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AlCoCrFeMo0.05Ni2 high-entropy alloy (HEA) has great potential for high-temperature applications. However, its FCC matrix will decompose during annealing, which seriously limits its high-temperature applications. Here, the lattice distortion, Gibbs free energy change, phonon spectra, density of states, and bond length distribution of the FCC matrix were calculated by first-principles calculations. The findings indicate that the primary barrier to the formation of a single homogeneous solid solution in the alloy is more closely associated with Gibbs free energy rather than the degree of lattice distortion. The vibration frequency of Al is not in sync with the overall structure, making it prone to desolvation at elevated temperatures. Furthermore, an analysis of bond lengths reveals that the Al–Ni bond length is significantly shorter than the theoretical value, facilitating the formation of a (Ni, Al)-rich phase. In contrast, the longer bond lengths of Al–Cr and Al–Mo facilitate the detachment of Cr and Mo from the (Ni, Al)-rich phase, resulting in the formation of (Cr, Mo)-rich phase. This in-depth investigation sheds light on the phase decomposition mechanism of high-entropy alloys, offering valuable insights for future research in this field.

Abstract The present work employs density functional theory to explore the structural, optoelectronic, and thermoelectric attributes of the halide-based double perovskite A2GeSnF6 (A = K, Rb, and Cs) compounds. The stable phonon dispersion spectrum affirms dynamical stability, whereas the enthalpy of formation and tolerance factor evaluated collectively verify structural stability. Considering the Tran Blaha modified Becke Johnson potentials (mBJ), the predicted direct band gaps along the symmetry point are 3.19 eV for K2GeSnF6, 3.16 eV for Rb2GeSnF6 and 3.12 eV Cs2GeSnF6. According to an in-depth examination of the optoelectronic features, A2GeSnF6 (A = K, Rb, and Cs), double perovskites are assuring contenders for optoelectronic devices due to their suitable bandgap. The extremely high figure of merit values (0.94–0.97) obtained from the numerical calculation of power factor and thermal conductivity suggest the intriguing prospects of these compositions for thermoelectric devices. These studies offer a perceptive comprehension of the materials for their potential applications in the future.

The present work employs density functional theory to explore the structural, optoelectronic, and thermoelectric attributes of the halide-based double perovskite A2GeSnF6 (A = K, Rb, and Cs) compounds. The stable phonon dispersion spectrum affirms dynamical stability, whereas the enthalpy of formation and tolerance factor evaluated collectively verify structural stability. Considering the Tran Blaha modified Becke Johnson potentials (mBJ), the predicted direct band gaps along the symmetry point are 3.19 eV for K2GeSnF6, 3.16 eV for Rb2GeSnF6 and 3.12 eV Cs2GeSnF6. According to an in-depth examination of the optoelectronic features, A2GeSnF6 (A = K, Rb, and Cs), double perovskites are assuring contenders for optoelectronic devices due to their suitable bandgap. The extremely high figure of merit values (0.94–0.97) obtained from the numerical calculation of power factor and thermal conductivity suggest the intriguing prospects of these compositions for thermoelectric devices. These studies offer a perceptive comprehension of the materials for their potential applications in the future. [ABSTRACT FROM AUTHOR]

Using the microscopic s-f model and Green's function theory, we study the temperature dependence of the band gap energy E g and the phonon energy ω and damping γ of ferro- and antiferromagnetic semiconductors, i.e., with different signs of the s-f interaction constant I. The band gap is a fundamental quantity which affects various optical, electronic and energy applications of the materials. In the temperature dependence of E g and the phonon spectrum, there is a kink at the phase transition temperature T C or T N due to the anharmonic spin–phonon interaction (SPI) R. Moreover, the effect of the SPI R and electron–phonon interaction (EPI) A on these properties is discussed. For I > 0 , R > 0 , E g decreases with increasing SPI and EPI, whereas for I < 0 , R > 0 , there is a competition; E g increases with raising the EPI and decreases for enhanced SPI. For R < 0 , in both cases, the SPI and EPI reduce E g . The magnetic field dependence of E g for the two signs of I and R is discussed. The SPI and EPI lead to reducing the energy of the phonon mode ω = 445 cm−1 in EuO ( I > 0 , R < 0 ), whereas ω = 151 cm−1 in EuSe ( I > 0 , R > 0 ) is enhanced with increasing EPI and reduced with SPI. Both the SPI and EPI lead to an increasing of the phonon damping in EuO and EuSe. The results are compared with the existing experimental data. [ABSTRACT FROM AUTHOR]

