Average Sound Velocity Research Articles

Crystal Growth and Thermal Properties of Quasi-One-Dimensional van der Waals Material ZrSe3.

ZrSe3 with a quasi-one-dimensional (quasi-1D) crystal structure belongs to the transition metal trichalcogenides (TMTCs) family. Owing to its unique optical, electrical, and optoelectrical properties, ZrSe3 is promising for applications in field effect transistors, photodetectors, and thermoelectrics. Compared with extensive studies of the above-mentioned physical properties, the thermal properties of ZrSe3 have not been experimentally investigated. Here, we report the crystal growth and thermal and optical properties of ZrSe3. Millimeter-sized single crystalline ZrSe3 flakes were prepared using a chemical vapor transport method. These flakes could be exfoliated into microribbons by liquid-phase exfoliation. The transmission electron microscope studies suggested that the obtained microribbons were single crystals along the chain axis. ZrSe3 exhibited a specific heat of 0.311 J g-1 K-1 at 300 K, close to the calculated value of the Dulong-Petit limit. The fitting of low-temperature specific heat led to a Debye temperature of 110 K and an average sound velocity of 2122 m s-1. The thermal conductivity of a polycrystalline ZrSe3 sample exhibited a maximum value of 10.4 ± 1.9 W m-1 K-1 at 40 K. The thermal conductivity decreased above 40 K and reached a room-temperature value of 5.4 ± 1.3 W m-1 K-1. The Debye model fitting of the solid thermal conductivity agreed well with the experimental data below 200 K but showed a deviation at high temperatures, indicating that optical phonons could substantially contribute to thermal transport at high temperatures. The calculated phonon mean free path decreased with temperatures between 2 and 21 K. The mean free path at 2 K approached 3 μm, which was similar to the grain size of the polycrystalline sample. This work provides useful insights into the preparation and thermal properties of quasi-1D ZrSe3.

Study on Ultrasonic Nondestructive Testing of Self-Compacting Concrete under Uniaxial Compression Test.

To study the variation law of ultrasonic parameters of self-compacting concrete before and after damage under uniaxial compression test conditions, the C30 self-compacting concrete blocks stored for 7 days and 28 days were subjected to ultrasonic nondestructive testing, and the variation law of the sound time, amplitude, and sound velocity before and after the damage of self-compacting concrete blocks was emphatically analyzed. The concrete acoustic detection software was introduced to judge and analyze the abnormal values of the parameters of each measuring point, and the defect distribution map of each test block was obtained. The results showed that after curing the self-compacting concrete test block for 7 days and 28 days, the average value of sound time before and after the failure of each measuring point of the test block is small, and the average value of sound time before the failure is less than that after; the average amplitude after failure is smaller than that before failure, and the amplitude of some measuring points will be smaller than that before. The average sound velocity after failure is less than that before failure, and the internal defects appear and the structure is not dense. This study provides a theoretical basis for the application of ultrasonic detection technology in the field of self-compacting concrete and also provides a practical basis for the stability monitoring and failure warning of self-compacting concrete.

Electronic Band Structures of the Possible Topological Insulator Pb2BiBrO6 and Pb2SeTeO6 Double Perovskite: An Ab Initio Study

Using the frameworks of density functional theory, we found a new class of three-dimensional (3D) topological insulators (TIs) in Pb2BiBrO6 and Pb2SeTeO6 double perovskites. Our ab initio theoretical calculations show that Pb2BiBrO6 and Pb2SeTeO6 are Z2 nontrivial, and their bandgaps are 0.390 eV and 0.181 eV, respectively. The topology comes from two mechanisms. Firstly, the band inversion occurs at Γ point in the absence of spin-orbit interactions and secondly, the bandgap is induced by the SOC. This results in a larger bandgap for this new class of topological insulators than conventional TI. In Pb2BiBrO6 double perovskites, our slab calculations confirm that the topology-protected surface metallic bands come from the BiBrO4 surface which means that one can build a transport device using Pb2BiBrO6 double perovskites with a PbO layer as an outmost protection layer. The mechanical stabilities such as bulk, shear, Young’s moduli, Poisson’s and Pugh’s ratio, longitudinal, transverse, and average sound velocity, together with Debye temperature are also studied. Our results show that these Pb2AA’O6 (A = Sb and Bi; A’ = Br and I) and Pb2SeTeO6 are mechanically stable.

