Calculated Lattice Parameters Research Articles

Study of the Structural, Elastic, Electronic and Optical Properties of the Ternary Acetylides A2MC2 (A = Na, K) and (M = Pb, Pt)

We studied the ternary acetylides A2MC2 (A = Na, K) and (M = Pb, Pt) with trigonal structures by using the density functional theory (DFT) as implemented in the CASTEP code. The calculated lattice parameters and atomic fractional coordinates were in agreement with previous calculations and experimental data. A set of isotropic elastic parameters and related properties, namely the module and shear moduli, Young’s modulus, Poisson’s ratio, average sound velocity and Debye temperature were numerically estimated in the frame work of the Voigt-Reuss-Hill approximation. The absorption, energy-loss and dielectric function were calculated. We studied the main contribution to the optical spectra from the transition from the top four valence bands towards the lower three first one of conduction based on the electronic structures.

Elastic, Electronic, and Optical properties of NaSnX (X=Sb, Bi, As): First principle calculations

In the present work, the structural, mechanical, electronic and optical properties of NaSnX (X=Sb, B, As) compounds have been investigated by means of first principles calculations. The generalized gradient approximation has been used for modeling the exchange-correlation effects. It has been observed that the calculated lattice parameters are in good agreement with the experimental and theoretical lattice parameters. Bulk modulus, shear modulus, Young’s modulus Poisson’s ratio, sound velocities and the Debye temperatures using the calculated elastic constants for NaSnSb, NaSnBi and NaSnAs compounds have been obtained. The electronic band structure and the projected density of states corresponding to the electronic band structure have calculated.and interpreted. The obtained electronic band structure for NaSnSb and NaSnBi compounds are metallic in nature, and the NaSnAs compound is also a narrow semiconductor. Based on the obtained electronic structures, we further calculated the frequency-dependent dielectric function, the energy-loss function, optical conductivity, and reflection along the x-and z-axes.

Incommensurate Phase Transition and Electronic Properties of BaMnF4

We present the ab initio study the electronic, mechanical and structural properties of BaMnF4. We duscuss the trends in the electronic and mechanical properties of BaMnF4 under pressure up to 80 GPa. BaMnF4 belongs to the family of BaMF4-type fluorides (M = Mn, Fe, Co, Ni, Mg, Zn) which share the same orthorhombic structure. The main focus of this study is to elaborate the changes brought about in the electronic and the structural properties by applied pressure. The calculated lattice parameters have been in agreement with the available experimental and theoretical value. Band gap of BaMnF4 in our calculation is about 2.0 eV, separating the empty upper-Hubbard t2g bands and occupied lower-Hubbard eg bands. The total and partial DOS corresponding to the electronic band structure are calculated. Comparative analysis of the results of these calculations shows that the band-gap energy of BaMnF4 decreases with increasing pressure and has a minima value at a critical pressure (appr. 65 GPa), after which it increases again. Some fundamental physical parameters such as elastic constants, bulk modulus, Poisson’s ratio, sound velocities and Debye temperature were calculated and interpreted, too.

Characterization of intermetallic phase in as-cast Si-doped Co–Cr–Mo alloys

This research aims to investigate the effects of Si concentrations on the microstructure and formation of the intermetallic phase of Co–Cr–Mo–xSi alloys. The Si concentration (x) was varied between 0.1, 0.5, 1.0, 3.0 and 5.0 wt%. The microstructure and intermetallic phase of the solution heat-treated Co–Cr–Mo alloys were characterized using SEM-EDX, XRD and TEM. The microstructure analysis revealed that Si concentration played a role in the evolution of intermetallic phase precipitating in Co–Cr–Mo alloys. Two types of intermetallic phased were found in the Si-doped Co–Cr–Mo alloys. The σ phase was identified in the alloys containing Si between 0.1-1.0 wt% while the increase in Si (3.0-5.0Si) contributed to the formation of the χ phase. The calculated lattice parameters of the intermetallic phase precipitated in the 3.0Si and 5.0Si alloys correlated well with those of Co5Cr3Si2 phase.

