Search

The structural, electronic, elastic, optical, phonon, and thermo-physical properties of the tetragonal X 2 CoH 5 (X = Ca, Sr) hydrogen storage compounds were thoroughly examined using first-principles calculations. The negative formation enthalpies (−76.03 kJ/mol.H 2 for Ca 2 CoH 5 and −72.55 kJ/mol.H 2 for Sr 2 CoH 5) highlight the structural stability of these materials. Phonon calculations revealed no imaginary frequency modes, confirming the dynamic stability of X 2 CoH 5. The mechanical stability of Ca 2 CoH 5 and Sr 2 CoH 5 was evidenced by the compliance of the elastic constants with Born stability criteria. The electronic band structure indicates that Ca 2 CoH 5 and Sr 2 CoH 5 are direct bandgap semiconductors with narrow bandgaps of ∼ 0.27 and 0.34 eV, respectively. The appraisal of Poisson's ratio (ν = 0.22 for X = Ca and 0.23 for Sr) and Pugh's ratio (B/G = 1.47 for X = Ca and 1.56 for Sr) suggests that both metal hydrides exhibit brittle mechanical behavior. Moreover, 3D plots of Young's modulus (E), shear modulus (G), linear compressibility (β), and Poisson's ratio (ν) uncover anisotropy within X 2 CoH 5. The hydrogen storage capabilities were scrutinized, and the present materials feature excellent volumetric hydrogen density (95.65 gH 2 l −1 for Ca 2 CoH 5 and 80.24 gH 2 l −1 for Sr 2 CoH 5), moderate gravimetric hydrogen density (3.38 wt% for Ca 2 CoH 5 and 2.06 wt% for Sr 2 CoH 5) and high hydrogen desorption temperature (584 K for Ca 2 CoH 5 and 558 K for Sr 2 CoH 5). Notably, the obtained volumetric hydrogen densities are in line with the volumetric capacity criteria set by the U.S. Department of Energy (DOE) for 2025. Finally, the optical and thermo-physical characteristics of X 2 CoH 5 compounds were also investigated in this work. • New X 2 CoH 5 (X = Ca and Sr) hydrides were studied using first-principles calculations. • The X 2 CoH 5 compounds are thermodynamically, dynamically and mechanically stable. • X 2 CoH 5 hydrides display semiconductor behavior, brittleness, and elastic anisotropy. • The Gravimetric capacity was calculated as 3.38 wt% for Ca 2 CoH 5 2.06 wt% for Sr 2 CoH 5. [ABSTRACT FROM AUTHOR]

The paper shows that work in a quantum system is quantized with energy; the quantum work is equivalent to the highest eigenenergy (the Debye energy) of the system and the superlubricity of solids is derived from the quantum work. The prerequisite for the superlubricity is that the lateral force at contact surfaces in sliding is less than the Debye force so that the phonon of the solids is not excited. [ABSTRACT FROM AUTHOR]

The Rashba effect of polaron in RbCl triangular quantum wells under the influence of a magnetic field is theoretically studied, and the expression of the ground state energy of the polaron is obtained within the Pekar variational method. The ground state energy of the polaron splits into two branches due to the Rashba effect. This phenomenon fully demonstrates that the influence of orbit and spin interaction in different directions on the energy of the polaron is not negligible. Because the contribution of the magnetic field cyclotron resonance frequency to the Rashba spin-orbit splitting is a positive value, the energy spacing becomes larger as the magnetic field cyclotron resonance frequency increases. Due to the spin-orbit coupling interaction, the energy splits at zero field. The total energy is reduced due to the presence of phonon. Therefore, the polaron state is more stable than the bare electron state, and the polaron energy splitting is more stable. [ABSTRACT FROM AUTHOR]

The infinite-layer cuprate ACuO2 (A = Ca, Sr, Ba) possesses the simplest crystal structure among numerous cuprate superconductors and can serve as a prototypical system to explore the unconventional superconductivity. Based on the first-principles electronic structure calculations, we have studied the electronic and magnetic properties of the infinite-layer cuprate SrCuO2 from a phonon perspective. We find that interesting fluctuations of charges, electrical dipoles, and local magnetic moments can be induced by the atomic displacements of phonon modes in SrCuO2 upon the hole doping. Among all optical phonon modes of SrCuO2 in the antiferromagnetic Néel state, only the A1g mode that involves the full-breathing O vibrations along the Cu-O bonds can cause significant fluctuations of local magnetic moments on O atoms and dramatic charge redistributions between Cu and O atoms. Notably, due to the atomic displacements of the A1g mode, both the charge fluctuations on Cu and the electrical dipoles on O show a dome-like evolution with increasing hole doping, quite similar to the experimentally observed behavior of the superconducting Tc; in comparison, the fluctuations of local magnetic moments on O display a monotonic enhancement along with the hole doping. Further analyses indicate that around the optimal doping, there exists a large softening in the frequency of the A1g phonon mode and a van Hove singularity in the electronic structure close to the Fermi level, suggesting potential electron-phonon coupling. Our work reveals the important role of the full-breathing O phonon mode playing in the infinite-layer SrCuO2, which may provide new insights in understanding the cuprate superconductivity. [ABSTRACT FROM AUTHOR]

