Calculated Lattice Constants Research Articles

First-principles calculations to investigate structural, electronic, and thermodynamic properties of ammonia monochloroborane (NH3BH2Cl) as a promising hydrogen storage candidate

This study aims to investigate the structural, electronic, mechanical, piezoelectric, and lattice dynamic proprieties of Ammonia monochloroborane NH3BH2Cl, using first-principles calculations. Both density functional theory and density functional perturbation theory are employed in the computations with generalized gradient approximation and plane waves pseudo-potential formalism. The calculated lattice constants and atomic positions are found in good agreement compared to the experimental values reported in the literature with a deviation of less than 2.85%. The determined density of states reveals that NH3BH2Cl can be considered as an insulator with a wide bandgap of 5.5 eV. Both total and partial density of states, electron local function (ELF), and Born effective charge have been computed to analyse the chemical bond nature of the studied compound. The obtained results indicate the existence of a strong covalent chemical bonding between B and H to form hydric B–H part δ‒, and between N and H to form protic part δ+ in NH3BH2Cl compound. Electronic, dielectric, piezoelectricity and elastic tensors, and vibration modes in Gamma point are calculated and analysed for the first time. The results reveal that NH3BH2Cl is mechanically and dynamically stable. Finally, this study demonstrates that NH3BH2Cl compound can be potentially used as hydrogen storage medium with a capacity of ∼8.5 wt%, besides in piezoelectric (a large value of d15) and wide bandgap devices.

Density Functional Theory studies of structural, electronic and optical properties of Fluorine Doped Magnesium Hydride

In order to overcome the disadvantages of magnesium hydride (MgH2) towards its applications in solar cell science and technology, doping with non-metals such as Fluorine (F) doping is a promising approach to tune its large band gap. In order to expose the hidden potential in F doped MgH2, details analysis of electronic and optical absorptions is needed. Theoretical calculations of structural, electronic and optical properties of F doped MgH2 are studied using first-principles approach within density functional theory (DFT) framework. The calculated lattice constants with PBE-GGA are in better agreement with experimental result. The bandgap value of 3.34 eV for the undoped MgH2 is close to experimental value. When one atom of F is introduced into MgH2 at Mg site, the doping effects modified the band gap from 3.34 to 2.72 eV. Also, by introducing one atom of F to H site, the band gap value reduced to 1.59 eV. Our findings confirmed that non-metal doping narrow the energy band gap of semiconductor materials. The results of optical absorptions indicate that F doped MgH2 at H has strong absorption behavior in the visible light frequency, which depicts its suitability for solar cell applications.

First-Principle Calculations to Investigate Structural, Electronic, Elastic, Mechanical, and Optical Properties of K2CuX (X=As, Sb) Ternary Compounds

Efficient materials with good optoelectronic properties are required for the good performance of photovoltaic devices. In this work, we present findings of a theoretical investigation of the structural, electronic, elastic, mechanical, and optical properties of K2CuX (X = As, Sb) ternary compounds. The computations were carried out by using the density functional theory (DFT) formalism as implemented in the quantum espresso (QE) software package. The calculated lattice constants of 19.1414 a.u (K2CuAs) and 20.0041 a.u (K2CuSb) are in agreement with the experimental results from the literature. The materials under study were found to have bandgaps of 1.050 eV (K2CuAs) and 1.129 eV (K2CuSb). The valence band was majorly formed by Cu-3d, As-2p, and Cu-4s states while the conduction band was majorly dominated by Cu-5p in K2CuAs, whereas in K2CuSb, the valence band was mainly formed by Cu-3d, Cu-4s, and Sb-3p states while the conduction band was majorly formed by Sb-3p and Cu-5p states. The investigated materials were found to be mechanically stable at zero pressure, ductile, and ionic. The optical absorption coefficient curves were found to cover the ultraviolet to visible (UV-Vis) regions, thus making K2CuAs and K2CuSb good UV-Vis absorbers hence their suitability for photovoltaic applications.

