Computed Lattice Constants Research Articles

First-Principles study of Ti-Based X2TiH5 (X = Mg, Ca, Sr) hydrides for Advanced hydrogen storage applications

The potential solution to the urgent issue of hydrogen storage in mobile applications is in the potential contribution of solid materials. Moreover, extensive study has been carried out on perovskite hydride materials to improve their efficiency in the field of hydrogen storage. The present work focuses on the computational investigation of X2TiH5 (X = Mg, Ca, and Sr) perovskite-type hydrides, taking into account diverse physical properties and their potential uses in hydrogen storage. The thermodynamic stability of X2TiH5 (X = Mg, Ca, and Sr) was assessed by analyzing their negative formation equilibrium. The compounds exhibiting tetragonal structures with Sr2TiH5 have the highest computed lattice constants, namely a = b = 5.69 Å and c = 7.91 Å. The electrical properties unequivocally indicate that the molecules being investigated have a metallic nature. Furthermore, the metallic hydrides provide promising possibilities as potential contenders for hydrogen storage applications. Furthermore, the optical properties of all the compounds were quantified. Finally, the calculated hydrogen storage capacities are 4.97 wt% for Mg2TiH5, 3.78 wt% for Ca2TiH5 and 2.21 wt% for Sr2TiH5. This study demonstrated X2TiH5 (X = Mg, Ca and Sr) have the potential for hydrogen storage, although Mg2TiH5 and Ca2TiH5 are the only compounds that meets the US-DOE criterion for 2020.

Newly synthesized Pb-based 312 MAX phases M3PbC2 (M = Zr and Hf): A First-principles study

The MAX phases' unique mixture of ceramic and metallic features makes them appealing for various technological uses. Zr3PbC2 and Hf3PbC2, two Pb-based MAX phases, were recently synthesized experimentally. The physical properties, such as structural properties as well as electronic, mechanical, hardness, thermal, and lastly, the optical properties of M3PbC2 (M = Zr and Hf) have been investigated using density functional theory (DFT) and analogized with those of other 312 MAX phases. The optimized cell volume and computed lattice constants match the experimental values. The calculated band structure certifies the metallic character, and DOS calculations confirmed the dominant contribution to conductivity from the Zr-4d and Hf-5d states. The stiffness constant (Cij) proved the mechanical stability of these compounds. The mechanical behavior of the studied compounds was explored by calculating the elastic moduli, hardness parameters, and fracture toughness, which are also compared to those of the 312 MAX phases. The tightly bound M–C covalent bonds within the crystal give these compounds high stiffness. The Mulliken population (both atomic and bond) was calculated to explore the bonding characteristics within them and the Vickers hardness of the titled phases. The degree of elastic anisotropy present within phases has been analyzed by calculating different indices. The phonon dispersion curves and phonon DOS (PHDOS) were computed to check the dynamical stability of the phases. Thermodynamic potential functions were calculated from the PHDOS. The thermal parameters were also studied, including the Debye temperature, melting temperature, Grüneisen parameter, and minimum thermal conductivity (Kmin). A thorough computation and analysis of the vital optical constants was done to explore their potential in diverse fields. The titled compounds are suitable for use as thermal barrier coating (TBC) materials and coating materials to prevent solar heating.

Comprehensive theoretical investigation of NaAlX (X=C, Si and Ge) half-Heusler compounds: Unveiling the multifaceted properties for advanced applications

In this work, we have extensively investigated the characteristics of ternary half-Heusler (HH) materials, specifically NaAlX (X[Formula: see text][Formula: see text][Formula: see text]C, Si and Ge), employing ab-initio computations in density functional theory (DFT) framework. Various aspects, including stability parameters, electronic, optical and thermoelectric (TE) parameters have been examined. The computed lattice constants of NaAlX (X[Formula: see text][Formula: see text][Formula: see text]C, Si and Ge) were found to be, respectively, 5.398, 6.301 and 6.389[Formula: see text]Å which are in excellent agreement with the previously available data. The electronic band structures showed that the studied materials exhibit semiconducting behavior with a corresponding band gap of 1.961, 0.999 and 0.846[Formula: see text]eV, respectively. Specifically, NaAlC and NaAlGe compounds were found to have a direct energy band gap at the [Formula: see text]-point, while NaAlSi displayed an indirect band gap at the [Formula: see text]–X point. Elastic and thermodynamic parameters were examined, confirming that the titled compounds possess mechanical, dynamic and thermal stability. Additionally, the optical response of the materials has been analyzed within an energy range of 0–13[Formula: see text]eV. The TE parameters exhibited maximum ZT values of 0.998, 0.992 and 0.990 for NaAlX (X[Formula: see text][Formula: see text][Formula: see text]C, Si and Ge) materials, respectively, at 300[Formula: see text]K, suggesting promising TE performance at room temperature.