Elastic, electronic, optical and thermoelectric properties of the novel Zintl-phase Ba2ZnP2

We report and discuss the results of a detailed first-principles calculations of the structural, elastic, electronic, optical and thermoelectric properties of the new Zintl phase dibarium zinc diphosphide Ba2ZnP2. The calculated structural parameters using the GGA-PBEsol functional are in excellent agreement with the available experimental counterparts. From the monocrystalline elastic constants numerically estimated through the stress-strain technique, a set of related properties, viz., mechanical stability, elastic anisotropy, brittle/ductile character, anisotropic sound velocities, polycrystalline elastic moduli, including isotropic bulk modulus, shear modulus, Young's modulus, Poisson's ratio, average sound velocity and Debye temperature, are deduced. The electronic and optical properties are investigated through the state-of-the art FP-(L)APW + lo method with the accurate TB-mBJ potential. Ba2ZnP2 is an indirect semiconductor with a gap of 1.24 eV. The charge-carrier effective masses are calculated. The valence band maximum is less dispersive than the conduction band minimum. The microscopic origins of the electronic states composing the energy bands are determined via the PDOS diagrams. Topological analysis of the charge density shows that a covalent character is dominantly ruling the Zn–P bond inside the block ZnP4, while an ionic bonding is mainly ruling the bond between the cation Ba and the polyanion ZnP4. Frequency-dependent macroscopic linear optical functions are predicted in a wide energy range 0–30 eV. Within the visible spectra, the calculated magnitude of the absorption coefficient, reflectivity and refractive index are in the ranges ∼4−35×104cm−1, 29−36% and 3.18−3.47, respectively. The semi-classical Boltzmann transport theory within the constant relaxation time approximation is used to study the thermoelectric properties. The title compound has a figure of merit of ∼1.77 at 300 K, which makes it a potential candidate for thermoelectric applications.

STRUCTURAL AND ELASTIC PROPERTIES OF AgNi10 ALLOY STUDIED WITH AB-INITIO CALCULATIONS

First-principles calculations based on density functional theory (DFT) are used to calculate the structural, elastic and thermodynamic properties of the supersaturated solid-solution AgNi10 alloy, applied mainly to electrical contact materials. In this work, for the exchange-correlation energy, the generalized gradient approximation (GGA) functional is used. The calculated structural and electronic properties of supersaturated solid-solution AgNi10 alloys show that the occupation of Ni in the Ag lattice is ordered. All single-crystal elastic stiffness constants of the energetically and mechanically optimized stable AgNi10 model are calculated using the finite strain method and using the Voigt-Reuss-Hill approximation. Various anisotropic indices like the universal anisotropic index, shear anisotropic index, directional dependence of Young’s modulus, bulk modulus and others are calculated to study the elastic anisotropy. The strong anisotropy in the elastic properties of AgNi10 was confirmed. Phonon dispersions were carried out, showing that the AgNi10 crystal has dynamic stability. The Debye temperature is calculated from the elastic data by estimating the average sound velocity in the AgNi10. Furthermore, the vibrational thermodynamic properties (free energy, enthalpy, entropy and heat capacity) of AgNi10 are obtained successfully.

