Structural, electronic, and optical properties of ZnO_(1-x)Se_x alloys using first-principles calculations

The structural, electronic, and optical properties of binary ZnO, ZnSe compounds, and their ternary ZnO 1-x Se x alloys are computed using the accurate full potential linearized augmented plane wave plus local orbital (FP-LAPW + lo) method in the rocksalt (B1) and zincblende (B3) crystallographic phases. The electronic band structures, fundamental energy band gaps, and densities of states for ZnO 1-x Se x are evaluated in the range 0 ≤ x ≤ 1 using Wu-Cohen (WC) generalized gradient approximation (GGA) for the exchange-correlation potential. Our calculated results of lattice parameters and bulk modulus reveal a nonlinear variation for pseudo-binary and their ternary alloys in both phases and show a considerable deviation from Vegard's law. It is observed that the predicted lattice parameter and bulk modulus are in good agreement with the available experimental and theoretical data. We establish that the composition dependence of band gap is semi-metallic in B1 phase, while a direct band gap is observed in B3 phase. The calculated density of states is described by taking into account the contribution of Zn 3d, O2p, and Se 4s, and the optical properties are studied in terms of dielectric functions, refractive index, reflectivity, and energy loss function for the B3 phase and are compared with the available experimental data.

Bandgap engineering to tune the optical properties of Be_xMg_(1-x)X(X=S, Se, Te) alloys

Structural, electronic, and optical properties of alloys Be_xMg_(1-x)X(X = S, Se, Te) in the assortment 0 < x < 1 were theoretically reported for the first time in zinc-blende(ZB) phase. The calculations were carried out by using full-potential linearized augmented plane wave plus local orbitals(FP-LAPW+lo) formalism contained by the framework of density functional theory(DFT). Wu-Cohen(WC) generalized gradient approximation(GGA), based on optimization energy,has been applied to calculate these theoretical results. In addition, we used Becke and Johnson(m BJ-GGA) potential,modified form of GGA functional, to calculate electronic structural properties up to a high precision degree. The alloys were composed with the concentrations x = 0.25, 0.5, and 0.75 in pursuance of ‘special quasi-random structures'(SQS)approach of Zunger for the restoration of disorder around the observed site of alloys in the first few shells. The structural parameters have been predicted by minimizing the total energy in correspondence of unit cell volume. Our alloys established direct band gap at different concentrations that make their importance in optically active materials. Furthermore, density of states was discussed in terms of the contribution of Be and Mg s and chalcogen(S, Se, and Te) s and p states and observed charge density helped us to investigate the bonding nature. By taking into consideration of immense importance in optoelectronics of these materials, the complex dielectric function was calculated for incident photon energy in the range 0-15 eV.

Electronic and thermoelectric properties of alkali metal-based perovskites CsYbF3 and RbYbF3

The electronic and thermoelectric properties of alkali metal-based fluorides CsYbF3 and RbYbF3 are studied by using Wien2k and BoltzTraP codes.The structural and thermodynamic stability of these materials are confirmed by tolerance factor(0.94 and 0.99 for RbYbF3 and CsYbF3)and negative formation energy.The optimized lattice constants and bulk moduli are consistent with the results reported in the literature.The reported band gap for RbYbF3 is 0.86 eV which decreases to 0.83 eV by the replacement of Cs with Rb.The electrical and thermal conductivities along with Seebeck coefficients decrease with temperature rising from 0 K to 800 K.The large values of thermoelectric parameters for positive chemical potentials show that the character is dominated by electrons.The studied materials have figures of merit 0.82 and 0.81 at room temperature respectively,for RbYbF3 and CsYbF3 and increase with temperature rising.Therefore,the materials under study may have potential application values in thermoelectric generators and refrigerators.

Vanadium based XVO3 (X=Na, K, Rb) as promising thermoelectric materials: First-principle DFT calculations

We investigate structural,mechanical,thermodynamic,and thermoelectric properties of vanadium-based XVO3(X=Na,K,Rb)materials using density functional theory(DFT)based calculations.The structural and thermodynamic stabilities are probed by the tolerance factor(0.98,1.01,and 1.02)with the negative value of enthalpy of formation.Mechanical properties are analyzed in the form of Born stability criteria,ductile/brittle nature(Poisson and Pugh's ratios)and anisotropy factor.To explore the electronic transport properties,we study the electrical conductivity,thermal conductivity,Seebeck coefficient and power factor in terms of chemical potential and temperature.High values of Seebeck coefficient at room temperature may find the potential of the studied perovskites in thermo-electrics devices.