DFT study of the half-metallic variant perovskites A2OsX6 (A = Rb/Cs; X = Cl/Br) for spintronic and thermoelectric applications

We present our results of the spin-polarized calculations on the structural, magneto-electronic, thermodynamic, and thermoelectric properties of vacancy-ordered double perovskites A₂OsX₆ (A = Rb/Cs; X = Cl/Br). We utilized the Wu-Cohen generalized gradient approximation (Wu-GGA) and the mBJ scheme to determine a more reliable electronic structure. The compounds exhibit negative formation energy, suitable tolerance factor, and a stable phonon spectrum, indicating their stability. The compounds show half-metallicity, acting as semiconductors with direct band gaps between 2 and 3 eV in the spin-up orientation while metallic in the spin-down. Each compound shows a total spin magnetic moment of 2.00 μB per formula unit, with Os-t²g states contributing the most (~1.5 μB). The computed thermoelectric coefficient indicates the usability of these compounds across a wide temperature range (200–800 K) with high electrical conductivity and low electronic thermal conductivity. The compounds exhibit high Seebeck coefficient and figure of merit (ZT), making them suitable for thermoelectric applications. With ferromagnetic and half-metallic characteristics, these compounds could be promising candidates for spintronics, thermoelectronic, and data storage applications.     

An ab-initio study of structural,opto-electronic and thermoelectric aspects of zinc sulfide and zinc telluride

In this study, structural, electronic, optical and thermoelectric aspects of Zinc Sulfide (ZnS) and Zinc Telluride (ZnTe) have been explored in detail. These calculations have been done by utilizing FP-LAPW method via Density Functional Theory (DFT). In order to attain accurate band gaps, opto-electronic properties are evaluated with modified Becke Johnson potential (mBJ). From band structure plots, both ZnS and ZnTe reveals direct (Γ_v–Γ_C) band gap semiconductors in nature with bandgap value equal to 3.5 and 2.3 eV while in Density Of States (DOS) major influence is observed due to p states of S/Te and d state of Zn. Prominent variation of optical responses such as high values of imaginary dielectric constants 𝜀1 (ω) and n (ω) refractive index suggests that ZnS and ZnTe are applicant materials for future photonics and microelectronic devices. The thermoelectric aspects were explored by Boltz Trap code to determine electrical and thermal conductivities, Seebeck coefficients, power factors and figure of merit. The figure of merits is closer to 1 while compared with p-type ZnS and ZnTe, n-type ZnS and ZnTe has good thermoelectric properties, which are attributed to low thermal conductivity of the hole and larger effective mass. The goal of this research is to investigate not only the detailed physical aspects but also to provide an overview of its future applications in optoelectronics, displays, sensors and microelectronic industry.     

A theoretical study of the structural,thermoelectric, and spin-orbit coupling influenced optoelectronic properties of CsTmCl3 halide perovskite

This first principles study explores the structural, electronic, optical, and thermoelectric properties of the CsTmCl₃ halide perovskite using density functional theory. The structural and thermoelectric properties are calculated without considering the spin-orbit coupling (SOC), while both the electronic and optical properties are calculated with and without the SOC effect. A comparison of the results obtained with and without SOC reveals that inclusion of the SOC effect reduces the band gap from 1.18 to 0.99 eV due to shifting of the Tm-d states toward the Fermi level. However, direct nature of the band gap remains the same in both the cases. The effect of SOC on the optical properties is, however, only visible in shifting of the third characteristic peak to lower energies. Strong optical absorption in the visible and ultraviolet regions shows effectiveness of CsTmCl₃ in the optical devices working in these regions. Moreover, the calculated transport properties reveal CsTmCl₃ as a useful thermoelectric material at room temperature.     

Elucidating linear and nonlinear optical properties of defect chalcopyrite compounds ZnX2Te4 (X=Al,Ga, In) from electronic transitions

We presented a theoretical study of electronic band structure of three compounds ZnAl₂Te₄, ZnGa₂Te₄ and ZnIn₂Te₄ using pseudo potential method within density functional theory. Calculated band structures show that all band gaps are direct with at Γ with values of 1.639eV for ZnAl₂Te₄, 1.026eV for ZnGa₂Te₄and 0.836eV ZnIn₂Te₄. The linear properties based on dielectric function and non-linear optical properties based on second harmonic generation (SHG) were computed. The origin of four critical points (peaks) determined from the second derivative of the imaginary part of the dielectric function is elucidated. The use of individual k-points and individual combination of valence and conduction bands dependent matrix of the dielectric function and the nonlinear optical susceptibility allowed to a precise determination of inter band optical transitions. Indeed, inter-band analysis shows the high intensity of non-linear effect compared to linear effect. Moreover, non-linear inter-band optical transitions involve lower valence bands and higher conduction bands.     