First-principles study of the mechanical and thermodynamic properties of ordered phase Mg3Cd under high pressure

Abstract The mechanical and thermomechanical properties of superlattice Mg3Cd (D019) in the pressure range 0–50 GPa were investigated using the first-principles method. The lattice constants, unit cell volume, and density were investigated. The calculated lattice constants are in good agreement with experimental and other theoretical values. The elastic moduli (such as bulk modulus, shear modulus, Young’s modulus) of polycrystalline materials were derived from the single-crystal elastic constants. In addition, Poisson’s ratio, B/G, and Cauchy pressure were investigated. The calculated results show that Mg3Cd is a ductile material and exhibits metallic properties under various pressures. The dependence of thermodynamic properties on temperature and pressure are also discussed by using the quasi-Debye model approximation.

First-principles calculations to investigate structural, elastic, electronic, thermodynamic, and thermoelectric properties of CaPd3B4O12 (B = Ti, V) perovskites

This study has explored numerous physical properties of CaPd3Ti4O12 (CPTO) and CaPd3V4O12 (CPVO) quadruple perovskites employing the density functional theory (DFT) method. The calculated lattice constants show inclinable compliance with the experimental results that ensure their structural stability. The mechanical permanence of these two compounds was observed by the Born stability criteria as well. The mechanical and elastic behaviors have been rationalized to investigate elastic constants, bulk, shear, and Young’s modulus, Pugh’s ratio, Poisson’s ratio, and elastic anisotropy indexes. The ductility and anisotropic indexes confirm that both materials are ductile and anisotropic in essence. The band structure of CPTO reveals a 0.88 and 0.46 eV direct narrow band gap while using TB-mBJ and GGA-PBE potentials, respectively, which is an indication of its fascinating semiconducting nature. Whereas, CPVO perovskite exhibits a metallic character. The calculated partial density of states indicates the strong hybridization between Pd-4d and O-2p orbital electrons for CPTO, whereas Pd-4d and V-3d-O-2p for CPVO. The study of the chemical bonding nature and electronic charge distribution graph reveals the coexistence of covalent O-V/Pd bonds, ionic O-Ti/Ca bonds, as well as metallic Ti/V-Ti/V bonding for both compounds. The Fermi surface of CPVO ensures a kind of hole as well as electron faces simultaneously, indicating multifarious band characteristics. The prediction of the static real dielectric function (optical property) of CPTO at zero energy implies its promising dielectric nature. The photoconductivity and absorption coefficient of CPBO display good qualitative compliance with the consequences of band structure computations. The calculated thermodynamic properties manifest the thermodynamical stability for CPBO, whereas phonon dispersions of CPVO exhibit stable phonon dispersion in contrast to slightly unstable phonon dispersion of CPTO. The predicted Debye temperature (θD) has been utilized to correlate its topical features including thermoelectric behaviors. The studied thermoelectric transport properties of CPTO yielded a higher Seebeck coefficient (186 μV/K), power factor (11.9 μWcm−1K−2), and figure of merit (ZT) value of about 0.8 at 800 K, indicating that this material could be a promising candidate for thermoelectric applications.

Ba(Y0.25Zr0.5Nb0.25)O3: A novel three B-sites perovskite synthesis and structural characterization

In this study, a new perovskite compound Ba(Y0.25Zr0.5Nb0.25)O3 with three B-site elements is reported. This was successfully synthesized by solid-state reaction method at 1300 °C for 6 h using BaCO3, Y2O3, Nb2O5 and ZrO2 as raw materials. The structural properties of Ba(Y0.25Zr0.5Nb0.25)O3 were studied by X-ray diffraction (XRD) technique and further refined by Rietveld method as well as the transmission electron microscopy (TEM). The result shows that the space group of Ba(Y0.25Zr0.5Nb0.25)O3 is Pm-3 m with lattice constant a= 4.2081 Å. By using the empirical formula with the ionic radius and tolerance factor, the calculated lattice constant (a=4.2079 Å) is similar to the measured value, which also proved that the lattice constant prediction model of ideal perovskites is still applicable to multi-B sites perovskites. Compared with BaZrO3, the partly substitution of Zr atoms by Y and Nb atoms has an improvement on increasement of the lattice constant. This study provides insights into the process of designing new perovskites as buffer materials to solve the lattice mismatch problem for large lattice constant perovskites thin film.

