Calculated Lattice Parameters Research Articles

Structural electronic and vibrational properties analysis of Li2CaX (X = Sn, Pb) heusler alloys: a comparative study

This study was focused on structural, electronic and vibrational properties of Li2CaSn and Li2CaPb with density functional theory. All properties of these compounds were computed by implementing General Gradient Approximation and using Quantum Espresso software programme. As a result of the calculations, it was found that the lattice parameter is 6.967 Å and bulk modulus is 33.94 GPa for Li2CaSn. Also, these values are 7.062 Å and 29.574 GPa for Li2CaPb. The calculated lattice parameters are in good agreement with the available experimental data. There is no previous theoretical calculation for Li2CaSn and Li2CaPb compounds. It was calculated that Li2CaSn and Li2CaPb have a semi-metal property. The full phonon dispersion curves of Li2CaSn and Li2CaPb compounds in the Heusler type structure were examined using the linear response method. Under 0 kbar pressure, Li2CaPb was unstable while Li2CaSn was dynamically stable. Calculations showed that when 38.42 kbar pressure is applied to the Li2CaPb compound, the Li2CaPb compound becomes dynamically stable. It is believed that this study will shape future studies.

Structure stability, mechanical properties and thermal conductivity of the new hexagonal ternary phase Ti2InB2 under pressure

ABSTRACT Recently, Wang et al. [Nat. Commun. 10 (2019) 2284] report a new compound, Ti2InB2, a stable boron-based ternary phase in the Ti-In-B system. This predicted compound is successfully synthesised using a solid-state reaction route and its space group is confirmed as (No. 187). In this work, the structural stability, mechanical properties, and thermal conductivity of the new hexagonal ternary phase Ti2InB2 under pressure up to 100 GPa have been carried out with first-principles calculations based on density functional theory. Our calculated lattice parameters in the ground state are consistent well with the theoretical prediction data. The calculations of elastic constants and phonon dispersion curves indicate that Ti2InB2 is mechanically and dynamically stable at least up to 100 GPa. Moreover, the pressure dependent elastic properties, such as bulk modulus B, shear modulus G, transverse sound velocity vt , longitudinal sound velocity vl , and Debye temperature Θ, are successfully obtained. It is found that Ti2InB2 behave in brittle manner under pressure up to 100 GPa. Meanwhile, the anisotropy of the directional linear compressibility and the Young’s modulus under pressure are also analysed for the first time. Finally, the minimum thermal conductivity of Ti2InB2 under different pressures are further evaluated by using both Clark’s model and Cahill’s model. The results show that Ti2InB2 exhibits relatively low thermal conductivity in the ground state and is suitable to be used as thermal insulating materials.

Study of the structural, mechanical and thermodynamic properties of the new MAX phase compounds (Zr1-xTix)3AlC2

The structural, electronic, mechanical and the thermodynamic properties of the MAX phases (Zr1-xTix)3AlC2 compounds have been investigated by using the full-potential plane-wave FP-LAPW method as implemented in the Wien2k code. The exchange-correlation (XC) energy of electrons was treated using the Perdew–Burke–Ernzerhof parametrization. The ground-state properties for the studied compounds were calculated and compared with available experimental and theoretical data. The calculated lattice parameters are reasonably comparable with experimental and theoretical results. The formation energy has been evaluated in order to determinate the stability of our compounds. The calculation of the electronic structure was predicted for the first time for the present MAX phase compounds. These results indicate that, all our compounds exhibit metallic behavior and this metallicity is due to the p-d hybridization. The elastic constants have also evaluated by the Hex-elastic package. The mechanical stability reveal that, all our compounds are stable mechanically. The bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio and Cauchy pressure were calculated and discussed in detail. Furthermore, the temperature and pressure effect on: Bulk modulus, Debye temperature and heat capacity at constant volume and constant pressure CV and CP, respectively have been investigated by the quasi-harmonic Debye model.