Theoretical investigation of the structural,elastic, electronic and optical properties of the ternary indium sulfide layered structures AInS2 (A = K,Rb and Cs)

Ab initio calculations were performed to investigate the structural, elastic, electronic and optical properties of the ternary layered systems AInS₂ (A = K, Rb and Cs). The calculated structural parameters are in good agreement with the existing experimental data. Analysis of the electronic band structure shows that the three studied materials are direct band-gap semiconductors. Density of states, charge transfers and charge density distribution maps were computed and analyzed. Numerical estimations of the elastic moduli and their related properties for single-crystal and polycrystalline aggregates were predicted. The optical properties were calculated for incident radiation polarized along the [100], [010] and [001] crystallographic directions. The studied materials exhibit a noticeable anisotropic behaviour in the elastic and optical properties, which is expected due to the symmetry and the layered nature of these compounds.     

Electrical transport properties of an organic semiconductor on polyaniline doped by boric acid

The electrical conductivity, thermoelectric power, and dielectric properties of polyaniline doped by boric acid (PANI‐B) have been investigated. The room temperature electrical conductivity of PANI‐B was found to be 1.02 × 10^?4 S cm^?1. The thermoelectric power factor for the polymer was found to be 0.64 µW m^?1 K^?2. The optical band gap of the PANI‐B was determined by optical absorption method, and the PANI‐B has a direct optical band gap of 3.71 eV. The alternating charge transport mechanism of the polymer is based on the correlated barrier hopping (CBH) model. The imaginary part of the dielectric modulus for the PANI‐B suggests a temperature dependent dielectric relaxation mechanism. Electrical conductivity and thermoelectric power results indicate that the PANI‐B is an organic semiconductor with thermally activated conduction mechanism. Copyright © 2008 John Wiley & Sons, Ltd.     

First-principle investigation of XSrH3 (X = K and Rb) perovskite-type hydrides for hydrogen storage

Hydrogen can be utilized as an energy source; therefore, hydrogen storage has received the most appealing examination interest in recent years. The investigations of hydrogen storage applications center fundamentally around the examination of hydrogen capacity abilities of recently presented compounds. XSrH₃ (X = K and Rb) compounds have been examined by density functional theory (DFT) calculations to uncover their different characteristics, as well as hydrogen capacity properties, for the first time. Studied compounds are optimized in the cubic phase, and optimized lattice constants are obtained as 4.77 and 4.99 Å for KSrH₃ and RbSrH₃, respectively. These hydrides have shown negative values of formation enthalpies as they are stable thermodynamically. XSrH₃ might be used in hydrogen storage applications because of high gravimetric hydrogen storage densities, which are 2.33 and 1.71 wt% for KSrH₃ and RbSrH₃, respectively. Moreover, electronic properties confirm the semiconductor nature of these compounds having indirect band gaps of values 1.41 and 1.23 eV for KSrH₃ and RbSrH₃, respectively. In addition, mechanical properties from elastic constants such as Young modulus and Pugh's ratio, also have been investigated, and these compounds were found to satisfy born stability conditions. Furthermore, Pugh's ratio and Cauchy pressure show that these hydrides have a brittle nature. Furthermore, thermodynamic properties such as entropy and Debye temperature have been examined using the quasiharmonic Debye model for different temperatures and pressures.     

First-principles calculations to investigate structural,electronic, optical,and transport properties of half-Heusler VFeZ (Z = N and P) compounds

This research work investigates the structural, electronic, optical, and thermoelectric characteristics of VFeZ (Z = N and P) half-Heusler compounds. The study employs the full-potential linearized augmented plane wave (FP-LAPW) method integrated into the WIEN2K algorithm, serving as the underpinning framework for density functional theory (DFT) analysis. In the study, we use the PBE generalized gradient approximation (PBE-GGA) to identify numerous parameters associated with structural and elastic properties. Lattice parameter results are in agreement with previous outcomes. Moreover, computed elastic parameters satisfy the criterion for stability. In the cubic structure VFeZ (Z = N and P) is ductile, to enhance the computations of electronic characteristics, Tran and Blaha's modified Becke-Johnson potential (TB-mBJ) is used. Our simulations demonstrate that the materials exhibit semiconductor behavior, with a direct band gap for VFeZ (Z = N and P). Strong UV absorption is found via optical experiments suggest compounds are suitable for optical application. Furthermore, study of the thermoelectric properties suggests its application in the thermoelectric generators.     