Utilizing density functional theory, the structural, electronic, vibrational, and thermophysical properties of L10 FePt, L12 Fe3Pt, and L12 FePt3 alloys are meticulously analyzed. Employing projected augmented wave pseudopotentials alongside the Perdew–Burke–Ernzerhof exchange‐correlation function, equilibrium lattice constants are computed, aligning closely with existing data, thus validating our approach. To ascertain the dynamical stability of these alloys, phonon frequencies and density of states across high symmetry directions of the Brillouin zone are computed, affirming their stability with positive phonon frequencies throughout. Furthermore, the electronic band structure, the total and projected density of states, electronic charge density, and Fermi surfaces of the alloys are delved. The thorough analysis of phonon dispersion curves, electronic band structures, and the density of states, charge densities, and Fermi surfaces provides conclusive insights into the properties and behavior of the alloys. In essence, comprehensive investigation offers valuable insights into the thermophysical properties of L10 FePt, L12 Fe3Pt, and L12 FePt3 alloys, spanning equilibrium lattice constants, phonon characteristics, and electronic properties. These findings significantly augment the understanding of the structural stability, phonon dynamics, and electronic behavior exhibited by these alloys. [ABSTRACT FROM AUTHOR]

The study used Density Functional Theory to simulate the properties of single-walled and double-walled boron nitride nanotubes. The cohesive energy calculations suggest that double-walled nanotubes are more stable than single-walled nanotubes. Double-walled nanotubes have a narrower bandgap than single-walled nanotubes. The smaller diameter of the nanotubes reduces available energy for vibrational modes. Double-walled nanotubes have larger Young's modulus, shear modulus, and bulk modulus than single-walled nanotubes. Both single-walled and double-walled nanotubes perform like auxetic materials in some directions. The group velocity of acoustic phonons in SWBNNTs (6, 0) is higher than in SWBNNTs (12, 0). [ABSTRACT FROM AUTHOR]

To comprehensively understand the physical properties of the MAB phases, a systematic exploration into their lattice dynamics, Raman, and infrared vibrations is undertaken for 24 previously screened stable Al/Si‐containing MAB phases with six crystal structures using density functional theory, where Raman experiments on Cr2AlB2 and Mo2AlB2 as well as the previous work confirm the high accuracy of these calculations with an error <5%. With a strong dependence on the atomic mass and chemical bonding, all Raman‐ and infrared‐active modes for these types are identified, including the atomic motion and wavenumbers. Unlike the 222 and 512 phases, the A atoms in the 212, 314, 414, and 416 phases do not participate in Raman vibrations. Moreover, a linear relationship is found between the Raman wavenumbers of the MAB phase and m−1/2, where m is the mass of primary vibrating atoms. Furthermore, the high coefficient of certainty (>0.90) underscores the robust explanatory power of m−1/2 for the vibrational wavenumber. [ABSTRACT FROM AUTHOR]

There is a strong quantum fluctuation effect in the low-dimensional magnetic materials, and multiple interaction mechanisms can be induced by structural asymmetry or external field perturbation. Whereas the system possesses types of hidden multiple-spin ordering, such as spin-nematic state or spin-chirality state etc.Therefore, low-dimensional magnetic materials show a series of novel physical properties. The vector-spin-chirality bound state driven by the inverse Dzyaloshinskii-Moriya mechanism can be coupled with phonons and has richer physical phenomena. A one-dimensional antiferromagnetic chain with spin chirality-phonons coupling model is studied in the conditions of sub-Ohmic ( 0 ＜ s ＜ 1), Ohmic ( s = 1) and super-Ohmic ( s ＞ 1), respectively. We investigate in detail the time evolution of the spin chirality under different strengths of spin-phonon coupling but with same initial state. Our analytical study reveals that the system undergoes a gapless first-order phase transition by increasing the spin chirality-phonon interaction. The incoherent spin fluctuations can be strongly suppressed due to the formation of spin-chirality bound state driven by the spin-phonon coupling of Dzyaloshinskii-Moriya type. The ratio between the spin fluctuations and the Debye frequency of phonons determines the critical point of spin-phonon interaction in a fixed s, beyond which the gapped spin-chiral state is resulted in. Our research will provide theoretical guidance for obtaining long-term spin coherent systems in the applications of quantum transport and quantum storage. [ABSTRACT FROM AUTHOR]

