Physics of the Solid State最新文献

Abstract

This study investigated the structural, mechanical, piezoelectric, and electromechanical properties of AlScN thin films using density functional theory (DFT) under varying levels of applied pressure, ranging from 0 to 20 GPa. The primary focus of this research is to explore the feasibility of optimizing AlScN thin films for surface acoustic wave (SAW) applications through pressure-induced modifications. Our findings reveal two significant outcomes. First, we observe a notable increase in the elastic constant C₃₃ as a function of pressure. This increase signifies a substantial enhancement in material stiffness, directly influencing wave propagation and velocity within the thin films. Second, a remarkable 68% improvement in the piezoelectric constant, d₃₃, is identified for Al_0.75Sc_0.25N at an applied pressure of 20 GPa compared to Al_0.75Sc_0.25N at 0 GPa. This enhancement has a profound impact on the electromechanical coupling characteristics of the material. These results underscore the potential for tuning the piezoelectric response of AlScN thin films using applied pressure, offering a promising avenue for enhancing the performance of SAW-based AlScN devices.

Abstract

The purpose of this study was to investigate the influence of dual doping with Fe and Co on the microstructural, morphological, and optical properties of ZnO nanoparticles (NPs). Zn_0.97–xFe_0.03Co_xO (x = 0, 0.01, 0.02, and 0.03) NPs were prepared via a solid-state reaction method using high-purity ZnO, Fe, and Co NPs. This study was performed using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV-visible spectrophotometry, photoluminescence (PL), and energy-dispersive X‑ray spectroscopy (EDS). XRD analysis revealed that all samples presented a pure hexagonal wurtzite str-ucture without any trace of Fe, Co, or their oxides, indicating that the dopant ions were well-substituted Zn ions. However, some peaks appear in the spectrum of the Zn_0.94Fe_0.03Co_0.03O sample, corresponding to the secondary spinel phases ZnCo₂O₄ and CoFe₂O₄. FE-SEM micrographs showed that all samples exhibited sphere-like particles, and their sizes, aggregation degree, and morphology were slightly influenced by the dopant content. The estimated bandgap values decreased from 3.24 eV for undoped ZnO to 3.17 eV for Zn_0.95Fe_0.03Co_0.02O NPs and then slightly increased. Moreover, the refractive index was evaluated from the bandgap energy using Moss, Ravindra Hervé-Vandamme, and Reddy models, and then compared. The PL spectra of all samples revealed strong and sharp emission peaks in the UV region, which increased in intensity as the Co content increased.

Abstract

Cu–Fe–Pd alloys have great versatility and the promise of extensive applications across numerous fields of industry and have become a focal point of scientific inquiry and exploration. The effect of order-disorder phase transformation on structure and thermal properties has been investigated in ternary Cu₇₅Fe₀₅Pd₂₀ alloy by using high-temperature X-ray diffraction and differential scanning calorimetry. High-temperature X-ray diffraction experiments for the sample pre-annealed at 723 K have revealed the formation of an L1₂‑type ordered structure up to 805 K and disordered face centered cubic (f.c.c.) structure above 805 K. The lattice parameter is observed to be larger than that predicted by Vegard’s rule. This is due to the fact that the addition of Fe weakens the interatomic forces in the alloy. The integrated intensity data was used to determine thermal parameters. The phase transition occurring at T_c is of the first order because a sudden change in lattice parameter and linear thermal expansion coefficient is observed. These parameters collectively suggest that the investigated alloys could be advantageous for the automobile and space industries.

Abstract

It is well established, both theoretically and experimentally, that unstrained monolayer graphene shows linear dispersion as defined by Dirac equation of massless Fermions. But, when it is subjected to anisotropic strain, the two Dirac points get shifted from their equilibrium positions and they merge when the applied strain attains a threshold value. Near the merging point, dispersion energy is found to deviate from linearity and band gap opens up turning graphene to behave as semiconductor. A detailed calculation shows that unlike normal semiconductors with direct band gap its dispersion energy is non-parabolic around the merging point and the curvature of non-parabolicity changes with the variation of the direction of the applied anisotropic strain. Not only that, the threshold value of strain for band gap opening varies periodically between specified maximum and minimum as the strain is applied in the directions further away from the zigzag edge. To study these atypical features, a generalized expression for strain induced non-linear dispersion relation of monolayer intrinsic graphene has been formulated under tight-binding approximation (TBA). Also, the band gap energy, density of states (DOS) and electron effective mass (EEM) have been determined as a function of the magnitude of strain as well as its direction of application.