First-principles calculations of structural, electronic and elastic properties of carbon allotropes

Recently, carbon allotropes have attracted people's attention again. Here, we aim to mainly study the structural, electronic properties and Raman spectra of 2H-D, 4H-D, 6H-D, 8H-D, 10H-ID and 10H-IID under pressure (0–70 GPa) by using first-principles calculations with density functional theory. The results show that the pressure in this range has less effect on the structural and electronic properties, but it has a relatively large effect on Raman spectrum. However, 6H-D and 8H-D under high pressure are not easy to determine which one is by Raman spectrum. In addition, the elastic and thermal properties at zero pressure were studied. Their independent elastic constants, bulk modulus, shear modulus, Pugh's ratio, Young's modulus, Vickers hardness, Debye temperature, average sound velocity and minimum thermal conductivity were given. They are comparable to those of diamond and agree with previous studies. Last but not the least, the Debye temperature and thermal conductivity increase with the increasing hexagonal content.

Electronic, mechanical, vibrational and optical properties of TaIrX (X = Ge and sn): a DFT approach

First-principles calculation investigated the structural, electronic, mechanical, thermodynamic, optical properties and the lattice dynamics of 18 valence electron half-Heusler alloys TaIrX (X = Ge and Sn). The results reveal that the two alloys have a semiconducting nature with flat bands at the valence band maximum, favouring p-type doping. Also, they are dynamically stable with phonon–phonon scattering. TaIrX (X = Ge and Sn) are mechanically stable and ductile. This is because their B/G ratios are higher than the critical ratio of 1.75. The optical properties, such as the real and dielectric function, absorption coefficient, refractive index, and electron energy loss, were investigated. The dielectric constants for TaIrGe and TaIrSn are 16.6 and 16.9, respectively . The refractive index of TaIrGe and TaIrSn are 4.08 and 4.11, respectively. The maximum reflectivity of the two alloys are 59.2%(57.6%) at 13.5 eV(10.6 eV) for TaIrGe (TaIrSn). The Debye temperatures and the average sound velocities of TaIrX (X = Ge and Sn) were also investigated.

A First-Principles Study of Structure, Elastic and Electronic Properties of GeTiO3 as Environmentally Innocuous Ferroelectric Perovskites

The structural parameters, elastic properties, spontaneous polarization, electronic band structure, and density of states (DOS) of GeTiO3 in tetragonal phase have been studied computationally using pseudopotential plane-wave (PP-PW) method based on the density functional theory (DFT). The generalized gradient approximation (GGA) was used to estimate the exchange-correlation energies. The equilibrium lattice parameter, unit cell volume, bulk modulus and its derivative are obtained and compared with the available theoretical data. The elastic characteristics such as elastic constants, Poisson’s ratio, elastic modulus, and anisotropy factor are obtained in the pressure range 0–50 GPa. Our computed results of elastic constant satisfy Born’s stability criterion. In view of Pugh’s prediction standard, the material is taken as ductile. Once the elastic constant is calculated, the Debye temperature of GeTiO3 compound is also evaluated from the average sound velocity. The density of states, band structures, and charge-density distribution are discussed and compared with previous computational results. The calculation within Berry’s phase approach indicate a high spontaneous polarization of tetragonal GeTiO3 (1.125 C/m2). Thus, the substance is identifi ed as a promising environmentally friendly ferroelectric material.

Theoretical study of ThO2 by first principles calculations

In this paper, the thermodynamic, structural properties and vibrational spectrum of thorium dioxide have been studied using the Density Functional Perturbation Theory (DFPT) and Density Functional Theory (DFT) in the framework of first principles calculations. Quantum espresso software, which is an open source computing code, has been used in order to compute the kohn-Sham equations to obtain the minimum total energy of crystal. The vibrational spectrum of the thorium dioxide was examined along various symmetrical directions, and the results showed the dynamical stability of the crystal system. The quasi-harmonic Debye-Einstein model as implemented in GIBBS2 Code was used to calculate the thermodynamic properties of thorium dioxide at high temperatures and pressures. The simulation results showed that the Debye temperature of thorium dioxide decreased with increasing temperature at a constant pressure and increased with increasing pressure at a constant temperature. Increasing the Debye temperature indicated an increase in the crystal stiffness and the average sound velocity. It was observed that the volumetric thermal expansion coefficient and gruneisen parameter decreased exponentially with increasing pressure at a constant temperature, while increased with increasing temperature at a constant pressure, indicating an increase in heat transfer in the crystal lattice

