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In this work, the band structure feature, charge carrier mobility, optical properties, and photocatalytic performance of platinum-based vacancy-ordered double perovskites Rb2PtX6 (X = Cl, Br, and I) are investigated. The results show the semiconducting character of all three materials with band gap values equal to 3.39 eV, 2.76 eV, and 1.45 eV, for Rb2PtCl6, Rb2PtBr6, and Rb2PtI6, respectively. Furthermore, the calculated electron and hole effective masses yield a higher relative mass of hole-electron pairs (D), resulting in a slow recombination rate in these materials. The optical properties are also calculated, where the entitled materials show high absorption intensities in the visible and ultraviolet regions. Moreover, it is discovered that the Rb2PtCl6 and Rb2PtBr6 compounds can produce both oxygen and hydrogen at the same time. In contrast, the Rb2PtI6 material has a poor water-splitting ability and may be a promising photocatalyst for CO2 photoreduction. [ABSTRACT FROM AUTHOR]

In the present paper, (ZnO)–(Co3O4) nanocomposite thin films have been prepared by using spray pyrolysis deposition on a glass substrate at 350∘C. After that, the as-obtained films have been characterized and analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and the double beam UV-visible (UV-vis) spectrophotometer. Furthermore, the Bruggeman model is used to predict the evolution of the optical dielectric constant (real and imaginary parts: ε r and ε i) to compare them with those obtained from the experimental results. The XRD pattern reveals that the nanocomposite film has diffraction peaks 2 θ = 3 1. 3 3 ∘ , 36.95∘ corresponding respectively to the (220), (311) planes of cubic Co3O4 and another about of 2 θ = 3 6. 2 6 ∘ corresponding to the (101) plane of Wurtzite ZnO. Using the Debye Scherrer formula, the crystallite size of (ZnO) 0. 5 –(Co3O 4 ) 0. 5 nanocomposite is found about 32 nm, while the obtained thickness of this nanocomposite is about 780 nm using the DekTak Stylus profilometer. Besides, the morphology analysis shows that the nanocomposite sample is well covered without holes and/or cracks and it has uniform dense grains. The evaluation of the transmittance, reflectance, refraction index, extinction coefficient, real and imaginary parts of dielectric constant as function of wavelength illustrates that the optical response of nanocomposite thin film (ZnO) 0. 5 –(Co3O 4 ) 0. 5 depends on the influence of two mediums of pure materials ZnO and Co3O4 and their interaction. In addition, the direct band gap vs incident photon energy obtained from the Tauc plot equation shows that this nanocomposite has three values of band gap energy which are E g 1 = 1. 5 4 eV, E g 2 = 2. 2 eV (correspond to pure Co3O4 film) and E g 3 = 3. 4 7 eV (correspond to pure ZnO film). Besides, the application of the Bruggeman equation indicates that the influence of the values of volume concentration and optical dielectric constant of the ingredient nanomaterials (ZnO and Co3O 4) is significant on the value of the effective dielectric constant of nanocomposite thin film. The specific result of this study is the similarity between the spectra obtained from the Bruggeman model and the measured one, which proves that the application of this model is useful for the prediction of the optical properties of the composite. [ABSTRACT FROM AUTHOR]

In the present paper, experimental investigations on structural, morphological, optical and electrical properties of Co3O4 thin film deposited by spray pyrolysis method are reported. Using the interplanar spacing of the XRD reflection and Scherrer formula, respectively, we observed that the obtained films identified crystallize in the cubic spinel structure with a = 0. 8 2 4 5  nm and d = 1 9  nm. From the SEM picture, a dense grain in the morphology of Co3O4 is detected which has a uniform spherical shape. In addition, transmittance, absorbance, optical bandgap and extinction coefficient of the film versus incident photon energy were calculated. We found that Co3O4 film has a direct bandgap and direct forbidden transition varying from 1.69 eV to 2.85 eV and 1.62 eV to 1.88 eV, respectively. Further, the variation of (DC) electrical resistivity with temperature (from the room temperature of 27∘C to 350∘C) shows that the electrical resistivity was decreased with increasing temperature indicating a semiconducting transport behavior. [ABSTRACT FROM AUTHOR]