Elastic Properties of Orthorhombic YBa2Cu3O7 under Pressure

The pressure dependence of the lattice and elastic constants of the orthorhombic YBa 2 Cu 3 O 7 are firstly investigated using the first principles calculations based on the density functional theory. The calculated lattice parameters at 0 GPa are in agreement with the available experimental data. By the elastic stability criteria under isotropic pressure, it is predicted that YBa 2 Cu 3 O 7 with and orthorhombic structure is mechanically stable under pressure up to 100 GPa. On the basis of the elastic constants, Pugh’s modulus ratio, Poisson’s ratio, elastic anisotropy, Debye temperature, and the minimum thermal conductivity of YBa 2 Cu 3 O 7 under pressure up to 100 GPa are further investigated. It is found that its ductility, Debye temperature, and minimum thermal conductivity increase with pressure.

Structural, Electronic, Mechanical, Thermodynamic, and Linear and Nonlinear Optical Properties of MoS2, MoSe2, and their MoS2xSe2(1−x) Alloys: Ab Initio Calculations

The Born effective charge tensors, high-frequency dielectric constants, phonon frequencies at Г symmetry point, and phonon dispersion curves of MoS2xSe2(1−x) (x = 0, 0.25, 0.5, 0.75, and 1) alloys are calculated based on density functional perturbation theory using optimized lattice parameters. The structural stability, stiffness, ductility, and plasticity of these alloys are explored in detail by calculating the polycrystalline structural properties. The calculated Born effective charges and Poisson’s ratio indicate the existence of a combination of ionic and covalent bonding between the transition metal and chalcogens in each layer. Based on the calculated phonon frequencies, the temperature dependence of the specific heat at constant volume, entropy, and Helmholtz free energy of MoS2xSe2(1−x) (x = 0, 0.25, 0.5, 0.75, and 1) alloys are calculated in the harmonic approximation. Structurally, the spatial inversion symmetry in the MoS2xSe2(1−x) (x = 0.25, 0.5, and 0.75) alloys is broken. This leads MoS2xSe2(1−x) (x = 0.25, 0.5, and 0.75) alloys to exhibit novel nonlinear optical properties that do not exist in the 2H-MoX2 (X = S, Se) compounds. So, the nonlinear optical properties are calculated by applying the 2n + 1 theorem to an electric-field-dependent energy functional. It is found that MoS2xSe2(1−x) (x = 0.25, 0.5, and 0.75) alloys exhibit remarkable large nonlinear optical susceptibility and electro-optic coefficients and would be promising candidates for use in nonlinear optical applications. Van der Waals interactions are included in all the first-principles calculations, to correctly describe the interaction between adjacent layers. The calculated lattice parameters, electronic energy bandgaps, phonon frequencies, and high-frequency dielectric constants of 2H-MoX2 (X = S, Se) compounds are in good agreement with available theoretical and experimental results.

TB-mBJ Calculations of Structural and Optoelectronic Properties of the Rhombohedral Phase of Bismuth Sodium Titanate (Bi<sub>0.5</sub> Na<sub>0.5</sub>)TiO<sub>3</sub>

In the present work, we report an ab initio investigation of the structural, electronic and linear optical properties of (Na0.5Bi0.5)TiO3 (NBT) in its rhombohedral phase, using a Full Potential Augmented Plane Waves (FP-LAPW) method in the frame work of Density Functional Theory (DFT) with the TB-mBJ potential for a better description of the electronic properties. Firstly a Full structure optimization was performed with a relaxation of atomics positions to minimize the Hellmann-Feynman forces exerted over the atoms. The calculated lattice parameters of the rhombohedral phase of NBT are in very good agreement with experimental values with a deviation of 0.9%. The electronic density of states are presented and commented. The calculated band structure shows that our compound has an indirect band gap of 3.30eV. Furthermore, the optical properties were presented, compared with experimental ones present in the literature and commented.

