Search

In this study, the structural, optoelectronic, thermodynamic, and thermoelectric properties of ABO3 (A=Cs, Rb and B= Ta, Nb) perovskite alloy are predicted. The full potential-linearized augmented plane wave (FP-LAPW) method is used within density functional theory (DFT). The calculated structural parameters of the title compounds are in excellent agreement with the available theoretical data. Moreover, the optical properties of the material in question are also examined and discussed. Based on the quasi-harmonic Debye model, the thermodynamic properties of the material in question have been predicted taking into account of the lattice vibrations. The change in the thermoelectric properties of the alloys of interest has been obtained using the BoltzTraP code. The electronic thermal conductivities (k/τ), Seebeck coefficients (S), power factors (PF), and electrical conductivities (σ/τ) have been calculated. The obtained calculation regarding the ZT merit factors is near 1 at room temperature, indicating that ABO3 (X=Cs, Rb and B= Ta, Nb) is a good candidate for thermoelectric applications at high and low temperatures.

Based on the density functional theory (DFT), a systematic theoretical investigation on the structural parameters and finite temperature thermo-physical properties of cubic silicon carbide (3C-SiC) is reported. Our results regarding the structural parameters, melting point, Knoop micro hardness, and thermal conductivity show generally satisfactory accord with experiment and other calculated findings of the present literature. The material of interest is predicted to transform from the zinc-blende (B3) phase to the rock-salt phase (B1) at a pressure of around 70 GPa, which corresponds to a volume collapse of around 18.1%. This agrees well with several experimental and previous theoretical data. Based on the Debye model, the thermo-physical properties at temperatures up to 2000 K and for pressures up to 70 GPa are analyzed and discussed. The authors’ results show a monotonous change of the thermo-physical properties of the material in question against temperature or pressure. This accords well with the general trend commonly reported in the present literature.

A computational study based on the density functional theory calculations is carried out for the band structure and optical spectra of bulk, tri-layer, bi-layer and monolayer CdS system in the hexagonal-wurtzite structure. The aim of this contribution is to see how the electronic and optical properties of CdS change when moving from the bulk form to the monolayer one through tri-layer and bi-layer Cds systems. Our results show that the monolayer form still has a direct (Г-Г) band gap, but with an increased magnitude with respect to that of bulk CdS. The optical properties of the tri-layer, bi-layer and monolayer form are found to be different from those of the bulk form. An anisotropic character has been shown by the optical spectra for light polarized parallel and perpendicular to the x axis of the crystal. Our findings indicate that novel electronic and optical properties may be obtained when passing from bulk to tri-layer, bi-layer and monolayer CdS system.

In this paper to compare the growth and optoelectronic properties of copper oxide (CuO) materials suitable for advanced application, CuO layers were synthesized on glass and SnO2:F). The X-ray diff...

The effect of alloy disorder on direct and indirect band gap energies in CdS x Te1−x semiconducting alloys has been investigated. The calculations are performed using a pseudopotential approach within the virtual crystal approximation (VCA). In the simplest approximation based on the VCA, the fundamental band gap bowing of CdS x Te1−x is found to be in disagreement with that of the experiment. The value of this bowing is highly improved by taking into account the compositional disorder effect (i.e. going beyond the VCA).

A solar cell of p-i-n type, containing hydrogenated amorphous silicon (a-Si:H) is simulated using the unidimensional computer code AMPS-1D. The objective of the present contribution is to investigate the effect of the thickness of the active layer a-Si:H(i) and the variation of its density of states (DOS) on the performances of the solar cell, namely the current of short circuit (JSC), the tension of open circuit (VOC), the form factor (FF) and the efficiency (Eff). Also we aim to determine the structural parameters characterizing each layer constituting the cell. Our results show that the best thickness for the active layer that gives good performances of the studied solar cell lies between 300 and 600 nm. Besides, the best DOS that provides better output parameters of the solar cell is determined to be in the range 5.1015–1016 cm−3. After optimization, our findings give values of Voc = 1.193 V, Jsc = 13.145 mA cm−2, FF = 0.807 which corresponds to an efficiency of Eff = 12.655%. The optimization has been done as a function of temperature and wavelength.