Theoretical study of the structure and fundamental properties of AZn2N2 (A = Ca,Sr, Ba)

The structure, stability, elastic, electronic, and optical properties of trigonal AZn₂N₂ (A = Ca, Sr, Ba) are simulated and compared in this work. The stability and physical properties of BaZn₂N₂ are mainly highlighted. According to the calculated results, three compounds are thermodynamically and mechanically stable, and they are brittle materials. The stability of trigonal BaZn₂N₂ is confirmed by using the different theoretical approaches. The direct band gap transition is allowed at the Γ point for each compound. The predicted direct band gaps are 1.733, 1.507, and 1.510 eV for CaZn₂N₂, SrZn₂N₂, and BaZn₂N₂, respectively. The valence band is mostly composed of the N-2p orbitals, while the conduction band is mainly contributed from the Ca-3d/Sr-4d/Ba-5d orbitals. The results show that the electron shows high mobility for carrier transport, and the value of exciton binding energy is less than 80 meV. Furthermore, compared to CaZn₂N₂ and SrZn₂N₂, BaZn₂N₂ shows excellent light absorption capacity in the visible region. This study indicates that BaZn₂N₂ is a desirable material for solar cell applications.     

Full potential study of the elastic, electronic, and optical properties of spinels MgIn2S4 and CdIn2S4 under pressure effect

The structural, elastic, electronic, and optical properties of cubic spinel MgIn₂S₄ and CdIn₂S₄ compounds have been calculated using a full relativistic version of the full-potential linearized-augmented plane wave with the mixed basis FP/APW+lo method. The exchange and correlation potential is treated by the generalized-gradient approximation (GGA). Moreover, the Engel-Vosko GGA formalism is also applied to optimize the corresponding potential for band structure calculations. The ground state properties, including the lattice constants, the internal parameter, the bulk modulus, and the pressure derivative of the bulk modulus are in reasonable agreement with the available data. Using the total energy-strain technique, we have determined the full set of first-order elastic constants C_ij and their pressure dependence, which have not been calculated or measured yet. The shear modulus, Young’s modulus, and Poisson’s ratio are calculated for polycrystalline XIn₂S₄ aggregates. The Debye temperature is estimated from the average sound velocity. Electronic band structures show a direct band gap (Г-Г) for MgIn₂S₄ and an indirect band gap (K-Г) for CdIn₂S₄. The calculated band gaps with EVGGA show a significant improvement over the GGA. The optical constants, including the dielectric function ε(ω), the refractive index n(ω), the reflectivity R(ω), and the energy loss function L(ω) were calculated for radiation up to 30 eV.     

Effect of variation of metal and non-metal elements on various properties of rare-earth-based inverse perovskites Gd3XY (X = Ga,In and Y = B,N)

Ferromagnetic rare-earth-based inverse perovskites Gd₃AlX (X = B, N) are studied using hybrid functionals in the framework of density functional theory. Different exchange correlation potentials are employed to analyze the structural parameters and geometry of the materials. The spin polarization and band structure explain the metallic behavior of these materials with high values of magnetic moment. The calculated elastic constants specify all materials are ordered perovskite compounds, among which Gd₃GaB, Gd₃GaN, Gd₃InN are brittle in nature while as Gd₃InB is ductile in nature. The quasi-harmonic Debye model was used to predict the thermodynamic properties of the material. The analysis of thermoelectric properties viz. Seebeck coefficient, electronic and thermal conductivities at higher temperature has been carried out. To check the optoelectronic response of the material various optical properties have been calculated up to 14 eV photon energy range. The competent thermoelectric and optoelectronic properties with high value of magnetic moment and ductile character suggests the application in thermoelectric and electro-optic devices.     

Bandgap engineering and optoelectronic properties of all-inorganic lead-free Pd-based double perovskites

The various physical properties of lead-free double perovskites A₂PdX₆ (A = K, Rb, Cs; X  = Cl, Br, I) are revealed for the first time. The calculated structural parameters of these Pd-based compounds are consistent with the experimental data. It is likely to possess a tetragonal structure for K₂PdI₆ at room temperature. Cs₂PdBr₆ is dynamically stable when the pressure is in the range of 0–6.95 GPa. The mechanical properties are analysed and all the compounds are mechanically stable. The band gap trend of the A₂PdX₆ compound is identified when the A-site cation and halide anion are varied. Three A₂PdBr₆ compounds exhibit suitable band gaps for photovoltaic applications. An optimum band gap can be achieved for Cs₂PdBr₆ when the moderate pressure is applied. In addition, the electron shows better mobility than that of the hole for three A₂PdBr₆ compounds. The optical absorption coefficient of the A₂PdBr₆ compound is improved when the A-site cation changes from Cs to Rb to K. Applying pressure is beneficial to enhance light absorption capacity of Cs₂PdBr₆. The findings of this work can provide guidance for the design of potential A₂PdBr₆ compounds for photovoltaic applications.     