Structure-property correlation studies of alkaline-earth metal—azides M(N3)2 (M = Sr, Ba)

Inorganic metal azides M(N3)2 (M = Sr, Ba) and metal nitrates M(NO3)2 (M = Sr, Ba) are interesting materials due to their wide range of industrial usefulness as gas generators, pyrotechnics, photo graphic materials and explosives. In this work, we explore the mechanical, vibrational (infrared, phonon dispersion), Born effective charge (BEC) and thermodynamic properties of these materials to understand the sensitivity correlation studies using plane wave pseudopotential method. As these materials are layered with crucial non bonding interactions, the generalized gradient approximation with Tkatchenko–Scheffler (for Sr(N3)2) and Ortmann–Bechstedt–Schmidt (for Ba(N3)2) dispersion correction methods are adopted to compute accurate ground state properties with norm-conserving pseudopotentials. The calculated lattice parameters, unit cell volumes, bond lengths are well reproduced with 1% deviation when compared to the experimental and previously reported theoretical data. The mechanical (single crystal, poly-crystalline elastic constants) property correlations corroborate with the experimental impact sensitivity trend. The vibrational, phonon dispersion spectra’s, BEC’s, thermodynamic properties calculated with density functional perturbative theory approach provide better conclusions about the dynamical stability and polarization (optical sensitivity) trends. From the BEC results we propose that M(NO3)2 (M = Sr, Ba) materials may find various optical applications too. Overall, we tried to explain the crucial reasons for the differences in energetic properties of the studied materials.

The Kinetic Behaviors of H Impurities in the Li/Ta Bilayer: Application for the Accelerator-Based BNCT.

Hydrogen bubble phenomenon is one of the key issues to be solved in the development of a long-life target system for boron neutron capture therapy (BNCT). In this study, we assessed the kinetic behaviors of H impurities in the nano-composite target from the atomic level. Firstly, two kinds of Li/Ta nanolayer models were constructed, based on the calculated lattice parameters and surface energies. The H solution energy, diffusion mechanism, and hydrogen bubbles formation in the Li/Ta nanostructured bilayer were studied, through theoretical modeling and simulation. Our results show that the Li/Ta interfaces are effective sinks of H atoms because the H solution energies in the interface are lower. Meanwhile, due to the relatively low diffusion barriers, the large-scale H transport through the interface is possible. In addition, although it is more likely to form hydrogen bubbles in the Ta layer, compared with the Li layer, the anti-blistering ability of Ta is more impressive compared with most of other candidate materials. Therefore, the Ta layer is able to act as the hydrogen absorber in the Li/Ta bilayer, and relieve the hydrogen damage of the Li layer in the large-scale proton radiations.

Effects of bismuth on structural and dielectric properties of cobalt-cadmium spinel ferrites fabricated via micro-emulsion route

Spinel ferrites have a significant role in high-tech applications. In the present work nano-crystalline ferrites having general formula Co0.5Cd0.5BixFe2−xO4 with (x = 0.0, 0.05, 0.1, 0.15, 0.2, and 0.25) are synthesized via micro-emulsion route. Powder x-ray diffraction (XRD) studies discover the FCC spinel structure. Crystalline size is calculated in a range of 11 nm–15 nm. Lattice parameter calculations are reduced due to its substitution which leads to the exchange of large ionic radius of Fe3+ for small ionic radius of Bi3+. The x-ray density is analyzed to increase with doping. Fourier transform infrared spectroscopy (FTIR) is performed to analyze absorption band spectra. The two absorption bands are observed in a range of 400 cm−1–600 cm−1, and they are the characteristic feature of spinel structure. Thermo-gravimetric analysis (TGA) reveals the total weight loss of nearly 1.98%. Dielectric analysis is carried out by impedance analyzer in a frequency span from 1 MHz to 3 GHz by using the Maxwell Wagner model. Dielectric studies reveal the decrease of dielectric parameters. The alternating current (AC) conductivity exhibits a plane behavior in a low frequency range and it increases with the applied frequency increasing. This is attributed to the grain effects in a high frequency range or may be due to the reduction of porosity. Real and imaginary part of impedance show the decreasing trend which corresponds to the grain boundary action. The imaginary modulus shows the occurrence of peak that helps to understand the interfacial polarization. Cole-Cole graph shows a single semicircle which confirms that the conduction mechanism is due to the grain boundaries at low frequency. Dielectric studies reveal the applicability of these ferrites in high frequency equipment, microwave applications, high storage media, and semiconductor devices.