In this research, the mechanical and phonon properties of UO in the rock-salt phase have been calculated systematically using density functional theory and ab-initio method in projector augmented wave pseudopotentials parameterization. The obtained lattice constant has good accordance with the experimental one at null pressure and temperature. The mechanical stability is confirmed because the positive elastic constants meet the Born-Huang criterion. The mechanical properties including bulk modulus, shear modulus, and Young’s modulus are evaluated using the Voigt-Reuss-Hill approximation. The value of Poisson’s ratio (v) is obtained to be nearly 0.36, which shows that this compound has an ionic bond and interatomic forces within the crystal are central. The elasticity analysis of the Kleinman parameter reveals that bond bending is dominant within the sublattice of UO. The vibrational density of states and phonon dispersion are investigated through the linear response approach. The results shows the dynamical stability of crystalline structure due to the inexistence of virtual frequencies in dispersion relations.

Using the microscopic s-f model and Green’s function theory, we study the temperature dependence of the band gap energy Eg and the phonon energy ω and damping γ of ferro- and antiferromagnetic semiconductors, i.e., with different signs of the s-f interaction constant I. The band gap is a fundamental quantity which affects various optical, electronic and energy applications of the materials. In the temperature dependence of Eg and the phonon spectrum, there is a kink at the phase transition temperature TC or TN due to the anharmonic spin–phonon interaction (SPI) R. Moreover, the effect of the SPI R and electron–phonon interaction (EPI) A on these properties is discussed. For I>0,R>0, Eg decreases with increasing SPI and EPI, whereas for I<0,R>0, there is a competition; Eg increases with raising the EPI and decreases for enhanced SPI. For R<0, in both cases, the SPI and EPI reduce Eg. The magnetic field dependence of Eg for the two signs of I and R is discussed. The SPI and EPI lead to reducing the energy of the phonon mode ω = 445 cm−1 in EuO (I>0, R<0), whereas ω = 151 cm−1 in EuSe (I>0, R>0) is enhanced with increasing EPI and reduced with SPI. Both the SPI and EPI lead to an increasing of the phonon damping in EuO and EuSe. The results are compared with the existing experimental data.

It is of great significance to study the nucleation mechanism of Si and P elements in the Fe 2 Mo-Laves phase to control their precipitation and improve the strength of steel. Based on the first-principles calculations, the effects of Si and P elements on the stability of Fe 2 Mo were studied. The addition of Si and P greatly increases the possibility of its formation in steel. When the Si and P concentrations are 37.5 %, the formation energy is the lowest. Si and P elements improve the stress deformation resistance and the stiffness of Laves phase, which makes Laves phase more stable in high-temperature environment. The addition of Si and P significantly improves the kinetic stability of Fe 2 Mo, but the improvement effect of P is not as good as that of Si. This study provides theoretical guidance for controlling the precipitation of the Fe 2 Mo-Laves phase in practical production. The addition of Si and P greatly increases the possibility of its formation in steel. The addition of Si and P significantly improves the kinetic stability of Fe 2 Mo, but the improvement effect of P is not as good as that of Si. [Display omitted] • Si and P elements have stronger interaction with Mo by replacing Fe in Fe 2 Mo phase. • When the Si and P concentrations are 37.5 %, the formation energy is the lowest. • The doping of Si and P elements improves the mechanical properties and thermal stability of Fe 2 Mo phase. • The improvement effect of Si doping on the kinetic stability of Fe 2 Mo is better than that of P. [ABSTRACT FROM AUTHOR]

