Real Part Of Optical Conductivity Research Articles

First-principles investigations of structural, electronic and optical properties of ternary chalcopyrite semiconductors [formula omitted] ([formula omitted], [formula omitted] and [formula omitted])

The copper-indium-based tetragonal chalcopyrite semiconductors CuInY2Y=S, Se and Te) have garnered significant attention due to their suitable bandgap for solar cell applications. In this study, we investigate the structural, electronic, and optical properties of CuInY2 using state-of-the-art density functional theory (DFT) with the modified Becke-Johnson (mBJ) semilocal exchange functional. Our band structure calculations reveals that these compounds exhibit a p-type semiconductors character with a direct band gap at the Γ point. The calculated band gaps are in good agreement with the experimental data. Density of state analysis shows that these compounds are primarily influenced by Cud-states at the upper valence band and their hybridization with Yp-states bellow the first valence band. Furthermore, we validate our results by calculating optical properties, including the dielectric function, absorption coefficient, the real part of optical conductivity, optical reflectivity, and the refractive index. Our refractive index findings show reasonable agreement with the experimental data. Our findings indicate that all three compounds exhibit high absorption (≈105cm−1) in the visible light range with CuInTe2 showing the highest absorption compared to CuInS2 and CuInSe2. Additionally, CuInS2 is less reflective (0.21%) in the visible light range in this series. These structures, with their suitable band gaps, are capable of absorbing a significant amount of light, making them prospective choices for solar cell applications.

Tuning optical properties of Au thin film using electric field for surface plasmon resonance biosensor application

The effect of electric field application on the optical properties of gold (Au) thin film for spectroscopic ellipsometry-based surface plasmon resonance (SPR) biosensor applications has been successfully studied. The optical properties, such as the complex refractive index, complex dielectric constant, real optical conductivity, and absorption coefficient, were determined by fitting data from the ψ and Δ functions obtained through measurements using a homemade rotating analyzer ellipsometer. The applied electric fields of 0.8 V/cm, 1.6 V/cm, 2.4 V/cm, and 3.2 V/cm were induced by applying voltages of 1 V, 2 V, 3 V, and 4 V for ellipsometer tests, and 1.6 V/cm to 3.2 V/cm for the SPR test. The Au thin film was deposited onto a glass slide using an evaporator for ellipsometer testing and a BK7 half-cylinder prism was employed for SPR testing. The experimental results show that the real part of the refractive index (n) increases in the spectral range from 1.5 eV to 2.2 eV and from 3 eV to 5 eV and tends to be constant in the range from 2.3 eV to 2.8 eV. Conversely, the imaginary part of the refractive index (k) decreases from 2.8 eV to 3.6 eV and tends to remain consistent from 3.9 eV to 5.0 eV. The dielectric constant (ε1) consistently shows a significant increase within the spectral range of 3 eV–5.0 eV, with a tendency to decrease between 2.1 eV and 2.4 eV. Meanwhile, the imaginary part (ε2) demonstrates an increase in the spectral range of 1.5 eV–2.4 eV and 3.3 eV–5.0 eV while maintaining relatively stable values in the energy spectral range of 2.6 eV–3.0 eV. Moving to the real part of optical conductivity (σ1), it increases within the spectral range from 1.5 eV to 2.4 eV and from 3.5 eV to 5 eV, with relatively constant values between 2.6 eV and 3.1 eV. The absorption coefficient (α) exhibits a decrease in the spectrum between 2.8 eV and 3.6 eV, but the values remain stable within the range of 3.9 eV–5.0 eV. The α slightly decreases in the energy range of 1.8 eV–2.6 eV. The outcomes obtained from these experiments are directly linked to the SPR results, revealing a noticeable shift in the SPR angle (θSPR) of 45.51°, 45.61°, and 45.73° and an increase in the minimum reflectance (Rmin) of 0.05, 0.09, and 0.13 for electric field strengths of 0 V/cm, 1.6 V/cm, and 3.2 V/cm, respectively. These results imply that the application of an external electric field to the surface of the Au thin film disrupts the matching condition between the evanescent wave vector and the surface plasmon wave vector, thereby altering the reflected light under resonance conditions indicated by an increase in the minimum reflectance and SPR angle. This development holds significant promise to further enhance the sensitivity of electro-optic modulation-based biosensors.