The first principles insights of aluminum-based hydrides for hydrogen storage application

Hydrogen storage is an urgent issue for mobile applications, to overcome this issue solid materials have a potential role for hydrogen storage applications. Moreover, the perovskite hydride materials have been extensively investigated for improvement in the field of hydrogen storage. However, this work is focused on the computational study of XAlH3 (X: Na, Mg) perovskite-type hydrides for different physical properties and hydrogen storage applications. Both materials were found thermodynamically, and mechanically stable from the negative formation energy and elastic properties. They exhibited cubic phases with computed lattice constants are 3.827 Å and 3.752 Å, respectively. The electronic properties indicated that both compounds have a metallic nature, and found the high contribution of Al-p state, and H-1s state near the Fermi level. However, the Hirshfeld net charge analysis detected, that charge transfer from Al and X (Na, Mg) atoms to H atoms. Furthermore, the metallic hydrides have promised candidates for hydrogen storage applications. Both compounds have observed non-magnetic behavior with zero magnetic moments. Elastic constants were calculated to determine the mechanical stability of the compounds, it was found that MgAlH3 is harder than NaAlH3, and it exhibited that higher Bulk, Shear, and Young's modulus. The Poisson's, and Pugh's (G/B) ratios suggested that ionic boning of the atoms, additionally, Pugh's ratio (B/G) and Cauchy pressure (Cp) confirmed that NaAlH3 ductile and MgAlH3 is brittle behavior. Besides this, Optical properties were determined for both compounds including the dielectric function, conductivity, refractive index, absorption, and loss function. It is found that the MgAlH3 compound optical more suitable than NaAlH3 due to calculated optical factors promised and both compounds are undertaken for solar cells, optoelectronics, and energy storage applications. Finally, the computed hydrogen storage capacity for NaAlH3 and MgAlH3 compounds are 6.01 wt%, and 5.56 wt% respectively. These results revealed that both have the potential materials for hydrogen storage, but NaAlH3 unique material to fulfill the US-DOE criteria of 2020.

An Examination of the Vibrational, Mechanical, Thermoelectric Features and Stability of Novel Half‐Heusler XVIn (X = Pd, Pt) by Density Functional Theory Computation

Modern manufacturing is primarily focused on providing things that are accessible, environmentally conscious, and energy efficient. An effort has been made herein to investigate the compounds that meet these requirements. The full‐potential linearized augmented plane wave method, in Wien2k code, is used to examine the structural, vibrational, mechanical, and transport properties of XVIn (X = Pd, Pt) half‐Heusler compounds. The generalized gradient approximation is used for structural optimization. The computed lattice constants are consistent with earlier theoretical and experimental results. The XVIn (X = Pd, Pt) investigation reveals that the material is inherently ductile and mechanically stable. It is found that XVIn (X = Pd, Pt) has a direct bandgap and a semiconducting property. The modified Becke–Johnson exchange approximation yields bandgap magnitudes of 0.25 and 0.55 eV for PdVIn and PtVIn, respectively. The Boltzmann transport offered by the BoltzTrap software is used to explore thermoelectric characteristics. The values of figure of merit (ZT) obtained for XVIn (X = Pd, Pt) compounds are very close to unity in the chemical potential range from −0.15 to 0.15 eV, indicating that they can be used to make thermoelectric devices with the maximum possible efficiency.