An Erratum to this paper has been published: https://doi.org/10.1134/S1063783423900018

Abstract

The theoretical investigation of acoustic phonons in Si/Ge three-dimensional quantum dots superlattices (supracrystals) is presented. The acoustic phonon energy spectra are calculated in the framework of the face-centered cubic cell molecular-dynamic model. The dependencies of phonon density of states and phonon group velocity on the phonon energy are studied; the average phonon velocity is found to be close to zero in the wide range of phonon energies (hbar omega > 10) meV. The results allow us to predict the extremely low value of the lattice thermal conductivity in supracrystals and correspondingly high value of the thermoelectric figure of merit ZT.

Abstract

In recent decades, much interest has been shown in nonlinear lattice vibrations because crystalline materials are subjected to high-amplitude impacts in many fields of human activity. One of the effects of nonlinearity in discrete periodic structures is the possibility of existence of spatially localized high-amplitude vibrations, referred to as discrete breathers (DBs), or intrinsic localized modes. The problem of searching for DBs in nonlinear chains (i.e., one-dimensional crystals) can be solved in a fairly simple way, because the variety of possible DBs is small in this case. However, no general approaches to the search for DBs have been developed for high-dimension crystal lattices. Such an approach was derived based on the works by Chechin, Sakhnenko et al., who developed the theory of bushes of nonlinear normal modes, which (as applied to crystals) were later referred to as delocalized nonlinear vibrational modes (DNVMs). It has recently been noted that all known DBs can be obtained by superimposing localizing functions on DNVMs with a frequency beyond the phonon spectrum of the lattice. Since the Chechin and Sakhnenko theory makes it possible to find all possible DNVMs by considering the lattice symmetry, it has become possible to formulate the problem of determining all possible DBs in a given lattice. This approach has recently been applied with success to the search for DBs in a two-dimensional triangular lattice. The purpose of this study is to analyze and describe DBs in a two-dimensional square lattice obtained using a localizing function. As a result, new types of DBs of a square lattice are obtained, including one-dimensional DBs (i.e., those localized only in one of two orthogonal directions) and zero-dimensional DBs (i.e., those localized in two directions).

Abstract

Samples of Ni-based super alloy are received by the method of direct metal deposition. Annealing at temperature 1180°С during 4 h is provided. Measurements of hardness, optical metallography, X-ray analysis are carried out. It was found that direct metal deposition of samples from Ni-based super alloy EP648 lead to Ni solid solution of alloying elements with face-centered cubic structure having lattice period a = 7.11 Å, also structure of Ni₂Cr, is slightly revealed by optical metallography. Annealing at temperature 1180°С during 4 h of the direct metal deposited samples of super alloy EP648 lead to hardness increasing from от 19 ± 4 HRC to 34 ± 0.3 HRС, the uniformity of values are observed. After annealing the face-centered cubic structure is revealed, high value of lattice period is saving; presence of the phase Ni₂Cr and sedimentation of Ni₃Cr₂ are found. Residual tensile macro stresses are found.

Abstract—

Steel 45 surface is aluminized by electroexplosive alloying. The aluminized surface is treated by an electron beam. The structure and mechanical properties of the surface layer are studied. The electroexplosive is shown to lead to the formation of a high-porous coating on the steel surface. The subsequent electron-beam treatment in a mode of melting the surface layer is accompanied by the formation of a smooth surface, the increase in the microhardness in a layer thickness of 45–50 µm by a factor of 3.5 as compared to that of the initial material. The physical nature of the increase in the strength properties of a steel surface layer is explained.

Abstracts

One of the most crucial tasks for the mining, ore, and wood processing industries is import substitution and reengineering of components from foreign machinery. In this study, the chemical composition and structure of a worn component from crushing equipment are investigated using reengineering principles. It is determined that the examined samples are made from high-chromium cast iron ChKh28, additionally alloyed with molybdenum, vanadium, and nickel. The closest foreign analogue of this material may be the steel grade DIN 1695-81: G-260Cr27. The research results indicate that the casting material underwent heating to temperatures of 950–1050°C, followed by holding at these temperatures for a minimum of 2 h with subsequent air cooling to temperatures of 160–200°C and tempering at 200°C for a minimum of 2 h. This is confirmed by the hardness of the specimens reaching 63–64 HRC and the high degree of equilibrium in their structural-phase state and phase homogeneity.