Hybrid DFT study of structural, electronic, magnetic and elastic properties of laves phase binary intermetallics RFe2 (R = La, Ce, Pr and Nd)

Hybrid density functional theory was used to investigate the structural, electronic, magnetic and elastic properties of the Laves phase binary intermetallics RFe2 (R = La, Ce, Pr and Nd) in C15 crystal structure. The calculated lattice constants of these materials are found in good agreement with the experiments. The band structures and density of states distribution confirm the metallic nature of all these intermetallics. The optimized energies in different magnetic phases and magnetic susceptibilities by post-DFT treatments confirm that all the understudy compounds are ferromagnetic in nature. Elastic parameters were calculated from the cubic elastic coefficients C11, C12 and C44. The elastic properties reveal that these intermetallics are incompressible, ductile, elastically anisotropic and mechanically stable. Based on the metallic nature and ferromagnetic properties, it is expected that these intermetallics are suitable materials for spintronic technology.

First-Principles Investigations on Structural Stability, Elastic Properties and Electronic Structure of Mg32(Al,Zn)49 Phase and MgZn2 Phase

Al–Mg–Zn alloys reinforced by T–Mg32(Al,Zn)49 phase had higher structure stability and strength than Al–Zn–Mg–(Cu) alloys reinforced by MgZn2 phase, but the reasons for these two kind of alloys was not well-known. To reveal the discrepancy between T phase and MgZn2 phase, the lattice parameters, cohesive energy, and electronic structure as well as the elastic properties were investigated based on density functional theory. Four types of T phase unit cell were employed according to symmetry of space group. The calculated lattice constants well-agreed with experimental data. Compared to MgZn2 phase, T phases obtained lower cohesive energy owing to their partial covalent bond, which may result in a higher structure stability. The elastic modulus E of T phase depended on the occupation of Al atom, and the effect of the occupation of Al atom on the structure and properties of T phase was also discussed.

Density functional study of electronic, elastic and optical properties of [formula omitted] (x=0, 0.25, 0.50, 0.75, 1) alloys

In this study, the structural, electronic, elastic and optical properties of GaAs, GaN and their ternary alloys GaAs1−xNx (x = 0.25, 0.50, 0.75) are investigated within density functional theory utilizing WIEN2K package. The calculations are performed using the exchange-correlation energy functional from Wu-Cohen GGA for the structural and elastic properties and (mBJ –LDA) functional for the electronic and optical properties. The results show the calculated lattice constants as a function of x are in the best agreement with Vegard's linear rule. In the case of electronic properties, the electronic band structures are calculated and the results show GaAs1−xNx alloys are direct band gap semiconductors with a reduction in the band gap for N concentration x = 0.25 and x = 0.50. The results also show that the minimum band gap for the considered alloys occurs for N concentrations x = 0.25. Regarding the optical properties, the imaginary and real parts of dielectric function within the random phase approximation are investigated. The major points in the imaginary part of dielectric function are identified according to the electronic band structure calculations for each concentration. Furthermore, the elastic properties of considered alloys are investigated and the elastic constants, the bulk modulus, the shear modulus, the Young's modulus, the anisotropy factor and Poisson's ratio are calculated.

First-principles calculations of the structural, mechanical, electronic, and optical properties of BaX2 (X=O, S, Se and Te) compounds

We used the first-principles to study the structural, mechanical, electronic, optical properties and phonon of alkali earth-metal Ba dichalcogenide BaX2 (X = O, S, Se and Te). First, our calculated lattice constants are in good agreement with the known experimental values. Secondly, the binding and formation energies, bulk modulus, Young's modulus, Poisson's ratio, Debye temperature, sound velocity and phonon dispersion curves of BaX2 compounds are given. Through basic physical property research, we found that the monoclinic structure of BaX2 (C2/c) is very likely to exist. The modulation of elastic, electronic and optical properties of this system may be achievable. Furthermore, both elastic and optical properties indicate that BaX2 is anisotropic. Finally, the electronic properties are studied by density of states and Mulliken population, indicating that all the compounds are mainly ionic properties.

