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We studied the structural, elastic, electronic, dynamic and optical properties of scandium and yttrium nitrides in the zinc blend structure. The GGA, LDA and GGA-PBESOL approaches, as well as the HSE hybrid functional, were used in the representation of the electronic exchange and correlation effects. The lattice constant, the bulk modulus and its pressure derivative calculated in the HSE hybrid approach are predictions. The elastic constants and B/G ratio infer that ScN and YN are elastically stable and ductile in nature. ScN and YN in the zinc blend structure show an isotropic linear compressibility and anisotropic Young's modulus, shear modulus and Poisson's ratio. The anisotropy and hardness in ScN and YN compounds are more pronounced in the LDA approach. The X–X (W–W) direct band gap in scandium (yttrium) nitride translates its semiconductor character in the zinc blend structure. The N: p orbit and small contribution of Sc: d (Y: d) site are responsible to the optical modes, while Sc: d (Y: d) site and small contribution of N: p orbit are the sign of acoustical modes. The absorption peaks are assigned to photo transitions energies from maximum valence band to minimum conduction band.

We derived the chemical compositions and the micro hardness of the two studied steels Fe20Mn5Cr and Fe9S28Mn. The contamination of these two compounds by oxygen gives the series M2O3 (M = Fe, Cr, Al). Rhombohedral crystal structure of these compounds was determined by means of the X-rays diffraction. First principles calculations were performed to investigate structural, elastic and mechanical properties of M2O3 (M = Fe, Cr, Al) compounds at equilibrium pressure. Fe2O3 and Cr2O3 are classified as ductile materials, while Al2O3 is brittle. The Debye temperature, the elastic wave velocities and the integration of elastic wave velocities in various directions of the single crystal were obtained. All these compounds are elastically and chemically stable. The calculated elastic constants are in good agreement with the experiment values in the approximation of the gradient generalized for the correlation and exchange potential. We calculated the partial and total densities of states PDOD and TDOS for M2O3 (M = Fe, Cr, Al) compounds. As a result, electronic bands, DOS at the Fermi level, were obtained for the first time especially for Fe2O3 and Cr2O3. Keywords: Band structure, Bulk moduli, Electronic properties

This study investigated the effect of aging on the precipitation and kinetics of second phase Mg17Al12 in AZ91 magnesium alloy (Mg-9 wt% Al-1 wt% Zn), using X-ray diffraction, microhardness measurements and differential scanning calorimetric analysis (DSC). With the last instrument, the all samples were heated from room temperature to 400 °C, at heating rates of 10–30 °C/min. The results were supplemented by measuring the average of activation energies, using isothermal treatments by Johnson–Mehl–Avrami (JMA) methods and by non-isothermal treatments using Ozawa, Boswell, Kissinger, Mahadevan, Augis and Bennett methods, were around 67.18 and 62.02 kJ/mol. The frequency factor k0 calculated by the isothermal treatment is equal to 1.24 109 s−1. In non-isothermal treatment, the numerical factor m and the Avrami parameter n is estimated to be approximately equal to 3 and 2.79 respectively. This value corresponding that the bulk nucleation with a constant number of nuclei was dominant in three-dimensional (polyhedron) controlled by interface reaction. Keywords: AZ91, DSC, Mg17Al12, Precipitation, Activation energy

In this paper, we present a detailed theoretical investigation on the structural, elastic, electronic and optical properties of the perovskite oxides SrThO3 and SrZrO3 by using the pseudo-potential plane wave (PP-PW) method. The computed lattice constants of SrXO3 (X = Th and Zr) are in excellent agreement with the available experimental data. SrThO3 and SrZrO3 are direct (Γ–Γ) and indirect (Γ–R) band gap semiconductors, respectively. Under pressure effect a crossover between the indirect band gap (R–Γ) and the direct band gap (Γ–Γ) curves occurs at about 35 GPa for SrZrO3, resulting in the energy minimum of direct gap (Γ–Γ) for this compound. The covalence in the Zr–O and Th–O bonds arises due to the hybridization between O–p and Zr–d (Th–d) states. Under pressure effect, the threshold energy becomes slightly greater (smaller) for SrZrO3 (SrTO3) for 3.21 (2.28) eV and the main peaks are shifted towards higher energies. Although the positions of all peaks shifted under pressure, they still have the same type as those at zero pressure, with decreasing the intensity of the main peaks.

The kinetics of discontinuous precipitation of Ag2Al intermetallic in alloy Al – 10% Ag is studied after 10-h holding in vacuum at 530°C and subsequent water quenching. The DSC and dilatometric curves are plotted for heating rates ranging from 5 to 20 K/min. The activation energy of formation of the Ag2Al γ-phase is computed from the DSC data with the help of the Boswell equation and by the Kissinger method.

