Lattice Vibration Frequencies Research Articles

Thermophysical properties of AlxCoCrCuFeNi high entropy alloys

The AlxCoCrCuFeNi (x = 0.25, 0.5, 1, 2) high entropy alloys (HEAs) were prepared by arc melting and spray casting techniques. Their microstructures, hardness, and thermophysical properties such as fusion enthalpy, entropy, thermal diffusion coefficients, thermal expansion coefficients, were investigated. XRD results indicated that AlxCoCrCuFeNi (x = 0.25 and 0.5) alloys were composed of a high-entropy FCC phase and Cu-rich nanophase. As the Al content increased to 1 and 2, the phase structures included the AlNi-rich B2 phase, FeCr-rich A2 phase and Cu-rich nanophase. With the increased Al content, the microstructures of AlxCoCrCuFeNi HEAs transitioned from coarse dendrites to petal-like dendrites, and the grains were continuously refined. Moreover, the Al additions reduced the density whereas increased the Vickers hardness of the alloys. The maximum hardness observed in Al2CoCrCuFeNi HEA was approximately 2.4 times greater than that of the Al0.25CoCrCuFeNi HEA. The thermal diffusion coefficients of alloys initially increased and subsequently decreased as the temperature elevated. The phase transformation induced by Al content was an effective method for rapidly homogenizing the internal temperature of alloys. Furthermore, the crystal structure, elemental segregation, lattice distortion, enthalpy and entropy of fusion, and lattice vibration frequency all mutually affected the thermal diffusion and expansion coefficients of AlxCoCrCuFeNi HEAs.

Impact of blending of phase change material for performance enhancement of solar energy storage

The contemporary challenge of energy scarcity underscores the vital necessity for effective energy storage solutions. Addressing this concern becomes particularly crucial given the abundance of solar energy available for harnessing. Thermal energy storage emerges as a pivotal approach in this context, with phase change materials serving as valuable components due to their affordability and widespread accessibility. Specifically, various inorganic salts find application as phase change materials, contributing to the development of cost-effective and readily available solutions for storing the ample energy derived from solar sources. This research assesses the impact of varying Sodium chloride (NaCl) proportions on the thermophysical properties of nitrate-based salts, specifically Sodium nitrate (NaNO3) and Potassium Nitrate (KNO3). The investigation reveals significant influences on latent heat, specific heat, and thermal conductivity. High levels of NaCl adversely impact the thermal properties, leading to a decrease in the latent heat of NaNO3 and KNO3 by 7.3 % and 4.4 %, respectively. This reduction resulted due to the disruption of the crystal structure caused by blending, which results in the initiation of melting at lower energy levels. Conversely, lower NaCl quantities, particularly 7.5 %, positively influence latent heat for both salts. Thermal conductivity and specific heat show enhancement with 7.5 % and 10 % NaCl, but further increases mitigate these properties. Microstructure analysis indicates that limited NaCl promotes a compact structure with strong bonding forces, while exceeding a threshold increases lattice vibration frequency. A network structure between NaNO3 and NaCl forms, becoming more compact and complex with increased NaCl content, impacting melting and solidification points. X-ray diffraction (XRD) analysis confirms the stability of both mixtures. The NaNO3–NaCl combination exhibits superior thermophysical properties compared to KNO3–NaCl, underscoring the importance of fine-tuning NaCl proportions for optimal performance in these salt mixtures.

Dynamic characteristics analysis of gear tooth modification in a three-stage gear system

Gears serve as vital elements in high-efficiency mechanical transmissions, playing a pivotal role in vehicles. Employing gear modification has the capacity to significantly enhance the dynamic properties of the Planetary Gear Transmission (PGT) systems. In this study, the investigation has been directed toward a three-stage PGT model system with a comprehensive consideration of various vibration-related factors that affect the dynamic behavior of the system. These factors are encompassed by Time Varying Mesh Stiffness (TVMS), torsion and bending forces experienced by connecting shafts, dynamic Transmission Error (TE), impact of gear meshing eccentric load forces, inherent flexibility in the supporting shaft structure, and influence of torque and power fluctuations originating from a multi-cylinder engine. The estimation of TVMS is carried out for both external-external and external-internal teeth meshing pairs, utilizing the Potential Energy Method (PEM). Subsequently, this study employs the lumped parameter method to establish a model with a specific objective of investigating the lateral-torsional-coupling behavior within adopted PGT model system. The lateral vibration displacement characteristics of the PGT model system is deeply analyzed, revealing the influence of speed on lateral vibration and displacement frequency domain characteristics through a 3D waterfall diagram. Furthermore, a Tooth Profile Modification (TPM) method is applied utilizing two distinct parameters namely [Formula: see text] TPM parameter and [Formula: see text] TPM parameter. The objective is to mitigate vibrations and evaluate the performance of the adopted PGT model after employing each TPM parameter through both TVMS and Root Mean Square (RMS).