Designing compositions for novel alloys requires a fundamental grasp of the role of each alloying element in its properties. This study delves into the influence of alloying elements in Ultra-High Strength Steels on essential high-temperature properties, including thermoelasticity, thermal stress, and strength, utilizing first-principles phonon calculations. These properties are pivotal for steels used in high-temperature applications. Our investigation quantitatively forecasts the impact of alloying elements on elastic properties, providing valuable insights for advanced alloy design in high-temperature environments. The introduction of alloying elements markedly amplifies the elastic modulus of Fe-based alloys. The Ni, Mo, Cr, and C elements significantly enhance the anisotropy of the alloy. While refining elastic modulus and mechanical properties, alloying elements induce thermal stress, posing a potential risk of high-temperature cracking. The quantitative analysis underscores the robust strengthening potential for C, Ni, Mo, and W elements, with interstitial C emerging as pivotal in enhancing mechanical properties. The findings of this study illuminate the diverse roles played by different alloying elements and offer theoretical guidance for the design of advanced Ultra-High Strength Steels.

In this work, we explore the physical properties of RbXH3 (X=Cr, Zr) perovskite hydrides for solid‐state hydrogen storage. The structural, mechanical, electronic, optical, and hydrogen storage properties were theoretically investigated using density functional theory and CASTEP software. The selected candidates were fully relaxed and optimized in the cubic phase space group Pm‐3 m. The structural phase stability was verified by means of thermodynamic, dynamic and mechanical stabilities. Mechanical analyses based on Poisson's ratio (ν), G/B ratio, and Cauchy pressure show that RbCrH3 and RbZrH3 exhibit brittle behavior with preference of ionic bonding. The electronic structures unveil half‐metallicity in RbCrH3 compound and metallic‐like behavior in RbZrH3. Furthermore, optical calculations were also conducted to gain additional insights into the physical properties of RbXH3 compounds. The gravimetric hydrogen storage (Cwt %) capacities have been calculated as 2.09 wt % and 1.64 wt % for RbCrH3 and RbZrH3, respectively. The hydrogen desorption temperatures have been obtained as 545.11 K and 548.15 K for RbCrH3 and RbZrH3, respectively. Our calculation propose RbCrH3 hydride as potential material for hydrogen storage application. [ABSTRACT FROM AUTHOR]

We examine the electronic and transport properties of a new phase PdSe monolayer with a puckered structure calculated by first-principles and Boltzmann transport equation. The spin–orbit coupling is found to play a negligible effect on the electronic properties of PdSe monolayer. The lattice thermal conductivity of PdSe monolayer exhibits remarkable anisotropic characteristic due to anisotropic phonon group velocity along different directions and its intrinsic structure anisotropy. The compromised electronic mobility despite a relatively low thermal conduction results in a moderate ZT value but significantly anisotropic thermoelectric performance in single-layer PdSe. The present work suggests that the remarkable thermal transport anisotropy of PdSe monolayer can be used for thermal management, and enhance the scope of possibilities for heat flow manipulation in PdSe based devices. The sizeable puckered cages and wiggling lattice implies it an ideal platform for ionic and molecular engineering for thermoelectronic applications. [ABSTRACT FROM AUTHOR]

In recent studies, it has been discovered that phonons can carry angular momentum, leading to a series of investigations into systems with three-fold rotation symmetry. However, for systems with two-fold screw rotational symmetry, such as α-MoO3, there has been no relevant discussion. In this paper, we investigated the pseudoangular momentum of phonons in crystals with two-fold screw rotational symmetry. Taking α-MoO3 as an example, we explain the selection rules in circularly polarized Raman experiments resulting from pseudoangular momentum conservation, providing important guidance for experiments. This study of pseudoangular momentum in α-MoO3 opens up a new degree of freedom for its potential applications, expanding into new application domains. [ABSTRACT FROM AUTHOR]

