Abstract The mechanical and thermodynamic properties of polyanionic hydrides XAlSiH (X = Sr, Ca, and Ba) were evaluated using density functional theory (DFT). The thermal parameters of XAlSiH ...hydrides, such as the Grüneisen parameter γ , heat capacity, and thermal expansion coefficient, were computed for the first time. The quasi-harmonic Debye model was used to determine these parameters over a range of pressures (0–40 GPa) and temperatures (0–1000 K). The gravimetric hydrogen storage capacities for BaAlSiH, SrAlSiH, and CaAlSiH were found to be 0.52%, 0.71%, and 1.05%, respectively. The hydrogen desorption temperatures for these compounds were also simulated at 748.90 K, 311.57 K, and 685.40 K. Furthermore, semiconducting behavior with an indirect bandgap value between 0.2 and 0.7 eV was exhibited by these compounds using the GGA and LDA approximation, and between 0.7 and 1.2 eV using the mBJ-GGA and mBJ-LDA approximation. Accurate elastic constants for single crystals were obtained from the calculated stress–strain relationships. The elastic constants for the XAlSiH compounds were significantly higher than those for other hydrides. The 001 direction was more compressible than the 100 direction in the hexagonal structure of XAlSiH. A lower bulk modulus than metallic hydrides was exhibited by these materials, indicating that XAlSiH compounds (X = Sr, Ca, and Ba) were highly compressible. The melting temperature for CaAlSiH was higher than that for SrAlSiH and BaAlSiH. Consequently, the decomposition temperature for XAlSiH (X = Sr and Ba) at which hydrogen was released from a fuel cell was lower than that for CaAlSiH. The bonding behavior of CaAlSiH was more directional than that of SrAlSiH and BaAlSiH. Brittle materials were XAlSiH (X = Sr, Ca, and Ba). Our PBE calculations yield linear compressibility and orientation-dependent Young’s modulus. Materials composed of hexagonal XAlSiH (where X represents Sr, Ca, or Ba elements) exhibit anisotropy in Young’s modulus but isotropy in bulk modulus.
•The total magnetic moment of all investigated compounds is obtained to be 2 µB.•The mechanical stability test performed on the computed elastic constants Cij demonstrate that investigated compounds ...are mechanically stable.•The GGA (GGA+U) and mBJ-GGA (mBJ-GGA+U) approximations are used for the calculation of electronic properties in the most stable phase B1.•These materials could be useful for spintronic application.
We report ab-initio calculation of the structural, magnetic, elastic, and electronic properties of the PrX (X = P, As and Bi). The structural stability and phase transition of PrX (X = P, As, Bi) compounds in (NaCl-type), (CsCl-type), (Zinc blende-type), WC-Bh (Hexagonal) and L10 (Tetragonal) structures in ferromagnetic state are investigated using the augmented plane wave plus local orbital (APW + lo) method within GGA + U, and mBJ-GGA + U approximations. Careful inspection of electronic properties indicates that most of the compounds exhibit half-metallic behavior. The total magnetic moment of all investigated compounds is obtained to be 2 µB. The mechanical stability test performed on the computed elastic constants Cij demonstrate that investigated compounds are mechanically stable. To elucidate chemical stability, chemical bonds are investigated and found to be mainly characterized by an ionic-covalent mixture. Moreover, elastic anisotropy of all compounds is calculated. Subsequently.
Analyses based on first-principles simulations have revealed new details about the mechanical and thermodynamic characteristics of NaBH4 and NaAlH4 complex hydrides in α, β and γ phases. Using the ...quasi-harmonic Debye model, thermal parameters like the Debye temperature, the heat capacity, and the thermal expansion coefficient of NaXH4 (X = B, Al) complex hydrides are calculated in α, β and γ phases at different pressures and temperatures for the first time. Single-crystal elastic constants may be derived from the stress-strain relationship calculations. Although NaBH4 has a stronger compressibility modulus than NaAlH4, the distance dB-H is shorter than dAl-H, which may be explained by the presence of the covalent bond in BH4 and AlH4 in NaXH4 (X = B, Al). The melting points of NaXH4 (X = B, Al) may be used to estimate the decomposition temperatures of hydrogen. β-NaBH4 has a higher melting point than α-NaAlH4. Thus, the decomposition temperature of NaAlH4 at which hydrogen is released from a fuel cell is expected to be lower than that of NaBH4. β-NaBH4 has a more directed bonding tendency than α-NaAlH4 does. Except for the phase γ-NaAlH4, the NaXH4 (X = B, Al) compounds are ductile. NaBH4 deforms more than NaAlH4 in uniaxial deformation, yet both are centrally strong solids. Our PBE calculations result in the linear compressibility and orientation-dependent Young's modulus. Tetragonal β-NaBH4 and α-NaAlH4 structures have an isotropic bulk modulus but an anisotropic Young's modulus.
