共查询到20条相似文献,搜索用时 31 毫秒
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《Physics letters. A》2019,383(25):3037-3042
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First principle calculations have been employed to investigate the effects of Y concentration, pressure and temperature on various properties of () alloys using density functional theory (DFT). The full potential linearized augmented plane wave (FP-LAPW) method within a framework of the generalized gradient approximation (GGA) is used to perform the calculated results of this paper. Phase stability of alloys is studied using the total energy versus unit cell volume calculations. The equilibrium lattice parameters of these alloys are in good agreement with the available experimental results. The mechanical stability of alloys is proved using elastic constants calculations. Also, the influence of Y concentration on elastic properties of alloys such as Young's modulus, shear modulus, Poisson's ratio and anisotropy factor are investigated and analyzed. By considering both Pugh's ratio and Poisson's ratio, the ductility and brittleness of these alloys are studied. In addition, the total density of states and orbital's hybridizations of different atoms are investigated and discussed. Moreover, the effect of pressure and temperature on some important thermodynamic properties is investigated. 相似文献
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《Physics letters. A》2019,383(19):2333-2338
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Physically natural assumption says that any relaxation process taking place in the time interval , may be represented as a composition of processes taking place during time intervals and where is an arbitrary instant of time such that . For the Debye relaxation such a composition is realized by usual multiplication which claim is not valid any longer for more advanced models of relaxation processes. We investigate the composition law required to be satisfied by the Cole-Cole relaxation and find its explicit form given by an integro-differential relation playing the role of the time evolution equation. The latter leads to differential equations involving fractional derivatives, either of the Caputo or the Riemann-Liouville senses, which are equivalent to the special case of the fractional Fokker-Planck equation satisfied by the Mittag-Leffler function known to describe the Cole-Cole relaxation in the time domain. 相似文献
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BN-AlN alloys are potential candidates to achieve wide band gap material for ultraviolet device applications. By combing density functional theory and evolutionary structure predictions, we systematically explore the thermodynamic, mechanical, dynamical and optical properties of alloys. Through structure search, three compounds (cubic (, and , space group P-43m), and tetragonal (, space group P-42m)) have been predicted. The calculated relative large formation enthalpies suggest that large miscibility gap exists in BAlN alloys. In addition, computed elastic constants and phonon show that these structures are mechanically and dynamically stable. From the state of the art LDA-1/2 we show that the direct band gap of BN-AlN evinces strong deviation from a linear dependence on B composition. We found -in particular- giant direct band gap bowing parameter of eV for the entire range of composition, where b parameter is found to be sensitive to composition x. From a detailed analysis of the physical origin of the optical gap bowing b, we found that structural and chemical contributions play the most significant effects behind the huge optical band gap bowing parameter of BAlN alloys. 相似文献
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《Physics letters. A》2019,383(17):2114-2119
We provide a detailed analysis of a topological structure of a fermion spectrum in the Hofstadter model with different hopping integrals along the -links (), defined on a honeycomb lattice. We have shown that the chiral gapless edge modes are described in the framework of the generalized Kitaev chain formalism, which makes it possible to calculate the Hall conductance of subbands for different filling and an arbitrary magnetic flux ϕ. At half-filling the gap in the center of the fermion spectrum opens for , a quantum phase transition in the 2D-topological insulator state is realized at . The phase state is characterized by zero energy Majorana states localized at the boundaries. Taking into account the on-site Coulomb repulsion U (where ), the criterion for the stability of a topological insulator state is calculated at , . Thus, in the case of , the topological insulator state, which is determined by chiral gapless edge modes in the gap Δ, is destroyed. 相似文献
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Onyekachi Kalu José Alberto Duarte Moller Armando Reyes Rojas 《Physics letters. A》2019,383(10):1037-1046