Copyright of Rare Metals is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study employs first principles and classical molecular dynamics approach to investigate distinct proton landscape and scattering events among aristotype and hettotype BaCeO 3 polymorph. We systematically sampled different migration pathways to examine the thermionic behaviour and lattice disorder against the activation energy profile as a function of operating temperatures. According to DFT outcomes, the asymmetric landscape among hettotype structures entails a feeble vacancy formation energy (E vac = 0.326 eV and 0.485 eV) with noticeable lattice strain (ε = 0.258 % and 0.167 %) and desirable proton transfer pathway relative to aristotype counterpart. The transport characteristics from molecular dynamics on the other hand reveals an accelerated proton transfer at intermediate temperatures (300–550 °C) due to symmetric hydrogen bonding around the proton neighbourhood with a curtailed translational barrier from the low frequency lattice phonons. However, repellent response at elevated temperatures (>550 °C) illustrates the advent of ambipolar characteristics (H+/O2−), structural phase transitions, defect scattering events and the rise of artificial barrier as localized proton traps via proton polaron and defect (V O.. ) interactions. The study as a result accentuates the demand of structural and dynamical coherence to extend the commercial utility of BaCeO 3 polymorph for the fuel cell technology. • Desirable proton landscape among hettotype structures favour rapid proton transport between (300–550 °C). • Low frequency lattice phonon curtails the local energy barrier for unimpeded proton migration below 550 °C. • Cationic disorder, ambipolar response and defect scattering events strengthens electrophysical fluctuations beyond 550 °C. • Very strong proton-polaron coupling beyond 600 °C trap protons due to localized artificial barrier and charge redistribution. [ABSTRACT FROM AUTHOR]

The development of a heat conductive formulation for rubber composites is essential for technical applications such as tire-curing bladders. The present study addresses the effects of three potential ceramic fillers, namely titanium carbide (TiC), silicon carbide (SiC), and alumina, on the mechanical and thermal properties of carbon black (CB)-filled butyl rubber composites. The composites were prepared using the melt compounding method. The curing, mechanical, and thermal conductivity properties of the composites were determined. The tensile strength and modulus of composites decreased slightly in the presence of ceramic fillers in lower amounts of filler loading (10 Phr). Further they reduced in a higher amount of filler loading (20 Phr). In addition, the thermal diffusivity coefficient of the composites increased in the presence of ceramic fillers with different values depending on the type and the amount of the filler with the rank of Al2O3 > SiC > TiC at 10 Phr of filler loading and SiC > TiC > Al2O3 at 20 Phr of filler loading. These different behaviors were discussed according to the state of filler dispersion in the rubber matrix and rubber–filler interactions according to the FeSEM visualization and the mechanical properties. [ABSTRACT FROM AUTHOR]

The origin of the ultralow thermal conductivity in amorphous Si thin films was investigated by comparing their phonon transport properties with those of single-crystal Si. The group velocity and thermal conductivity were measured at 300 K using nanoindentation and the 3 ω method, respectively. The phonon mean free path (MFP) and phonon frequency were determined using the measured properties and models. The scattering in the disordered structure of amorphous Si thin films caused a significant decrease in the phonon MFP with an increase in the phonon frequency, leading to ultralow thermal conductivity. However, the group velocity was unaffected by the disordered structure. [ABSTRACT FROM AUTHOR]

The energy band gaps (EgL, EgΓ and EgX) and electronic band structure in the pentanary AlxIn1-xPySbzAs1-y-z semiconducting alloy are determined. Additionally, the Fröhlich coupling parameter, the phonon frequencies (ωLO, ωTO), transverse effective charge (eT*), high-frequency dielectric constant (ε∞), static dielectric constant (ε0) and refractive index (n) are calculated. A combination of the virtual crystal approximation and the empirical pseudopotential approach is used in our study. The calculations are done at room temperature and normal pressure. The studied properties for the new alloy under investigation lattice-matched to the InP substrate give a good agreement with the experiment. It is discovered that materials with lower coupling constants are advantageous for a parametric interaction to be cost-effective. It is expected that this paper's findings will apply to a wide range of industrial applications. [ABSTRACT FROM AUTHOR]