First-principles predictions of the structural, electronic, optical and elastic properties of the zintl-phases AE3GaAs3 (AE = Sr, Ba)

We report results of a detailed first-principles study of physical parameters associated with the structural, electronic, optical and elastic properties of the ternary gallium-arsenides Sr3GaAs3 and Ba3GaAs3. Calculated equilibrium structural parameters are in excellent agreement with the available experimental counterparts, providing evidence of the reliability of the reported results. Monocrystalline elastic constants are numerically estimated and analyzed. From the monocrystalline elastic constants, a set of related properties, viz. mechanical stability, anisotropic sound velocities, polycrystalline elastic properties, including bulk modulus, shear modulus, Young's modulus, Poisson's ratio, average sound velocity and Debye temperature, are deduced. Crystal direction dependences of the linear compressibility and Young's modulus are analyzed and visualized by plotting their spatial distributions. From analysis of the energy band dispersions, it is found that the title compounds are semiconductors with direct band gaps positioned in the visible sunlight spectrum in the energy window 1.271–1.285 eV. Origins of the electronic states composing the energy bands are determined using the PDOS diagrams. Effective masses of holes and electrons are numerically evaluated at the valence band and conduction band extremes towards the three major crystalline directions. Anisotropies of the hole and electron effective masses are visualized by plotting their dependencies on the crystalline direction. Frequency-dependent linear optical parameters are predicted in an energy window from 0 eV to 14 eV for incident electromagnetic radiation polarized parallel to the three principal crystalline directions.

First-principles study of anisotropic thermoelectric properties of hexagonal KBaBi

Fast-track computational prediction of efficient thermoelectric materials is crucial for designing future thermoelectric generators. In the present study, an attempt has been made to estimate the thermoelectric figure of merit (ZT) of hexagonal KBaBi, a topological insulator by employing first-principles calculations based on Density Functional Theory (DFT) and Boltzmann transport theory. KBaBi, a member of ternary honeycomb compounds has been chosen due to its high band valley degeneracy and hence high density of states effective mass which may lead to possible high-power factor (S2σ). Therefore, to estimate the ZT, properties such as mechanical, phononic, electronic, and transport phenomena of KBaBi have been evaluated. It is observed that KBaBi exhibits low average sound velocity (va) and Debye temperature (θD) resulting from soft acoustic phonon modes. The study reveals larger Seebeck coefficients than the minimum requirement of 200 ​μV/K along a-axis (Sa) and c-axis (Sc) for n and p-type KBaBi respectively, over a broad range of temperature and carrier concentration. Moreover, the calculated relaxation time (τ) based on deformation potential theory suggests the higher p-type conductivity (σ) along c-axis. It also unveils reasonably low lattice thermal conductivities (klat) along a (2.09 Wm−1K−1) and c-axes (2.99 Wm−1K−1) at room temperature. Finally, we report a promising ZT of 1.04 for p-type KBaBi along c-axis despite having strong bipolar effect.

A Thermophysical Perspective of the Inter-relationship between Debye Temperature and Electron Density

A comprehensive thermophysical analysis of the linkage between the Debye temperature θD and electron density ne has been presented. Assuming that the Debye cut-off frequency ωD is related to the effective oscillation frequency ω of screened ion cores of a metallic material, a simple analytical relationship could be established between θD, bonding electron density ne, and materials density ρm. Alternately, it is possible to establish a consistent set of electron density n e values using θD, which in the case of pure metals is shown to exhibit a linear scaling with Miedema’s thermochemical electron density n e M values. The temperature, pressure, and composition dependencies of θD are addressed uniformly in terms of isobaric and isothermal volume variations of ne; besides, invoking the subregular solution formalism for expressing composition-induced molar volume variation simple approximations for melting temperature Tm and vibrational entropy $$ S_{T}^{\text{o}} $$ have been suggested in terms of electron density. Estimates of θD, $$ S_{298}^{\text{o}} $$ , and average sound velocity have been obtained for metastable bcc U1−xZrx solid solution.