Investigation of high-pressure effect on the physical properties of FrNBr3 (N[dbnd]Ca, Sr) non-toxic halide perovskites

Utilizing ab-initio modeling, this study analyzes the possibility of replacing Lead with Francium halide perovskite for use in potential photovoltaic or optoelectronic device applications. Density functional theory is employed to estimate the structural, electronic, bonding, optical, anisotropic elastic, and mechanical characteristics of FrNBr3 (NCa, Sr) at various hydrostatic stresses scaling from 0 to 80 GPa. The calculation of the tolerance factor validates the structural stability. At 0 GPa pressure, the computed lattice constants for FrCaBr3 and FrSrBr3 are 5.78 Å (5.38 Å) and 6.03 Å (5.62 Å), respectively, using GGA (HSE03) approximation potential. FrNBr3 (NCa, Sr) perovskites show increased band gap values using the HSE03 method. Notably, these HSE03-derived values align with the trends observed in the GGA-PBE scheme, under both normal and hydrostatic pressure conditions. As pressure increases, both the lattice constant and unit cell volume decrease significantly. The estimated direct band gaps demonstrate the semiconducting nature of the compounds under ambient pressure. However, when pressure increases, the band gap narrows, increasing conductivity, and makes it as one of the great contenders of microelectronics as well as tandem photovoltaics due to its shift from ultraviolet to visible light energy region. Applying pressure enhances the optical properties, showcasing its utility in various semiconductor applications within the visible ranges and overcoming its limited usage in the ultraviolet domain. In the same vein, the application of hydrostatic pressure significantly impacts mechanical properties without compromising stability. The ductile and anisotropy character become more pronounced when pressure is exerted.

Atomic Insights into the Structural Properties and Displacement Cascades in Ytterbium Titanate Pyrochlore (Yb2Ti2O7) and High-Entropy Pyrochlores

Pyrochlore oxides (A2B2O7) are potential nuclear waste substrate materials due to their superior radiation resistance properties. We performed molecular dynamics simulations to study the structural properties and displacement cascades in ytterbium titanate pyrochlore (Yb2Ti2O7) and high-entropy alloys (HEPy), e.g., YbYTiZrO7, YbGdTiZrO7, and Yb0.5Y0.5Eu0.5Gd0.5TiZrO7. We computed lattice constants (LC) (ao) and threshold displacement energy (Ed). Furthermore, the calculation for ao and ionic radius (rionic) were performed by substituting a combination of cations at the A and B sites of the original pyrochlore structure. Our simulation results have demonstrated that the lattice constant is proportional to the ionic radius, i.e., ao α rionic. Moreover, the effect of displacement cascades of recoils of energies 1 keV, 2 keV, 5 keV, and 10 keV in different crystallographic directions ([100], [110], [111]) was studied. The number of defects is found to be proportional to the energy of incident primary knock-on atoms (PKA). Additionally, the Ed of pyrochlore exhibits anisotropy. We also observed that HEPy has a larger Ed as compared with Yb2Ti2O7. This establishes that Yb2Ti2O7 has characteristics of lower radiation damage resistance than HEPy. Our displacement cascade simulation result proposes that HEPy alloys have more tendency for trapping defects. This work will provide atomic insights into developing substrate materials for nuclear waste applications.

First principles studies on optoelectronics and transport properties of KSrY (Y = Sb, Bi) for renewable energy application

Currently, producing equipment and goods of all kinds that are economical, energy-efficient, and ecologically friendly is the main objective. In this study, an attempt has been made to look into these materials that meet these requirements. The structural, elastic, optoelectronic and transport characteristics of KSrY (Y = Sb,Bi) Half-Heusler were studied employing Full-potential, linearized augmented plane wave programs (FP_LAPW) approach as embedded in WIEN2K. The structural optimization was performed employing generalized gradient approximation (GGA). The computed lattice constants were reasonable in compliance with previous theoretical and experimental findings. The investigated KSrY (Y = Sb,Bi) were mechanically stable and brittle by nature. The KSrY (Y = Sb,Bi) compounds are discovered to have semiconducting nature with direct bandgap. The magnitudes of the bandgap for the KSrBi and KSrSb are 1.749 eV and 2.457 eV, respectively, using the mBJ approximation. The investigated materials on the basis of calculated band gap and optical spectra demonstrate the ability of the compounds to absorb both visible and UV light, henceforth application in optoelectronic devices. The Boltzmann transport theory included in the BoltzTraP package was used to study thermoelectric characteristics. The obtained figures of merit (ZT) values for the KSrY (Y = Bi, Sb) compounds are all close to unity at room temperature, suggesting optimum thermoelectric efficiency can be employed in thermoelectric devices.