First-principles study on the structure, fracture toughness, and thermodynamic properties of a new-designed Co30Ni30 Fe20Cr20 high-entropy alloy

In this work, the structural stability, fracture toughness, and thermodynamic properties of Co30Ni30Fe20Cr20 high-entropy alloy (HEA) has been investigated by using first-principles calculations combined with special quasi-random structures. The calculated lattice constant of 3.485 Å was in good agreement with the experiments, and the obtained formation enthalpy value of −1.17 eV/atom indicated that this particular HEA was stable. The results showed that the Fracture energy of the [111] direction was much lower than the [001] and [110] directions. Therefore, the bond strength of the [111] direction was inferred to be the weakest. Finally, the entropy, internal energy, and specific heat capacity of the Co30Ni30Fe20Cr20 HEA increased with increasing temperature, while the free energy and bulk modulus decreased. Thus, the results obtained in this work could be used for studying and designing high performance CoCrFeNi HEAs.

Effect of Cooling Rates and rapidly quenched on Al-Si alloy

Due to its unique properties, the material could be applicable in the automotive industry for the manufacture of exhaust valves, for wear parts, and probably as a material for selected aggressive chemical environments. The solidification behavior of the Al-80.5 % Si-19.5 (A), Al-79% Si21% (B) and Al-77.5 % Si-22.5 % (C) alloys at slowly cooling and Rapidly quenched are reported and discussed. The samples were characterized by X-ray diffraction to calculated lattice constant, optical microscopy and mechanically by (Tensile test, and Hardness) in order to evaluate the response of the heat treatment on the different starting microstructures and mechanical properties.It was found that the lattice parameters for all Si contents decreases with increasing Si content in the solid solution. All mineral compounds formed during hardening were examined by optical microscopy. The highest maximum tensile strength was 120 MPa in the sample Al-22.5Si (Slowly cooled) and 126MPa in the sample Al-22.5Si (rapidly quenched) in the same weight, and highest hardness was 77 HB in the sample Al-22.5Si (Slowly cooled), and 81 HB in the sample Al-22.5Si (rapidly quenched).

Ab initio investigations of electronic structure, mechanical properties, phonon stability, and thermodynamics of the Mg–Er system

We report the results of a first principles study of electronic structure, elastic properties, ideal strengths, phonon stability and thermodynamic properties of the Mg–Er system. The calculations have been carried out within density-functional theory (DFT) and density-functional perturbation theory (DFPT) frameworks. The calculated lattice constants, cell volumes, bulk moduli and their pressure derivations, as well as formation enthalpies are in good agreement with the existing experimental and theoretical data. The single-crystal elastic constants and polycrystalline moduli were derived from the energy-strain relationships and Hill model, we show that Pm-3m-MgEr, I-43m-Mg24Er5, and I4/mmm-MgEr2 systems are all thermodynamically and mechanically stability. The ideal tensile and shear strengths of three phases have been evaluated from first-principles method. Especially, the phonon dispersion relations and densities of states of Pm-3m-MgEr, I-43m-Mg24Er5, and I4/mmm-MgEr2 alloys are investigated systematically from the linear response method of DFPT. Furthermore, the Raman-active and Infrared-active phonon modes at the center of Brillouin Zone (BZ) have been assigned combining with the factor group theory. Our calculated results indicate that three magnesium-erbium phases are also all dynamically stable. Accordingly, within the calculated phonon vibrations and quasi-harmonic Debye model, the vibration entropy and the lattice heat capacity of three phases have also been predicted.