The thermoeletric performance of nanoporous SnSe assembled by hollow cage cluster

The n-type and p-type thermoelectric property of nanoporous SnSe assembled by hollow cage cluster is studied by First-principles calculations and Boltzmann transport theory. The nanoporous SnSe presents low Shear modulus (3.16 GPa), low Shear sound velocity (925 m/s), low average sound velocity (1203 m/s), low Debye temperature (101 K) and large Gruneisen parameter (3.3), which implies that weak Sn-Se atomic interactions and strong anharmonicity of the bonding arrangement. Owing to the cubic structure of nanoporous SnSe, the thermoelectric property along different direction is isotropous. For n type, the optimal ZT at 800 K is 2.25, while the highest ZT of p type is 1.81. The strong differences between n type and p type are mainly dominated by the Seebeck coefficient, which is related to the carrier effective mass. This work not only demonstrates the excellent property of nanoporous SnSe, but also provides insights to understand the transport performance of cage structure.

Theoretical prediction of the physical characteristic of Na3MO4 (M=Np and Pu): The first-principles calculations

Recently, the orthorhombic structures of Na3MO4 (M=Np and Pu) have been successfully synthesized by Smith et al. In this paper, the physical characteristics namely lattice parameters, elastic constants Cij, polycrystalline moduli, anisotropic properties, Vicker's hardness Hv and Debye temperature of them have been systematically predicted for the first time by employing the first-principles calculations. The predicted Cij reveal that the Na3NpO4 and Na3PuO4 are mechanically stable. The obtained polycrystalline moduli indicated that both of Na3MO4 behaves the brittle behavior with the Hv is less than 10.0 GPa. Furthermore, the anisotropy properties of Na3MO4 are further illustrated by using three different kinds of anisotropy factors and direction-dependent of the bulk moduli B, shear moduli G and Young's moduli E. Finally, the averaged sound velocity vm and Debye temperature θD are investigated and analyzed.

Invariance of the Effective Phase Velocity of a Hydroacoustic Field in the Deep Ocean

The distribution of sound pressure and phase gradients is studied in the deep sea along the signal-propagation paths in the near illumination zone (NIZ) and the far illumination zone (FIZ), as well as in the shadow zone (SZ). It is shown that the characteristics of the field formed by the leaking, captured, and water modes differ significantly. It is established that the phase gradients and the dependences of the “effective phase velocity” (EPV) on the distance in the SZ are stable and determined by a single invariant regularity. An analytical description of this dependence is proposed. It is also found that the value of the EPV in the zones with dominant water modes is close to the average sound velocity in the waveguide.

Sound Velocity in a Thin Shallowly Submerged Terrestrial-Marine Quaternary Succession (Northern Adriatic Sea)

Estimating sound velocity in seabed sediment of shallow near-shore areas submerged after the Last Glacial Maximum is often difficult due to the heterogeneous sedimentary composition resulting from sea-level changes affecting the sedimentary environments. The complex sedimentary architecture and heterogeneity greatly impact lateral and horizontal velocity variations. Existing sound velocity studies are mainly focused on the surficial parts of the seabed sediments, whereas the deeper and often more heterogeneous sections are usually neglected. We present an example of a submerged alluvial plain in the northern Adriatic where we were able to investigate the entire Quaternary sedimentary succession from the seafloor down to the sediment base on the bedrock. We used an extensive dataset of vintage borehole litho-sedimentological descriptions covering the entire thickness of the Quaternary sedimentary succession. We correlated the dataset with sub-bottom sonar profiles in order to determine the average sound velocities through various sediment types. The sound velocities of clay-dominated successions average around 1530 m/s, while the values of silt-dominated successions extend between 1550 and 1590 m/s. The maximum sound velocity of approximately 1730 m/s was determined at a location containing sandy sediment, while the minimum sound velocity of approximately 1250 m/s was calculated for gas-charged sediments. We show that, in shallow areas with thin Quaternary successions, the main factor influencing average sound velocity is the predominant sediment type (i.e. grain size), whereas the overburden influence is negligible. Where present in the sedimentary column, gas substantially reduces sound velocity. Our work provides a reference for sound velocities in submerged, thin (less than 20 m thick), terrestrial-marine Quaternary successions located in shallow (a few tens of meters deep) near-shore settings, which represent a large part of the present-day coastal environments.