We report the results of first-principles calculations regarding the structural parameters, elastic moduli, electronic structure and optical properties of the ternary rhombohedral layered compounds, KLaSe2 and RbLaSe2. These calculations were performed by employing the pseudo-potential plane-wave (PP-PW) method. Although the calculated structural parameters (a, c, V, c/a, bond-length d) using different exchange and correlation approximations are found in nice harmony with the available experimental data, the best agreement is obtained with the GGA-PW91 functional. The effect of the K–Rb substitution is noted very clearly on the degree of ionic bonding of the A–Se bond (A = K, Rb). The electronic band structure and the density of states (DoS) plots reveal the semiconducting characteristics of both compounds with an indirect bandgap energy, E g of about 2 eV. The mechanical stability of the ALaSe2 compounds is investigated for the first time by calculating the single-crystal elastic constants C i j using the stress-strain approach. In order to understand the linear optical properties of the studied systems, frequency-dependent polarized optical functions were computed for an energy range from 0.0 eV to 18 eV. Our calculated optical spectra reveal the isotropic nature of the optical properties of the ALaSe2 compounds. [ABSTRACT FROM AUTHOR]

Abstract XLa 2 S 4 (X = Ba; Ca) sulfides are widely used as materials for application in infrared region, but the theoretical studies on these materials are limited and incomplete. Using the augmented plane wave + local orbitals (APW + lo) method with different approximation functionals, we performed a systematic theoretical study on the structural, electronic, optical and elastic properties of XLa 2 S 4 (X = Ba; Ca). The calculated band gaps E g of BaLa 2 S 4 and CaLa 2 S 4 using the modified Becke-Johnson potential in the form proposed by Tran and Blaha (TB-mBJ approximation) are 2.63 eV and 2.80 eV, respectively, which agree well with the experimental data. The dependence of main optical properties such as the absorption coefficient, refractive index, extinction coefficient, electron energy-loss spectrum, and optical reflectivity of BaLa 2 S 4 and CaLa 2 S 4 on photon energy were calculated and discussed. The independent elastic constants and elastic moduli of BaLa 2 S 4 and CaLa 2 S 4 were determined by precise calculations. The degree of elastic anisotropy of XLa 2 S 4 (X = Ba; Ca) has been evaluated from 3D curved surface representations of Young's modulus. The results of the band structure and optical properties calculations suggest that XLa 2 S 4 (X = Ba; Ca) are potential materials for solar conversion applications. Highlights • The TB-mBJ band gaps of BaLa 2 S 4 and CaLa 2 S 4 are 2.63 eV and 2.80 eV, respectively, which agree well with the experimental data. • Optical properties of BaLa 2 S 4 and CaLa 2 S 4 studied in detail for a wide range of photon energy. • The independent elastic constants and elastic moduli of BaLa 2 S 4 and CaLa 2 S 4 were determined. • XLa 2 S 4 (X = Ba; Ca) are considered potential materials for solar energy conversion applications. [ABSTRACT FROM AUTHOR]

Using the FP-APW + lo method, the structural, electronic, and optical properties of the Zintl BaAg 2 Te 2 compound were investigated. The calculated unit cell parameters are well matching with the experimental results. In addition, the study of electronic properties reveals that BaAg 2 Te 2 is a semiconductor with a direct bandgap of about 1.445 eV. The optical constants such as loss energy, refractive index, reflectivity, and absorption coefficient have been calculated and analyzed. These constants show a clear anisotropy caused by the different electron polarizability in the x-, y-, and z-directions. Moreover, the direct bandgap and good optical absorption make BaAg 2 Te 2 promising candidates for photovoltaic applications. The thermoelectric properties of the BaAg 2 Te 2 compound in the x, y, and z directions have been studied to obtain the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, power factor, and figure of merit (ZT) against temperature and carrier concentrations. Our investigations showed an improvement in the ZT values of BaAg 2 Te 2 with increase in temperature. Moreover, the BaAg 2 Te 2 demonstrated optimal ZT values along the y-axis. [ABSTRACT FROM AUTHOR]