The structural, electronic, half-metallic and magnetic properties of Sr3Mn2O7, Sr3Mn2O7 and Sr3FeMnO7 have been investigated using the full-potential linearized augmented plane wave method. Besides, the thermodynamic properties of the materials of interest have been studied using the quasi-harmonic Debye model accommodating the lattice vibrations effects. Our results showed that Sr3Mn2O7 is an indirect half-metallic material with a band gap of 0.73 eV, while Sr3Fe2O7 and Sr3FeMnO7 exhibit a metallic behavior. The materials of interest are found to exhibit 100% spin polarization at the Fermi energy which make them potential candidates for electron-spin-based futuristic devices. The effect of pressure and temperature on the studied properties is found to be highly effective in tuning some of the macroscopic properties of the compounds in question. Our findings compare well with those existing in the literature.

We present a theoretical study on electronic structure and chemical trends of zinc-blende GaP under compression up to 100 kbar obtained from a pseudopotential approach calculations. The influence o...

The electronic and optical features of InSb spherical quantum dots have been investigated by a pseudopotential approach as a function of their radius taken in the range 1-10 nm. The direct- and indirect band gaps along with the electron and heavy hole effective masses are all found to be diminished as the quantum dot radius is increased. However, the refractive index, the static- and high frequency dielectric constant as well as the transverse effective charge are shown to be augmented by increasing the quantum dot radius. It is noted that the quantum confinement is of great impact on all the studied quantities for quantum dot radius below 6 nm. This could result in more opportunities to obtain desired optoelectronic properties that cannot be obtained in the bulk InSb materials.

We report on ab-initio all electrons spin-polarised density-functional calculations for the band structure, optical spectra and magnetisation of bulk MnAs with NiAs-type lattice structure with emph...

The size-dependent energy gaps, electron and heavy hole effective masses, phonon frequencies and polaron related parameters in InSb spherical quantum dots are investigated. The calculations are performed using a pseudopotential approach. Good agreement is obtained between our results and those of the literature for bulk InSb. When proceeding from bulk to nano-scale, all studied properties are found to be changed significantly. This is attributed to the quantum confinement effect.

Using ab initio total energy based on density functional theory calculations, the phase transition, band structure, optical spectra and magnetic moment of MnO in the rock salt structure have been investigated. All studied quantities are discussed with respect to their dependence on pressure. Our results show a phase transition of MnO from the semiconducting rock salt to a metallic CsCl at pressure of 67.12 GPa. Applied pressure is found to play an important role in the modulation of optical properties. The optical absorption coefficient indicates that MnO more readily absorb photons under high pressure. The total magnetic moment for rock salt MnO at zero pressure agrees reasonably well with those reported in the literature and decreases monotonously with increasing pressure.

International audience

The present work deals with electronic band structure and derived optical spectra of MgxZn1−xO in the hypothetical rocksalt structure. The computations are performed using full-potential linearised...

The structural, electronic, and half-metallic properties of double perovskite RBaMn2O6-δ (X = Nd, Pr, La and δ = 0, 1) compounds are carried out by employing full-potential linearized augmented plane wave (FP-LAPW) method. Perdew-Burke-Ernzerhof-generalized gradient approximations (PBE-GGA) are used for the exchange-correlation potential. Features such as the lattice constant, bulk modulus, and its pressure derivative are reported. The optimized lattice parameters are found to be in good accord with experiment. Based on the calculated band structures, we found that the RBaMn2O6 (R = Nb, Pr, La) are half-metallic ferromagnets with a magnetic moment of 10, 9, and 7 μB/fu and half-metallic flip gaps of 1.31, 1.43, and 1.17 eV, respectively. Our compounds are identified as potential candidates for spintronic applications and magnetoelectronic fields.