Phase transitions and spectral shifts: a quantum mechanical exploration of vibrational frequency in magnesium ferrite.

Spinel ferrites represent an integral subset of magnetic materials, with their inherent properties largely influenced by cation occupancy and spin interaction. In this study, we present an in-depth theoretical exploration of the phase transition landscape of pure magnesium-ferrite, deploying hybrid functionals and a local Gaussian basis set to scrutinize the relaxed lattice structure, relative energy, magnetic properties, electronic characteristics, and vibrational frequencies. Our investigation reveals that the ground state of magnesium-ferrite is an open-shell system with an inverse structure. This is characterized by the complete occupancy of octahedral sites by magnesium atoms, with Iron atoms dispersed between both tetrahedral and octahedral sites. We found a relative energy difference of 0.41 eV between the antiferromagnetic ground configuration and the ferro arrangement within the inverse structure. Furthermore, our research also delved into the impact of spin rearrangement and inversion (X = 0.0, 0.5 and 1) on Raman and infrared spectra. Notably, the lattice distortion from the cubic form, apparent in the optimized structure, resonates in the IR and Raman spectra, resulting in significant splitting. The frequencies calculated in this study align well with experimental values, suggesting that the literature's current assignments warrant reevaluation in light of this new data. The results presented herein can be instrumental in detecting the phase of Mg ferrites from experimental spectra, thereby paving the way for a more profound comprehension of their properties and possible uses.

Many Body Aspects on the Lattice Vibrational Properties of Germanene and Silicene along Highly Symmetry Directions

The investigation of lattice vibrational properties in monolayer two-dimensional honeycomb lattices comprising 2D group-IV semiconductor materials such as Germanene and Silicene (Low Buckled structure) holds immense significance in the realm of research, owing to their potential integration into the forthcoming electronic sector for information technology. The ductile nature of 2D group-IV semiconductor materials enables seamless integration with existing semiconductor technology on substrates, setting them apart from Graphene. Our primary objective revolves around comprehending the lattice vibrational properties of Germanene and Silicene (LB) through the examination of their honeycomb and buckled lattice structures. We use the Adiabatic Bond Charge Model with a Python program to derive vibrational frequencies at the Г points along highly symmetrical directions. Moreover, we extensively analyze the acoustical and optical contributions to the lattice vibrational frequencies. We anticipate that the phonon frequencies along the Г‒M direction for 2D atomically thin Germanene and Silicene will yield reasonably similar outcomes to those other research groups achieve.

Molecular dynamics study on dynamic interlayer friction of graphene and its strain effect

Abstract This study delves into the mechanism of dynamic sliding friction between layers of graphene and its strain effect, through numerical analysis using molecular dynamics simulations. To eliminate the influence of commensurability and edge effect, a friction pair model with annular graphene as a slider is established. The research explores the quantifying effects of temperature, normal load, sliding velocity, support stiffness, and axial strain on the friction between graphene layers. The coupling effect of temperature and other influencing factors is also clarified. The results indicate that the interlayer friction increases with normal load by decreasing the interlayer spacing and increasing the atomic vibration amplitude. The ploughing phenomenon does not appear since the edge effect is eliminated by the model. Friction is initially enhanced at higher sliding velocities, but is later reduced by severe residual deformation and lattice resonance frequency. The support stiffness regulates interlayer friction by affecting the atomic vibration amplitude of the graphene lattice. Mechanism analysis shows that the number of effective contact atoms increases under axial strain, and the lattice vibration frequency is the main way to regulate the interlayer friction by strain effect. Our findings provide a fundamental understanding of the strains engineering of nanoscale friction and reveal the influence mechanism of affecting factors on the dynamic friction of graphene.