First principles calculations are applied in the study of FeMP (M = Ti, Zr, Hf) compounds. We investigate the structural, elastic, mechanical and electronic properties by combining first-principles calculations with the CASTEP approach. For ideal polycrystalline FeMP (M = Ti, Zr, Hf) the shear modulus, Young’s modulus, Poisson’s ratio, elastic anisotropy indexes, Pugh’s criterion, elastic wave velocities and Debye temperature are also calculated from the single crystal elastic constants. The shear anisotropic factors and anisotropy are obtained from the single crystal elastic constants. The Debye temperature is calculated from the average elastic wave velocity obtained from shear and bulk modulus as well as the integration of elastic wave velocities in different directions of the single crystal. Keywords: FeTP, FeHfP, Electronic band structure, Bulk moduli

The lead free halides double perovskites show a particular interest in the conception of perovskites solar cells. We predicted the lattice constant and the atomic Wycko position of these lead free halide double perovskites Cs2AgBiX6 (X = Br, Cl) under pressure effect. The alloying ability of crystal, elastic constants and related parameters, electronic and optical properties have been studied using pseudo potential plane wave method based on the density functional theory. The investigated lead free halide double perovskites Cs2AgBiX6 (X = Br, Cl) show a weaker resistance to compression along the a-axis. This result also proves the existence of a directional bonding between atoms and a weaker resistance to compression along the a-axis The band structure indicates that Cs2AgBiX(X = Br, Cl) are X–L indirect gap semiconductors. Our computed bulk modulus and its pressure derivative of double perovskites Cs2AgBiX6 (X = Br, Cl) are predictions. The calculated elastic constants of Cs2AgBiX6 (X = Br, Cl) at equilibrium and under pressure effect are predictions.

The effect of additional Mg on the microstructure, mechanical properties, and transformation kinetics during aging in Al–3.3 wt.% Cu alloy was studied. The compositions and microstructure were examined by X-ray diffraction, Differential scanning calorimetry (DSC) and scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDS). The results show that the Mg in the Al–Cu alloy mainly precipitated to the grain boundaries during the process of transformation and formed a ternary Al2CuMg metallic compound and the rate of discontinuous precipitation reaction decreases with increasing concentration of Mg. The activation energy of crystallization was evaluated by applying the Kissinger equation.

We focus on detailed investigation of structural, elastic, electronic, and optical properties of inorganic complex chloride and bromide CsInCl3 and CsInBr3 in zinc blende structure within GGA and LDA. The lattice constant for CsInCl3 and CsInBr3 computed with GGA approach is closer to experimental value, where the estimated error is 0.2% and 0.28%. Elastic moduli at equilibrium and under pressure effect for CsInCl3 and CsInBr3 are studied for the first time. CsInCl3 and CsInBr3 are elastically stable, ductile, show lower hardness and have dominantly covalent bonding character. Band structure of CsInCl3 and CsInBr3 computed with GGA (LDA) indicate an indirect band gap L-X: 1.583 eV (1.186 eV) and L-W: 0.831 eV (0.75 eV) which traduce their semiconducting character. We report the predicted GGA and LDA electron and hole effective masses m e ∗ and m p ∗ for CsInCl3 and CsInBr3. The Cs: p site is empty in the first conduction band, consequently, transitions occur from Cl: p (Br: p) state to Cs: p site. Lattice constant and bond lengths d X − I n of CsInX3 (X = Cl, Br) are proportional to the radius of X atom. The anisotropy is more pronounced in the LDA approach for CsInCl3 and CsInBr3. The indirect band gap L-X becomes L-W at about 0.5 GPa for inorganic complex chloride CsInCl3, while CsInBr3 has a tendency to the metallic character.

We report the performance of glass/Mo/CuInSSe(CISSe)/(Zn2SnO4, CdS, SnS2)/ZnO thin films structures using solar cell capacitance simulator (SCAPS). Thin films solar cells with CuInSSe absorber layer reduce the cost and have comparable performance parameters with the conventional ones. The temperature effect on efficiency and fill factor is less noticeable in solar cell with Zn2SnO4 buffer layer. The average temperature gradient of CdS, SnS2 and Zn2SnO4 based cells value is -0.317 %/K, -0.533 %/K and -0.539 %/K. An efficiency of 18.53 % has been achieved with Zn2SnO4 buffer for Voc, Jsc and FF of 0.5153 V, 45.4 mAcm−2 and 79.17. The desired thickness of the CuInSSe (CISSe) absorber layer is estimated as 1.8 μm. The best performance obtained with Zn2SnO4 buffer can be explained by its higher transmission in the short wavelength range because its high gap 3.35 eV compared to those of CdS 2.4 eV and SnS2 2.24 eV.

