Haci Ozisik

Mechanical, electronic, and optical properties of Bi2S3 and Bi2Se3 compounds: first principle investigations

AbstractThe structural, mechanical, electronic, and optical properties of orthorhombic Bi2S3 and Bi2Se3 compounds have been investigated by means of first principles calculations. The calculated lattice parameters and internal coordinates are in very good agreement with the experimental findings. The elastic constants are obtained, then the secondary results such as bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, anisotropy factor, and Debye temperature of polycrystalline aggregates are derived, and the relevant mechanical properties are also discussed. Furthermore, the band structures and optical properties such as real and imaginary parts of dielectric functions, energy-loss function, the effective number of valance electrons, and the effective optical dielectric constant have been computed. We also calculated some nonlinearities for Bi2S3 and Bi2Se3 (tensors of elasto-optical coefficients) under pressure. FigureEnergy spectra of dielectric function and energy-loss function (L) along the x- and z-axes for Bi2S3

Structural, electronic, and elastic properties of K-As compounds: a first principles study.

First-principle calculations are performed to investigate the structural, elastic and electronic properties of K-As compounds (KAs in NaP, LiAs and AuCu-type structures, KAs2 in MgCu2-type structure, K3As in Na3As, Cu3P and Li3Bi-type structures, and K5As4 in A5B4-type structure). The lattice parameters, cohesive energy, formation energy, bulk modulus, and the first derivative of bulk modulus (to fit to the Murnaghan’s equation of state) of the considered structures are calculated and reasonable agreement is obtained, and the phase transition pressure is also predicted. The repeated calculations on the electronic band structures and the related partial density of states are also given. The calculated second-order elastic constants based on the stress-strain method and the other related quantities such as Young’s modulus, shear modulus, Poissons ratio, sound velocities, Debye temperature, and shear anisotropy factors for considered structures are presented, and trends are discussed.

Ab initio investigations of the strontium gallium nitride ternaries Sr3GaN3 and Sr6GaN5: promising materials for optoelectronic

Sr3GaN3 and Sr6GaN5 could be promising potential materials for applications in the microelectronics, optoelectronics and coating materials areas of research. We studied in detail their structural, elastic, electronic, optical as well as the vibrational properties, by means of density functional theory framework. Both of these ternaries are semiconductors, where Sr3GaN3 exhibits a small indirect gap whereas Sr6GaN5 has a large direct gap. Indeed, their optical properties are reported for radiation up to 40 eV. Charge densities contours, Hirshfeld and Mulliken populations, are reported to investigate the role of each element in the bonding. From the mechanical properties calculation, it is found that Sr6GaN5 is harder than Sr3GaN3, and the latter is more anisotropic than the former. The phonon dispersion relation, density of phonon states and the vibrational stability are reported from the density functional perturbation theory calculations.

Anisotropic elastic and vibrational properties of Ru2B3 and Os2B3: a first-principles investigation

The structural, mechanical and lattice dynamical properties of Ru2B3 and Os2B3 have been investigated by using a first-principles method based on the density functional theory within the generalized gradient approximation. The single crystal elastic constants are numerically estimated using strain–stress approach. The polycrystalline aggregate elastic parameters are calculated from the single elastic constants via the Voigt–Reuss–Hill approximations. Subsequently, the ductility and brittleness are characterized with the estimation from Pughs rule (B/G) and Cauchy pressure. Additionally, the Debye temperature is calculated from the average elastic wave velocity obtained from bulk and shear moduli. The calculated parameters are consistent with the previous experimental and theoretical data. These borides are both mechanically and dynamically stable in the considered structure.

First-principles studies of the structural, elastic, and lattice dynamical properties of ZrMo2 and HfMo2

ABSTRACT A comprehensive investigation of the structural, elastic, and lattice dynamical properties for ZrMo2 and HfMo2 with C14, C15, C36, and CeCu2 phases are conducted using density functional total energy calculations. The results have showed that C15 phase for both materials is energetically more stable than C14, C36 and CeCu2 phases. We have also estimated the mechanical behaviours of these compounds, including mechanical stability, bulk modulus, Youngs modulus, shear modulus, Poissons ratio, ductility, and anisotropy. Additionally, the lattice dynamical properties are analyzed and discussed exhaustively for these phases. The calculated properties agree well with available experimental and theoretical data.