Nanoparticles of were synthesized by a simple sol gel route with the combination of chelating agents. Effect of cadmium on the phase, structural, morphological and optical properties of the synthesized nanoparticles has been studied and reported by using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FTIR) and UV–Vis diffuse reflectance spectroscopy (UV–vis DRS). The crystal size, lattice parameters, unit cell volume, X-ray density, inter-planar distances and bond length were obtained and analyzed from the XRD data. The X-ray analysis reveals the formation of a single phase with a hexagonal wurtzite structure, where an increase of the cell volume was achieved as the Cd content was increased as well. Synthesized nanoparticle were nearly spherical at nano-size regime and are loosely agglomerated as observed from the SEM analysis. EDX spectra of the composition confirmed the appropriate stoichiometric ratio. A fundamental absorption peak centered at 375 nm was observed from the UV–visible absorption spectra which shifted towards a higher wavelength correlating the narrowing of the energy band gap due to increase in Cd content. The structural adjustment from the IR spectra confirmed the stretching vibration of Zn–O in the lattice with Cd content. 相似文献
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《Physics letters. A》2019,383(25):3180-3186
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《Physics letters. A》2019,383(18):2229-2234
In this work, the exchange bias behavior and magnetocaloric effect have been studied in Mn7Sn4 alloy. The X-ray powder diffraction pattern recorded at room temperature indicates that the sample crystallizes in a single phase with Ni2In-type hexagonal structure (space group ). The maximum magnetic entropy change value across paramagnetic/ferrimagnetic transition is about 3.3 J kg−1 K−1 under the magnetic field change of . With further cooling, the reentrant spin-glass-like state is obtained below 150 K, for which the exchange bias effect has been observed. The exchange bias field is ∼7.8 mT and ∼6.7 mT at when the cooling field is and 0.5 T, respectively. The magnetic behavior and the origin of exchange bias in Mn7Sn4 are discussed. 相似文献
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Dapeng Liu Binod R. Giri Milán Szőri Béla Viskolcz Et-touhami Es-sebbar Aamir Farooq 《Proceedings of the Combustion Institute》2021,38(1):967-976
NOx mitigation is a central focus of combustion technologies with increasingly stringent emission regulations. NOx can also enhance the autoignition of hydrocarbon fuels and can promote soot oxidation. The reaction between allyl radical (C3H5) and NOx plays an important role in the oxidation kinetics of propene. In this work, we measured the absolute rate coefficients for the redox reaction between C3H5 and NOx over the temperature range of 1000–1252 K and pressure range of 1.5–5.0 bar using a shock tube and UV laser absorption technique. We produced C3H5 by shock heating of C3H5I behind reflected shock waves. Using a Ti:Sapphire laser system with frequency quadrupling, we monitored the kinetics of C3H5 at 220 nm. Unlike low-temperature chemistry, the two target reactions, C3H5 + NO → products (R1) and C3H5 + NO2 → products (R2), exhibited a strong positive temperature dependence for this radical-radical type reaction. However, these reactions did not show any pressure dependence over the pressure range of 1.5–5.0 bar, indicating that the measured rate coefficients are close to the high-pressure limit. The measured values of the rate coefficients resulted in the following Arrhenius expressions (in unit of cm3/molecule/s):To our knowledge, these are the first high-temperature measurements of allyl + NOx reactions. The reported data will be highly useful in understanding the interaction of NOx with resonantly stabilized radicals as well as the mutual sensitization effect of NOx on hydrocarbon fuels. 相似文献
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《Physics letters. A》2020,384(36):126930
We consider quantum bosons with contact interactions at the Lowest Landau Level (LLL) of a two-dimensional isotropic harmonic trap. At linear order in the coupling parameter g, we construct a large, explicit family of quantum states with energies of the form , where and are integers. Any superposition of these states evolves periodically with a period of until, at much longer time scales of order , corrections to the energies of order may become relevant. These quantum states provide a counterpart to the known time-periodic behaviors of the corresponding classical (mean field) theory. 相似文献
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J.E. Hirsch 《Physics letters. A》2019,383(1):83-90
We find that the bulk moment of inertia per unit volume of a metal becoming superconducting increases by the amount , with the bare electron mass and the classical electron radius. This is because superfluid electrons acquire an intrinsic moment of inertia , with the London penetration depth. As a consequence, we predict that when a rotating long cylinder becomes superconducting its angular velocity does not change, contrary to the prediction of conventional BCS-London theory that it will rotate faster. We explain the dynamics of magnetic field generation when a rotating normal metal becomes superconducting. 相似文献