Anomalous optical properties of bismuth ultrathin film using spectroscopic ellipsometry in the visible - Ultraviolet range

We report the study of optical properties of Bismuth (Bi) thin films with different thicknesses (tBi = 25 nm, 20 nm, 15 nm, and 5 nm) using spectroscopic ellipsometry in the visible – ultraviolet light range (1.4 – 5.3 eV). A broad absorption hump and three broad absorption peaks, as represented by the imaginary part of the dielectric constant and real part of optical conductivity, occur at 2.0 eV and 2.8 eV; 3.8 eV, and 5.0 eV, respectively, for tBi of 25 nm, 20 nm, and 15 nm. The absorption features might be related to electron transition involving px, py orbitals to pz orbital throughout the high symmetry line of Bi's first Brillouin zone. These absorption peaks decreased as tBi decreased from 25 nm to 15 nm. However, a significant increase in those absorption peaks when tBi = 5 nm accompanied by extra absorption peaks at 2.6 eV, 3.0 eV, and 4.1 eV. This anomalous is possibly due to the transition from three-dimension to two-dimension by the quantum confinement effect, leading to the increase of density of state as the Bi goes to ultrathin-film thickness. We did the first principle calculation (density functional theory) based on bulk Bi and Bi thin film to support this observation. By using more precise optical properties of this material, our study may provide insight into the future development of Bi-enabled technologies.

Quantum Study of the Optical Conductivity of Composite Films Formed by Bilayer Graphene and Single-Walled Carbon Nanotubes under Axial Stretching

In this article, quantum methods are used to study the optical properties of composite films formed by AB-stacked bilayer graphene and chiral single-walled carbon nanotubes (SWCNT) (12, 6) with a diameter of 1.2 nm. The analysis of optical properties is carried out on the basis of the results of calculating the diagonal elements of complex optical conductivity tensor in the wavelength range of 0.2–2 μm. Two cases of electromagnetic radiation polarization are considered: along the X axis (along the graphene bilayer) and along the Y axis (along the nanotube axis). The calculations are performed for three topological models (V1, V2, V3) of composite films, which differ in the width of the graphene bilayer and in the value of the shift between graphene layers. It is found that in the case of polarization along the X axis, the profile of the real part of optical conductivity in the region of extremal and middle UV radiation is determined by SWCNT (12, 6), and in the region of near UV and visible radiations, it is determined by bilayer graphene. In the case of polarization along the Y axis, the profile of the real part of optical conductivity in the region of extremal, near UV, and visible radiation is determined by SWCNT (12, 6), and in the region of the mid-UV range, it is determined by bilayer graphene. Regularities in the change in the profile of the surface optical conductivity of bilayer graphene-SWCNT (12,6) composite films under the action of stretching deformation along the Y axis are revealed. For models V1 (width of the graphene nanoribbon is 0.5 nm, the shift between layers is 0.48 nm) and V2 (width of the graphene nanoribbon is 0.71 nm, the shift between layers is 0.27 nm), the shift of the conductivity peaks in the region of extreme UV radiation along the wavelength to the right is shown. For the model V3 (width of the graphene nanoribbon is 0.92 nm, the shift between layers is 0.06 nm), the shift of the conductivity peaks to the right along the wavelength is observed not only in the region of extreme UV radiation, but also in the region of visible radiation. It is assumed that graphene-SWCNT (12,6) composite films with island topology are promising materials for photodetectors in the UV-visible and near-IR ranges.