Optical and electronic properties of orthorhombic and trigonal AXO3 (A=Cd, Zn; X=Sn, Ge): First principle calculation

ABSTRACT Electronic structure and optical properties of the CdXO3 and ZnXO3 (X˭Ge, Sn) compounds have been investigated based on density functional theory. According to the predictive results, reveal that the CdXO3 and ZnXO3 would be candidates for a high performance lead free optical crystal, which will avoid the environmental toxicity problem of the lead-based materials.

The stabilities, electronic structures and elastic properties of Rb As systems

The structural, electronic and elastic properties of Rb—As systems (RbAs in NaP, LiAs and AuCu structures, RbAs2 in the MgCu2 structure, Rb3As in Na3As, Cu3P and Li3Bi structures, and Rb5As4 in the A5B4 structure) are investigated with the generalized gradient approximation in the frame of density functional theory. The lattice parameters, cohesive energies, formation energies, bulk moduli and the first derivatives of the bulk moduli (to fit Murnaghans equation of state) of the considered structures are calculated and reasonable agreement is obtained. In addition, the phase transition pressures are also predicted. The electronic band structures, the partial densities of states corresponding to the band structures and the charge density distributions are presented and analysed. The second-order elastic constants based on the stress-strain method and other related quantities such as Youngs modulus, the shear modulus, Poissons ratio, sound velocities, the Debye temperature and shear anisotropy factors are also estimated.

A new quaternary semiconductor compound (Ba2Sb4GeS10): Ab initio study

Abstract The newly synthesised Ba2Sb4GeS10 compound is notable because of the interesting features of the quaternary Sb-containing materials. The first principle method has been used to determine the physical properties of this compound. In particular, the electronic structure has been analysed using both conventional GGA-PBE and HSE06 functional. The values of the band gap for PBE and HSE06 calculations were 1.324 and 1.84 eV, respectively. The calculated elastic constants were used to predict polycrystalline mechanical properties. The estimated Vickers hardness (2.7 GPa) values show that Ba2Sb4GeS10 is soft matter. Moreover, the vibrational properties of the compound have been studied. The calculation of the elastic constants and phonon dispersion curves indicates that the Ba2Sb4GeS10 compound is stable both mechanically and dynamically. Furthermore, the minimum thermal conductivity and optical properties, such as dielectric functions and energy loss function, have also been discussed in detail in this paper.

Mechanical, electronic, and optical properties of Bi₂S₃ and Bi₂Se₃ compounds: first principle investigations.

AbstractThe structural, mechanical, electronic, and optical properties of orthorhombic Bi2S3 and Bi2Se3 compounds have been investigated by means of first principles calculations. The calculated lattice parameters and internal coordinates are in very good agreement with the experimental findings. The elastic constants are obtained, then the secondary results such as bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, anisotropy factor, and Debye temperature of polycrystalline aggregates are derived, and the relevant mechanical properties are also discussed. Furthermore, the band structures and optical properties such as real and imaginary parts of dielectric functions, energy-loss function, the effective number of valance electrons, and the effective optical dielectric constant have been computed. We also calculated some nonlinearities for Bi2S3 and Bi2Se3 (tensors of elasto-optical coefficients) under pressure. FigureEnergy spectra of dielectric function and energy-loss function (L) along the x- and z-axes for Bi2S3

Ab-initio studies of some rare-earth borides: CeB2, PrB2, NdB2, and PmB2

Abstract The structural, mechanical and thermal properties of CeB2, PrB2, NdB2, and PmB2 compounds in hexagonal AlB2-type (P6/mmm) and ReB2-type structures (P63/mmc) are investigated using density functional theory. The results indicate that those compounds with hexagonal AlB2 structure are the most stable among the considered structures. The mechanical properties are calculated according to the elastic constants by means of the Voigt–Reuss–Hill averaging scheme. The temperature dependence of various quantities such bulk modulus, Debye temperature, thermal expansion, heat capacity, and Grüneisen parameter have been analyzed using the quasi-harmonic Debye model.