We have calculated the bond lengths d F 3 → F 5 , 7 , 8 , d F 4 → F 5 , 6 , 8 , d F 2 → F 5 , 7 , 8 , d F 1 → F 6 , 7 , 8 , d F 1 → 8 − Y 1 , 2 , 3 , d F 9 → Y 1 , 2 , 3 , d F 1 → 8 − F 9 and single-crystal elastic stiffness constants, Cij and polycrystalline elastic moduli at different pressures by using GGA-PBE, GGA-PBESOL and LDA approach for cubic YF3. Yttrium fluoride is found to be elastically stable in the pressure range 0–40 GPa. Shear modulus, linear compressibility and Poisson's ratio have maximum and minimum values along with different crystallographic directions, which explain their predicted anisotropy. The direct Γ-Γ band gap value 5.082 eV indicates towards the insulating character of YF3. The broad band gap is a sign that this compound should function as an emission center. We predicted the first and second-order pressure coefficients of direct and indirect band gaps using the GGA-PBE, GGA-PBESOL and LDA approaches. The estimated volumetric thermal expansion coefficient, constants volume and constant pressure heat capacities and entropy at zero pressure and 300 K are 1.66 × 105 K−1, 82.56 J m o l − 1 K − 1 and 83.59 mol-1 K−1, respectively. The edge of the optical absorption is located at 48.5 nm which is caused by the V1−C1 transition at the Γ point in the Brillouin zone that corresponds very well to the direct band gap at Γ- Γ.

We report structural, elastic, electronic, dynamical and optical properties of beryllium selenide in zinc blend and NiAs phases. The zinc blend structure is the most stable at room temperature and equilibrium hydrostatic pressure. The HSE hybrid functional underestimates the lattice parameters compared to the GGA-PBE and LDA, but gives a fundamental gap closer to its experiment value. We derive bulk modulus, shear modulus, Young's modulus and Poisson's ratio using Voigt, Reuss and Hill approximations. Computed elastic constants in NiAs structure are predictions. Waves velocities for beryllium selenide in zinc blend (NiAs) phase along [100], [110] ([100], [110], [111]) directions are predictions. The indirect band gap Γ-X (2.852 eV) and Γ-K (0.536 eV) for BeSe in zinc blend and NiAs structures translates the semiconductor nature. Hybridization occurs between Se: p and Be: s states at the top of the valence band and traduces the covalent bonding character. The first conduction band is quite wide in both structures, where the contribution is due to Se: p, Se: s and Be: s sites. The electronic transition occurs from Se: p orbital of valence band to Be: s site of conduction band. Absorption peaks are attributed to the photo transition energies from the maximum valence band to the minimum conduction band under ultra violet light irradiation.

We studied the structural, elastic, electronic and optical properties of the orthorhombic NaMgH 3 , NaMgH 2 F, NaMgHF 2 and NaMgF 3 compounds. By means of the self-consistent CASTEP code, pseudopotentials, density functional theory in the LDA and GGA approximations, basic physical properties, such as lattice constant, shear modulus, elastic constants ( C ij ) and optical constants are computed. This study includes elastic parameters of mono and poly-crystalline aggregates. Derived elastic constants, such as bulk, Young's and Shear modulus, Poisson coefficient, Debye temperature and brittle/ductile behavior are estimated with the polycrystalline approach, using Voigt–Reuss–Hill theory. The calculations show that the orthorhombic Pnma structures are mechanically and dynamically stable in the pressure range (0–20 GPa). The calculated density of states shows that the orthorhombic compounds are insulators.

The decomposition kinetics of Algerian Tamazarte kaolinite (TK) was investigated using thermogravimetric analysis (TG). Differential thermal analysis (DTA) and TG experiments were carried out between room temperature and 1400 °C, at different heating rates from 10 to 40 °C/min. The activation energies, measured by DTG from isothermal treatments using Johnson–Mehl–Avrami (JMA) and Ligero methods and by non-isothermal treatments using Ozawa, Boswell and Kissinger methods, were around 151 and 144 kJ/mol, respectively. The Avrami parameter of growth morphology (indicating the crystallization mode) was found to be around 1.57 using non-isothermal treatments; however, when using isothermal treatments it is found to be equal to 1.35. The numerical factor, which depends on the dimensionality of crystal growth, is found to be 1.53 using Matusita equation. The frequency factor calculated by the isothermal treatment is equal to 1.55×10 7 s −1 . The results show that the bulk nucleation is followed by three-dimensional growth of metakaolinite with polyhedron-like morphology controlled by diffusion from a constant number of nuclei.

We studied the profiles of the micro hardness in the nuances 9SMn28, 42CrMo4 and CK45, which have a rapid decline to the depth 0.1 mm, and then slowly decrease to the value of the characteristic of the casting material. The surface layer contains mostly the iron nitrides phases FeyN (y = 1, 2, 3, 4). We use first principles to study the electronic and magnetic properties of some structural phases. We calculated the lattice parameters of all the compounds; our results show good agreement with other calculations. The estimated formation energies first show a decrease then an increase with the nitrogen content. The contribution of the PDOS is due to the Fe-3d and N-2p states in Fe(1–4)N. We used experimental and theoretical studies to determine all of the phases existing in a nitride layer.