Ab-inito simulation of the structural, electronic and optical properties for the vacancy-ordered double perovskites A2TiI6 (A = Cs or NH4); a time-dependent density functional theory study

In the present work, we have performed a detail analysis of the established Ti-based perovskites compounds and calculated the structural, electronic and optical properties of the vacancy-ordered double perovskites A2TiI6 (A = Cs+ or NH4+) that simulated using ab-initio approach within the framework of density functional theory (DFT) and time-dependent DFT (TDDFT). The Ti-based halide perovskites possess several interesting properties, including high stability, suitable band gap and excellent optical absorption. The calculations predict a direct band gap that is in agreement with the reported values. The real and imaginary parts of the dielectric function ε(ω), absorption coefficient α(ω), reflective index R(ω), refractive index n(ω), extinction coefficient k(ω), energy loss spectrum L(ω) and the real part of optical conductivity have been calculated. The obtained results show good agreement with the available experimental results, particularly in the low-energy region of the spectra. Based on a suitable direct band gap and strong absorption coefficient, these materials are suitable candidates for photovoltaic applications and are suggested as ideal potential materials for single-junction solar cells.

Electronic Structure of Pyrochlore Iridate Pr2Ir2O7: Interplay Between Spin-Orbit Coupling and Hubbard Potential

We have investigated the electronic structure of pyrochlore iridate Pr2Ir2O7 compound with Fd-3m space group using first-principle density functional theory calculations. [Formula: see text] calculations show that the PrAFM–IrNM state in Pr2Ir2O7 compound is energetically more favorable than the other phases. Combining of the interaction of electronic correlation (U) and spin-orbit coupling (SO) leads to three different phases for this material. (1) An anti-ferromagnetic metal is found by the [Formula: see text] ([Formula: see text][Formula: see text]eV) approximation without taking into account the spin orbit interaction. (2) A metal-semimetal transition appears, when the spin-orbit coupling is applied. (3) A semi-conductor characteristic with a narrow gap increases slightly by varying the Hubbard potential of nonmagnetic Ir atoms from 0.5[Formula: see text]eV to 1.5[Formula: see text]eV. The effect of the spin orbit (SO) coupling and the interaction (U) clearly influences the Fermi region of the calculated band structures and densities of states of this system. The hydrostatic pressure effect on the energy gap has shown a further advantage in predicting the desired gap value for this kind of materials. The optical properties, including the dielectric function, refractive index, reflectivity and real part of optical conductivity, are calculated for radiation up to 8[Formula: see text]eV. Overall, however, for both [Formula: see text] values of Pr2Ir2O7, the compound shows similar optical characteristics.

Density-matrix renormalization group study of optical conductivity of the Mott insulator for two-dimensional clusters

The real part of optical conductivity $\text{Re}\sigma(\omega)$ of the Mott insulators has a large amount of information on how spin and charge degrees of freedom interact with each other. By using the time-dependent density-matrix renormalization group, we study $\text{Re}\sigma(\omega)$ of the two-dimensional Hubbard model on a square lattice at half filling. We find an excitonic peak at the Mott-gap edge of $\text{Re}\sigma(\omega)$ not only for the two-dimensional square lattice but also for two- and four-leg ladders. For the square lattice, however, we do not clearly find a gap between an excitonic peak and continuum band, which indicates that a bound state is not well defined. The emergence of an excitonic peak in $\text{Re}\sigma(\omega)$ implies the formation of a spin polaron. Examining the dependence of $\text{Re}\sigma(\omega)$ on the on-site Coulomb interaction and next-nearest neighbor hoppings, we confirm that an excitonic peak is generated from a magnetic effect. Electron scattering due to an electron-phonon interaction is expected to easily suppress an excitonic peak since spectral width of an excitonic peak is very narrow. Introducing a large broadening in $\text{Re}\sigma(\omega)$ by modeling the electron-phonon coupling present in La$_{2}$CuO$_{4}$ and Nd$_{2}$CuO$_{4}$, we obtain $\text{Re}\sigma(\omega)$ comparable with experiments.