Our present article reports the carbon substitution-driven changes in the behavior of BeSi 1- x C x P 2 and BeGe 1- x C x P 2 (x = 0.25 and 0.5) chalcopyrite alloys using the full-potential augmented plane wave plus local orbital (FP-APW + lo) based first-principles calculations. The lattice constants (a and c) of BeSi 1- x C x P 2 and BeGe 1- x C x P 2 are shortened, and the bulk moduli are improved as carbon atoms replace Si and Ge atoms. The computed negative formation energy (E f) indicate adequate thermodynamic stability of the BeSi 1- x C x P 2 and BeGe 1- x C x P 2 alloys. The bandgaps pristine BeSiP 2 and BeGeP 2 computed as 1.84 eV and 1.54 eV, respectively, using the modified Tran-Blaha (TB) Becke Johnson (mBJ) transition potential, matching well to the experimental results. However, the C substitution is found to narrow the bandgap of BeSiP 2 and BeGeP 2 considerably. Similarly, C substitution is found to reduce electrons' and holes' effective mass and enhance the absorption coefficient of BeSi 1- x C x P 2 and BeGe 1- x C x P 2 alloys up to (α ∼ 10 5 c m − 1 ). Our predictions indicate that the physical properties of BeSiP 2 and BeGeP 2 chalcopyrite can be modified effectively by replacing C in the Si and Ge sites, which makes them promising for optoelectronic applications. Lattice parameters and bulk modulus versus C concentration of BeSiP 2 and BeGeP 2. [Display omitted] • Some physical properties of C doped BeSiP 2 and BeGeP 2 chalcopyrite are investigated. • The calculated electronic and optical properties of pure BeSiP 2 and BeGeP 2 compare well with the available data. • The substitution of carbon decreases the value of bandgaps, hole and electron masses. • Doping BeSiP 2 and BeGeP 2 enhance the absorption in visible light making them promising for optoelectronic applications. [ABSTRACT FROM AUTHOR]

We report the results of the full-potential linearized augmented plane wave (FP-LAPW) calculations on the structural, elastic, optoelectronic and magnetic properties of $$\hbox {CdHo}_{2}\hbox {S}_{4}$$ spinel. Both the generalized gradient approximation (GGA) and Trans-Blaha modified Becke-Johnson potential (TB-mBJ) are used to model the exchange-correlation effects. The computed lattice parameter, internal coordinate and bulk modulus are in good agreement with the existing experimental data. According to the calculated elastic moduli, $$\hbox {CdHo}_{2}\hbox {S}_{4}$$ is mechanically stable with a ductile nature and a noticeable elastic anisotropy. The ferromagnetic phase of $$\hbox {CdHo}_{2}\hbox {S}_{4}$$ is energetically favourable compared to non-magnetic one, with a high magnetic moment of about 8.15 $$\upmu _{\mathrm{B}}$$ . The calculated band structure demonstrates that the title compound is a direct band gap semiconductor. The TB-mBJ yields a band gap of $$\sim $$ 1.86 and $$\sim $$ 2.17 eV for the minority and majority spins, respectively. The calculated optical spectra reveal a strong response in the energy range between the visible light and the extreme UV regions. [ABSTRACT FROM AUTHOR]

In this work, we have investigated the structural, phase transition, optoelectronic and magnetic properties of AmO 2 using the full potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method. The exchange-correlation potential was treated with the generalized gradient approximation (GGA). Moreover, the GGA+ U approximation (where U denotes the Hubbard Coulomb energy U term) is employed to treat the f electrons properly. The structurally stable AmO 2 compound is the Fm3m phase and at a pressure between 40 and 60 GPa underwent a phase transition to the Pnma phase. Our present calculations have considered ferromagnetic and simple antiferromagnetic ground states and the AF state is favored. However, the experimental situation suggests a complex magnetic structure, perhaps involving multipolar ordering. Our band structure calculation with GGA and GGA+ U predicted the metallic behavior of AmO 2 ; however, with the spin–orbit coupling (SOC) added to the Coulomb energy U term, semiconducting ground states with antiferromagnetism is correctly predicted. The projected density of states from the energy-band structure indicates that the band gap opening is governed by the partially filled Am “5 f ” state, and the calculated gap is approximately 1.29 eV. Moreover, the optical properties reveal strong response of AmO 2 in the UV region. [ABSTRACT FROM AUTHOR]