First-principles study of mechanical and electronic properties of bent monolayer transition metal dichalcogenides

The mechanical and electronic properties of transition metal dichalcogenide (TMD) monolayers corresponding to transition groups IV, VI, and X are explored under mechanical bending from first principles calculations using the strongly constrained and appropriately normed (SCAN) meta-GGA (MGGA). SCAN provides an accurate description of the phase stability of the TMD monolayers. Our calculated lattice parameters and other structural parameters agree well with experiment. We find that bending stiffness (or flexural rigidity) increases as the transition metal group goes from IV to X to VI, with the exception of PdTe$_2$. Variation in mechanical properties (local strain, physical thickness) and electronic properties (local charge density, band structure) with bending curvature is discussed. The local strain profile of these TMD monolayers under mechanical bending is highly non-uniform. The mechanical bending tunes not only the thickness of the TMD monolayers but also the local charge distribution as well as the band structures, adding more functionalization options to these materials.

Theoretical investigation of the phase stability and elastic properties of TiZrHfNb-based high entropy alloys

First principles calculations are performed to study the effects of alloying elements (X = Al, Si, Sc, V, Cr, Mn, Cu, Zn, Y, Mo, Ta, W and Re) on the phase stability and elastic properties of TiZrHfNb refractory high entropy alloys. Both equimolar and non-equimolar alloys are considered. It is shown that the calculated lattice parameters, phase stability and elastic moduli of equimolar TiZrHfNbX are consistent with the available experimental and theoretical results. The substitutions of alloying elements at Ti, Zr, and Hf sites with various contents show similar effects on the phase stability and elastic properties of the TiZrHfNb-based alloys. The substitutions on Nb site are found to generally decrease the stability of body centered cubic phase. Close connections between the charge densities at the Wigner-Seitz cell boundary and the bulk moduli of TiZrHfNb-based alloys are found. The present results provide a quantitative model for exploring the phase stability and elastic properties of TiZrHfNb-based alloys from the electronic structure viewpoint.

Effect of Fe doping on the structural, optical and electronic properties of BaTiO3: DFT based calculation

In this paper, the effect of high concentrated Iron (Fe) doping on the structural, electronic and optical properties of Barium Titanate (BaTiO3) based on density functional theory (DFT) are reported. The calculated lattice parameters show that the phase of BaTiO3 transformed into tetragonal from cubic phase after Fe doping. The electronic structure shows that Fe creates some defect states in the energy band which create weak coordinate covalent bond because of metal-metal interaction. The complex dielectric function, absorption, reflectivity, refractive index, optical conductivity and energy-loss spectrum for BaTiO3 and Fe doped BaTiO3 are calculated, and the results show a dramatic behavior near Fermi level after Fe doping.