We focus on the ferric end-member of phase H: ε-FeOOH using density functional theory at the PBEsol+U level. At 300 K, we find that ε-FeOOH undergoes a hydrogen bond symmetrization at 37 GPa and a sharp high-spin to low-spin transition at 45 GPa. We find excellent agreement with experimental measurements of the equation of state, lattice parameters, atomic positions, vibrational frequencies, and optical properties as related to the band gap, which we find to be finite and small, decreasing with pressure. The hydrogen bond symmetrization transition is neither first- nor second-order, with no discontinuity in volume or any of the elastic moduli. Computed IR and Raman frequencies and intensities show that vibrational spectroscopy may provide the best opportunity for locating the hydrogen bond symmetrization transition experimentally. We find that ε-FeOOH is highly anisotropic in both longitudinal- and shear-wave velocities at all pressures, with the shear wave velocity varying with propagation and polarization direction by as much as 24% at zero pressure and 43% at 46 GPa. The shear and bulk elastic moduli increase by 18% across the high-spin to low-spin transition. [ABSTRACT FROM AUTHOR]

This paper aims to study the reflection characteristics of optical beams in a hybrid graphene–hexagonal boron nitride (hBN)–graphene structure, which has been located on SiO2-Si layers. An analytical model is presented to derive the reflection characteristics by using the transfer matrix method. The upper Reststrahlen band has been chosen as the studied frequency range. It is shown that the characteristics of the reflected beam can be effectively controlled by varying the chemical potential of graphene sheets. The obtained results represent a high value of the reflected group delay ( τ r = 15.3 p s ) at the frequency of 24.9 THz. The presented investigation will be helpful to control the group delays of reflected beams and can be utilized for the design of innovative graphene–hBN devices in the mid-infrared wavelengths. [ABSTRACT FROM AUTHOR]

WTe2 recently attracted considerable attention as a layered material exhibiting ferroelectricity, giant magnetoresistance, and pressure-induced superconductivity. In this study, we performed Raman spectroscopy on bulk WTe2, including the low-frequency region. An unfamiliar Raman peak (P0) was found at approximately 9 cm−1 in addition to the seven already known peaks (P1–P7). Furthermore, the angular and polarization dependence of the spectra revealed the peak P0 had A 1 symmetry. The symmetry is consistent with the experimental results and first-principles calculations by other groups. Our work paves the way for studying the symmetry of the low-frequency phonons in atomic-layer ferrolectric films using Raman spectroscopy. [ABSTRACT FROM AUTHOR]

The temperature-dependent luminescence spectra were analyzed to determine the parameters of the electron–phonon interaction (Huang–Rhys factor and the average phonon energy) for nanocomposites with colloidal CdSe/CdS/ZnS quantum dots (deposited on the surface of a glass substrate and embedded in a thin polymer film of polyisobutylene, and in a frozen colloidal solution in toluene). The measured values of the parameters are analyzed in comparison with model calculations and data obtained using the low-frequency Raman spectroscopy. It is found that in the case of a vitrified colloidal solution of quantum dots in toluene, the matrix effect leads to a noticeable change in the parameters of the electron–phonon interaction. [ABSTRACT FROM AUTHOR]

A thermal model of kinetic friction is assigned to a classical loaded particle moving on a fluctuating smooth surface. A sinusoidal wave resembles surface fluctuations with a relaxation time. The Hamiltonian is approximated to the mean energy of the wave describing a system of Harmonic oscillators. The quantization of amplitudes yields in terms of annihilation and creation operators multiplied by a quantum phase. Further, we consider acoustic dispersion relation and evaluate the friction coefficient from the force autocorrelation function. While the sliding particle remains classical describing a nano-particle or a tip with negligible quantum effects like tunneling or delocalization in the wave function, the quantized model of the surface fluctuations results in the temperature dependence of the kinetic friction coefficient. It follows an asymptotic value for higher temperatures and supper-slipperiness at low temperatures. [ABSTRACT FROM AUTHOR]

Layering two-dimensional van der Waals materials provides a high degree of control over atomic placement, which could enable tailoring of vibrational spectra and heat flow at the sub-nanometer scale. Here, using spatially resolved ultrafast thermoreflectance and spectroscopy, we uncover the design rules governing cross-plane heat transport in superlattices assembled from monolayers of graphene (G) and MoS2 (M). Using a combinatorial experimental approach, we probe nine different stacking sequences, G, GG, MG, GGG, GMG, GGMG, GMGG, GMMG, and GMGMG, and identify the effects of vibrational mismatch, interlayer adhesion, and junction asymmetry on thermal transport. Pure G sequences display evidence of quasi-ballistic transport, whereas adding even a single M layer strongly disrupts heat conduction. The experimental data are described well by molecular dynamics simulations, which include thermal expansion, accounting for the effect of finite temperature on the interlayer spacing. The simulations show that an increase of ∼2.4% in the layer separation of GMGMG, relative to its value at 300 K, can lead to a doubling of the thermal resistance. Using these design rules, we experimentally demonstrate a five-layer GMGMG superlattice "thermal metamaterial" with an ultralow effective cross-plane thermal conductivity comparable to that of air.