Morphological and electrical properties of AlMg thin films and the impact of the elaboration conditions on their quality are investigated. For this purpose, thin layers of AlMg of different Mg content were deposited by vacuum evaporation on a monocrystalline silicon substrate in the MECA2000 evaporator. The properties were studied by the X-ray diffraction technique (XRD), XRF, the optical and mechanical profilometer and the four-probe method. The interpretation of the X-ray diffraction spectra allowed us, among other things, to affirm that the films are poly-crystalline with β and δ phases. Generally, the lattice parameter of the Al-Mg samples was slightly higher compared to the bulk one amassif. As a result, our samples show a general increase in grain size as the thickness increases. Observations with optical profilometry, we have established that the surface is of dense appearance with presence of many grains. The results of the measurement of the roughness show increased values with the increase of x at.% Mg whose maximum is at 190 nm corresponding to a x at.% Mg of 97.As for the electrical measurements, they report a maximum resistivity of 3.6 × 10−3 Ω.cm. Keywords: Thin films, Al-Mg alloys, Grains size

The GGA functional PW91 were used in order to predict the structural, electronic, optical and elastic properties of α and β of d- Glucose. Such compounds, in their solid form, are widely used in chemical and pharmaceutical industry. The pure crystalline forms of glucose α-d-glucose and β-d-glucose have the same space group (McDonald and Beevers, 1950) [1]. We note that despite the fact that the two compounds have the same space group, upon cooling, the interatomic distances change and a new compound occurs. On the other hand, the cooling also influences the physical properties (structural, elastic, electronic and optical properties). The objective of this paper is associated with the control of the physical states of molecular materials when they are subjected to polymorphic changes. The laws and physical parameters that govern these transformations remain fundamentally misunderstood., Highlights 1. The variation in volume, density, crystal structure, elastic constants (C12, C13) etc, reveals that there is a structural relaxation characteristic of the anomeric conversion α-Glucose↔β-Glucose and the slow structural relaxations characteristic of the state glassy. 2. We notice that the mean interatomic distances are in total agreement with those given experimentally either in α-d-glucose or β-d-glucose, which means that the DFT is a good calculation tool for this type of compounds. 3. A qualitative comparison of the transition enthalpy E between the two phases showed that the α-phase is more stable than the β one of 39 meV at 0 K. 4. The difference in interatomic and intermolecular distances influences the spectra of the calculated optical function.

We report ab initio density functional theory calculations of the structural, elastic, electronic and optical properties of the double perovskite oxides Sr2AlXO6 (X=Ta, Nb, V). We have predicted a direct Г–Г band gap in Sr2AlXO6 (X=Ta, Nb) and an indirect Г–X band gap for Sr2AlVO6. The fundamental band gap increases linearly when the pressure is enhanced in the range 0–20 GPa. The frequency dependent of complex dielectric function, absorption, reflectivity and electron energy loss function were investigated in the range 0–40 eV. Features such as lattice constant, bulk modulus, elastic constants, band structure, total and local densities of states have been computed.

We present calculations of the structural, elastic and electronic properties of nonferrous Ti, Zr, and Hf pure metals in both parent and martensitic phases in bcc and hcp structures respectively. They are based on the generalized gradient approximation (GGA) within the density functional theory. The shear modulus, Young's modulus and Poisson's ratio for Ti, Zr, and Hf metals have were calculated and compared with the corresponding experimental values. Using elastic constants obtained from calculations under the GGA, the bulk modulus along the crystallographic axes of single crystals is calculated. This is in good agreement with experiment for Ti and Zr, whereas the hcp structure for Hf is a prediction. At zero temperature and zero pressure, the bcc crystal structure is found to be mechanically unstable for Ti, Zr, and Hf. In our calculations the hcp structure is correctly found to be stable at the equilibrium volume. In the electronic density of states, the smaller n(EF) is, the more stable the compound is, in agreement with the results obtained from the total energy minimum.

The PLANE WAVE pseudo-potential method within density functional theory (DFT) has been used to investigate the structural, elastic, electronic and optical properties of XCaF3 (X = K and Rb) insulating. The studied compounds show a weak resistance to shear deformation compared to the resistance to the unidirectional compression. KCaF3 and RbCaF3 are considered ductile. The elastic constants and related parameters were predicted. The stiffness is more important in KCaF3, whereas, the lateral expansion is more important in RbCaF3. KCaF3 and RbCaF3 have R- Г indirect band gap. The main peaks in the imaginary part of the dielectric function correspond to the transition from the occupied state F−p to the unoccupied states Ca: s or K, Rb: p. At lower energies, KCaF3 and RbCaF3 show the same optical properties. Under pressure effect, the peaks of imaginary part of dielectric function were shifted toward high energy.

The structural, electronic and elastic properties of the M 2 SiC phases were studied, where M are 3d, 4d, and 5d early transition metals. The valence electron concentration (VEC) effect of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W on these properties was examined. The C 44 saturates for a VEC value in surrounding of 8.5 for each serie. Hf-s, Ta-s and W-s electrons mainly contribute to the density of states at the Fermi level, and should be involved in the conduction properties. The distortion increases with increasing VEC and decreasing k c / k a factor except for the series M=Ti, V and Cr, where it is lower at the VEC value of 8.5 (it follows a parabolic variation). The M 2 SiC was characterized by a profound anisotropy for the shear planes (1010) and compressibility in the direction is higher than that along the cone except for W 2 SiC, where it is lower.