ICMMS-2: Influence of Gamma Radiation on Nonlinear Optical, Semiconducting and Dielectrical Properties of In0.95Mn0.05Se Thin Films

In0.95Mn0.05Se films with of thickness 750 nm were evaporated by using thermal evaporation technique, this film was irradiated by γ radiation with doses (0,40 and 120 KGy). Both of dispersion energy (Ed) and oscillating energy (Eo) were determined. The values of lattice dielectric constant (eL) and free carrier concentration/effective mass) (N/m*) were calculated. On the other hand, the values of first order of moment (M-1), the third order of moment (M-3) and static refractive index (no), were determined. Both of dielectric loss (e) and dielectric tangent loss (e\) for these films increased with photon energy (hν). Also, the same behavior was noticed for the real part of optical conductivity (σ1) and imaginary part of optical conductivity (σ2). The Linear optical susceptibility (χ(1)) increases with (hν)for all compositions. The nonlinear optical parameters such as, nonlinear refractive index (n2), the third-order nonlinear optical susceptibility (χ(3)), non-linear absorption coefficient (βc) , were determined theoretically. Both of the electrical susceptibility (χe) and relative permittivity (er) increase with photon energy and had a highest value near the energy gap. The semiconducting results such as, density of the valence band, conduction band and Fermi level position (Ef) were calculated.

Investigation of structural, electronic and optical properties of potassium and lithium based ternary Selenoindate: Using first principles approach

Here we reported the first principle-based calculations for the structural and optoelectronic properties of AInSe2 (A ​= ​K and Li) chalcopyrite type single crystals with-in the framework of density functional theory (DFT). The calculated structural parameters using the local density approximation (LDA) and general gradient approximation (GGA) are in a best agreement with existing experimentals and others theoretical results. The band structures and density of states of these materials are investigated and discussed in detail. Our calculations reveal a direct band-gap semiconductor type nature for both materials. The calculated band gaps follow that Eg (LiInSe2) ​> ​Eg (KInSe2) showing a good agreement for a decrease in bond energy for the corresponding In-s and Se-p anti-bonding orbital states. Furthermore, the frequency dependent linear optical properties, such as the complex dielectric functions, energy loss function, absorption coefficient, reflectivity, refractive index, the extinction coefficient and the real part of optical conductivity are also computed and discussed in detail. Our calculated optical results were found to be in a good agreement with the results from the literature There exists a significant variation in optical characteristics of both these materials. Our predicted calculated results would guide to understand the experimental and theoretical work on the basic material properties of these materials including crystal structures, optoelectronic properties, as well as their device applications.

Insight DFT studies about the optoelectronic properties of Fe and Ga doped Mg-based hydrides: Efficient materials for optical devices

We reported and discussed results for the first time for the electronic and optical properties of Fe doped MgH2 and Ga doped MgH2Fe hydride materials by first-principles calculations using generalized gradient approximation (GGA) within the density functional theory (DFT). The effective contributions of various electronic bands and density of states calculations confirms a quite weak bonding nature between Fe, Mg and H atoms in Fe doped MgH2 system. Also, the addition of Ga, the interaction between Mg and H atoms show weak bonding along with extensive reduction in the PDOS of both Mg and H atoms closer to Fermi level. The optical properties such as dielectric function, refractive index, extinction coefficient, absorption, reflectivity spectra, electron energy loss function and the real part of optical conductivity were calculated and discussed in detail. The observed sharp energy loss peak values for both the studied systems match up with the edge of plasma energy and corresponds to plasma frequency which indicates transition between semiconductor and dielectric characters. The base for the absorption was discussed in detail in addition to observed spectral peaks on the basis of their electronic band structures and crystal field nature.

Substrate-induced electronic localization in monolayer MoS2 measured via terahertz spectroscopy.