Solvothermal synthesis of n-type Bi2(SexTe1\u2212x)3 nanoplates for high-performance thermoelectric thin films on flexible substrates

To improve thermoelectric performance of materials, the utilization of low-dimensional materials with a multi-alloy system is a promising approach. We report on the enhanced thermoelectric properties of n-type Bi2(SexTe1−x)3 nanoplates using solvothermal synthesis by tuning the composition of selenium (Se). Variation of the Se composition within nanoplates is demonstrated using X-ray diffraction and electron probe microanalysis. The calculated lattice parameters closely followed Vegard’s law. However, when the Se composition was extremely high, an impurity phase was observed. At a reduced Se composition, regular-hexagonal-shaped nanoplates with a size of approximately 500 nm were produced. When the Se composition was increased, the shape distribution became random with sizes more than 5 μm. To measure the thermoelectric properties, nanoplate thin films (NPTs) were formed on a flexible substrate using drop-casting, followed by thermal annealing. The resulting NPTs sufficiently adhered to the substrate during the bending condition. The electrical conductivity of the NPTs increased with an increase in the Se composition, but it rapidly decreased at an extremely high Se composition because of the presence of the impurity phase. As a result, the Bi2(SexTe1−x)3 NPTs exhibited the highest power factor of 4.1 μW/(cm∙K2) at a Se composition of x = 0.75. Therefore, it was demonstrated that the thermoelectric performance of Bi2(SexTe1−x)3 nanoplates can be improved by tuning the Se composition.

First principles investigation of the structural, electronic, optical and elastic properties of [formula omitted]alloys

The structural, electronic, optical and elastic properties of CsCdxPb1−xCl3alloys are studied using the plane-wave pseudopotential method under the framework of density functional theory (DFT). The Perdew–Burke–Ernzerhof functional (GGA−PBE)is employed to treat the exchange and correlation potentials. The supercell approach (SC)and the virtual crystal approximation (VCA)are also used to model the CsCdxPb1−xCl3alloys. Because of the symmetry constraint in the VCAapproach, the calculated lattice parameters of these alloys only within SCapproach show linear behavior in agreement with the Vegard's law. Using the approach of Zunger and co-workers, the microscopic origin of the energy band gap bowing of these alloys is investigated in terms of the volume deformation, charge exchange and structural relaxation. The energy band gap of these alloys is also predicted to be suitable for solar absorber applications. The real and imaginary parts of the macroscopic dielectric function (MDF)of CsCdxPb1−xCl3alloys are studied using the single-particle picture within random phase approximation (RPA). The calculated static dielectric constant of these alloys increases when Cdconcentration decreases. To study the excitonic effects (EXC), the macroscopic dielectric function of these alloys is also calculated through the solution of the Bethe-Salpeter equation (BSE)using Tamm-Dancoff approximation within many-body perturbation theory. The variation of some polycrystalline structural properties of these alloys such as the Bulk modulus, Young's modulus, Poisson's ratio, Pugh's ratio, shear and Zener's anisotropy parameters as a function of the Cdconcentration are studied using perturbation density functional theory (PDFT). The calculated results show that these alloys are mechanically stable and rather elastically anisotropic. This study provides a detailed theoretical analysis of the CsCdxPb1−xCl3alloys and can give helpful guidance for further relevant research.

First-principles study of rocksalt Mg x Zn1− x O: band structure and optical spectra

ABSTRACT The present work deals with electronic band structure and derived optical spectra of Mg x Zn1− x O in the hypothetical rocksalt structure. The computations are performed using full-potential linearised augmented plane wave method. The exchange–correlation potential is described using the Wu-Cohen and Tran-Blaha modified Becke–Johnson generalised gradient approximation (TB-mBJ-GGA). The calculated lattice parameter deviates by less than 1% from experiment showing a net improvement when compared with previous calculations. Moreover, its variation with respect to x does not violate Vegard's law. The TB-mBJ-GGA approach improves the magnitude of the fundamental band gap with respect to experiment. The rocksalt Mg x Zn1− x O is found to be an indirect gap semiconductor for x = 0, 0.25, 0.50 and 0.75 and a direct gap semiconductor for x = 1. The nature of the gap for rocksalt Mg x Zn1− x O is still in controversy and further investigations are required in this respect. The optical spectra of Mg x Zn1− x O are analysed and discussed. Our findings yield values of 1.55 and 1.25 for the static refractive index and 2.4 and 1.55 for the static dielectric constant for rocksalt ZnO and rocksalt MgO, respectively.