[Display omitted] In this work, the effects of refractory transition metal elements on the properties of quaternary equimolar ratio high entropy carbides composed of ⅣB, ⅤB and ⅥB transition metals and C element were studied by first-principles calculations and experiments.The calculation results show that all 75 kinds of high entropy carbides were thermodynamically and mechanically stable and can be formed spontaneously. Among them, Hf can promote the synthesis of high entropy carbides, while Cr has the opposite effect. In addition, single phase solid solution structures can be formed for all 73 HECs except (TiZrHfCr)C and (ZrHfVCr)C. Thereafter, the mechanical properties of these 75 quaternary HECs were compared. The calculation results show that W, Mo, and Ta have a positive effect on improving the elastic modulus, fracture toughness, hardness and melting point of high entropy carbides, while Cr has the opposite effect. The calculation results of phonon spectra show that the six high entropy carbides represented by (TiHfNbTa)C, (TiVNbTa)C, (TiZrNbTa)C, (TiZrNbCr)C, (TiZrNbMo)C and (TiZrNbW)C have lattice dynamic stability. (TiHfNbTa)C, (TiVNbTa)C, (TiZrNbTa)C, (TiZrNbMo)C and (TiZrNbW)C face-centered cubic high entropy carbides were prepared by spark plasma sintering and the microstructure and properties were tested. The experimental results are basically consistent with the calculated results. [ABSTRACT FROM AUTHOR]

In this paper, the phonon spectra of ZrSe 2 , HfS 2 , and HfS 2 /ZrSe 2 heterojunctions are calculated based on the density-functional perturbation method for biaxial tensile strains to study their stability and thermal properties. It was found that monolayers of ZrSe 2 and HfS 2 should not be subjected to > 8% biaxial tensile strain, and HfS 2 and HfS 2 /ZrSe 2 heterojunctions should not be subjected to > 6%. By looking at the graphs of enthalpy, entropy, free energy, and heat capacity under strain for the three systems, it is found that the effect on heat capacity is greater after destabilization in the monolayer system and after destabilization in the heterojunction structure, it is greater for the free energy. Enthalpy, entropy and free energy all increase continuously with increasing temperature, and heat capacity increases continuously with the rising temperature at temperatures < 200 K and tends to remain constant when the temperature is >200 K. Fig. 1 (a and b) Geometric structures of monolayers of HfS 2 and ZrSe 2. (c) The structure of the HfS 2 /ZrSe 2 heterojunction. [Display omitted] In this paper, the phonon spectra of ZrSe 2 , HfS 2 , and HfS 2 /ZrSe 2 heterojunctions are calculated based on the density-functional perturbation method for biaxial tensile strains to study their stability and thermal properties. It was found that monolayers of ZrSe 2 and HfS 2 should not be subjected to >8 % biaxial tensile strain, and HfS 2 /ZrSe 2 heterojunctions should not be subjected to >6 %. By looking at the graphs of enthalpy, entropy, free energy, and heat capacity under strain for the three systems, it is found that the effect on heat capacity is greater after destabilization in the monolayer system and after destabilization in the heterojunction structure, it is greater for the free energy. Enthalpy, entropy and free energy all increase continuously with increasing temperature, and heat capacity increases continuously with the rising temperature at temperatures <200 K and tends to remain constant when the temperature is >200 K. [ABSTRACT FROM AUTHOR]

The paper is devoted to model phonon spectra calculations of argyrodite family crystals, namely: Ag7GeSe5I and Cu7GeSe5I (Ag7SiS5I and Cu7SiS5I). The specificity of the crystalline structure of these crystals is realization of variable partial populating different crystallographic orbits with Cu, I and Ag atoms (in 24 (g) and 48 (h) Positions Multiplicity, Wyckoff letter, Site symmetry of the space group F 43m ), which are associated with high superionic conductivity in crystals of this family. Compared in this paper are model phonon spectra calculated with account of three different configurations of orbital populations with Cu and Ag atoms (6 + 1, 5 + 2 and 4 + 3), by choosing the same lattice model for the unit cell and the set of force constants of each crystal. The calculations were performed by finding the eigenvalues of the generalized dynamic matrix perturbed by the modulation function of the mass defect obtained in the concept over spatial symmetry. It is shown that the phonon spectra do not undergo significant qualitative changes, which can serve as indirect evidence of the possibility to realize the jumping mechanism of super-ionic conductivity in these crystals in the high-temperature phase. [ABSTRACT FROM AUTHOR]

Motivated to understand phonon spectrum renormalization in the ground state of the half-filled Su–Schrieffer–Heeger model, we use the Born–Oppenheimer approximation together with the harmonic approximation to evaluate semi-analytically the all-to-all real-space ionic force constants generated through both linear and quadratic electron-phonon coupling. We then compute the renormalized phonon spectrum and the corresponding lattice zero-point energy (ZPE) as a function of the lattice dimerization. Crucially, the latter is included in the system’s total energy, and thus has a direct effect on the equilibrium dimerization. We find that inclusion of a small quadratic coupling leads to very significant changes in the predicted equilibrium dimerization, calling into question the use of the linear approximation for this model. We also argue that inclusion of the ZPE is key for systems with comparable lattice and electronic energies, and/or for finite size chains. Our method can be straightforwardly generalized to study similar problems in higher dimensions.