The quaternary iridium based hydrides NaAeIrH6 (Ae = Ca, Ba and Sr) are promising candidates as hydrogen storage materials. We have studied the structural, elastic, electronic, optical and thermodynamic properties of NaAeIrH6 (Ae = Ca, Ba and Sr) within the generalized gradient approximation, the local density approximation (LDA) and mBj in the frame of density functional perturbation theory. These alloys have a large indirect Γ–X band gap. The thermodynamic functions were computed using the phonon density of states. The origin of the possible transitions from valence band to conduction band was illustrated. By using the complex dielectric function, the optical properties such as absorption, reflectivity, loss function, refractive index and optical conductivity have been obtained.

The structural, elastic, electronic and optical properties of the gallium monohydrides BaGaXH (X=Si, Ge, Sn) have been investigated by means of first principles calculations. The low values of the B/G ratio of these compounds correspond to the brittle nature, which is due to the hydrogen presence. The bulk modulus, Young's modulus, shear modulus decrease from Si to Sn for BaGaXH (X=Si, Ge, Sn) in the same column in the periodic table. Also the Debye temperature of these compounds has a relative high θ D value indicating that they possess good thermal conductivity. The mean sound velocities have a progressive decrease from silicon (Si) to tin (Sn).

M 3 X (M=Cr, V; X=Si, Ge) compounds are studied using first-principles calculations based on the Density Functional Theory (DFT). It is found that the bulk of Cr 3 X (X=Si, Ge) compounds are comparable to those of Al 2 O 3 , the nearest-neighbor distance D M−M and D M−X in these compounds increase and the bulk modulus decrease, there is a strong interaction between M and M (M=Cr the interaction is stronger). Also the interaction between M (M=Cr, V) and X (X=Ge) is negative, an anti-bonding-type interaction is dominant between these atoms.

Some physical properties of the cubic perovskites CsXF3 (X = Ca, Sr and Hg) have been investigated using pseudopotential plane-wave method based on the density functional theory. The calculated lattice parameters within GGA and LDA agree reasonably with the available experimental data. The elastic constants and their pressure derivatives are predicted using the static finite strain technique. We derived the bulk and shear moduli, Young's modulus, Poisson's ratio and Lame’s constants for ideal polycrystalline aggregates. The analysis of B/G ratio indicates that CsXF3 (X = Ca, Sr and Hg) are ductile materials. The thermal effect on the volume, bulk modulus, heat capacity and Debye temperature was predicted.

A theoretical study of the structural, electronic, optical and thermodynamic properties of Na x Rb 1 −x H and Na x K 1 −x H ternary alloys in NaCl phase has been carried out using the first-principles method. We modeled the alloys at some selected compositions with ordered structures described in terms of periodically repeated supercells. The dependences on the composition of the lattice constant, band gap, dielectric constant, refractive index, Debye temperature, mixing entropy and heat capacities were analyzed for x =0, 0.25, 0.50, 0.75 and 1. The lattice constants of Na x Rb 1 −x H and Na x K 1 −x H exhibit a marginal deviation from Vegard's law. A strong deviation of the bulk modulus from linear concentration dependence was observed for both alloys. We found that the composition dependence of the energy band gap is highly non linear and the large bowing coefficient for Na x Rb 1− x H is sensitive to the composition. Using the approach of Zunger and co-workers, the microscopic origins of the gap bowing were detailed and explained. The thermodynamic stability of these alloys was investigated by calculating the phase diagram. The thermal effect on some macroscopic properties was investigated using the quasi-harmonic Debye model. There is a good agreement between our results and the available experimental data for the binary compounds, which is a support for those of the ternary alloys that we report for the first time.

A first-principles plane-wave pseudopotential method based on the density functional theory is used to investigate the structural, elastic and electronic properties of M4N5 and M5N6 (M = a transition metal (TM) Nb, Ta). C33 elastic constant for all compounds is found to be much larger than C11, indicating that a-axis is more compressible than c-axis. Interestingly, we find that C33 and C11 are significantly larger than other elastic constants, resulting in a pronounced elastic anisotropy.

The structural, elastic, electronic and thermal properties of the MAX phases Ti2SiC and Cr2SiC are studied by means of the pseudo-potential plane wave method within GGA and LDA. The effect of pressure on the normalized lattice constants a/a0 and c/c0 and the internal parameter z is investigated. Our results of elastic constants, sound velocities and Debye temperature are predictions. The Ti2SiC and Cr2SiC compounds behave as ductile material and show a stronger anisotropy. The analysis of the band structure and density of states show that these compounds are electrical conductors, having a strong directional bonding between Ti and C and Cr and C atoms assured by the hybridization of Ti–d and Cr–d atom states with C–p atom states. The thermal effect on the primitive cell volume, bulk modulus, heat capacities CV and CP were predicted using the quasi-harmonic Debye model.