Fiber Optic Acoustic Vibration Sensors for Ultrasound Measurement in Low-Pressure CO₂ Environment

The detection of acoustic signals in the Martian environment is significant to understand the issues such as the evolution of the universe, structure of matter, origin of life, and future migration of humans. We proposed a method for testing ultrasonic wave by using fiber-optic Fabry-Perot vibration sensors in a low-pressure CO 2 environment. We conducted high-precision sound wave amplitude and speed measurement tests with different center frequencies at 21, 25, 34, and 40 kHz under different gas compositions, pressures, and distances. Results showed that under the conditions of 15 °C and gas pressure in the range of 600 Pa to 1 MPa, the measured average sound velocity of ultrasonic signals at each frequency was 268.79 m/s in the CO 2 environment, which was lower than the velocity of 336.18 m/s measured in the air environment. The results in this study can be applied to theoretical and experimental studies of future Mars probes pertaining to ultrasonic positioning and detection.

Composition Dependence of Elastic Moduli of Mixed Cobalt-Zinc Ferrites Prepared by Citrate Precursor Method

CoxZn1-xFe2O4 nanoparticles were prepared by chemical citrate precursor synthesis method. The Young’s modulus ‘E’ and the rigidity modulus ‘n’ of mixed cobalt-zinc ferrites have been determined by the ultrasonic pulse transmission technique at 1 MHz. The elastic modules of the ferrites were corrected to zero porosity using the formulae of Harselman and Fulrath. The observed variation of the elastic module with composition has been interpreted on the basis of binding forces between the atoms of the spinal lattice. A linear relationship between Debye temperature ØD and average sound velocity Vm has also been observed.

Study of the Structural, Elastic, Electronic and Optical Properties of the Ternary Acetylides A2MC2 (A = Na, K) and (M = Pb, Pt)

We studied the ternary acetylides A2MC2 (A = Na, K) and (M = Pb, Pt) with trigonal structures by using the density functional theory (DFT) as implemented in the CASTEP code. The calculated lattice parameters and atomic fractional coordinates were in agreement with previous calculations and experimental data. A set of isotropic elastic parameters and related properties, namely the module and shear moduli, Young’s modulus, Poisson’s ratio, average sound velocity and Debye temperature were numerically estimated in the frame work of the Voigt-Reuss-Hill approximation. The absorption, energy-loss and dielectric function were calculated. We studied the main contribution to the optical spectra from the transition from the top four valence bands towards the lower three first one of conduction based on the electronic structures.

Theoretical investigation of the electronic and thermoelectric behavior of CoV2O4 alloy

Density functional theory (DFT) within Wien2k code is utilized to compute the mechanical, thermal, electronic, magnetic and thermoelectric properties of the cubic spinel CoV2O4. The ground state lattice constant of CoV2O4 alloy agrees with previous literature. The calculated elastic constants of CoV2O4 predict that the present alloy is anisotropic, elastically stable and brittle. Beneficial acoustical applications are expected for the present alloy due to its high calculated Debye temperature and average sound velocities values. The longitudinal and transverse sound velocities modes of vibrations are found maximum along [110] directions compared to [100] and [111] directions. The calculated DOS and band structure show that CoV2O4 is electronically stable. The present alloy possesses a total magnetic moment of 12.0 [Formula: see text] and is classified as a half-metallic ferromagnet. CoV2O4 shows [Formula: see text]-type behavior and favors holes as charge carriers. The present alloy owns beneficial thermoelectric properties and can be used in thermoelectric applications.