We study terahertz (THz) optoelectronic properties of monolayer (ML) MoS2 placed on different substrates such as SiO2/Si, sapphire, and quartz. Through the measurements of THz Fourier transform spectroscopy (2.5-6.5THz) and THz time-domain spectroscopy (TDS, 0.2-1.2THz), we find that the real part of optical conductivity increases for ML MoS2 on SiO2/Si and sapphire substrates and decreases for it on quartz with increasing radiation frequency. It is shown that the complex optical conductivity for ML MoS2, obtained from THz TDS measurements, can fit very well to the Drude-Smith formula. Thus, the dependence of optical conductivity of ML MoS2 on different substrates can be understood via a mechanism of electronic localization, and the electron density, relaxation time, and localization factor of the sample can be determined optically. Furthermore, we examine the influence of temperature on these key parameters in ML MoS2 on different substrates. The results obtained from this Letter indicate that THz spectroscopy is a very powerful tool in studying and characterizing ML MoS2-based electronic systems, especially in examining the electronic localization effect which cannot be directly measured in conventional electrical transport experiment. This Letter is relevant to an in-depth understanding of the optoelectronic properties of ML MoS2 and of the proximity effect induced by different substrates.

Tunable Non-linear Optical, Semiconducting and Dielectric Properties of In1−xMnxSe Thin Films

In1−xMnxSe (x = 0, 0.05, 0.1 and 0.15) thin films were evaporated by using the thermal evaporation technique. Both dispersion energy (Ed) and oscillating energy (Eo) were determined. The values of lattice dielectric constant (eL) and free carrier concentration/effective mass) (N/m*) were calculated. On the other hand, the values of the first order of moment (M−1), the third order of moment (M−3) and static refractive index (no) were determined. The dielectric loss (e′) and dielectric tangent loss (e″) for these films increased with photon energy and had the highest value near the energy gap Eg. Also, the same behavior was noticed for the real part of optical conductivity (σ1) and imaginary part of optical conductivity (σ2), the relation between Volume Energy Loss Function (VELF) and Surface Energy Loss Function (SELF) was determined. The Linear optical susceptibility (χ(1)) increased with photon energy for all compositions. The nonlinear optical parameters such as nonlinear refractive index (n2), the third-order nonlinear optical susceptibility (χ(3)) and non-linear absorption coefficient (βc), were determined theoretically. Both the electrical susceptibility (χe) and relative permittivity (er) increased with photon energy and had the highest value near the energy gap. The semiconducting results such as density of the valence band, conduction band, and Fermi level position (Ef) were calculated.

Enhanced Optical Conductivity, Nonlinear Optical and Semiconducting Properties of Mg1−xCuxO/PMMA Nanocomposite

Mg1−xCuxO/PMMA nanocomposite films (where x = 0.05, 0.1, 0.15 and 0.2) samples were prepared using solid state reaction technique. The values of both dispersion energy (Ed) and oscillating energy (Eo) were determined optically, which decreased with Cu content as a result of increasing the conductivity and carriers mobility’s with Cu, and also the free carrier concentration/effective mass (N/m*) decreased with Cu content. On the other hand, the first order of moment (M−1), the third order of moment (M−3) and static refractive index (no), were determined. The both of dielectric loss (e′) and dielectric tangent loss (e″) decreased with Cu, which increase the carriers mobility’s leading to decrease both of (e′) and (e″), on the other hand Cu ratio also increasing the mobility’s of carriers which increase both of real part of optical conductivity (σ1) and imaginary part of optical conductivity (σ2). The Linear optical susceptibility (χ(1)) increases with hν for all samples. The nonlinear optical parameters such as nonlinear refractive index (n2), the third-order nonlinear optical susceptibility (χ(3)), non-linear absorption coefficient (βc) increase with Cu, this means the samples had an ability to change their optical properties by doping. Both of the electrical susceptibility (χe) and relative permittivity (er) increase with Cu ratio. The semiconducting results such as, density of conduction band/electron effective mass [Nc/m*e (cm−3)], density of valence band/hole effective mass [Nv/m*h (cm−3)] were calculated.

Optical investigation of topological semimetal SrMnSb2**Project supported by the National Natural Science Foundation of China (Grant No. 11774400) and the National Key Basic Research Program of China (Grant Nos. 2015CB921102 and 2017YFA0302903).