Using the plane-wave pseudopotential method, the total energy and electronic structure calculations of XyTa1−yTa2N3, y = 1 (X=B, C, N, O, F) alloys have been performed to understand the structural stability and electronic properties. The exchange–correlation has been treated using the generalized gradient approximation (GGA). The virtual crystal approximation (VCA) was used to study the order/disorder to examine the effect of the substitution of B, N, C, O and F for Ta in the cell corner on the structural stability. The results show that the substitution of B, C, N, O and F for Ta at the corner sites slightly changes the lattice constant. We have evaluated the ground state quantities such as lattice constant, bulk modulus and elastic constants. We derived the bulk and shear moduli, Young’s modulus and Poisson’s ratio for an ideal polycrystalline c(X)(Ta2N3)(X=B,C,N,O,F) aggregate. Also, the results of densities of states are presented. The elastic, mechanical and electronic properties of c(X)(Ta2N3)(X=B,C,N,O,F) alloys are predicted. Also, the Debye temperature ( θ D ), TDOS at the Fermi level n ( E f ) , the X-p (X==B,C,N,O) states and the enthalpies of formation of the XTa2N3 compounds are investigated.

A computed investigation on the structural, elastic, electronic, phonon frequencies and thermal properties of AlxScyB1−x−yN quaternary alloys in the zinc-blend phase has been made with first-principles methods. The information on the lattice constant, lattice matching to AlN substrate and energy band gaps is indispensable for various practical applications. We have studied the effect of Sc concentration y (y = 0, 0.152, 0.303, 0.455 and 0.607) on the lattice constant, bulk modulus, elastic constants C11, C12 and C44, band gaps, optical phonon frequencies (ωTO and ωLO), static and high-frequency dielectric coefficient ɛ(0) and ɛ(∞) and dynamic effective charge Z*. We remark an important deviation from the linear concentration dependence of the lattice constant and bulk modulus. The shear moduli, Young's modulus, Poisson's ratio were estimated in the frame work of the Voigt–Reuss–Hill approximation. The resistance to changes in bond length and lateral expansion in AlxScyB1−x−yN increase with increasing y concentration. We observe that at y concentration about 0.11, the Г–X indirect fundamental gap becomes Г–Γ direct fundamental gap in AlxScyB1−x−yN. There is well agreement between our results and the experiment data for AlN binary compound which is a support for those of the quaternary alloys that we report for the first time.

The structural, elastic, electronic and optical properties of the cubic M 3 N 4 (M = Zr, and Hf) have been studied for different pressure. The computational method is based on the Pseudo-Potential Plane-Wave method (PP-PW). The exchange correlation has been treated using the Generalized Gradient Approximation (GGA). We have evaluated the ground-state quantities such as lattice parameter, bulk modulus and its pressure derivative as well as the elastic constants. The elastic constants and their pressure dependence are calculated using the static finite strain technique. We derived the bulk and shear moduli, Young’s modulus and Poisson’s ratio for ideal polycrystalline Zr 3 N 4 and Hf 3 N 4 aggregate. Also, we have presented the results of the band structure and densities of states. Furthermore, in order to understand the optical properties, the dielectric function, optical reflectivity, refractive index, extinction coefficient, and absorption coefficient are calculated for radiation up to 20 eV. We predicted the elastic, electronic and optical properties of Zr 3 N 4 and Hf 3 N 4 compounds.

A theoretical study on the structural, elastic, electronic and lattice dynamic properties of Al x Y y B 1− x − y N quaternary alloys in zinc-blend phase has been carried out with first-principles methods. Information on the lattice parameter, the lattice matching to available substrates and energy band-gaps is a prerequisite for many practical applications. The dependence of the lattice parameter a , bulk modulus B , elastic constants C 11 , C 12 and C 44 , band-gaps, optical phonon frequencies ( ω TO and ω LO ), the static and high-frequency dielectric coefficients e (0) and e ( ∞ ) and the dynamic effective charge Z ⁎ were analyzed for y =0, 0.121, 0.241, 0.362 and 0.483. A significant deviation of the bulk modulus from linear concentration dependence was observed. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young's modulus, Poisson's ratio are numerically estimated in the frame work of the Voigt–Reuss–Hill approximation. The resistance to changes in bond length and lateral expansion in Al x Y y B 1− x − y N increase with increasing y concentration. We observe that at y concentration about 0.035 and 0.063, Al x Y y B 1− x − y N changes from brittle to ductile and Γ–X indirect fundamental gap becomes Γ–Γ direct fundamental gap. There is good agreement between our results and the available experimental data for the binary compound AlN, which is a support for those of the quaternary alloys that we report for the first time.

Various physical properties of the cubic perovskite-type oxide BiScO3 have been investigated using the pseudo-potential plane-wave (PP-PW) method based on the density functional theory (DFT). The computed equilibrium lattice parameters agree well with the available theoretical data. The elastic constants and their pressure dependence are predicted using the static finite strain technique. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young’s modulus, Poisson’s ratio, average sound velocity and Debye temperature are numerically estimated in the framework of the Voigt–Reuss–Hill approximation for BiScO3 polycrystalline aggregate. The analysis of the site-projected l -decomposed density of states, charge transfer and charge density shows that bonding is predominantly of ionic nature. We distinguish hybridization between Sc-d states and O - p states in the valence bonding region. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the thermal effect on the lattice constant, bulk modulus, heat capacities and thermal expansion coefficient is calculated.