•Although NaBH4 has a stronger compressibility modulus than NaAlH4.•The mechanical stability demonstrate that investigated compounds are mechanically stable.•Tetragonal β-NaBH4 and α-NaAlH4 structures have an isotropic bulk modulus but an anisotropic Young's modulus.•These materials could be useful for storage of hydrogen application.
The inverse Heusler alloys such as Ti
2
CoSi, Mn
2
CoAl and Cr
2
ZnSi were studied in the framework of density functional theory using FP-LAPW linearised augmented plane wave method in order to ...determine the different physical properties such as structural, electronic, magnetic and thermoelectric. The generalised gradient approximation (GGA) was used to treat the exchange-correlation energy and the Beck-Johnson (mBJ) approach was used to calculate the electronic properties. In all studied compounds, the stable type Hg
2
CuTi was energetically more favourable than Cu
2
MnAl type structure. The results show that two compounds (Ti
2
CoSi and Mn
2
CoAl) are both ferromagnetic (FM) while Cr
2
ZnSi is antiferromagnetic (AFM). The compounds Ti
2
CoSi and Mn
2
CoAl have a total magnetic moment of 3 and 2 μ
B,
respectively, whereas the Cr
2
ZnSi alloy has a total magnetic moment equals zero. The Ti
2
CoSi, Mn
2
CoAl and Cr
2
ZnSi compounds exhibit half-metallic (HM) character with 100% spin polarisation at the Fermi level. Finally, the semi-classical Boltzmann theory implicit in the BoltzTraP code was used to calculate the electronic transport coefficients such as thermal and electrical conductivity, the Seebeck coefficient and the factor of merit.
To study the structural properties of X
2
Se
2
C (
X
= Ta, Nb) MXenes, we have used an FP-LAPW method based on functional density theory GGA-PBE-sol, which is based on the method of plane waves ...increased by linear waves at full potential. From the most stable state, we determined other properties such as electronic, optical, and mechanical ones. Band structure calculations reveal the metal character of GGA. MXenes exhibit hexagonal crystal structures at zero temperature. Calculated elastic constants show the alloy's mechanical stability and ductility. Due to its high elasticity anisotropy, the alloy possesses excellent tensile strength. The dielectric function, absorption, reflectance, optical conductivity, and other optical properties were also investigated. In the ultraviolet region, X
2
Se
2
C (
X
= Ta, Nb) is an effective absorber and has a high refractive index.
Graphical abstract
The projected density of state (PDOS) of (a) Nb
2
Se
2
C and (b) Ta
2
Se
2
C.
A comprehensive study of structure, phase stability, optical and electronic properties of LiAlH4 and NaBH4 light-metal hydrides is presented. The calculations are carried out within density ...functional theory using the full potential linear augmented plane wave method. The exchange-correlation potential is treated within the local density approximation and the generalized gradient approximation (GGA) to calculate the total energy. Furthermore, the Engel-Vosko GGA approach is employed to compute electronic and optical properties such as reflectivity spectra. The phases , β and γ of LiAlH4 and NaBH4 hydrides are investigated, the phase transition from the β to the high-pressure γ phase is determined for NaBH4 and is accompanied by a 1% volume decrease. For LiAlH4, no phase transition is detected. The materials under consideration are classified as wide band gap compounds. From the analysis of the structures at different phases, it is deduced that the hydrides show strong covalent interaction between B (Al) and H in the BH4− (AlH4−) anions and ionic bonding character between BH4− and Na+ for NaBH4, and AlH4− and Li+ for LiAlH4. The complex dielectric function, absorption coefficient and the reflectivity spectra are also computed and analyzed in different phases.
