Thermal response of electronic, optical, mechanical properties, phonon frequencies, and sound velocity of InPxAsySb1-x-y/InAs quaternary semiconductor system

The temperature dependence of acoustic velocities, thermal properties, and phonon frequencies, mechanical, electronic, and optical properties for the InPxAsySb1-x-y/InAs system has been studied. The physical properties of the binary components InSb, InP, and InAs that constitute the quaternary alloy were used in this research. The study has been done using the empirical pseudo-potential method (EPM) under the virtual crystal approximation (VCA). The thermal properties, phonon frequencies, and acoustic velocities for the InPxAsySb1-x-y/InAs system under the effect of temperature have not been fully studied. Therefore, we have focused on these properties under the influence of temperature. Due to the lack of the published theoretical and experimental values on these properties, our findings will provide a significant reference for future experimental work.

Polaritonic crystal formed of a tunnel-coupled microcavity array and an ensemble of quantum dots

Propagation of polariton excitations in a defect-containing one-dimensional lattice of microcavities with embedded ultracold atomic nanoclusters (quantum dots) is being considered. The virtual crystal approximation is used to study the properties of electromagnetic excitation spectrum resulting from random variations of the atomic subsystem composition and positions of micropores, as well as from a homogeneous elastic deformation of the considered one-dimensional structure. The group velocity dependence of polariton excitations on structural defect concentration and on deformation parameter is being numerically modeled.

Lattice parameters and electronic bandgap of orthorhombic potassium sodium niobate K$$_{0.5}$$Na$$_{0.5}$$NbO$$_{3}$$ from density-functional theory

We perform a theoretical analysis of the structural and electronic properties of sodium potassium niobate K$$_{1-x}$$ 1 - x Na$$_{x}$$ x NbO$$_{3}$$ 3 in the orthorhombic room-temperature phase, based on density-functional theory in combination with the supercell approach. Our results for $$x=0$$ x = 0 and $$x=0.5$$ x = 0.5 are in very good agreement with experimental measurements and establish that the lattice parameters decrease linearly with increasing Na contents, disproving earlier theoretical studies based on the virtual-crystal approximation that claimed a highly nonlinear behavior with a significant structural distortion and volume reduction in K$$_{0.5}$$ 0.5 Na$$_{0.5}$$ 0.5 NbO$$_{3}$$ 3 compared to both end members of the solid solution. Furthermore, we find that the electronic bandgap varies very little between $$x=0$$ x = 0 and $$x=0.5$$ x = 0.5 , reflecting the small changes in the lattice parameters. Graphic abstract

Engineering the Thermal Conductivity of Doped SiGe by Mass Variance: A First-Principles Proof of Concept

Thermal conductivity of bulk Si0.5 Ge0.5 at room temperature has been calculated using density functional perturbation theory and the phonon Boltzmann transport equation. Within the virtual crystal approximation, second- and third-order interatomic force constants have been calculated to obtain anharmonic phonon scattering terms. An additional scattering term is introduced to account for mass disorder in the alloy. In the same way, mass disorder resulting from n- and p-type dopants with different concentrations has been included, considering doping with III-group elements (p-type) such as B, Al, and Ga, and with V-group elements (n-type) such as N, P, and As. Little effect on the thermal conductivity is observed for all dopants with a concentration below 1021 cm−3. At higher concentration, reduction by up to 50% is instead observed with B-doping in agreement with the highest mass variance. Interestingly, the thermal conductivity even increases with respect to the pristine value for dopants Ga and As. This results from a decrease in the mass variance in the doped alloy, which can be considered a ternary system. Results are compared to the analogous effect on the thermal conductivity in doped Si.

Theoretical calculation for the phonon spectrum and thermodynamic functions of vanadium and its hydride

Based on density functional theory(DFT), using virtual crystal approximation and generalized gradient approximation(GGA)with pseudopotential method, the lattices and energies for five crystallines of vanadium hydrides are optimized and calculated. The phonon densities of states are calculated based on density functional perturbation theory(DFPT). The standard Heat capacities, Entropies, Helmholtz free energies and Gibbs functions of vanadium and its hydride are deduced at 298.15K. The calculated results are discussed and compared with experimental data.

An innovative technique for electronic transport model of group-III nitrides

An optimized empirical pseudopotential method (EPM) in conjunction with virtual crystal approximation (VCA) and the compositional disorder effect is used for simulation to extract the electronic material parameters of wurtzite nitride alloys to ensure excellent agreement with the experiments. The proposed direct bandgap results of group-III nitride alloys are also compared with the different density functional theories (DFT) based theoretical results. The model developed in current work, significantly improves the accuracy of calculated band gaps as compared to the ab-initio method based results. The physics of carrier transport in binary and ternary nitride materials is investigated with the help of in-house developed Monte Carlo algorithms for solution of Boltzmann transport equation (BTE) including nonlinear scattering mechanisms. Carrier–carrier scattering mechanisms defined through Coulomb-, piezoelectric-, ionized impurity-, surface roughness-scattering with acoustic and intervalley scatterings, all have been given due consideration in present model. The direct and indirect energy bandgap results have been calibrated with the experimental data and use of symmetric and asymmetric form factors associated with respective materials. The electron mobility results of each binary nitride material have been compared and contrasted with experimental results under appropriate conditions and good agreement has been found between simulated and experimental results.

Structural stability, hardness, fracture toughness and melting points of Ta1-xHfxC and Ta1-xZrxC ceramics from first-principles

We systematic investigated the influence of substitution of Hf and Zr atoms for Ta atoms in TaC using first-principles supercell (SC) method and virtual crystal approximation (VCA) methods, including the impurity formation energy, lattice constant, volume, elastic constants, elastic moduli, melting points, fracture toughness and density of states of the Ta 1-x Hfx C and Ta1-x Zrx C ceramics in the whole range of content 0≤ x ≤1. Our calculated results show that the stability of Ta 1-x Hf x C and Ta 1-x Zrx C increases with the increase of Hf and Zr content, and Ta1-x Zrx C is more stable than Ta1-x Hfx C at the same content of Hf and Zr. The lattice constants and volumes dilate with the increase of Hf and Zr content. Furthermore, Ta1-x Hfx C and Ta1-x Zrx C carbides are mechanically stable and brittle. The bulk modulus of Ta1-x Hfx C and Ta1-x Zrx C decreases with the increasing content of Hf and Zr. Moreover, the hardness, fracture toughness, and melting point of Ta1-x Hf x C and Ta1-x Zrx C solid solutions have the peak. In particular, Ta0.8Hf0.2C has the highest hardness, largest fracture toughness and highest melting temperature.