Abstract A thermal model of kinetic friction is assigned to a classical loaded particle moving on a fluctuating smooth surface. A sinusoidal wave resembles surface fluctuations with a relaxation time. The Hamiltonian is approximated to the mean energy of the wave describing a system of Harmonic oscillators. The quantization of amplitudes yields in terms of annihilation and creation operators multiplied by a quantum phase. Further, we consider acoustic dispersion relation and evaluate the friction coefficient from the force autocorrelation function. While the sliding particle remains classical describing a nano-particle or a tip with negligible quantum effects like tunneling or delocalization in the wave function, the quantized model of the surface fluctuations results in the temperature dependence of the kinetic friction coefficient. It follows an asymptotic value for higher temperatures and supper-slipperiness at low temperatures.

Based on density functional theory (DFT) approach, investigations on the structural, thermodynamic, electronic, optoelectronic, phonon, mechanical, and the hydrogen gravimetric storage density of CsSnX3 (X ​= ​O, S, Se and Te) perovskite systems is presented herein. While results of the computed lattice constant values for the investigated perovskite systems increased with an increase in the size of the anion X (X ​= ​O, S, Se, Te), the electronic bandgap values of 1.42, 1.02, 0.64, and 0.40 ​eV is obtained for CsSnO3, CsSnS3, CsSnSe3, and CsSnTe3 respectively. Among the studied systems, CsSnO3 and CsSnS3 are found to be dynamically stable, with CsSnO3 material being the most stable among the studied compounds owing to its frequencies in the real state of the phonon dispersion curve. To study the hydrogen storage properties of the materials in this present study: CsSnO3, CsSnS3, CsSnSe3, and CsSnTe3 the crystal structures have been modified by replacing the heteroatoms (O, S, Se, and Te) with hydrogens which is given as: CsSnO_H4, CsSnS_H4, CsSnSe_H4 and CsSnTe_H4. The gravimetric density (GD) suggests a strong agreement with the calculated band structure and decreases as the amount of band gap becomes enormous, where the CsSnO reveals a highest capacity of 0.74 which decrease as we go from O–Te for two atomic hydrogens. The CsSnTe shows the lowest gravimetric density of 0.526. Also, the formation energies obtained for CsSnO3_H4 estimated to be −31.599 ​kJ ​mol−1 ​has the highest energy however, these was observed to decrease as we go from oxygen to S ​> ​Se ​> ​Te. Moreover, the desorption temperature which is necessary for physical application reveals that the investigated materials are in line with the required range of desorption temperature for practical applications 289 ​K ​°K proposed by US-DOE, which implies that there are no barriers for hydrogen desorption from CsSnX3_H4 compounds. Therefore, it can be deduced that CsSnX3_H4 is a reversible hydrogen storage material. However, CsSnO3_H4 the best desorption temperature, this means that the presence of O atom in the perovskite improves the adsorption energy of interaction between the crystal lattice and the hydrogen molecules and decrease in the order of S ​> ​Se ​> ​Te respectively.

Constructing interconnected thermally conductive networks in a polymer matrix is essential for efficient heat transport in thermally managed materials. Thermally conductive network structures typically have meager thermal resistance, and heat transfer into the material is rapidly exported along such networks. However, increasing the thermally conductive networks inside the polymer matrix is still challenging. This paper prepared high thermal conductivity composites with "primary‐secondary" thermal conductivity networks by combining two processes: constructing three‐dimensional thermally conductive skeletal networks and physically blending fillers, using epoxy resin as the matrix. The performance test results showed that the thermal conductivity of the composites reached 1.65 W/(m K) when the boron nitride (BN) content reached 33.5 wt%, which was 842.8% and 150% higher than that of pure epoxy (EP) and composites with randomly dispersed fillers. This highly efficient heat transfer behavior is mainly due to the synergistic effect of the two‐level thermally conductive network, which weakens the scattering effect of phonons to a great extent. Also, the dielectric properties of the composite material, especially the transport of carriers inside the material under strong electric fields, were discussed in this paper. This work provides ideas and methods for preparing electrical and electronic devices applied to high power density. [ABSTRACT FROM AUTHOR]