First-principles calculations to investigate the electronic and optical properties of Cu2ZnSnS4 with Ag and Se codoping

In recent years, Cu2ZnSnS4 has drawn great attention owing to its outstanding performance, such as nontoxic and earth-abundant elements, suitable band gap, and high absorption coefficient. In the present study, we have explored the impact of the partial substitution of Cu and S with Ag and Se on the optoelectronic properties of Cu2ZnSnS4. The results suggest that the calculated lattice constants of A2ZnSnX4 (A = Cu, Ag; X = S, Se) with the PBE functional are in good agreement with the experimental values. Furthermore, the band gap obtained by the PBE0 functional for A2ZnSnX4 is consistent well with the experimental data. (Cu0.5Ag0.5)2ZnSn(S0.5Se0.5)4 displays an optimum direct band gap with 1.40 eV and shows wide and high absorption coefficient. Our work demonstrates that the studied compound is proposed to be a promising candidate for environmentally friendly photovoltaic material.

Density functional theory investigation of the mechanical, electronic and optical properties of Pb-free vacancy-ordered double perovskites K2PdCl6 and K2PdBr6

The current work has investigated the mechanical, electronic and optical properties of Pb-free vacancy-ordered double perovskites K2PdCl6 and K2PdBr6 by using first-principles calculations based on the framework of density functional theory (DFT). The calculated lattice constants of K2PdCl6 and K2PdBr6 are close to the experimental data. It is determined by calculating the Goldschmidt’s tolerance factors and elastic constants of K2PdCl6 and K2PdBr6 that they can be stabilized into 3D cubic crystal structures. The calculated Poisson and Pugh’s ratios indicate that K2PdCl6 is a brittle material, while K2PdBr6 exhibits ductile behavior. Both K2PdCl6 and K2PdBr6 are indirect band gap semiconductors, which show suitable band gaps of 2.151 eV and 1.368 eV for optoelectronic devices, respectively. In addition, the optical properties of K2PdCl6 and K2PdBr6 in the photon energy range of 0–6 eV further reveal the application potential of these compounds in single-junction and tandem solar cells as well as other optoelectronic devices.

Pressure induced structural, electronic and optical properties of wurtzite beryllium monoxide (w-BeO) from first-principle calculations

All-electron density functional calculations of structural, electronic and optical properties of wutrzite beryllium oxide (w-BeO) are carried out at different applied hydrostatic pressure. Calculated lattice constants decrease (a, c), while bulk modulus increases with increasing pressure. Direct fundamental band-gap (Eg) of w-BeO increases with increasing pressure and vice versa and the variation provides first and second order pressure coefficient of band-gap. The calculated volume deformation potential of band-gap of w-BeO is −11.5972 eV. Optical properties of w-BeO at zero and high pressures have been studied in terms of dielectric function ε(ω) and related ancillary optical parameters. Each optical parameter is marginally anisotropic. Calculated components of refractive index at each pressure signify uniaxial characteristics of the w-BeO. Calculated components of static dielectric constant, refractive index and reflectivity decreases, while critical point energy in the spectra of each component of ε2(ω), k(ω), σ(ω) and α(ω) increases with increasing pressure and vice versa. Calculated optical energy-gap (Eopt) of w-BeO increases like Eg with increasing pressure and vice versa. The transmission cutoff energy (ECutoff) is shifted towards the higher energy region with increasing pressure.

The effect of the A-site cation on the stability and physical properties of vacancy-ordered double perovskites A2PtI6 (A = Tl, K, Rb, and Cs)

In this article, a theoretical study on the structural, mechanical, electronic and optical properties of vacancy-ordered double perovskites A2PtI6 (A ​= ​Tl, K, Rb, and Cs) is conducted for the first time. The calculated lattice constants of each compound are consistent well with the reported experimental data. The tetragonal phase is adopted for Tl2PtI6 and K2PtI6, while Rb2PtI6 and Cs2PtI6 show the cubic phase. The results suggest that four compounds show good stability and the stability order is Cs2PtI6 ​> ​Rb2PtI6 ​> ​K2PtI6 ​> ​Tl2PtI6. The mechanical stability and ductile nature of each compound are confirmed. It is found that A2PtI6 (A ​= ​Tl, K) and A2PtI6 (A ​= ​Rb, Cs) are indirect and direct bandgap semiconductors, respectively. The predicted indirect and direct band gaps of four compounds are between 1.2 and 1.6 ​eV based on the HSE06 method. Rb2PtI6 and Cs2PtI6 have similar absorption curves. Moreover, Tl2PtI6 and K2PtI6 show stronger light absorption capacity. These four compounds are potential candidates for photovoltaic applications.