Ab initio insight into the physical properties of MgXH3 (X = Co, Cu, Ni) lead-free perovskite for hydrogen storage application.

Renewable energy systems are vital for a sustainable future, where solid-state hydrogen storage can play a crucial role. Perovskite hydride materials have attracted the scientific community for hydrogen storage applications. The current work focuses on the theoretical study using density functional theory (DFT) to evaluate the characteristics of MgXH3 (X = Co, Cu, Ni) hydrides. The structural, vibrational, electronic, mechanical, thermodynamic, and hydrogen storage properties of these hydrides were investigated. The equilibrium lattice parameters were calculated using the Birch-Murnaghan equation of state-to-energy volume curves. The elastic constants (Cij) and relevant parameters, such as Born criteria, were calculated to confirm the mechanical stability of the hydrides. The Cauchy pressure (Cp) revealed brittle or ductile behavior. The outcomes of the Pugh ratio, Poisson ratio, and anisotropy were also calculated and discussed. The absence of negative lattice vibrational frequencies in phonon dispersion confirmed the lattice's dynamic stability. The heat capacity curves of thermodynamic properties revealed that hydrides can conduct thermal energy. The metallic character and ample interatomic distances of hydrides were confirmed by the band structure and population analysis, which confirmed that hydrides can conduct electrical energy and adsorb hydrogen. The density of state (DOS) and partial DOS unveiled the role of specific atoms in the DOS of the crystal. The calculated gravimetric hydrogen storage capacity of MgCoH3, MgCuH3, and MgNiH3 hydrides was 3.64, 3.32, and 3.49wt%, respectively. Our results provide a deeper understanding of its potential for hydrogen storage applications through a detailed analysis of MgXH3 (X = Co, Cu, Ni) perovskite hydride material.

First-principles study on the lattice vibration, anisotropy, tensile strength and electronic properties of CuxHfySiz intermetallics

The stability, lattice vibrations, anisotropy in elasticity and stress–strain behavior of the CuxHfySiz ternary silicide were calculated by first-principles methods. According to the formation enthalpy and lattice vibration frequency, the CuxHfySiz phase is confirmed to be stable. The elastic constants show that these ternary borides are mechanically stable. Based on the BH/GH rule, CuHfSi is 1.788 and more significant than 1.75, which should be ductile. The elastic hardness indicates that CuHfSi2 shows the largest hardness among CuxHfySiz phases, which is 18.9 GPa. It is speculated that CuHfSi2 may be the most muscular hardness in these four types of intermetallics. The size of anisotropy expressed by anisotropy and elastic modulus three-dimensional diagram is Cu4Hf3Si4 > Cu4Hf3Si2 > CuHfSi > CuHfSi2. The structural stability, hardness and chemical bonds were further explained by electronic structures.

The lattice vibration, mechanical anisotropy, stress-strain behavior and electronic properties of HfxSiy phases: A first-principles study

The lattice vibrations, elastic anisotropy, electronic properties and stress-strain behavior of HfxSiy phases were predicted using a first-principles calculations. The enthalpies of formation and lattice vibration frequencies of HfxSiy confirmed that they are phase-stable. The results of the elastic hardness show that they are elastically anisotropic. The order of anisotropy is Hf3Si2 > HfSi > Hf2Si > HfSi2 > Hf5Si3 > Hf5Si4. HfSi2 has a maximum hardness value of 19.7 GPa and is less than 20 GPa, indicating that it is not a potential superhard material. The results of stress-strain stretching increase with stretching and start a decreasing trend after the stress value reaches its highest point. Finally, we predicted sound velocity and Debye temperature.