Structural, electronic, elastic and magnetic properties of heavier $$\hbox {REIr}_{3}$$ (RE $$=$$ Gd, Tb and Ho) intermetallic compounds

We present results on the bonding nature, structural, electronic, magnetic and elastic properties of $$\hbox {REIr}_{3}$$ (RE $$=$$ Gd, Tb and Ho) intermetallic compounds adopting simple cubic $$\hbox {AuCu}_{3}$$ -type structure obtained using the full-potential linearlised augmented plane wave (FP-LAPW) method based on density functional theory. The local spin density approximation (LSDA) with Hubbard parameter (LSDA $$+\,U$$ ) has been used for exchange and correlation effects to get accurate results because of the presence of highly localised 4f electrons of rare-earth (RE) (RE $$=$$ Gd, Tb and Ho) atoms. The calculated lattice parameter is found to be consistent with the experimental results. The calculated magnetic moments predict ferromagnetic behaviour of these compounds. The electronic and bonding properties have been solved in terms of band structure, density of states (DOS) and charge density plots. These results confirm the metallic nature of these compounds. The bonding appearances of these compounds have also been interpreted from charge density plots. The elastic constants, shear modulus and Cauchy’s pressure are computed and they reveal that $$\hbox {GdIr}_{3}$$ and $$\hbox {TbIr}_{3}$$ compounds are ductile while $$\hbox {HoIr}_{3}$$ shows brittle character.

The effect of hydrostatic pressure on melt-castable energetic materials bis-oxadiazole-bis-methylene dinitrate: A density functional theory study

Using density functional theory calculations, the structural and electronic properties of the melt-castable energetic materials of bis-oxadiazole-bis-methylene dinitrate (BODN) were studied. The calculated lattice parameters, molecular geometry and band gap by the semi-empirical dispersion (Grimme) corrected generalized gradient approximation functional of Perdew-Burke-Ernzerhof (GGA-PBE-G06) are in good agreement with experimental and theoretical results. Also, the pressure effect on BODN was studied in this work. It is found that although the calculated lattice parameters a, b and c are all decreased monotonically with pressure up to 25 GPa, the b-axis is the easiest compressible. The compression behaviors of geometry were investigated, and found the bond C1–N1 and C3–O2 respective in the oxadiazole and alkyl nitric ester groups were more compressible than the others. The molecular interactions were examined by the Hirshfeld surface and 2D-fingerprint analysis. Moreover, the predicted band gap under high-pressure conditions was discussed as well.

Structural and Judd-Ofelt intensity parameters of a down-converting Ba2GdV3O11:Eu3+ nanophosphors

A white light emitting Barium gadolinium vanadate, Ba2GdV3O11:Eu3+, is developed using time-saving combustion synthesis technique. The Rietveld analysis of the optimum luminescent composition (Ba2Gd0.97V3O11:0.03Eu3+) confirmed that it crystallizes into the monoclinic system with P21/a space group. The calculation of lattice parameters unveiled the unit cell expansion which in turn governed the asymmetry around activator. The photoluminescent analysis showed an efficient energy transfer from vanadate absorption of Ba2GdV3O11 host to Eu3+, resulting in a very intense characteristic emission of the Eu3+. The PL decay investigations of Ba2GdV3O11:0.03Eu3+ nanophosphor gave the radiative lifetime and total spontaneous emission probabilities. Judd-Ofelt parameterization provided the refractive index of the host and stimulated emission cross section for 5D0?7F4 (8.03) transition in Ba2GdV3O11:0.03Eu3+ phosphor. The quantum efficiency of 5D0 state in Ba2Gd0.97Eu0.03V3O11 phosphor was calculated to be 79%, resulting in a pure white emission. All results demonstrate that Ba2Gd0.97V3O11:0.03Eu3+ is a potential candidate for single-phased WLEDs.