Investigations of physical properties of lithium-based chalcopyrite semiconductors: non-toxic materials for photovoltaic applications

The ab-initio calculations have been executed for structural, electronic and optical properties of LiAlTe2, LiGaTe2 and LiInTe2 chalcopyrite structured solids and these calculations are grounded on the principle of density functional theory employed into the full potential augmented plane wave method. The computed lattice constants oscillating from a = 6.257 Å to 6.450 Å and c = 12.044 Å to 12.256 Å for LiXTe2 (X=Al, Ga and In) and also these values consistent with experimentally existed lattice constants. From the study of electronic band-gap, it confirms that these compounds are good semiconductors with direct band-gaps from 2.22 eV, 1.48 eV and 1.61 eV for LiXTe2 (X=Al, Ga and In). The result of optical properties confirms that these chalcopyrite semiconductors can be the fortunate compounds for the photovoltaic applications.

First-principles calculations to investigate structural, elastic, electronic and thermodynamic properties of NbCoSn and VRhSn Half-Heusler compounds

In this study, we investigated the structural, elastic, electronic, and thermodynamic properties of NbCoSn and VRhSn HH compounds using the first-principles calculations as implemented in the density functional theory (DFT). The computed lattice constants of NbCoSn and VRhSn compounds were found to be consistent with the available theoretical as well as the experimental data. The compounds are mechanically stable since their elastic constants satisfy the Born-Huang criteria for cubic system stability. Due to the absence of imaginary phonons, NbCoSn is dynamically stable, whereas VRhSn is unstable. NbCoSn is harder than VRhSn HH because it has a higher Vicker’s hardness and shear modulus. Both compounds feature band gaps, indicating that they are semiconductors. When compared to NbCoSn HH compound, VRhSn has a narrow band gap. Furthermore, thermodynamic properties are computed and thoroughly explored. As a result of the findings, NbCoSn and VRhSn HH compounds are viable thermoelectric materials; however, doping and alloying could be employed to enhance the stability of VRhSn HH compound.

Unveiling the fundamental physical properties of Cu2-xNaxZnSnX4 (X = S, Se) alloys for solar cell applications: a theoretical investigation

Quaternary chalcogenide compounds Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) are the promising absorber materials for solar cell applications. The impact of Na as an isovalent dopant for Cu on the structure, thermodynamic stability, mechanical, electronic, and optical properties of CZTS and CZTSe is examined for the first time. The computed lattice constants of Cu2-xNaxZnSnS4 (CNZTS) and Cu2-xNaxZnSnSe4 (CNZTSe) (x = 0, 0.5, 1, 1.5, and 2) are increased and decreased as a function of x for a and c, respectively. The stability of CNZTS and CNZTSe is ensured by their negative formation energies. The results show that all alloys are mechanically stable and ductile materials. The band gaps of CZTS and CZTSe are greatly broadened when Cu is replaced by Na. The tunable band gaps of CNZTS and CNZTSe are in the range of 1.19–3.08 eV and 0.65–2.30 eV, respectively. It is found that two novel compounds have suitable band gap values for solar cell applications, such as Cu1.5Na0.5ZnSnS4 (1.47 eV) and CuNaZnSnSe4 (1.43 eV). In addition, Cu1.5Na0.5ZnSnS4 and CuNaZnSnSe4 show good carrier mobility. The analysis of optical properties displays that CuNaZnSnSe4 exhibits a stronger absorption coefficient than those of CZTS and Cu1.5Na0.5ZnSnS4 at 300–500 nm. Combined with the band gap and light absorption, CuNaZnSnSe4 is the most promising material for solar cell applications.

Structure and electronic properties of LnScO3 compounds: A GGA + U calculation

The lattice parameters, bond lengths, bond angles (octahedra tilt angles), Goldschmidt tolerance factor, density of states and electronic band structure of rare-earth scandates LnScO3 (Ln = Eu, La, Nd, Pr, Sm and Tb) in orthorhombic structure have been investigated in the generalized gradient approximation (GGA) + U method with the on-site Coulomb interaction parameter Ueff varying from 1 to 10 eV. The lattice constants, octahedra tilt angles (except for (Eu,Tb)ScO3 compounds), mean 〈Sc-O〉 and 〈Ln-O〉 bond lengths increased almost linearly with effective U parameter values. However, the tolerance factor has decreased (except for (Eu,Tb)ScO3 compounds). Density of states and electronic band structure computations show that LnScO3 compounds are insulator materials and have direct electronic band gap. The electronic band gap of the compounds first increases and then decreases with increasing Ueff. (GGA) + U calculation shows a strong hybridization between Sc-3d and O-2p states. Rare-earth (Ln)-5d states contribute somewhat to this hybridization. The electronic charge distribution and (P)DOS calculation results show that the bonding behavior of LnScO3 compound is a combination of covalent and ionic nature. Our results show that the structural and electronic properties are affected by the application of the Hubbard U term in GGA calculations and the computed lattice constants, bond distances and octahedra tilt angles deviate more from the experimental values. On the other hand, it was observed that the electronic band gap approached the experimental values at the optimal Ueff values determined for the compounds.