On-Shaft Wireless Vibration Measurement Unit and Signal Processing Method for Torsional and Lateral Vibration

Microelectromechanical systems accelerometers have opened new possibilities for vibration monitoring of a rotating machinery. They enable mounting accelerometers directly to the rotating component of the machine, e.g., shaft. This enables not only the measurement of a lateral vibration but also a torsional vibration of the machine. This increases the vibration data gathered from the machine by one measurement instrument. This article presents an on-shaft wireless universal measurement unit (UMU) with innovative combination of features, such as a high measurement range and easy mounting. The UMU has a two-sensor configuration where two accelerometers are mounted to the opposite sides of a shaft. This enables to utilize a novel signal processing method to separate torsional and lateral vibration from the data. The signal processing method combines and modifies methods presented in the published literature. The results presented in this article demonstrate that the UMU together with the presented signal processing method can measure frequencies of torsional and lateral vibration accurately. However, the amplitude comparison between the UMU and reference sensors cannot be done adequately because they are measuring either different components of the machine or different physical properties.

The Limit of the Lateral Fundamental Frequency and Comfort Analysis of a Straddle-Type Monorail Tour Transit System

The straddle-type monorail tour transit system is a light overhead steel structure, and the lateral stiffness is generally low. However, the limit of the lateral natural vibration frequency is not clear in the current codes of China, and designers may ignore it. Weak lateral stiffness will lead to a violent vibration during vehicle operation and crowds walking, affecting human comfort and structural safety. Based on a practical project, we tested the acceleration of a monorail vehicle under full load conditions, and its running stability and ride comfort were assessed. Then, the impact of pedestrians on lateral vibration under some working conditions was measured and analyzed. Furthermore, the influence of different structural parameters on the lateral fundamental frequency was investigated. The results showed the following: (i) The vehicle’s running stability and riding comfort was good. However, human comfort was poor due to the weak lateral stiffness of the structure, which was affected by human-induced vibration. (ii) The comprehensive response of the structure increased with the increase in walking frequency, increased with the increase in the number of people working or weight, and the growth speed slowed down. (iii) The structural stiffness was most sensitive to the change in steel column diameter. (iv) The recommended value of the lateral fundamental frequency limit for different spans of the straddle-type monorail tour transit system was put forward. The recommended lower limit of fundamental frequency for a 15 m span is 5.0 Hz, for an 18 m span it is 3.5 Hz, and for a 25 m span it is 2.8 Hz.

Polygonal Wear Mechanism of High-Speed Train Wheels Based on Lateral Friction Self-Excited Vibration

This work details research on the formation mechanism of wheel polygonalization in high-speed trains and its effect factors by numerical modeling in order to prevent the increasingly prevalent problem of wheel polygonal wear. The lateral self-excited vibration model of a wheel was developed using the LuGre friction model and self-excited vibration theory. The properties of wheel self-excited vibration and the crucial condition of Hopf bifurcation were investigated; the process of wheel polygonal wear was simulated and the results were validated using field tracking data. The results demonstrated that periodic self-excited vibration generated by Hopf bifurcation is a required condition for polygonal wheel attrition at a given speed. The wheel’s polygonal wear has the following characteristics: “Constant speed—Self-excited—Fixed frequency—Divisible.” The order of the polygon is determined by the ratio of the wheel lateral self-excited vibration frequency to its rotational frequency. Wheel polygonal wear was caused by the vertical dynamic force of the wheel rail. The findings of the study can serve as a theoretical foundation for the prediction and reduction of wheel polygonal wear.

Predicting Lattice Vibrational Frequencies Using Deep Graph Neural Networks.

Lattice vibrational frequencies are related to many important materials properties such as thermal and electrical conductivity as well as superconductivity. However, computational calculation of vibrational frequencies using density functional theory methods is computationally too demanding for large number of samples in materials screening. Here we propose a deep graph neural network based algorithm for predicting crystal vibrational frequencies from crystal structures. Our algorithm addresses the variable dimension of vibrational frequency spectrum using the zero padding scheme. Benchmark studies on two data sets with 15,000 mixed-structure and 35,552 rhombohedra samples show that the aggregated R2 scores of the prediction reach 0.554 and 0.724. We also evaluate the structural transferability by predicting the vibration frequencies for 239 individual cubic target structures. The R2 scores for more than 40% of the targets are greater than 0.8 and can reach as high as 0.98 for the model trained with mixed samples, while the average mean absolute error is 43.69 Thz showing low transferability across structure types. Our work demonstrates the capability of deep graph neural networks to learn to predict lattice vibration frequency when sufficient number of training samples are available.