The multi-body system’s elasticity and vibrational behavior is an old topic. The conventional method to study this issue is to transform a multi-body system to an abstracted network model consisting of nodes connected by central-force springs. In recent years, abnormal mechanical responses, including negative Poisson ratio, vanishing shear modulus, non-trivial topological characteristics, are discovered in such network systems making this topic be with lasting charms. In this paper, we investigate the vibrational modes of a series of distorted square lattice networks. The distorted degree for this network is only characterized by one parameter, the twisting angle θ. By studying their phonon spectrums, we find a band gap between the two lowest modes of the distorted square lattice. The gap width is linearly correlated to θ, and the gap will be closed when θ reaches a specific value. Our results may find applications in device protection and energy harvesting.

Cu6PS5Br compound belongs to the large family of complex chalcohalides crystallizing in the argyrodite structures. The main peculiarity of the copper-containing argyrodites is high ionic conductivity of Cu+ ions, which makes it possible to use as the functional electronic materials. In the present study, the crystal structure of Cu6PS5Br argyrodite have been analyzed and described using the superspace symmetry concept. The program operating under the Maple environment and suitable for theoretically calculating the phonon spectra of the Cu6PS5Br argyrodite crystal has been developed. Zone structures have been calculated and presented for a series of model Сu6PS5Br phases. The eigenvalues of the generalized dynamic matrix have been found as well as the dispersion dependences have been built for the directions –X–M–R––M of the Brillouin zone.

The article presents the results of investigations of copper selenide Cu1.75Se using the NMR method. The 77Se NMR spectrum for Cu1.75Se is a single line with full width at half maximum (FWHM) of 4 kHz at the temperature of 250 K. Within the temperature range of 200-450 K, the rates of transverse and longitudinal relaxation are equal. This phenomenon is mainly typical of a liquid, where the homonuclear dipole-dipole interaction is effectively averaged due to the Brownian motion of molecules. In this case, the main mechanism that averages the dipole-dipole interaction is the motion of copper ions. Below 200 K, copper ions are partially localized due to the phase transition, and the behavior of the spin-spin and spin-lattice relaxation rates (as well as their values) are different. [ABSTRACT FROM AUTHOR]

Vibrational spectra of β-LiNH4SO4 crystals in the ferroelectric phase (space group No. 33) are studied. The vibrational symmetry is classified using group-theoretical analysis. Vibrational frequencies of crystal structural elements are calculated ab initio within the framework of electron density functional theory and perturbation theory. Raman scattering spectra of β-LiNH4SO4 crystals are calculated and compared with the experimental data. The main structural components playing one of the major roles in the optical studies are discussed based on the theoretical calculations. [ABSTRACT FROM AUTHOR]

We report an ab initio investigation of a hydrogen-based high- T _c superconductor candidate—crystalized C _4 H _4 in the cubic-gauche ( cg -C _4 H _4 ) structure, with the symmetry of space group I _213 . We find the cg -C _4 H _4 structure to be stable under ambient environment; and the evaluation of the electron-phonon coupling strength indicates that the heavily doped cg -C _4 H _4 can generate superconductivity with a T _c ∼ 72 K. The high frequency vibrational modes of hydrogen atoms are found to play an important role in the total electron-phonon interaction strength, and the reduction of structural symmetry compared with graphene further enhances the electron–phonon coupling of the carbon framework. Our investigation illustrates a BCS route to realizing the hydrogen-based high T _c superconductivity.