Insight into electronic structure and optical properties of Nb and F co-doped SnO2 with hybrid functional theoretical method

Structural, electronic and optical properties of Nb and F co-doped SnO2 were mainly investigated using density functional theory (DFT). Hybrid density functional theory was employed to obtain band structure, density of states (DOS) and optical properties. The calculated lattice parameters of pure SnO2 by PBEsol functional (a = 4.774 Å and c = 3.218 Å) are in good agreement with experimental date (a = 4.742 Å and c = 3.206 Å). When co-doping with Nb&F, the length of octahedron (4.136 Å) closely matches with pure SnO2 (4.112 Å) in direction of perpendicular to the c-axis. The direct band gaps of 3.80 eV, 3.38 eV 3.63 eV, 3.23 eV, 3.06 eV have been obtained for pure, F, Nb, Nb&F and Nb&2F doped SnO2 respectively, and the dispersed conduction band after doping does not significantly affect the electron effective mass of the conduction band minimum (CBM). A study of band alignment shows the clearly increasing valence band maximum (VBM) and the slightly decreasing CBM occur after doping. Analyses of the charge density difference and Bader charge suggest that Sn–O bond shows covalent characteristic, but the degree of ionization decreases in following order: Nb > Nb&F > Nb&2F > SnO2 > F. In terms of optical properties after doping, the optical absorption side slightly red or blue shift, and the reflectivity in the visible spectrum is greatly low.

Preparation and characterization of antimony sulphide nanostructure

Designing and Controlling of the size and morphology of the nanostructured materials is important for photovoltaic and photocatalytic applications. Herein, we report a new efficient approach to prepare different nanostructures of antimony sulphide. The conventional hydrothermal routes can be modified to control the size and morphology of the materials we have been prepared pedicellate flower-like nanostructure of antimony sulphide by quenched hydrothermal method (modified hydrothermal method). The prepared nanostructured materials were analysed using XRD, SEM. The powder X-ray diffraction pattern shows the Sb2S3 crystals belong to the orthorhombic phase with calculated lattice parameters a = 1.190 nm, b = 1.132 nm, and c = 0.390 nm. The morphological changes have been recorded using scanning electron microscope.

Structure, microstructure, optical and photocatalytic properties of Mn-doped ZnO nanoparticles

In this work, Zn1−xMnxO samples were synthesized by the hydrothermal method by varying the dopant ratio from x = 0.01 to 0.05 with 0.01 increment. Structural, optical and photocatalytic properties of Mn-doped ZnO were analyzed based on their concentration dependence. Structural behavior of the nanoparticles was studied by X-ray diffraction technique and it was found that Zn1−xMnxO samples were hexagonal Wurtzite structure with no secondary phase. The effect of Mn element in Zn1-xMnxO composition was clarified by calculating lattice parameters, cell volumes, stress, microstrain, the locality of the atoms dislocation density, displacement of atoms and bond length. SEM images revealed random agglomeration. The band gap and Urbach energies of Zn1−xMnxO structures were determined and discussed. Different models were used to calculate refractive index and the refractive index was found in the range of 2.05–2.72. Mn-doped ZnO nanoparticles exhibited lower degradation rate constants (k = 0.0004–0.0009 min−1) than that of pure ZnO (k = 0.0014 min−1). Doping Mn increased the Urbach energy value.

Investigation of structural, mechanical, dynamic, electronic and optical properties of seleno-germanates A[formula omitted]GeSe[formula omitted] (A = Mg, Ca and [formula omitted]-Sr) from first principles

In this work we systematically investigated the structural, mechanical, electronic, dynamical and optical properties of A2GeSe4 (A = Mg, Ca and Sr) seleno-germanate compounds by density functional calculations. Synthesis of Mg2GeSe4 and Sr2GeSe4 have been reported, while Ca2GeSe4 is a hypothetical compound. The lattice parameters, equilibrium volume, lattice constants, cohesive and formation energies and bulk moduli were calculated. Our calculated lattice parameters and equilibrium volumes are in reasonable agreement with available experimental data. Elastic constants satisfy the Born stability criteria, confirming mechanical stability of all three compounds. Vibrational properties, studied using a finite displacement method, revealed no negative phonon frequencies across the Brillouin zone and therefore the compounds are dynamically stable. Hybrid functional and many-body perturbation theory were employed for the study of the electronic band structure and optical properties. Band structure results suggest that Mg2GeSe4 and Ca2GeSe2 are indirect band gap and Sr2GeSe4 a direct band gap semiconductor. The Bethe–Salpeter equation (BSE) was solved to include excitonic effect for an accurate description of optical properties. Optical absorption spectra show significant optical anisotropy. Band gaps estimated from BSE are 2.58, 2.30 and 2.86 eV for Mg2GeSe4, Ca2GeSe4 and Sr2GeSe4 respectively. The calculated band gaps suggests that Mg2GeSe4, Ca2GeSe4 and Sr2GeSe4 are semiconductors with potential to absorbed light in the ultra-violet and upper visible regions. The computed band edges from a Mulliken's analysis suggest that the A2GeSe4 compounds have suitable conduction band minima (CBM) potentials of −0.97, −1.45 and −1.86 V, respectively, versus the normal hydrogen electrode (NHE) for water reduction. The calculated BSE gaps and CBM minima of A2GeSe4 suggest that they are suitable candidates that can be exploited for applications in non-linear optics, photovoltaic (multi-junction solar cells) and visible response photo-catalytic materials.