Ab-initio study of lead-free double Perovskites Cs2AgZBr6 (Z = Bi, Sb) for Solar cells and other renewable energy applications

Ab-initio computations are performed to analyze the Lead-free double perovskites Cs2AgZBr6 (Z ​= ​Bi, Sb)for solar cells and renewable energy. Modified Becke and Johnson potential (TB-mBJ) has been adopted to compute the electronic and optical properties. The computed lattice constants are found in good agreement with the reported experimental data. Band gaps calculations for Cs2AgBiBr6 and Cs2AgSbBr6 reveal their indirect nature and are quantified 2.0 ​eV and 1.39 ​eV which make them potential candidates for visible light solar cells. The optical spectra have been elaborated in terms of dielectric constants, absorption of light, refractive index, and reflection of light. The maximum absorption bands are recorded in the wavelength range of 620 ​nm–310 ​nm. Finally, thermoelectric properties are calculated by BoltzTraP code, which depicts high values of Seebeck coefficient and low thermal conductivity. Thus, performed theoretical calculations suggest the studied materials for potential application in renewable energy field.

Theoretical study of mixed-halide influence on the stability and electronic properties of CsCd(Cl/Br)3

First-principles calculations have been performed to investigate the structural stability, electronic and optical properties of CsCdCl3-xBrx (x = 0, 1, 2, 3) halide perovskites for the first time. The computed lattice constants of these compounds are consistent with the previous theoretical and experimental data. Based on the calculations of formation energies, we find that CsCdCl3 and CsCdCl2Br are highly stable, while CsCdClBr2 and CsCdBr3 are marginally stable. These compounds are dynamically and mechanical stable. All the compounds are indirect band gap semiconductors, and they exhibit large band gaps, which are not suitable for solar cells.

Newly Synthesized Ta‐Based MAX Phase (Ta1−xHfx)4AlC3 and (Ta1−xHfx)4Al0.5Sn0.5C3 (0 ≤ x ≤ 0.25) Solid Solutions: Unravelling the Mechanical, Electronic, and Thermodynamic Properties

Investigation of the mechanical, electronic, and thermodynamic properties of recently synthesized (Ta1−xHfx)4AlC3 and (Ta1−xHfx)4Al0.5Sn0.5C3 (0 ≤ x ≤ 0.25) solid solutions is conducted using density functional theory for the first time. The computed lattice constants are in good agreement with prior results. The calculated stiffness constants are used to check the mechanical stability of the studied compositions. The bulk modulus (B), shear modulus (G), and Young's modulus (Y) are found to be influenced by Hf and Sn substitution. The titled solid solutions are brittle in nature. The 3D presentations of elastic moduli and elastic anisotropy factors are used to disclose the anisotropic mechanical features of the considered compositions. The electronic band structure, density of states, and charge density mapping (CDM) show the metallic nature, the contribution from different states to electronic conductivity, and atomic bonding characteristics. The electronic band structure and CDM are also used together to investigate the change in bonding strength due to Hf and Sn substitutions. The Debye temperature (ΘD), minimum thermal conductivity (Kmin), Grüneisen parameter (γ), and melting temperature (Tm) of the studied solid solutions are estimated and analyzed. A good correlation is found between the mechanical and thermodynamic properties.