The isothermal and non-isothermal ageing of an Al-2.4 wt% Cu alloy have been studied using X-ray diffraction analysis and differential scanning calorimetry (DSC) at different heating rates. Quantitative metallography methods have been applied to measure the corresponding transformed volume fractions at various temperatures and times of precipitation. The variation of the heating rate using DSC technique has allowed us to calculate two kinetics parameters of precipitation which are the Avrami exponent and the activation energy of the process using Kissinger, Ozawa and Bosswell methods. These parameters are similar to those found for the precipitation reaction of θ′ and θ (Al2Cu) phases.

The structural, elastic, electronic, optical and thermal properties of the semiconductor perovskite CsPbCl 3 were investigated using the pseudo-potential plane wave (PP-PW) scheme in the frame of generalized gradient approximation (GGA) and local density approximation (LDA). The computed lattice constant agrees reasonably with experimental and theoretical ones. The CsPbCl 3 crystal behaves as ductile material. The valence bands are separated from the conduction bands by a direct band gap R – R . We distinguished hybridization between Pb-p states and Cl-p states in the valence bonding region. Under compression at P =30 GPa, this material will have a metallic character. The thermal effect on the lattice constant, bulk modulus, Debye temperature and heat capacity C V was predicted using the quasi-harmonic Debye model. To the author's knowledge, most of the studied properties are reported for the first time.

Structural, elastic, electronic and thermal properties of the MAX phase Nb2SiC are studied by means of a pseudo-potential plane-wave method based on the density functional theory. The optimized zero pressure geometrical parameters are in good agreement with the available theoretical data. The effect of high pressure, up to 40 GPa, on the lattice constants shows that the contractions along the c -axis were higher than those along the a -axis. The elastic constants C i j and elastic wave velocities are calculated for monocrystal Nb2SiC. Numerical estimations of the bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, average sound velocity and Debye temperature for ideal polycrystalline Nb2SiC aggregates are performed in the framework of the Voigt–Reuss–Hill approximation. The band structure shows that Nb2SiC is an electrical conductor. The analysis of the atomic site projected densities and the charge density distribution shows that the bonding is of covalent–ionic nature with the presence of metallic character. The density of states at Fermi level is dictated by the niobium d states; Si element has a little effect. Thermal effects on some macroscopic properties of Nb2SiC are predicted using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The variations of the primitive cell volume, volume expansion coefficient, bulk modulus, heat capacity and Debye temperature with pressure and temperature in the ranges of 0–40 GPa and 0–2000 K are obtained successfully.

The structural, elastic, electronic, optical and thermodynamic properties of the cubic perovskite-type hydride KMgH 3 have been investigated using pseudo-potential plane-wave method based on the density functional theory. Computed equilibrium lattice constant agrees well with the available experimental and theoretical data. The elastic constants and their pressure dependence are predicted using the static finite strain technique. A linear pressure dependence of the elastic stiffnesses is found. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young’s modulus, Poisson’s ratio, average sound velocity and Debye temperature are numerically estimated in the frame work of the Voigt–Reuss–Hill approximation for KMgH 3 polycrystalline aggregate. The analysis of the site-projected l -decomposed density of states and charge density shows that the bonding is predominantly of ionic nature. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the temperature effect on the lattice constant, bulk modulus, heat capacity and Debye temperature is calculated.

The structural, electronic, optical and thermodynamic properties of Sr x Ca 1− x O, Ba x Sr 1− x O and Ba x Ca 1− x O ternary alloys in NaCl phase were studied using pseudo-potential plane-wave method within the density functional theory. We modeled the alloys at some selected compositions with ordered structures described in terms of periodically repeated supercells. The dependence of the lattice parameters, band gaps, dielectric constants, refractive indices, Debye temperatures, mixing entropies and heat capacities on the composition x were analyzed for x = 0, 0.25, 0.50, 0.75 and 1. The lattice constant for Sr x Ca 1− x O and Ba x Sr 1− x O exhibits a marginal deviation from the Vegard's law, while the Ba x Ca 1− x O lattice constant exhibits an appreciable upward bowing. A strong deviation of the bulk modulus from linear concentration dependence was observed for the three alloys. The microscopic origins of the gap bowing were detailed and explained. The composition dependence of the dielectric constant and refractive index was studied using different models. The thermodynamic stability of these alloys was investigated by calculating the phase diagram. The thermal effect on some macroscopic properties was investigated using the quasi-harmonic Debye model. There is a good agreement between our results and the available experimental data for the binary compounds which may be a support for the results of the ternary alloys reported here for the first time.

The structural, elastic, electronic, optical and thermodynamic properties of the perovskite chloride CsCdCl3 were investigated using the pseudo-potential plane wave (PP-PW) within the Generalized Gradient Approximation (GGA) and Local Density Approximation (LDA). The computed lattice parameter agrees well with experimental and previous theoretical works. Based on the elastic constants and their related parameters, the crystal rigidity and mechanical stability have been discussed. Energy band structure shows that the investigated material is Γ – R indirect energy band gap semiconductor. The static dielectric constant and static refractive index are indeed, proportional to the fundamental indirect band gap. The thermal effect on the lattice parameter, bulk modulus, volume expansion coefficient, Gruneisen parameter, heat capacities and Debye temperature were predicted using the quasi-harmonic Debye model. To the best of the authors’ knowledge, most of the studied properties are reported for the first time.