Experimental study on flow-induced vibration response characteristics of leaching tubing in salt cavern gas storage

To address flow-induced vibration failure problems of water solution leaching tubing string in salt cavern gas storage, a laboratory experimental device for flow-induced vibration of leaching tubing string was developed based on the similarity principle, and the corresponding experimental bench was built, according to the on-site parameters of the M gas storage well in Jianghan Oilfield, China. The vibration simulation experiments were carried out, and the displacement and amplitude-frequency response data at the bottom end of the tubing string were measured. The influences of different operation parameters and structure modes, such as water injection flow rate, two-port distance, screen structure and circulation mode, on the vibration characteristics of the tubing string were explored, the failure mechanism of the leaching tubing string was revealed, and the corresponding vibration failure control methods were proposed. The results obtained demonstrate that, first, at the moment of pump start-up (corresponding to well opening on-site), the tubing string produced obvious water hammer phenomenon. With the increase of the water injection flow rate, the vibration displacement and frequency of the center tube first increase and then decrease, when the water injection flow rate is less than 1.55 L/min (corresponding to the on-site flow rate of 40 m3/h), the risk of vibration failure of leaching tubing can be reduced. Second, when the two-port distance is greater than 0.16 m (corresponding to the on-site two-port distance of 45 m), the amplitude and frequency of lateral vibration of the center tube increase significantly, and the risk of lateral vibration deformation of leaching tubing increases. Third, adding a symmetrical hole screen at the bottom of the center tube can significantly reduce the vibration displacement and frequency of leaching tubing, and improve the safety of the operation tubing string. Fourth, the vibration displacement and amplitude of the leaching tubing in the reverse circulation mode are smaller than those in the positive circulation mode. When the cavern shape requirements are met on-site, the vibration of the tubing string can be effectively reduced by using the reverse circulation cavern leaching.

Lattice Dynamics Calculations for Mg1-XZnxO Solid Solutions

Abstract In this study, Mg1-xZnxO solid solutions are studied by modelling lattice dynamics, using the methods of classical molecular dynamics. These time-efficient methods are of great interest since they allow using large crystallic structures, which reduce artificial defect periodicity. The main program used is General Utility Lattice Program (GULP). The Buckingham potential is used for modelling interatomic forces. The parameters for this potential are found for different effective ionic charges by using lattice parameters and vibrational frequencies obtained from ab initio calculations performed in the program CRYSTAL14. With these potentials, the dispersion relations and densities of states have been calculated for MgO, ZnO and Mg1-xZnxO. Calculations have been made for different Mg and Zn contents in the wurtzite and cubic phase solid solutions, respectively, using the supercell method and a large number of Brillouin zone sampling points. New interatomic potentials for interactions Mg-O, O-O, Zn-O have been obtained. These potential parameters have been verified and the phonon dispersion curves and DOS for MgO and ZnO utilising these potential parameters have been compared to other studies, both experimental and theoretical. By adding more Zn in the cubic phase (c-MgO) solution, no local vibrational modes are observed; however, there is a clear spectral widening and a noticeable change in the low frequency region (100–300 cm−1) of the DOS. Adding more Mg in wurtzite phase (w-ZnO) solution, on the other hand, results in local vibrational modes in the mid (350 cm−1) and high frequency (650 cm−1) regions.

Theoretical High Pressure Study of Phonon Density of State and Debye Temperature of Solid C60: Grüneisen Approximation Approach

A nanomaterial equation of state has been combined with Grüneisen approximation in present work to investigate the influence of high pressure on phonon density of state function of C60 through evaluating variations of lattice vibration frequencies and variation of mode density. Furthermore, the effect of high pressure on Debye temperature has been determined by using a formula of volume dependence of Debye temperature. Volume compression ratio in C60 has been computed, using a nanomaterial equation of state. Expressions of pressure dependence of phonon density of state and Debye temperature have been combined with volume compression ratio value. The evaluated result of volume compression ratio and phonon density of state have been compared with the experimental observations and good agreement can be seen.