Cu6PS5Br compound belongs to the large family of complex chalcohalides crystallizing in the argyrodite structures. The main peculiarity of the copper-containing argyrodites is high ionic conductivity of Cu+ ions, which makes it possible to use as the functional electronic materials. In the present study, the crystal structure of Cu6PS5Br argyrodite have been analyzed and described using the superspace symmetry concept. The program operating under the Maple environment and suitable for theoretically calculating the phonon spectra of the CuPS5 Br argyrodite crystal has been developed. Zone structures have been calculated and presented for a series of model Cu6PS5 Br phases. The eigenvalues of the generalized dynamic matrix have been found as well as the dispersion dependences have been built for the directions G-X-M-R-G-M of the Brillouin zone. [ABSTRACT FROM AUTHOR]

In this paper, first-principles calculations and density functional perturbation theory (DFPT) based on the ab-initio approach, have been utilized to investigate mechanical, elastic anisotropy, dynamical, and thermal properties of nuclear fuel UO. The results reveal that the obtained equilibrium lattice parameter at zero temperature and pressure has a good consistency with the experimental lattice constant. The elastic constants are evaluated using the strain-stress method. These coefficients are estimated to be positive and satisfied the Born-Huang relations, which is indicative of the mechanical stability of this compound. The mechanical properties such as shear modulus, bulk modulus, and Young's modulus of UO are calculated, and the results show the compound's stiffness. Pugh's criterion (B/G) is obtained to be approximately 3.5, which confirms that UO is a ductile substance. Elasticity analysis including universal anisotropy and Zener's anisotropy factor reveals that UO falls into the category of anisotropic materials. The phonon spectrum curve is calculated using DFPT along the high symmetric paths and no negative frequencies are observed in the dispersion relations, implying the dynamical stability of the crystalline structure. The quasi-harmonic Debye (QHD) model is employed to study the thermophysical properties such as Debye temperature, isochoric heat capacity, coefficient of thermal expansion, entropy, and Grüneisen parameter at high pressures and temperatures. We found that molar specific heat was more affected by the temperature than pressure. [Display omitted] • The quasi-harmonic Debye model (QHD) has been used in this study. • Phonon dispersion diagram reveals that UO is dynamically stable in cubic phase. • The obtained elastic constants have shown that this ceramic is mechanically stable. • Thermodynamic properties under high pressures and temperatures are studied. • The elastic anisotropy properties of UO alloy are evaluated for the first time. [ABSTRACT FROM AUTHOR]

Based on first-principles calculations with generalized gradient approximation as exchange-correlation functional, the structural, electronic, mechanical, thermal, and phonon properties of III-phosphide binary compounds, namely BP, AlP, GaP, and InP, with cubic zincblende structure have been investigated. The calculations were performed in the framework of density functional theory and density functional perturbation theory (DFPT) implemented in the Quantum ESPRESSO package. The results obtained for the structural and electronic properties are in good agreement with available theoretical and experimental results. The results of our electronic calculations indicate semiconducting properties for these binary compounds. Furthermore, the frequency bandgaps and phonon density of states were also investigated. The computed mechanical constants predict that BP, AlP, GaP, and InP are elastically stable. Finally, we determined the heat capacity and entropy for these binary compounds within a quasiharmonic Debye model using DFPT for comparison. [ABSTRACT FROM AUTHOR]

The structural, vibrational, phonon dispersion spectrum, and thermodynamic properties of LaCoO 3 were investigated using first-principles calculations using density functional theory. Calculations were performed using the projector augmented wave (PAW) pseudopotentials within the generalized-gradient approximation (GGA) and local density approximation (LDA) models for the exchange and correlation functional. In addition, GGA + U and LDA + U were used to describe the 3 d electrons. The phonon dispersion spectrum and phonon density of states of LaCoO 3 were calculated with the finite displacement method. The related thermodynamic properties such as heat capacity, entropy, free energy, and the coefficient of thermal expansion were calculated at various temperatures from the lattice dynamical data obtained by quasi-harmonic approximation. The phonon dispersion spectrum results indicate that the LaCoO 3 structure is dynamically stable. The phonon dispersion and the peaks of the infrared (IR) and Raman spectrum in the frequency range of 0–700 cm −1 were analyzed and assigned. The calculated thermodynamic properties agree well with the experimental results. [ABSTRACT FROM AUTHOR]