Investigation of total and partial magnetic moments of Mn2NiAl with pressure at a several temperatures

ABSTRACTThe first principles calculations of structural and magnetic properties of the Heusler material Mn2NiAl, have been studied using a full potential linearized augmented plane wave (FP-LAPW) within the density-functional theory (DFT). The phase stability of the cubic austenitic (L21) structure for Mn2NiAl in both Cu2MnAl (Fm3 m space group) and Hg2CuTi (F43 m space group) type of structures with ferromagnetic and antiferromagnetic states, has been treated by applying the generalized gradient approximation proposed by Wu and Cohen (WC-GGA) alongside with the martensitic structure of Mn2NiAl. The analysis of phase stability, cohesive energy and the calculated formation enthalpy of Mn2NiAl reveal that the ferromagnetic MnMnNiAl is the most stable type of structure. Moreover, the calculated lattice parameters are found to be in good agreement with theoretical data. The variation of total magnetic moments MT(μB), MMn (μB), MNi (μB) and MAl (μB) in Mn2NiAl with pressure at varying temperature (0, 273 and 344 K), have been calculated.

Structural, Electronic, and Magnetic Properties of Hard Magnetic SmNi2Fe Compound: a DFT Study

Permanent magnets with high magnetic properties are used in many areas like motors, generators, magnetic separators, handles, electron tubes, magnetic resonance imaging systems, health, electronics, automotive, and mining. Due to their easy and inexpensive production methods, most common permanent magnets are ferrite magnets. However, the quest for finding new and alternative permanent magnets is still in progress. Thus, in this study, lattice parameters (a, c), equilibrium lattice volume (V), density (ρ), formation energy (Ef), Wyckoff positions, magnetic moments, density of states. and electronic band structure of SmNi2Fe are investigated using density functional theory (DFT) calculations. For exchange-correlation relations, PBE method within generalized gradient approximation (GGA) and (GGA + U) is used. With a 8.628 μB (GGA) and 9.886 μB (GGA + U) total magnetic moment, SmNi2Fe shows a strong permanent magnetism. Obtained negative formation enthalpy of SmNi2Fe (− 1.526 eV/f.u.) clearly shows that studied material can be synthesized experimentally. Besides, density of states and spin polarized electronic band structures indicate that SmNi2Fe is metallic. Calculated lattice parameters of SmNi2Fe are in good agreement with literature.

First-principles study of elastic and electronic properties of layered ternary nitride SrZrN2 under pressure

ABSTRACTThe structural, elastic, and electronic properties of SrZrN2 under pressure up to 100 GPa have been carried out with first-principles calculations based on density functional theory. The calculated lattice parameters at 0 GPa and 0 K by using the GGA-PW91-ultrasoft method are in good agreement with the available experimental data and other previous theoretical calculations. The pressure dependence of the elastic constants and the elastic-dependent properties of SrZrN2, such as bulk modulus B, shear modulus G, Young's modulus E, Debye temperature Θ, shear and longitudinal wave velocity VS and VL, are also successfully obtained. It is found that all elastic constants increase monotonically with pressure. When the pressure increases up to 140 GPa, the obtained elastic constants do not satisfy the mechanical stability criteria and a phase transition might has occurred. Moreover, the anisotropy of the directional-dependent Young's modulus and the linear compressibility under different pressures are analysed for the first time. Finally, the pressure dependence of the total and partial densities of states and the bonding property of SrZrN2 are also investigated.

First-Principles Calculations of Thermoelectric PbSe<sub>2</sub> Compound to Predict its Elastic Properties

The influencing effect of pressure on structural stability and elastic properties of PbSe2 compound is mainly investigated by first-principles method and homogenization method of the Y parameter. The optimized structural parameters at zero pressure are a=b=6.446Å, c=7.887Å (GGA method) and a=b=6.316Å, c=7.651Å (LDA method), which has good agreement with the experimental and theoretical values. Our calculated lattice parameters and Se-Se bond length are in excellent agreement with experimental data. PbSe2 compound is energetically stable with a good alloying ability. The elastic constants are calculated, and then the bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio and anisotropy factor are determined. Besides, Y parameter method is used to investigate changes of the Poisson ratio, Young’s and shear moduli of PbSe2 within different normal orientation crystal planes. Results show that: 1) Young’s modulus is about 48.37 GPa from GGA and 58.87 GPa from LDA by Reuss-Voigt-Hill estimation, which is averaged about 53.62 GPa; 2) The PbSe2 compound is ductile according to B/G ratio. The universal anisotropic index AU shows that PbSe2 exhibits a fairly high elastic anisotropy.