We report on spin-polarized first-principles calculations within the generalized gradient approximation of structural parameters, dielectric function spectra, and total magnetic moment of hypothetical zinc-blende Zn1−xMoxTe. Good accord is generally obtained between our results and those available from the literature. A close inspection of the composition dependence of the features of interest shows that the lattice parameter violates the Vegard’s law, the magnetism and character of the material in question depend strongly on the composition x and the spin channel, the optical response function shifts toward either higher or lower photon energies (depending on x) and the total magnetic moment increases with increasing the Mo concentration.

The feasibility of a distributed Bragg reflector (DBR) based on wide band gap II-VI semiconducting alloys is reported. The reflectivity spectra of a Zn0.66Mg0.34Se/Zn0.74Cd0.26Se DBR are calculated within the stratified medium theory using matrix representation. The composition x for each alloy is taken in such a manner to obtain a convenient difference between the respective refractive indices of each constituent material. Both normal and oblique incidence are considered. For both cases the effect of the number of pairs has been studied. We found out that the reflectivity maximum is enhanced as the number of pairs increases. The DBR bandwidth is found to be dependent on the refractive indices difference. The reflectivity spectrum is shifted towards smaller wavelengths, and the Bragg wavelength is diminished as the angle of incidence is augmented.

This work aims to study the structural and elastic properties of tetragonal lead dioxide (β-PbO2) material using first-principles calculations. Features such as lattice parameters, bulk modulus and its first pressure derivative, elastic constants, mechanical parameters, sound velocities, Debye temperature and melting temperature have been investigated, and their dependence on pressure in the range 0–1 GPa has been analyzed and discussed. Upon compression, the stiffness of the material of interest is found to become larger as compared to that at zero pressure. Moreover, its tetragonal structure fulfills the mechanical stability criteria in all studied pressure range. Besides, the analysis of Pugh’s ratio shows that PbO2 behaves in a ductile manner.

The compositional dependence of piezoelectric stress and strain constants and electromechanical coupling coefficient of GaxIn1-xSb have been investigated. The calculations were performed us...

The electronic structures and optical properties of the Zn1−xBexSe semiconductor ternary alloys have been investigated by using the full-potential linear augmented plane wave (FP-LAPW) method. From this study, the energy band gap has a value of about 1.2 eV for zinc-blende ZnSe. However, for Zn0.50Be0.50Se and BeSe, the fundamental band gap energy is found to occur at the highly symmetric X point in the Brillouin zone and has values of about 2.3 eV and 2.8 eV, for Zn0.50Be0.50Se and BeSe, respectively. Optical parameters, such as dielectric constant, refractive index and reflectivity are calculated and analyzed. The results demonstrated that the compounds Zn1−xBexSe have the potential to be used for optoelectronic applications. Keywords: Band structure, Optical properties, Zn1−xBexSe alloys, FP-LAPW method

The structural, electronic and thermodynamic properties of XZrS3 (X = Ba,Sr,Ca) compounds with orthorhombic Pbnm and cubic Pm-3m phases have been investigated and reported. The calculations have been performed using various density functionals within the generalized gradient approximation. The obtained lattice parameters for the Pnma phase reveal very good agreement with experiment. The computed electronic band structures show that in the cubic phase the material of interest is an indirect band-gap (R–Г) semiconductor, whereas it is a direct band gap (Г–Г) in the orthorhombic phase. The semiconducting XZrS3 (X = Ba,Sr,Ca) compounds are found to satisfy the stability criteria against volume change. Based on the quasi-harmonic Debye model, the thermodynamic properties of the material in question have been predicted taking into account the lattice vibrations. The variation of the lattice constant, bulk modulus, heat capacity, Debye temperature and thermal expansion coefficient as a function of pressure in the range 0–30 GPa and temperatures of 0–1500 K has been computed. Our findings show that external effects such as temperature and pressure are highly effective in tuning some of the macroscopic properties of the compounds under study.