Information on the energy band gaps, the lattice parameters and the lattice matching to available substrates is a prerequisite for many practical applications. A pseudopotential plane-wave method as implemented in the ABINIT code is used to the As x P y N 1− x − y Al quaternary alloys lattice matched to AlP substrate to predict their energy band gaps and optical properties. The range of compositions for which the alloy is lattice-matched to AlP is determined. Very good agreement is obtained between the calculated values and the available experimental data. The Debye temperature increase when the bulk modulus is enhanced. We study the variation of elastic constants, the optical phonon frequencies ( ω TO and ω LO ), the static and high-frequency dielectric coefficient ɛ (0) and ɛ (∞) and the dynamic effective charge Z * with P concentration ( y ).

The stability, structural parameters, elastic constants, electronic and optical properties of perovskites CsCaH 3 and RbCaH 3 were investigated by the density functional theory. The calculated lattice parameters are in agreement with previous calculation and experimental data. The energy band structures, density of states, born-effective-charge and Mulliken charge population were obtained. The perovskites CsCaH 3 and RbCaH 3 present a direct band gap of 3.15 eV and 3.27 eV at equilibrium. The top of the valence bands reflects the s electronic character for both structures. Furthermore, the absorption spectrum, refractive index, extinction coefficient, reflectivity, energy-loss spectrum, and dielectric function were calculated. The origin of the spectral peaks was interpreted based on the electronic structures. The static dielectric constant and refractive index are indeed, inverse proportional to the direct band gap.

The structural, elastic, electronic and optical properties of XO (X= Ca, Sr and Ba) compounds were investigated by the density functional theory. A good agreement was found between our calculated results and the available theoretical and experimental data of the lattice constants. Young's modulus, Poisson ratio, bulk modulus, elastic constants and their pressure derivatives are also calculated. SrO and BaO compounds present a transition phase at 39.72 and 27.28 GPa. The SrO compound shows a change from direct band gap ( Γ – Γ ) to indirect band gap ( Γ – X ) at about 15 GPa. The top of the valence bands reflects the s electronic character for all structures. We investigate the effective mass of electrons as function of pressure at the Γ point for CaO, SrO and BaO compounds. Calculations of the optical spectra have been performed for the energy range 0–60 eV. The origin of the spectral peaks was interpreted based on the electronic structures. The enhancement of pressure increases the static dielectric function and refractive index of CaO, SrO and BaO.

We report a detailed study of the compositional dependence of the structural, elastic, electronic and dynamical properties of the In1 -x-yAlxGayP quaternary alloys matched to AlP using pseudo-potential plane-wave method based on the density functional theory. The reliability and accuracy of the predicted physical properties mentioned above for In1-x-yAlxGayP/AlP are tested by comparing the calculated lattice constant, elastic constants and phonon dispersion curves for the binary AlP with the available experimental and theoretical data in the literature. © 2012 Elsevier Ltd. All rights reserved., Deanship of Scientific Research, King Saud University: RGP-VPP-088, The authors (A. Bouhemadou and S. Bin-Omran) extend their appreciation to the Deanship of Scientific Research at King Saud University for funding the work through the research group project No RGP-VPP-088.

A first-principles plane-wave pseudopotentials method based on the density functional theory (DFT), is used to investigate the structural, mechanic and electronic of Laves phase V2M (M = Zr, Hf, Ta) compounds. It is found that V2Hf is mechanically unstable because this compound do not satisfy the conditionC_11-C_12> 0 below 6.27 GPa, it becomes stable beyond this pressure, the bulk modulus B revealing the largest B values for V2Ta compound which are the stable ground state phases according to the total energies. Also there is a strong interaction between V and V, the interaction between M (M = Zr, Hf, Ta) and V is more strong and between M and M is the strongest.

The influence of MgO addition on the structure and properties of mullite prepared through reaction sintering of Algerian kaolin and Al2O3 was investigated. The raw powders were wet ball milled, dried and cold compacted using a uniaxial press. The green compacts were sintered 8 hours at 1600 and 1650°C. The microstructure of samples was characterized using a scanning electron microscope. Mechanical and thermal properties were characterized using Vicker’s hardness tester, a universal testing machine and a dilatometer. It was found that the increase of MgO content from 0 to 3 wt-% increased the hardness of samples sintered 8 hours at 1600°C from 1039 to 1316.57 HV. Also, the increase of MgO content in samples sintered 8 hours at 1600 and 1650°C increased the compressive strength up to a maximum then decreased it. For a sintering temperature of 1600°C, the increase of MgO content up to 2 wt-% increased the flexural strength, but a further increase of MgO to 3 wt-% decreased it again, while for a sintering temperature of 1650°C, the increase of MgO content from 0 to 3 wt-% increased the flexural strength from 103.45 to 472.25 MPa. Amongst MgO containing samples, the increase of MgO content increased the coefficient of thermal expansion; however, it remained lower than the coefficient of thermal expansion of the sample without MgO addition.