In this study, we predict the structural phase transitions as well as opto-electronic properties of the filled-tetrahedral (Nowotny–Juza) NaZnAs compound. Calculations employ the full potential (FP) linearized augmented plane wave (LAPW) plus local orbitals (lo) scheme. The exchange–correlation potential is treated within the generalized gradient approximation of Perdew–Burke and Ernzerhof (GGA-PBE). In addition, Tran and Blaha (TB) modified Becke–Johnson (mBJ) potential is also used to obtain more accurate optoelectronic properties. Geometry optimization is performed to obtain reliable total energies and other structural parameters for each NaZnAs phase. In our study, the sequence of the structural phase transition on compression is Cu 2 Sb-type → β → α phase. NaZnAs is a direct (Γ–Γ) band gap semiconductor for all the structural phases. However, compared to PBE-GGA, the mBJ approximation reproduces better fundamental band gaps. Moreover, for insight into its potential for photovoltaic applications, different optical parameters are studied. [ABSTRACT FROM AUTHOR]

Over the years, vanadates are attracting sizable consideration of the researchers owing to their versatile functional properties. Through an ab initio computational approach, a comprehensive study was performed on terbium orthovanadate (TbVO 4); the study includes an investigation on its electronic structure, magnetic behavior, as well as mechanical and optical properties. The computations are performed by employing the "full-potential linearized augmented plane wave plus local orbital (FP-LAPW ​+ ​lo)" methodology framed with "density functional theory (DFT)". To incorporate the "exchange correlation energy/potential" functional into total energy calculations, the "Perdew-Burke and Ernzerhof" approach to "generalized gradient approximation" was employed by using WIEN2k computational code. In addition, to analyze the d-orbital electrons of vanadium (V) and the f-orbital electrons of terbium (Tb) more precisely, the GGA ​+ ​U approximation is also used. The computational obtained results of structural parameters are found to be in good agreement with the experimentally measured one. Moreover, TbVO 4 showed mechanical stability and ductility as well. The computed electronic structure reveals that TbVO 4 is a direct gap semiconductor compound with band gap energy comparable to that of the experimentally one. The magnetic moment and density of states results confirm that TbVO 4 is an antiferromagnetic material. For completeness, the optical and mechanical anisotropy are also simulated and analyzed. [Display omitted] • Some Physical properties for tetragonal TbVO 4 in its antiferromagnetic state are investigated. • The calculated ground states properties for TbVO 4 compare well with the available data. • The electronic properties calculation reveals that this compound is wide-direct band gap. • The mechanical, optical and magnetic characteristics for TbVO 4 are investigated for the first time. [ABSTRACT FROM AUTHOR]

To study the structural, electronic, and optical properties of the half-Heusler CoCr Z ( Z = Al, Ga), we have performed ab initio calculations using the full-potential with the mixed basis (APW + lo) method within the generalized gradient approximation. The structural properties as well as the band structures, and total and atomic projected densities of states are computed. From electronic band structures we have found that both compounds have a semimetallic nature. We also studied the evolution of electronic structure of CoCrAl under external hydrostatic pressure. It is found that the pseudo gap around the Fermi level increases continuously with increasing pressure, while the electronic density of states at the Fermi level does not change significantly. Furthermore, the optical properties, such as the dielectric function and refractive index were evaluated and discussed under pressure up to 20 GPa, and the electrical conductivity and electron energy loss were calculated for radiation up to 30 eV. The same way, we have studied the magnetic properties of CoCrAl for lattice expansion up to a = 1.1 a0 where a transition from the paramagnetic phase to the half-metallic phase is expected. [ABSTRACT FROM AUTHOR]