We characterize for the first time the emission of acoustic waves from cultured cells irradiated with X-ray photon radiation. Human cancer cell lines (MCF-7, HL-60) and control cell-free media were exposed to 1 Gy X-ray photons while recording the sound generated before, during and after irradiation using custom large-bandwidth ultrasound transducer. The effects of dose rate and cell viability were investigated. We report the first recorded acoustic signals captured from a collective pressure wave response to ionizing irradiation in cell culture. The acoustic signal was co-terminous with the radiation pulse, its magnitude was dependent on radiation dose rate, and live and dead cells showed qualitatively and quantitatively different acoustic signal characteristics. The signature of the collective acoustic peaks was temporally wider and with higher acoustic power for irradiated HL-60 than for irradiated MCF-7. We show that X-ray irradiation induces two cultured cancer cell types to emit a characteristic acoustic signal for the duration of the radiation pulse. The rapid decay of the signal excludes acoustic emissions themselves from contributing to the inter-organism bystander signal previously reported in intact animals, but they remain a potential component of the bystander process in tissues and cell cultures. This preliminary study suggests that further work on the potential role of radiation-induced acoustic emission (RIAE) in the inter-cellular bystander effect is merited. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) exhibits excellent thermal conductivity. Recently, thermal conductivity that amounts to 261.5 W/m-K has been obtained in polycrystalline SiC ceramic liquid-phase sintered (LPS) with Y 2 O 3 -Sc 2 O 3 additives at 2050 °C under a nitrogen atmosphere. From the additive used to the sintering atmosphere selected, many factors affect the thermal conductivity of the SiC. In this review, important factors that are known to determine the thermal conductivity of LPS-SiC (lattice oxygen/nitrogen content, porosity, grain size, grain boundary structure, phase transformation, and additive composition) have been evaluated. While reviewing the impact of each factor on thermal conductivity, hidden correlations among different factors are also discussed. Among the factors that are claimed to be important, we suggest a few factors that are more critical to thermal conductivity than others. Based on the most critical factors on the thermal conductivity of LPS-SiC, a complete engineers' guide for high thermal conductivity LPS-SiC is proposed. [ABSTRACT FROM AUTHOR]

Using the first-principle simulations and the Boltzmann transport equation, our study investigated the properties of single-layer SnBi 2 Se 4 and PbBi 2 Se 4 , including stability, elasticity, electronic and thermoelectric transport properties. We discovered that both 2D materials have acceptable cleavage energies ranging from 0.27 to 0.28 J/m2 and that they are indirect semiconductors with narrow band gaps of 0.68 eV and 0.94 eV, respectively. Interestingly, the valence band maximum exhibits 'multi-valley' energy dispersion. Furthermore, SnBi 2 Se 4 and PbBi 2 Se 4 have comparable electron and hole mobility of about ∼102 cm2/Vs and ∼103 cm2/Vs, respectively resulting in high conductivity and a high thermoelectric power factor. Owing to low group velocities and strong phonon–phonon scattering rates, the materials exhibit low lattice thermal conductivities of 2.59 W/mK (SnBi2Se 4) and 1.73 W/mK (PbBi 2 Se 4). Thus, they demonstrate high thermoelectric figures of merit, namely 0.31 (SnBi2Se 4) and 0.37 (PbBi 2 Se 4) at 300 K, which rise further to 1.22 and 1.82, respectively, at 700 K. Our results suggest that these two single-layer materials are promising candidates for use in nanoelectronics and thermoelectric appliances. [ABSTRACT FROM AUTHOR]

Thermoelectric conversion devices based on group IV semiconductor elements can improve conversion efficiency by reducing the thermal conductivity of the material. In particular, it is known that introducing Sn into the system can dramatically reduce the conductivity. It has been experimentally shown that the thermal conductivity of polycrystalline Ge and polycrystalline Si1−xGex can be reduced by introduction of Sn. However, there is no experimental report on the effect of Sn atoms on the phonons responsible for thermal conduction. In this study, we investigated the mechanism of thermal conductivity reduction due to the introduction of Sn by inelastic x-ray scattering measurements on a Ge1−xSnx single-crystalline thin film with 9% Sn composition. The phonon dispersion of Ge1−xSnx was obtained as a result of the measurements, and the slope of the acoustic mode in the phonon dispersion curve of Ge1−xSnx was smaller than that of Ge. The phonon group velocity is expressed as the slope of the dispersion curves of the acoustic mode. Therefore, it was suggested that the reduction of the phonon group velocity by the introduction of Sn partly contributes to the reduction of the thermal conductivity of Ge1−xSnx. Local vibration mode (LVM), which was independent of wavenumber, was also observed in the low-energy region, and we attribute the origin to the local structure of Sn–Sn pairs formed in Ge1−xSnx. Such LVM has also been reported in bulk single- and polycrystalline Si1−xGex and polycrystalline Si1−x−yGexSny and is considered to influence the thermal conductivity reduction. [ABSTRACT FROM AUTHOR]