This article reports the electronic, optical and structural properties of XPN2 (X = H, Cu) chalcopyrite semiconductors by implying the density functional theory (DFT) with full potential linearized ...augmented plane wave plus local orbitals (APW+lo) method. The calculated electronic and structural parameters such as energy band gap, anion displacement, tetragonal ratio and lattice parameters have shown good agreement with the previous experimental and theoretical results. The optical properties are described by calculating the absorption coefficients, dielectric function along with real and imaginary part of the dielectric function. Voigt-Reuss-Hill approximations are used to calculate the set of macroscopic elastic moduli including average elastic wave velocity, Young, shear and bulk moduli, Debye temperature and Poisson's coefficient for chalcopyrite CuPN2 and HPN2. Finally, the semi-classical Bolzmann theory is applied with BolzTrap code to compute the transport properties such as thermal electrical conductivity, figure of merit and Seebeck coefficient for these materials.
Electronic band structure, optical and thermodynamic properties of ternary hydrides MBeH
3
(M = Li, Na, and K) were studied using ab initio density functional theory (DFT). The effect of the adopted ...approximation to the exchange-correlation functional of the DFT is explicitly investigated by considering four different expressions of two different classes (local-density approximation and generalized-gradient approximation). The calculated magnitude of B classifies MBeH
3
(M = Li, Na, and K) as easily compressible materials. The bonding interaction in these compounds is quite complicated. The interaction between M and BeH
6
is ionic and that between Be and H comprises both ionic and covalent characters. The electronic structure of the complex hydride was investigated by calculating the partial and total densities of states, and electron charge density distribution. Large gaps in the density of states appear at the Fermi energy of LiBeH
3
, NaBeH
3
, and KBeH
3
indicating that these classes of hydrides are insulators. Optical properties, including the dielectric function, reflectivity, and absorption coefficient, each as a function of photon energy, are calculated and show an optical anisotropy for LiBeH
3
and KBeH
3
. Through the quasi-harmonic Debye model, in which the phononic effects are considered, temperature dependence of volume V(T), bulk modulus B(T), and thermal expansion coefficient α(T), constant-volume and constant-pressure specific heat (C
v
and C
p
) and Debye temperature Θ
D
, the entropy S, and the Grüneisen parameter γ were calculated at wide pressure and temperature ranges. The principal aspect of the obtained results is the close similarity of MBeH
3
(M = Li, Na, and K) compounds.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•The total magnetic moment of all investigated compounds is obtained to be 2 µB.•The mechanical stability test performed on the computed elastic constants Cij demonstrate that investigated compounds ...are mechanically stable.•In the ultraviolet region, RhFeMnZ and IrMnCrZ (where Z = Si, Ge) are effective absorbers and have a high refractive index.•These materials could be useful for spintronic application.
High-spin-polarised materials are the most promising candidates for spintronic devices. Here, the spin-polarised electronic structure, magnetism, mechanical, and optical properties of RhFeMnZ and IrMnCrZ (where Z = Si, Ge) Quaternary Heusler alloys were calculated by first-principles calculations. The calculations show that type III for the RhFeMnSi, RhFeMnGe, and IrMnCrSi and type I for the IrMnCrGe compound configuration is the most stable crystal structure for the studied alloys. The four alloys were found to have a half-metallic ferromagnetic structure with indirect band gaps in the majority spin channels of 0.957, 0.66, 0.745, and 0.891 eV for RhFeMnSi, RhFeMnGe, IrMnCrSi, and IrMnCrGe, respectively. They exhibit an appreciable total magnetic moment of 4 μB for RhFeMnZ (Z = Si, Ge) and 2 μB for IrMnCrZ (Z = Si, Ge). The results show that RhFeMnZ and IrMnCrZ (where Z = Si, Ge) are ferromagnetic half-metals with 100 % spin polarisation. The results of the elastic constants demonstrate the mechanical stability of RhFeMnZ and IrMnCrZ (where Z = Si, Ge) alloys. Optical properties such as dielectric function, absorption, reflectance, optical conductivity, and other optical properties were also probed. In the ultraviolet region, RhFeMnZ and IrMnCrZ (where Z = Si, Ge) are effective absorbers and have a high refractive index. Alloys are promising candidates for potential applications in spintronic devices.