We investigate the temperature-dependent infrared spectroscopy of SrMnSb2, which is a semimetal with multiple Fermi surfaces. A notable blue shift of the plasma minimum in reflectivity upon cooling indicates that the carrier density varies with temperature. In the real part of the optical conductivity , a linearly-increased component which extrapolates to zero conductivity at finite frequency has been identified, which suggests dispersion of gapped Dirac band structures near the Fermi level. A two-Drude model, representing two different types of carriers, is introduced to describe the real part of optical conductivity. We separate the contributions of two-Drude model in dc conductivity, and demonstrate that the transport properties of SrMnSb2 are mainly affected by the narrow-Drude quasiparticles. Compared with the similar phenomena observed in CaMnSb2 and SrMnBi2, we can infer that the two-Drude model is an appropriate approach to investigate the multiband materials in AMnSb2 and AMnBi2 families.

Effects of a magnetic field on the optoelectronic properties of mono- and bi-layer transition metal dichalcogenides

We report a theoretical study on the effects of an external magnetic field on the electronic and optical properties of mono- and bi-layer MoS2, and bilayer MoS2/WS2 heterostructures. The direction of an applied magnetic field determines (i) the strength of the coupling between the atomic orbital moments of the structure and the field, and (ii) Zeeman contribution to the splitting of the VB and CB levels with the amplitude of the applied field. Whereas for a magnetic field applied perpendicular to the structure, calculated real part of optical conductivity reveals optical transitions red-shifted compared to zero magnetic field case, conductivity is unaffected by the the amplitude of an in-plane applied magnetic field. We show that through modifying atomic d-orbitals conduction and valence band states by an applied electric field, we can determine and control the impact of a magnetic field on the optical response of these materials. We employ our parametrized tight-binding model with non-orthogonal sp3d5 orbitals and spin–orbit coupling, which was advanced to include the effects of an external magnetic field through Peierls substitution in the wave vector and the Zeeman energy term.

Influence of band offset, nanostructuring, and applied electric field on the optoelectronic properties of vertically stacked MoS2/WS2 materials

We theoretically investigate the electronic and optical properties of multilayer vertically stacked ${\mathrm{MoS}}_{2}/{\mathrm{WS}}_{2}$ heterostructures, focusing on the role of the ${\mathrm{MoS}}_{2}\text{\ensuremath{-}}{\mathrm{WS}}_{2}$ band offset, number of monolayers in the heterostructure, effects of an applied electric field, and size reduction in lateral direction, leading to ${\mathrm{MoS}}_{2}/{\mathrm{WS}}_{2}$-based nanowires and nanoplatelets. Given that different values of the ${\mathrm{MoS}}_{2}\text{\ensuremath{-}}{\mathrm{WS}}_{2}$ band offset have been reported, we show that the band offset determines the ordering of the energy levels in the valence band and spin projections at the $K$ point of the Brillouin zone. These variations as function of the value of the band offset are suppressed in an external electric field. For multilayer ${\mathrm{MoS}}_{2}/{\mathrm{WS}}_{2}$-based nanostructures, our calculations reveal nanowires and nanoplatelets with S-atom edges exhibit a metallic character, but nanowires with one S-atom and other Mo/W edge show the band gap with electrons located in ${\mathrm{MoS}}_{2}$ and holes in ${\mathrm{WS}}_{2}$ layer. The band gap can be controlled by the size of the nanowire in lateral direction and number of layers. The calculated real part of optical conductivity show that the lowest optical transitions originate from the optical transitions in ${\mathrm{MoS}}_{2}$ layers. The electronic structure is obtained from a parametrized tight-binding model that includes nonorthogonal ${sp}^{3}{d}^{5}$ orbitals and spin orbit coupling. Our results are gauged with respect to those extracted from density functional theory and $GW$ methods to ensure the high quality of our predictions.

Lattice Dynamics of Gd1−xYxMn2O5 Investigated by Infrared Spectroscopy

We present infrared (IR) reflectivity of Gd1-xYxMn2O5 with x = 0, 0.2, 0.4, 0.6, 0.8, and 1 in the frequency range 30–1000 cm−1. A total of 18 IR active phonons were observed for GdMn2O5 (x=0) and three additional phonons have been observed with increasing x, marking a total of 21 phonons in YMn2O5 (x=1). A systematic investigation was performed to map out the structural distortion through the lattice vibration and discuss the consequences of frequency shifts in phonon modes. In addition, we have calculated the real part of optical conductivity (σ1(ω)) which reflects the semiconducting nature of Gd1-xYxMn2O5.