Research on the Approximate Calculation Method of the Fundamental Frequency and Its Characteristics on a Tensioned String Bridge

As a new type of composite bridge, the dynamic structural characteristics of a tensioned string bridge need to be deeply studied. In this paper, based on the structural characteristics of a tensioned string bridge, the Rayleigh method is used to derive formulas for calculating the frequencies of vertical, antisymmetric and lateral bending vibrations. The characteristics of the vertical and lateral bending vibration frequencies are summarized. The fundamental frequencies of the antisymmetric vertical bending and lateral bending of the tensioned string bridge are the same as that of the single-span beam under the corresponding constraint conditions. The shape and physical characteristics of the main cable have no effect on the frequency. The vertical bending symmetrical vibration frequency of the tensioned string bridge is greater than the corresponding symmetrical vibration frequency of the simply supported beam. The shape and physical characteristics of the main cable have a greater impact on the vertical bending symmetrical vibration frequency than the lateral bending frequency, and the vertical bending symmetrical vibration frequency increases with an increasing rise-to-span ratio. The tension force of the main cable has no influence on the frequency of tensioned string bridges. The first-order frequency of the tensioned string bridge is generally the vertical bending symmetrical vibration frequency. By adopting a tensioned string bridge structure, the fundamental frequency of a structure can be greatly increased, thereby increasing the overall rigidity of the structure. Finally, an engineering example is applied with the finite element parameter analysis method to study the vibration frequency characteristics of the tensioned string bridge, which verifies the correctness of the formula derived in this paper. The finite element analysis results show that the errors between the derived formula in this paper and the finite element calculation results are less than 2%, indicating that the formula derived in this paper has high calculation accuracy and can meet the calculation accuracy requirements of engineering applications.

Optimizing the Proton Conductivity with the Isokinetic Temperature in Perovskite‐Type Proton Conductors According to Meyer–Neldel Rule

AbstractPerovskite‐type metal oxides such as Y‐doped BaMO3 (M = Zr/Ce) have drawn considerable attention as proton‐conducting electrolytes for intermediate temperature ceramic electrochemical cells. Improving the proton conductivity at lower temperatures requires a comprehensive understanding of the proton conduction mechanism. By applying high pressure or varying the Ce content of Y‐doped BaMO3, it is demonstrated that the proton conductivity follows the Meyer–Neldel rule (MNR) well. In the Arrhenius plot, the conductivities intersect at an isokinetic temperature, where the proton conductivity is independent of activation energy. Considering the relationship between isokinetic temperature and lattice vibration frequency, a high isokinetic temperature is observed in materials with stiff lattices, consisting of light atoms and small MO bond length. Based on consideration of the MNR, it is suggested that the enhancement of proton conductivity at low temperature can be well achieved by tuning lattice vibration frequency toward a desired isokinetic temperature.

Raman scattering of light on overtone states of transverse and longitudinal polar optical modes in a single crystal of lithium tantalate

Raman scattering spectra in single crystals of lithium tantalate at 180-degree scattering geometry in a wide spectral frequency range (50 ÷ 2800 cm−1) were studied. Raman peaks were found in 1300 ÷ 2000 cm−1 region with frequencies exceeding doubled frequencies of LiTaO3 crystal lattice fundamental vibrations of A1 and E-type. The conditions for the manifestation of bound polar phonons in lithium tantalate Raman spectra were analyzed. The spectral intensity of Raman scattering in the overtone region of the spectrum of lithium tantalate was calculated taking into account the presence of a biphonon, and a satisfactory agreement between theory and experiment was obtained.

Isotope effect in Raman scattering spectra of 32S8–34S8 solid mixtures

Raman spectra of crystalline sulfur samples of the mixed isotopic composition (32S8)1−x(34S8)x, where 0 ≤ x ≤ 1, have been studied. These spectra demonstrate synchronization of oscillations of S8 molecules of the same isotopic composition which leads to "breathing" mode splitting at 211–216 cm−1 (Davydov splitting). The level of splitting depends on the molecule content of the corresponding isotope and attains its maximum value of 4.5 cm−1 for monoisotopic samples. If the molecules of different isotopic composition of 32S8 and 34S8 are adjacent, the difference in their eigen frequencies excludes the effect of splitting. For the other vibrational modes, the change in the relative content of 32S8 and 34S8 leads to proportional change in the intensity of the spectral bands with invariable frequencies of stretching vibrations or gradual change in the frequencies of lattice vibrations.