Semiconductor nanocrystals possessing broadly size‐ and facet‐dependent optical properties

Cu₂O cubes, octahedra, and rhombic dodecahedra have been shown to exhibit continuous light absorption and emission band shifts with increasing particle sizes from 10 nm to sub‐microcrystals. They also possess clear facet‐dependent optical properties. Ag₃PO₄, Ag₂O, SrTiO₃, and CeO₂ crystals show similar optical size and facet effects. Thus, spectral shifts over a broad size range far beyond the quantum‐size regime should be generally observable in many semiconductor materials. Facet‐dependent optical properties of a semiconductor can be understood to arise from the presence of an ultrathin surface layer with subtle bond and orbital level variations for different crystal faces. Although these optical features seem unexpected, they should be the general behaviors of semiconductor crystals. As more examples of these optical effects are available, we will find that these intrinsic properties of semiconductors have been ignored in the past. Furthermore, if valence and conduction band positions are broadly tunable by particle size, the knowledge should have tremendous impacts on the applications of semiconductors, where band energies are important to efficient interfacial charge transfer.     

A comparative study of physical and thermoelectrical characteristics of the new full-Heusler alloys Ag2TiGa and Ag2VGa with ab initio calculations

This paper will focus on the comparative study of the structural, electronic, magnetic, optical, and thermoelectric properties of the two Heusler systems Ag₂TiGa and Ag₂VGa in the inverse L2₁ Hg₂CuTi structure. Using the density functional theory-based wien2k code, which implements the computational methods used in this study, namely GGA, GGA-mBJ, GGA + U, and GGA + SOC (spin-orbit coupling). The band structures show that all two structures studied are metallic. The spin density of states of Ag₂VGa has evident spin splitting near the Fermi level , and the total magnetic moment of the Ag₂VGa structure is 2.19 μ_B, which indicates that Ag₂VGa is magnetic. The full-Heusler Ag₂VGa material can be used as spintronic materials due to their high spin polarization (about 50%). While Ag₂TiGa has low polarization so it is bad electronically, but better thermoelectrically than Ag₂VGa. So, the full-Heusler Ag₂TiGa material may also be considered as a potential candidate for thermoelectric applications at room temperature. Studies of the two new Heusler alloys may provide a theoretical reference for subsequent theoretical research and experimental synthesis of Ag-based Heusler alloys.     

Synthesis, structural and optical properties of novel borylated Cu(II) and Co(II) metal complexes of 4-benzylaminobiphenylglyoxime

4-Benzylaminobiphenylglyoxime ligand and its Cu(II) and Co(II) complexes were prepared. -bridge containing 4-benzylaminobiphenylglyoxime complexes were obtained by replacing of the bridging protons of the dioxime complexes with BF₂ group. These compounds have been characterized by elemental analysis, spectroscopic (ICP-OES, infra-red) and magnetic susceptibility measurements. Thermal decomposition of the complexes is studied in nitrogen atmosphere. The final decomposition products are found to be the corresponding metal oxides. The optical constants such as optical conductivity, dielectric constant, refractive index were determined for the complexes. The analysis of the optical absorption data revealed that the band gap E_g was direct transitions. The optical dispersion parameters were determined according to Wemple and Didomenico method.     

Atomically Thin Arsenene and Antimonene: Semimetal–Semiconductor and Indirect–Direct Band‐Gap Transitions

The typical two‐dimensional (2D) semiconductors MoS₂, MoSe₂, WS₂, WSe₂ and black phosphorus have garnered tremendous interest for their unique electronic, optical, and chemical properties. However, all 2D semiconductors reported thus far feature band gaps that are smaller than 2.0 eV, which has greatly restricted their applications, especially in optoelectronic devices with photoresponse in the blue and UV range. Novel 2D mono‐elemental semiconductors, namely monolayered arsenene and antimonene, with wide band gaps and high stability were now developed based on first‐principles calculations. Interestingly, although As and Sb are typically semimetals in the bulk, they are transformed into indirect semiconductors with band gaps of 2.49 and 2.28 eV when thinned to one atomic layer. Significantly, under small biaxial strain, these materials were transformed from indirect into direct band‐gap semiconductors. Such dramatic changes in the electronic structure could pave the way for transistors with high on/off ratios, optoelectronic devices working under blue or UV light, and mechanical sensors based on new 2D crystals.