The quantum effects at the nano-metric level have been observed in a variety of confined structures, particularly in semiconductor quantum dots. In this contribution, the electronic and optical properties of GaSb spherical semiconductor quantum dots are investigated. For the calculations, the pseudo potential approach was employed. The size dependence of the energy gaps at Г, X and L points, the effective masses of electrons and heavy-holes, the refractive index, and the dielectric function for a studied GaSb spherical quantum dot are analyzed and discussed. When the degree of quantum confinement effect was changed by decreasing the radius of the spherical quantum dots, a striking charge in comparison to the bulk values has been obtained. Our results indicate that as the quantum dot radius is raised, most of properties rapidly decrease. This demonstrates an improvement in the mobility of the material. However, the refractive index and the dielectric constant are increased with increasing the radius of the nano-crystal.

The influence of compositional disorder on ZnxCd1−xS energy band gaps and carrier effective masses has been investigated. The calculations are performed using a pseudopotential approach under the virtual crystal approximation (VCA). A correction to the VCA has been introduced so as to take into consideration the disorder effect. Our results show that the theoretical model used in the present contribution should include the disorder effect in order to describe more accurately the fundamental band gap bowing parameter of the experimental dependence. However, the disorder effect upon electron, light-hole and heavy-hole effective masses in the material system of interest is shown to be weak. Moreover, the trend of the conduction Г, X and L valleys and the nature of the optical fundamental band gap are found to be weakly altered by the alloy disorder. The different photo-catalytic activity of wurtzite and zinc-blende CdS is discussed for a new understanding.

First-principles all electrons density-functional calculations for the band structure and magnetization of Zn1 − xCoxO ternary magnetic alloys, in three phases namely zinc-blende, rocksalt and wurtzite have been reported. The computations are spin-polarized. An inspection of our electronic properties showed that the alloy system of interest exhibits a semiconducting character where the nature of the gap depends on the considered phase. An analysis of electronic charge density suggests that the bonding has a partially covalent character for ZnO which becomes weaker as far as the Co concentration increases. CoO is found to reach a total magnetization of 3 µB per cell for zinc-blende and rocksalt phases and 6 µB per cell for wurtzite phase.

The optoelectronic properties and mechanical stability of lead-free halide double perovskite, Cs2AgInCl6, with emphasis on their dependence on strain are reported. The computations are performed by employing first-principles calculations within a hybrid functional. The author’s calculation shows a direct (Г → Г) band gap for unstrained Cs2AgInCl6 with a recorded value of 3.62 eV which accords to within 2% with experiment. The obtained optical spectra show superior properties with strong absorption spectra of Cs2AgInCl6 for photovoltaics. The unstrained material under focus is found to be mechanically stable. The electronic and optical nature of Cs2AgInCl6 are affected under strain improving thus the potential applications of the material of interest for optoelectronic and photovoltaic applications.

We report a theoretical investigation on the finite temperature thermophysical properties of tetragonal lead dioxide (β-PbO2) material using ab initio calculations in the framework of the density functional theory within the generalized gradient approximation. The thermophysical properties for temperatures up to 600 K are determined and analyzed in detail using the quasi-harmonic Debye model. Experimentally, the β-PbO2 transforms to α-PbO2 at around 1 GPa. For that, the maximum value of pressure considered here is taken to be 1 GPa. Our findings show that the thermophysical properties of interest vary monotonically with both temperature and pressure which is consistent with previous studies of semiconducting materials. At zero pressure and temperature of 300 K, the isothermal bulk modulus and the Debye temperature are found to be around 113 GPa and 370.5 K, respectively.

A pseudopotential approach is used to study the lattice and elastic properties of the wide band-gap GaN at zero and high pressures up to 120 kbar. When the pressure is 0 kbar, our findings are generally in agreement with the data reported in the literature. The pressure dependence of lattice constant, polarity, transverse effective charge, elastic constants and their related mechanical parameters, and microhardness has been examined and discussed. Our results show that all these features exhibit a monotonic behaviour against pressure. Upon compression up to 120 kbar, our results suggest that the material in question remains mechanically stable with higher stiffness, becomes more resistant to the deformations or deflections and its chemical bond and rigidity become stronger.