First-principles calculations to investigate structural, electronic, half-metallic and thermodynamic properties of hexagonal UX2O6 (X=Cr,V) compounds

Abstract Full potential linearized augmented plane wave plus local orbital's (FP-LAPW + LO) method within density functional theory (DFT) is used to investigate the structural, electronic and half-metallic properties of hexagonal UX2O6 (X = Cr,V). Features such as the lattice constant (a and c), bulk modulus and its pressure derivative are reported. The calculated lattice parameters are in good agreement with available experimental results. Band structure and overall densities of states have proved UV2O6 as an indirect half-metallic material with a band gap of 2.88 eV and UCr2O6 as a magnetic semiconductor. The results obtained, make the hexagonal UX2O6 a candidate material for future spintronic applications. 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 variation of the lattice constant, bulk modulus and heat capacity as a function of pressure in the range 0–40 GPa and temperatures of 0–1500 K is computed. Our findings show that external effects are highly effective in tuning some of the macroscopic properties of the compounds under study.

X-ray diffraction analysis for the determination of elastic properties of zinc-doped manganese spinel ferrite nanocrystals (Mn0.75Zn0.25Fe2O4), along with the determination of ionic radii, bond lengths, and hopping lengths

Zinc-doped manganese spinel ferrite nanocrystals with chemical formula Mn0.75Zn0.25Fe2O4 were synthesized by the chemical co-precipitation method. The structural properties of the synthesized nanoparticles were studied by X-ray diffraction analysis (XRD), whereas morphological analysis was performed by high-resolution transmission electron microscopy (HR-TEM) and scanning electron microscopy. The XRD study confirmed the formation of single-phase spinel face-centered cubic nanocrystals with an average size of approximately 19 nm. HR-TEM analysis gave an average particle size of approximately 15 nm, with the nanocrystals being almost spherical. The selected-area electron diffraction pattern obtained in the HR-TEM study clearly indicated the polycrystalline nature of the nanocrystals. The Fourier transform infrared spectrum confirmed the formation of a pure spinel ferrite structure. Williamson-Hall plot analysis, using the XRD data, was used to obtain information on the different elastic properties, such as residual strain, stress, and energy density, considering the uniform deformation model, the uniform stress deformation model, and the uniform deformation energy density model. The results were compared with the results obtained by the size-strain plot method. The XRD data were used to determine the lattice parameter, which was found to be 0.81 nm. With use of the calculated lattice parameter, the ionic radii, bond lengths of the tetrahedral and octahedral sites, and hopping lengths of the spinel ferrite nanocrystals were calculated. Finally, a magnetic study using a vibrating-sample magnetometer showed that the nanocrystal sample is superparamagnetic.

Pressure effect on the structural, elastic and thermodynamic properties of the BeP2N4 compound: First-principles investigation

Using the pseudopotential plane wave method based on density functional theory with the local density approximation functional, pressure dependence of the structural, elastic and thermodynamic properties of the BeP2N4 compound was investigated. Calculated lattice parameters, structural stability and phase transition pressure of both polymorphs of BeP2N4, namely phenakite and spinel phases, are in good agreement with available data. Pressure dependence of the single-crystal and polycrystalline elastic moduli and their related properties were calculated and discussed. Thermal conductivity minimums for both BeP2N4 polymorphs were estimated through Clarke's and Cahill's models. Elastic anisotropy was analyzed for both considered polymorphs. Pressure and temperature dependences of some macroscopic thermodynamic parameters were computed for both phases of the title compound.