai 1945  Guelma
 Faculty of Mathematics, Computer Science and Materials Science
Guelma, Guelma, Algeria