The thallium substitution effect on structural, electronic, and optical properties of chalcopyrite-type material AgGaS 2 is investigated via first-principles approaches. The computed band gap energy of pure AgGaS 2 is about 2.59 ​eV using Tran-Blaha (TB)-modified Becke Johnson (mBJ) exchange potential, which is in good accord with experimental measurements. This band gap value was observed to decrease to be 1.91 ​eV, 1.61 ​eV, and 1.28 ​eV when Tl is substituted into Ga site, respectively, for 25%, 50%, and 75% concentrations. Besides, the AgTlS 2 band gap was also calculated and found to be 0.61 ​eV. This investigation establishes that Tl substitution increases both hole and electron carrier mobility of the pure AgGaS 2 compound. By analyzing the band alignment diagram, it was observed that the Tl substitution increases the valence band offset (VBO) and decreases the conduction band offset (CBO), which can lead to the improvement of open-circuit voltage V OC. Moreover, the optical analysis reveals that Tl substitution enhances the optical properties of AgGaS 2 by reducing the transparency and improving the refractive index and the absorption in the visible light region. Based on obtained results, it is predicted that the band gap and the optical properties of the AgGaS 2 chalcopyrite can be effectively tuned by Tl substitution over the Ga sites, making AgGa 1-x Tl x S 2 alloys promising candidates for optoelectronic and photovoltaic applications. [Display omitted] • Thallium substitution effect on electronic and optical properties of AgGaS 2 was for the first time studied. • The new AgGa 1-x Tl x S 2 (x ​= ​0.25, 0.5, 0.75) alloys are direct-gap semiconductors with band gap values of 1.91 ​eV, 1.61 ​eV, and 1.28 ​eV, respectively. • The Tl substitution into Ga sites increases the carrier's mobility and the VBO. • The new AgGa 1-x Tl x S 2 alloys possess a high absorption coefficient ensures their use in photovoltaic applications. • Tl substitution tuned the optoelectronic properties of AgGaS 2 , making AgGa 1-x Tl x S 2 promising for solar cells applications. [ABSTRACT FROM AUTHOR]

In this article, we present a study of the properties of two-dimensional (2D) derivatives of MAX phases, namely W 2 XT 2 (X = C, N; T = O, F) MXenes, which have become hot spots of research for their intriguing physical properties. In pursuing this first-principles study, we realized W 2 X pristine MXene by eliminating the Ga atomic layer from the W 2 GaX MAX phase, which is then functionalized with oxygen and fluorine. These materials exhibit electronic states above the Fermi level primarily of W- d nature, indicating their metallic nature similar to the parent MAX phases. The distribution of up and down spin electronic states is highly symmetrical, depriving the W 2 XT 2 MXenes of spontaneous magnetization. They demonstrated prominent optical properties where the W 2 NF 2 exhibits approximately 70% reflection of infrared (IR) light, while W 2 CF 2 reflects around 47%. On the contrary, W 2 NO 2 and W 2 CO 2 reflect 33% and 20% of the incident IR light, respectively. At an energy of 0 eV, the refractive indices recorded for W 2 CF 2 , W 2 CO 2 , W 2 NF 2 , and W 2 NO 2 were 5.11, 2.29, 8.56, and 3.47, respectively. When exposed to IR light, they showed remarkable ultraviolet (UV) light absorption of 23.62 × 104 cm−1 and 20.71 × 104 cm−1 for W 2 NF 2 and W 2 CF 2 , respectively. The absorption of IR light by W 2 CO 2 and W 2 NO 2 was relatively smaller, with values of 12.52 × 104 cm−1 and 8.30 × 104 cm−1, respectively. The interesting optical characteristics of the W 2 XT 2 MXene make them promising for utilization in advanced optical devices. • Exploration of Novel Tungsten-based MXenes. • Constituents and Functional Groups Influence. • Intriguing Electronic Properties. • Symmetrical Spin Electronic States. • Interesting Optical Characteristics. [ABSTRACT FROM AUTHOR]

We have studied the structural, optical, electronic and thermoelectric properties of the CaCd 2 X 2 (X = P, As) compounds by using the full-potential augmented plane wave plus local orbitals method (FP-APW + lo). The exchange-correlation potential was treated using both the gradient generalized approximation (WC-GGA) and local density approximation (LDA). The estimated structural parameters, including the lattice parameters and internal coordinates agree well with the available experimental data. Our computed band structure shows that both studied compounds are semiconductors, with direct band gaps (Γ-Γ) of approximately 1.78 eV and 1.2 eV for CaCd 2 P 2 and CaCd 2 As 2 , respectively, using GGA-TB-mBJ approach. The calculated optical spectra reveal a strong response of these materials in the energy range between the visible light and extreme UV regions, making them a good candidate for optoelectronic devices. Thermoelectric parameters, such as thermal conductivity, electrical conductivity, Seebeck coefficient, power factor and figure of merit were calculated. We note that both the CaCd 2 P 2 and CaCd 2 As 2 compounds show promising thermoelectric properties. [ABSTRACT FROM AUTHOR]