Pressure-induced structural and electronic phase transitions of uranium trioxide

The crystal structures, phonon spectra, and electronic properties of uranium trioxide (${\mathrm{UO}}_{3}$) under high pressure have been systematically explored using a particle swarm optimization structure prediction method in conjunction with first-principles calculations. Our calculated lattice constants and the transition pressure of the two experimentally reported phases of $\ensuremath{\gamma}$- and $\ensuremath{\eta}\ensuremath{-}{\mathrm{UO}}_{3}$ are consistent with previous experiments. At pressures of 13, 62, 220 GPa, three new structures of $P{6}_{3}$/$mmc$, $Pm\overline{3}n$, and $Fm\overline{3}m$ are predicted in sequence to be thermodynamically stable. Based on our calculated elastic constants and phonon spectra, we indicate that these three phases are mechanically and dynamically stable. Interestingly, upon phase transition from $P{6}_{3}$/$mmc$ to $Pm\overline{3}n$, ${\mathrm{UO}}_{3}$ undergoes a semiconductor-to-metal electronic transition. In addition, we report results of specific heat, entropy, bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and Debye temperature. Our results provide key insights into understanding the structural as well as the electronic behaviors of ${\mathrm{UO}}_{3}$ under the condition of external pressure.

Structural aspects and magnetic properties of Nd3+ doped nickel-zinc ferrites

Magnetic properties and structural analysis of Nd(Neodymium) doped Ni0.65Zn0.35Fe2O4 using XRD, Rietveld Analysis, FTIR Spectroscopy and VSM are reported.Confirmation of secondary phase formation with increased Nd content is established. Cation distribution for neodymium substituted nickel-zinc ferritesis proposed by considering the deficiency of Fe3+ in NiZnFe2O4 due to secondary phase formation of NdFeO3. The quality of present cation distribution was confirmed through close agreement of experimentally calculated lattice constant and Rietveld refinement. Changes in saturation magnetization with increased Nd content are explained on the basis of intensifying effect on energy exchange (inter-sublattice) between Ni–O–Nd and Ni–O–Fe concnerning Fe–O–Fe interaction, effect of replacing lower magnetic moment Nd3+ (3.62 μB) in place of Fe3+ (5 μB) and exchange developed between the cations existing at B-sites due to creation of oxygen vacancies.

Elastic, electronic, optical and thermoelectric properties of perovskite: BaTbO3

We investigate the electronic structure, elastic, optical and thermoelectric properties of single-perovskite BaTbO3 by means of the density functional theory approach employing generalized gradient approximation and an on-site coulomb potential. The calculated lattice constants are found to be in good agreement with the available experimental results. The elastic property calculations reveal that BaTbO3 is mechanically stable and ductile in nature. The spin polarized density of states and band structure calculations shows a semiconducting state with band gap ~ 1 eV with anti-ferromagnetic ground state. Based on the obtained values of optical parameters, BaTbO3 is found to be optically active both in the ultra-violet and visible region of the spectrum. Furthermore, thermoelectric properties are evaluated by using BoltzTraP code based on Boltzmann transport theory employing constant relaxation time and rigid band approximation in the temperature range 300 – 1200 K. The noticeable value of power factor is observed at higher temperature region with the maximum value ~ 12 μWcm−1K−2 at 1200 K and the lattice thermal conductivity is significantly low in the entire temperature range. The maximum value of ZT found to be ~ 0.35. The results reveal that this compound can be used as a good optoelectronic application as well as thermoelectric material in the high temperature region.