Nonlinear optical properties of single crystal of L-OOMHCL incorporation with Glycine Oxalic Acid (GOA) with high chemical stability for optoelectronic applications

In this report, a good nonlinear optical material with high criteria such as optical nonlinearity, chemical and thermal stability for life time system capability. The crystallographic orientation belongs to monoclinic crystal structure with the non-centrosymmetric space group, the prominent peaks were observed as (101), (112) and (300). The calculated lattice parameter values are, a = 6.21 Å, b = 3.67 Å, c = 12.12 Å, α = 90°, β = 103.21°, γ = 90° monoclinic space group of P21/n. A broad and strong peak at 3427 cm−1 was assigned to NH stretch, the OH and CH stretching of the compound were confirmed by the peaks present at 3043 cm−1 and 2934 cm−1. Moreover, the peaks at 1398 cm−1 represent the tartaric acid, another strong peak at 1261 cm−1 was assigned to CH2 twisting. In addition, the DTA curve shows a sharp endothermic peak at 109 °C, which corresponds to the melting point of the compound at this stage the sample lost its 20% of weights due to dehydration. From TGA curve, the L-OOMHCL crystal has good thermal stability up to melting point as there is no major weight loss below that temperature. However, it shows the more weight loss of 95% after the melting point due to the removal of volatile substances. Thus, it confirms the full degradation around 600 °C. The dielectric constant and the dielectric loss of L-OOMHCL crystal were carried out at three different temperatures 313 K, (40 °C) 333 K (60 °C) and 353 K (80 °C) for frequencies varying from 50 Hz to 5 MHz. Finally, we have calculated the refractive index value at the cutoff wavelength 214 nm and the 2.012 which is larger than unity, this results in greater development of polarization in the presence of dc electrical fields, hence leading to greater mobility.

Analysis of mechanical behaviour of L-arginine hydrobromide monohydrate (LAHBr) single crystal grown by unidirectional growth technique

A single crystal of L-arginine Hydrobromide Monohydrate (LAHBr) with excellent crystalline perfection was grown by a modified way of unidirectional technique. The criteria behind this modified version were to reduce the temperature gradient of the solution which will enhance the quality of the single crystal. The formation of the crystal was confirmed by calculating lattice parameters from powder x-ray diffraction technique. The quality of the single crystal was analyzed by high-resolution x-ray diffraction which suggests that single crystal was free from grain boundaries and have the value full width half maxima is 9.36 arc second. Owing to high crystallinity, the single crystal was further underwent mechanical analysis using nanoindentation technique. Its structural, as well as physical transformation have been assessed by laser and shock damage threshold techniques. The presence of surface defects was examined by scanning electron microscope (SEM) and it is in tune with the high resolution x-ray diffraction method.

First-principles calculation of the electronic structure, optical, elastic and thermodynamic properties of cubic perovskite LiBeF3

The elastic, electronic structure, optical and thermodynamic properties of cubic fluoroperovskite crystal LiBeF3 were investigated using the ab initio method. The calculated lattice parameter, elastic constants Cij, bulk modulus B and shear modulus G at 0 GPa and 0 K are agreed well with previous reports. The obtained band structure shows that LiBeF3 has an indirect energy band gap of 7.64 eV, which is consistent with the known results. Then, the dielectric function, absorption coefficient, and refractive index were investigated. It was found that the absorption part of LiBeF3 is located at the ultraviolet-light region. Finally, the thermodynamic properties of LiBeF3, including the bulk modulus B, relative volume, heat capacities, thermal expansion α and relative Debye temperature at various temperatures and pressures, are discussed. The optical and thermodynamic properties, and their relationships of cubic crystal LiBeF3 are reported for the first time. Our results indicate that LiBeF3 compound is a promising optoelectronic and optics applications.