Theoretical Prediction of the Structural, Elastic, Electronic and Thermodynamic Properties of Binary CoP3 and Ternary FeCoP3 Skutterudites Materials

The structural, elastic, electronic and thermodynamic properties of skutterudite binary compound CoP3 and the ternary alloy FeCoP3 were investigated by using the full-potential linearized augmented plane-wave plus local orbitals method within the approximation GGA-PBEsol functional. The computed lattice constants, bulk moduli and the pressure derivative of the bulk moduli at the equilibrium are in good agreement with the published experimental data. The brittleness and ductility of these materials were studied by the analysis of the elastic constants and other mechanical parameters, where we have found that both CoP3 and FeCoP3 are ductile materials. The electronic band structure calculation, using the modified Becke-Johnson potential (TB-mBJ), shows that the skutterudite binary compound CoP3 at equilibrium, present a narrow indirect bandgap of 0.524[Formula: see text]eV where the ternary alloy FeCoP3 is a metal behavior. Finally, we investigated the impact of pressure [Formula: see text] and temperature [Formula: see text] on the lattice parameters, heat capacities [Formula: see text], Debye temperatures [Formula: see text] and the entropies [Formula: see text] using the quasi-harmonic Debye model.

First-Principles Study on PdMnSn and PtMnSn Compounds in C1b Structure

The phase stability, the electronic, mechanic and lattice dynamical properties of C1b-type PdMnSn and PtMnSn compounds were investigated using first principles density functional calculations within the generalized gradient approximation. The computed lattice constants of PdMnSn and PtMnSn compounds were in line with the experimental and theoretical data in the published literature. The elastic constants in the C1b structure for PdMnSn and PtMnSn compounds were carried out using the energy-strain method. The computed values of three independent elastic constants, both compounds are mechanically stable in the C1-type crystal structure and met the stability criteria. The electronic structure, total and partial density values of states, and total magnetic moment of these compounds were calculated and the evaluations were carried out by comparing with the existing results. Dynamic properties of PdMnSn and PtMnSn compounds were obtained using the density functional perturbation theory. Both of the compounds were dynamically stable due to the absence of the imaginary phonon frequencies. In addition, it was found that the compounds had a rapid rise in specific heat capacities from 0 to 300 K.

Structural, elastic, electronic and transport properties of CoVX (X = Ge and Si) compounds: A DFT prediction

This paper concerns a predictive investigation of the structural and elastic stability, electronic structure, and thermoelectric properties of CoVX (Ge and Si) Half-Heusler materials. The structural constants and mechanical stability are computed utilizing the (GGA-PBE) approximation. The computed lattice constants of CoVX (Ge and Si) compounds are in good accordance with other theoretical reports. Furthermore, the mechanical parameters and the related elastic constants reveal that CoVX (Ge and Si) alloys are mechanically stable and ductile. To ameliorate the computation of the energy band gap, the (TB-mBJ) method was employed. It is shown that the CoVX (Ge and Si) compounds are an indirect band-gap semiconductors. At room temperature, the computed figure of merit of CoVGe and CoVSi compounds is about unity, which denote that the CoVGe and CoVSi compounds have good thermoelectric performance and can be applied for the production of electricity in the transport devices.

DFT investigations into the physical properties of a MAB phase Cr4AlB4

In this work, we have investigated the structural, mechanical, electronic, thermal, vibrational, and optical properties of a new MAB phase Cr4AlB4 for the first time within the framework of density functional theory (DFT) and compared with other MAB phases, Cr2AlB2 and Cr4AlB6. The computed lattice constants are in excellent agreement with the available experimental as well as theoretical values. The new compound is found to be mechanically and dynamically stable as evident from the calculated elastic properties and phonon dispersion spectra. From the theoretical analysis of Pugh’s ratio, Poisson’s ratio, and Cauchy pressure, all the MAB compounds studied here are brittle in nature. The calculated hardness of the studied MAB compounds shows good agreement with the available measured values for other MAB phases. The synthesized Cr4AlB4 is expected to be a material of high potentials for use in hypersonic vehicles, scramjet engines, and thermal management electronics as it possesses high bulk modulus, high stiffness constants, high Debye temperature, as well as high thermal conductivity. The calculated electronic band structures reveal the metallic characteristics of the studied MAB phases. The electron density of states suggests that the chemical bonding is a mixture of covalent, metallic and polar covalent in nature. The optical reflectivity suggests that the studied MAB compounds are promising materials for protection against solar heating. Temperature and pressure dependent thermal properties are investigated through quasi-harmonic Debye model for the first time. The present results might be complementary data for future experimental and theoretical works.

Structural, elastic and optoelectronic properties of Sr-based perovskite-type oxides SrXO3 (M = Th, Zr) via first-principles calculations

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