Highlights: [•] REGa3 (RE=Sc or Lu) compounds are mechanical stabile. [•] Both ScGa3 and LuGa3 exhibit metallic behavior just like other REGa3 compounds. [•] Melting temperature Tm (K) for ScGa3 and LuGa3 are 1244.2 and 1143.8. [•] High absorption observed in the visible energy region. [•] The present study would be helpful for future experimental/theoretical explorations. [ABSTRACT FROM AUTHOR]

Highlights: [•] The tetragonal NaZnP has brittle nature. [•] The Cu2Sb-type phase of NaZnP is a direct band gap semiconductor. [•] The TB-mBJ approximation yields larger fundamental band gaps. [•] The bonding in Cu2Sb–NaZnP is of covalent-ionic character. [•] High reflectivity (60%) and refractive index (3.9) are observed for the compound. [ABSTRACT FROM AUTHOR]

Abstract We report the results of the FP-APW + lo calculations of the structural, electronic, optical and thermo-electric properties of the CdY 2 Ch 4 (Ch = S, Se) compounds under hydrostatic pressure effect. The calculated ground state properties agree well with the available experimental data. The investigated materials are semiconductors, with direct band gaps (Γ- Γ) of approximately 2.18 eV, 1.53 eV for CdY 2 S 4 and CdY 2 Se 4 , respectively, using GGA-TB-mBJ approximations. Under external pressure up to 20 GPa, both compounds show a linear decrease of energy gaps against pressure. Moreover, our calculated optical spectra over photon energies ranging from 0 to 20 eV suggest that CdY 2 Ch 4 (Ch = S, Se) spinel compounds express a strong response in the energy range between the visible light and extreme UV regions, highlighting their possible application in the optoelectronic devices. Furthermore, the calculated thermoelectric properties indicate that both the CdY 2 S 4 and CdY 2 Se 4 compounds show interesting thermoelectric properties. Highlights • Electronic, optical and thermoelectric properties for CdY2X4 (X = S, Se) compounds are investigated for the first time. • The electronic calculation reveals a semiconducting nature of these compounds. • Both compounds show a strong response in visible light and extreme UV regions which make them potential candidate for optoelectronic devices. • Both the CdY2S4 and CdY2Se4 compounds show attractive thermoelectric properties [ABSTRACT FROM AUTHOR]

In this paper, we study theoretically the structural, electronic, optical, elastic and thermoelectric properties of MgSc 2 X 4 (X ​= ​S; Se) compounds using first-principles calculations. The calculated band structure reveals that MgSc 2 S 4 and MgSc 2 Se 4 are direct-gap semiconductors. The optical features of MgSc 2 S 4 and MgSc 2 Se 4 as functions of photon energy were calculated for energy range of 0–20 ​eV. MgSc 2 X 4 (X ​= ​S; Se) are promising optoelectronic, and thermoelectric compounds whose absorption rates can reach 4 orders of magnitude in the visible range, and 6 orders of magnitude in ultraviolet range. Both chalcogenides possess high brittleness with the Pugh's ratio (B / G), and Cauchy pressure C 12 − C 44 of 1.60 and − 4.485 GPa (for MgSc 2 Se 4); 1.61 and − 3.655 GPa (for MgSc 2 S 4). MgSc 2 S 4 and MgSc 2 Se 4 reveal similar Z T e values. The obtained properties of MgSc 2 X 4 (X ​= ​S; Se) are well confirmed by experimental results. Weighted band structures of MgSc 2 S 4 and MgSc 2 Se 4 as obtained by TB-mBJ. Image 1 • Structural, and electronic properties of MgSc 2 X 4 (X ​= ​S; Se) spinel compounds. • The distribution of the conduction bands depends on the hybridization S/Se- p orbitals and Sc- d orbitals. • High absorption rate in the visible and ultraviolet ranges. • High brittleness of MgSc 2 S 4 , and MgSc 2 Se 4. • Good thermoelectric and optoelectronic properties. [ABSTRACT FROM AUTHOR]