The Effects of Fe and Si Elements on Structural, Mechanical, and Electronic Properties of an Fe–Si–Ti System by First‐Principles Calculations

Herein, first‐principles calculations with density functional theory are used to investigate the structural, mechanical, and electronic properties of Fe–Si–Ti alloys, aiming to study the effects of Si and Fe in titanium alloys. The calculated lattice parameters are in good agreement with previous data. Alloying with Si/Fe can produce more brittle/ductile materials, due to the weaker/stronger metallic bonds. Furthermore, the effect of alloying with Si and Fe on the anisotropic properties is negligible. The increasing range of Debye temperatures by alloying with Si is greater than that by alloying with Fe. The capacity of Si to enhance the interatomic bonding force is greater than that of Fe due to the stronger covalent bonds. Similarly, the charge density reflects that the capacity of Si to enhance the interatomic bonding force is better than that of Fe for titanium alloys. In addition, the metallic conductivity of these alloys is verified, with there being no gaps at the Fermi level. The localization of electrons in the SiTi alloy is observed to be relatively strong around the Fermi level. In addition, the amplitude of the top of the valence band and the bottom of the conduction band is smooth, showing great effective mass.

Investigation on Inclusions in Non-oriented Silicon Steels

Inclusions in non-oriented electrical steels were automatically measured using Explorer 4 and extracted with a non-aqueous solution electrolytic method to observe their three-dimension morphology. Extracted inclusions were collected and prepared for micro-XRD test, which is performed to identify the crystal structure of inclusions. Inclusions mainly consist of AlN with P63mc structure, MnS with Fm-3m structure and Al2O3 with R-3c structure, and calculated lattice parameters of inclusions almost agree with that listed in standard PDF cards.

Comparative study on dielectric and structural properties of undoped, Mn-doped, and Ni-doped ZnO nanoparticles by impedance spectroscopy analysis

In this work, the results of the structural and dielectric investigation of pure, Mn-doped, and Ni-doped ZnO nanoparticles (NPs), which have been prepared by simple sol–gel method using zinc acetate as precursor, are studied. The synthesized samples are examined via XRD at 300 K, FE-SEM, FTIR, and μ Autolab/FRA2 impedance spectroscopy techniques. XRD results and calculated lattice parameters of all synthesized samples have revealed that diffraction peaks are well matched to the JCPDS card No. 036-1451. FE-SEM obtained images confirm the formation of NPs. The FTIR graphs exhibit the characteristics transmittance peaks at 510.01 cm−1, 514.36 cm−1, and 509.43 cm−1 for pure, Mn-doped, and Ni-doped ZnO, respectively. This technique also authenticates the existence of ZnO NPs and doped ones. The dielectric measurements of all synthesized samples have been done in the ranges of 10−3 to 106 Hz. Dielectric investigations reveal that the size of the NPs and dopant type have a great effect on the dielectric manner of samples. The obtained experimental results exhibit that the dielectric constant, loss tangent, electric modulus, and AC electrical conductivity parameters have intense frequency dependence. AC conductivity increases with frequency increment but decreases with doping, making it a potential option for device applications. In principle, an increment in capacitance and dielectric constants values has caused a decrement in frequency, while on the contrary, frequency increasing exhibits an increment of the AC electrical conductivity and electric modulus values. Finally, the magnetic studies extracted from electrical measurement are investigated.

Comprehensive comparison of two tracking codes for single-particle dynamics evaluation of a next-generation storage ring light source

Next-generation light sources based on the multibend achromat concept place great reliance on the accuracy of beam dynamics modeling. To ensure the success of such light sources, confirmation of design performance with at least two independent codes is prudent. The APS Upgrade (APS-U) lattice has been designed using the code elegant, which has existing and new features that are needed by the design. Corresponding, independent improvements have recently been made to the accelerator toolbox (at), in order to permit an independent check of nonlinear dynamics predictions. The new developments include the modeling of combined-function bending magnets with straight geometry and improved fringe field effects of quadrupole magnets. Calculations of linear and nonlinear lattice parameters and particle tracking results were compared, showing remarkable agreement was found between the two independently developed codes. This provides significant confirmation of the feasibility of the APS-U design.