Theoretical Investigations Of Physical Properties Research Articles

Theoretical investigation of physical properties of Sr 2 XNbO 6 (X = La, Lu) double perovskite oxides for optoelectronic and thermoelectric applications

The cubic Sr2XNbO6 (X = La, Lu) double perovskite oxides (DPOs) have been examined by density functional theory (DFT). Structural, elastic, electronic, thermoelectric (TE), and optical characteristics are computed by utilizing the full-potential linearized augmented plane wave method (FP-LAPW). It is probed that Sr2LaNbO6 and Sr2LuNbO6 are semiconductors with direct band gap (Eg) of 4.02 and 3.7 eV, respectively at theΓ symmetry points. To ensure the structure's stability, the Goldschmidt tolerance factor (τ) and the enthalpy of formation energy ( ∆E) are determined. Shear modulus (G), poisson's ratio (χ), elastic coefficient (Cij), anisotropy (A), bulk moduli (B), young's modulus (Y), and pughratio (B/G) are computed. Furthermore, thermoelectric (TE) features such as seebeck coefficient (S), figure of merit (ZT), electrical conductivity (σ), power factor (PF), and thermal conductivity (K) are determined by using BoltzTrap code. The estimated values of ZT reveal that Sr2LuNbO6 is a more promising material for TE applications. Optical characteristics such as absorption coefficient α(ω), dielectric constant ε(ω), optical conductivity σ(ω), refractive index n(ω), and reflectivity R(ω) are also calculated. Computation indicated that Sr2XNbO6 (X = La, Lu) are promising materials for TE and optoelectronics applications in the UV region.

Theoretical investigations of physical properties of Pt-based half-Heusler alloys PtMnZ (Z = Se, Sn, Te) for spintronic applications

ABSTRACT The structural, mechanical, thermal, electronic and magnetic properties of Pt-based half-Heusler alloys XYZ (X = Pt, Y = Mn, Z = Se, Sn, Te) are determined using FP-LAPW method based on density functional theory (DFT). The exchange–correlation potential is treated with the generalised gradient approximation described by Perdew–Burke–Ernzerhof (PBE-GGA), GGA plus band correlated Hubbard parameter (GGA + U) approximations. Structural results reveal that the PtMnZ half-Heusler alloys (Z = Se, Sn, Te) have metallic character. The negative values obtained for formation energies confirm that our compounds can be synthesised and stabilised experimentally ensuring the stability of these compounds, which is confirmed too by the results of mechanical properties. The thermodynamic ones are also studied through Debye quasi-harmonic model such as Debye temperature and the heat capacity. The calculated electronic properties unveil the metallic nature of the studied compounds. The computed magnetic properties reveal that the total magnetic moment is mainly emanated from the transition metal element. Results suggest that PtMnZ (Z = Se, Sn, Te) compounds are promising candidates for spintronic devices.

Theoretical investigation of physical properties of the spinel ZnFe2O4 compound: Ab-initio calculation

ABSTRACT The electronic, magnetic, optical and transport properties of ZnFe2O4 compound are calculated using the density functional theory implemented on Wien2k code with GGA + U approximation. The results obtained are in good agreement with the experimental results. In the visible range, ZnFe2O4 has a coefficient of absorption over 104/cm. The first and main critical point calculated with GGA + U appears at 2.10 eV, which is known as optical absorption edge. In addition, the X-ray Magnetic Circular Dichroic (XMCD) spectra exhibit two peaks in L3 edge revealing the existence of Fe3+ and Fe2+ ions, occupying the octahedral sites. Finally, using XMCD and XAS methods, we can calculate the spin and orbital moments of bulk spinel ferrite ZnFe2O4 compound.

Theoretical investigations of physical properties of AlxScyB1− x− yN quaternary alloys

A computed investigation on the structural, elastic, electronic, phonon frequencies and thermal properties of Al x Sc y B 1− x− y N quaternary alloys in the zinc-blend phase has been made with first-principles methods. The information on the lattice constant, lattice matching to AlN substrate and energy band gaps is indispensable for various practical applications. We have studied the effect of Sc concentration y ( y = 0, 0.152, 0.303, 0.455 and 0.607) on the lattice constant, bulk modulus, elastic constants C 11, C 12 and C 44, band gaps, optical phonon frequencies ( ω TO and ω LO ), static and high-frequency dielectric coefficient ɛ(0) and ɛ( ∞) and dynamic effective charge Z*. We remark an important deviation from the linear concentration dependence of the lattice constant and bulk modulus. The shear moduli, Young's modulus, Poisson's ratio were estimated in the frame work of the Voigt–Reuss–Hill approximation. The resistance to changes in bond length and lateral expansion in Al x Sc y B 1− x− y N increase with increasing y concentration. We observe that at y concentration about 0.11, the Г– X indirect fundamental gap becomes Г– Γ direct fundamental gap in Al x Sc y B 1− x− y N. There is well agreement between our results and the experiment data for AlN binary compound which is a support for those of the quaternary alloys that we report for the first time.

Monodisperse poly(triacetylene) oligomers extending from monomer to hexadecamer: joint experimental and theoretical investigation of physical properties

A series of monodisperse Et3-Si-end-capped poly(triacetylene) (PTA) oligomers ranging from monomer to hexadecamer was prepared by a fast and efficient statistical deprotection-oxidative Hay oligomerization protocol. The PTA oligomers exhibit an increasingly deep-yellow color with lengthening of the pi-conjugated backbone, feature excellent solubility in aprotic solvents, and exhibit melting points up to > 22 degrees C for the hexadecameric rod. This new dramatically extended oligo(enediyne) series now enables to investigate the evolution of the physico-chemical effects in PTAs beyond the linear 1/n versus property regime into the higher oligomer region where saturation becomes apparent. We report the results of joint experimental and theoretical studies, including analysis of the 13C NMR spectra, evaluation of the linear (UV/ Vis) and nonlinear [third-harmonic generation (THG) and degenerate four-wave mixing (DFWM)] optical properties, and characterization of the redox properties with cyclic and steady-state voltammetry. Up to the hexadecameric rod, an increasingly facile one-electron reduction step is observed, showing at the stage of the dodecamer, a leveling off tendency from the linear correlation between the inverse number of monomer units and the first reduction potential. The effective conjugation length (ECL) determined by means of UV/Vis spectroscopy revealed a pi-electron-delocalization length of about n = 10 monomeric units, which corroborates well with the oligomeric length for which in the 13C NMR spectrum C(sp2) and C(sp) resonances start to overlap. Third-harmonic generation (THG) and degenerate four-wave mixing (DFWM) measurements revealed for the second-order hyperpolarizability gamma a power law increase gammma-alpha-n(a) for oligomers up to the octamer with exponential factors a= 2.46+/-0.10 and a=2.64+/-0.20, respectively, followed by a smooth saturation around n = 10 repeating units. The power law coefficient a calculated with the help of the valence effective Hamiltonian (VEH) method combined to a sum-over-states (SOS) formalism corroborates well with the values found by both THG and DFWM experiments. Up to the PTA heptamer, INDO (intermediate neglect of differential overlap)-calculated gas-phase ionization potentials and electron affinities obey a linear relationship as a function of the inverse number of monomer units displaying a strong electron-hole symmetry. The onset of saturation for the electron affinity is calculated to occur around the octamer, in accordance with experimentally obtained results from electrochemical measurements.