First principle study on electronic structure, structural phase stability, optical and vibrational properties of Ba2ScMO6 (M = Nb, Ta)

First principle calculations are performed to investigate the electronic structure, structural phase stability, optical and vibrational properties of double perovskite oxide semiconductors namely Ba2ScMO6 (M = Nb, Ta) in the cubic symmetry using WIEN2k. In order to study the ground state properties of these compounds, the total energies are calculated as a function of reduced volumes and fitted with Brich Murnaghan equation. The estimated ground state parameters are comparable with the available experimental data. Calculations of electronic band structure on these compounds reveal that both Ba2ScNbO6 and Ba2ScTaO6 exhibit a semiconducting behavior with a direct energy gap of 2.78 and 3.15 eV, respectively. To explore the optical transitions in these compounds, the real and imaginary parts of the dielectric function, refractive index, extinction coefficient, reflectivity, optical absorption coefficient, real part of optical conductivity and the energy-loss function are calculated at ambient pressure and analyzed. The collective Raman active modes of the atoms of these materials are also calculated in order to understand the structural stability of these compounds.

Electronic structure, structural phase stability, optical and thermoelectric properties of Sr2AlM'O6 (M' = Nb and Ta) from first principle calculations

First principle calculations are performed to investigate the electronic structure, structural phase stability, optical properties and thermoelectric properties of double perovskite oxide semiconductors namely Sr2AlM'O6 (M' = Nb and Ta) in the cubic symmetry using WIEN2k. In order to study the ground state properties of these compounds, the total energies are calculated as a function of reduced volumes and fitted with Brich Murnaghan equation. The estimated ground state parameters are comparable with the available experimental data. Calculations of electronic band structure on these compounds have been carried out using generalized gradient approximations and modified Becke-Johanson potential (TB-mBJ). The calculated band gap for Sr2AlNbO6 and Sr2AlTaO6 with GGA and TB-mBJ reveal that these compounds exhibit semiconducting behavior with a direct band gap. To explore the optical transitions in these compounds, the real and imaginary parts of the dielectric function, refractive index, extinction coefficient, reflectivity, optical absorption coefficient, real part of optical conductivity and the energy-loss function are calculated at ambient conditions and analyzed both with GGA and TB-mBJ potentials. Investigations of the thermoelectric properties of these compounds have been carried out by the calculations of transport coefficients based on Boltzmann transport theory in order to analyze the variation of Seebeck's coefficient at different temperatures for various carrier concentrations based on the electronic structure near the valence band maxima.

Elastic and Optoelectronic Properties of KCdF3: ab initio Calculations through LDA/GGA/TB-mBJ within FP-LAPW Method

Ab initio calculations are performed on the electronic, structural, elastic and optical properties of the cubic per-ovskite KCdF3. The Kohn—Sham equations are solved by applying the full potential linearized augmented plane wave (FP-LAPW) method. The exchange correlation effects are included through the local density approximation (LDA), generalized gradient approximation (GGA) and modified Becke-Johnson (mBJ) exchange potential. The calculated lattice constant is in good agreement with the experimental result. The elastic properties such as elastic constants, anisotropy factor, shear modulus, Young's modulus and Poisson's ratio are calculated. KCdF3 is ductile and elastically anisotropic. The calculations of the electronic band structure, density of states (DOS) and charge density show that this compound has an indirect energy band gap (M—Γ) with a mixed ionic and covalent bonding. The contribution of the different bands is analyzed from the total and partial density of states curves. Optical response of the dielectric functions, optical reflectivity, absorption coefficient, real part of optical conductivity, refractive index, extinction coefficient and electron energy loss, are presented for the energy range of 0–40 eV. The compound KCdF3 can be used for high-frequency optical and optoelectronic devices.