Nanosized perovskite ferroelectrics are widely employed in several electromechanical, photonics, and thermoelectric applications. Scaling of ferroelectric materials entails a severe reduction in the lattice (phonon) thermal conductivity, particularly at sub‐100 nm length scales. Such thermal conductivity reduction can be accurately predicted using the information of phonon mean free path (MFP) distribution. The current understanding of phonon MFP distribution in perovskite ferroelectrics is still inconclusive despite the critical thermal management implications. Here, high‐quality single‐crystalline barium titanate (BTO) thin films, a representative perovskite ferroelectric material, are grown at several thicknesses. Using experimental thermal conductivity measurements and first‐principles based modeling (including four‐phonon scattering), the phonon MFP distribution is determined in BTO. The simulation results agree with the measured thickness‐dependent thermal conductivity. The results show that the phonons with sub‐100 nm MFP dominate the thermal transport in BTO, and phonons with MFP exceeding 10 nm contribute ≈35% to the total thermal conductivity, in significant contrast to previously published experimental results. The experimentally validated phonon MFP distribution is consistent with the theoretical predictions of other complex crystals with strong anharmonicity. This work paves the way for thermal management in nanostructured and ferroelectric‐domain‐engineered systems for oxide perovskite‐based functional materials. [ABSTRACT FROM AUTHOR]

The synthesis of nanosized organic benzil (C 6 H 5 CO) 2 crystals within the mesoporous SiO 2 host matrix was investigated via X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and ab initio lattice dynamics analysis. Combining these methods, we have proved that the main structural properties of benzil nanocrystals embedded into SiO 2 host membranes with pore diameters of 6.0, 7.8, 9.4, and 13.0 nm are preserved compared to a bulk benzil crystal. Space confinement has an insignificant impact on the lattice vibrational properties of benzil crystals implanted into the host matrices. The ab initio lattice dynamics calculation of the phonon spectrum in the Brillouin zone center shows the mechanical and dynamical stability of benzil lattice, revealing very low optical frequency of 11 cm − 1 at point Γ. [ABSTRACT FROM AUTHOR]

Vanadium carbides (VC 1-x) exhibit stoichiometric flexibility due to the presence of various carbon vacancies, which significantly influence their fundamental physical properties. Despite this, a comprehensive understanding of how carbon vacancies affect the mechanical and thermal properties of vanadium carbides remains elusive. Previous research has primarily focused on stoichiometric VC and has yet to fully explore the impact of carbon vacancies. This study reveals that stoichiometric VC is less stable when compared to ordered substoichiometric VC 1-x and employs first-principles calculations to obtain thermodynamic, mechanical, and transport properties of VC 1-x. The ordered carbon vacancy leads to an increase in the V–V bond density and volume. Due to the anharmonic effect, the ordered carbon vacancy impairs heat capacity and thermal expansion. The hardness and toughness decrease with increasing carbon vacancy concentrations. The Boltzmann transport equation is used to calculate electrical and thermal transport properties, which shows that growing scattering effects reduce thermal transport capacity. The results provide accurate data support for vanadium carbide research and theoretical support for designing ultra-high temperature ceramic materials. [ABSTRACT FROM AUTHOR]

Mechanical, electronic, thermodynamic phase diagram and optical properties of the FeVSb half-Heusler have been studied based on the density functional theory (DFT) framework. Studies have shown that this structure in the MgAgAs-type phase has static and dynamic mechanical stability with high thermodynamic phase consistency. Electronic calculations showed that this compound is a p-type semiconductor with an indirect energy gap of 0.39 eV. This compound’s optical response occurs in the infrared, visible regions, and at higher energies its dielectric sign is negative. The Plasmon oscillations have occurred in 20 eV, and its refraction index shifts to zero in 18 eV.

In recent studies, it has been discovered that phonons can carry angular momentum, leading to a series of investigations into systems with three-fold rotation symmetry. However, for systems with two-fold screw rotational symmetry, such as α-MoO3, there has been no relevant discussion. In this paper, we investigated the pseudoangular momentum of phonons in crystals with two-fold screw rotational symmetry. Taking α-MoO3 as an example, we explain the selection rules in circularly polarized Raman experiments resulting from pseudoangular momentum conservation, providing important guidance for experiments. This study of pseudoangular momentum in α-MoO3 opens up a new degree of freedom for its potential applications, expanding into new application domains.