The phonon spectra, phonon optical activities, thermal expansion and thermodynamic properties of ordered quaternary carbides M 2 TiAlC 2 (M = Cr, Mo, W) and their ternary counterparts Ti 3 AlC 2 and Cr 3 AlC 2 are studied by first-principles phonon calculations. Phonon eigenvectors of all Raman and infrared modes are analyzed. We find that vibrational frequencies of some Raman active modes (A 1g and E 2g ) can be correlated to the strength and reduced mass of covalent M (4f) C or metallic M (4f) Al bond in all studied structures. Phonon mode-Grüneisen parameter and macroscopic Grüneisen constants are evaluated from phonon spectra. The thermal expansion coefficients, specific heats and isothermal bulk moduli at finite temperatures are obtained under the quasiharmonic approximation (QHA). The average linear thermal expansion coefficient (LTEC) values are found to be α L = 11.30 × 10 −6 K −1 , 7.15 × 10 −6 K −1 , 8.67 × 10 −6 K −1 , 10.29 × 10 −6 K −1 and 15.70 × 10 −6 K −1 for Cr 2 TiAlC 2 , Mo 2 TiAlC 2 , W 2 Ti 2 AlC 2 , Ti 3 AlC 2 and Cr 3 AlC 2 in a range from 300 K to 1400 K, respectively. The hypothetical Cr 3 AlC 2 phase shows strong anharmonic effects in the calculated thermal expansion profile above 600 K. Using Slack-model, the thermal conductivities are also evaluated, and the values are κ = 36.1 W/m K (34.4 W/m K, 27.2 W/m K) for Cr 2 TiAlC 2 (Mo 2 TiAlC 2 , W 2 Ti 2 AlC 2 ) at room temperature. [ABSTRACT FROM AUTHOR]

The results from calculation of the energy spectra and densities of states of phonons in bulk and two-dimensional crystals of monomolecular thickness from molybdenum disulfide and ditelluride are presented. They demonstrate the dominant role of the interaction of atoms within a single monomolecular layer in the phonon characteristics of these materials. [ABSTRACT FROM AUTHOR]

In this paper, we study the phonon thermal properties of a ladder nanostructure in harmonic approximation. We present a model consisting of two infinite chains with different masses. Then, we investigate the effect of different masses on the phonon spectrum. Moreover, as a specific case, in the absence of the second neighbor interaction, we calculate the phonon density of states/modes. Finally, we consider the thermal conductivity of the system. The results show that the phonon spectrum shifts down to the lower frequencies by increasing the masses. Furthermore, a frequency gap appears in the phonon spectrum. By increasing the springs constants, the thermal conductance decreases.

For a further understanding of the phase transitions mechanism in type-I silicon clathrates K8Si46, ab initio self-consistent electronic calculations combined with linear-response method have been performed to investigate the vibrational properties of alkali metal K atoms encapsulated type-I silicon-clathrate under pressure within the framework of density functional perturbation theory. Our lattice dynamics simulation results showed that the pressure induced phase transition of K8Si46 was believed to be driven by the phonon instability of the calthrate lattice. Analysis of the evolution of the partial phonon density of state with pressure, a legible dynamic picture for both guest K atoms and host lattice, was given. In addition, based on phonon calculations and combined with quasi-harmonic approximation, the specific heat of K8Si46 was derived, which agreed very well with experimental results. Also, other important thermal properties including the thermal expansion coefficients and Grüneisen parameters of K8Si46 under different temperature and pressure were also predicted. [ABSTRACT FROM AUTHOR]

The vibrational spectrum, phonon dispersion curve, and phonon density of states (DOS) of β-octahydro-1,3,5,7- tetranitro-1,3,5,7-tetrazocine (β-HMX) crystal were obtained by molecular simulation and calculations. As results, it was found that the peaks at low frequency (0–2.5 THz) are comparable with the experimental Terahertz absorption and the molecular vibrational modes are in agreement with previous reports. Thermodynamic properties including Gibbs free energy, enthalpy, and heat capacity as functions of temperature were obtained based on the calculated phonon spectrum. The heat capacity at normal temperature was calculated using linear fitting method, with a result consistent with experiments. [ABSTRACT FROM AUTHOR]

Pristine Janus monolayers (MXY; M ​= ​Mo, W and X/Y = S, Se, Te) in 2H and 1T phases and their corresponding vdW heterostructures with black phosphorene are studied under density functional theory calculations. Phonon spectrum confirms dynamic stability of all monolayers in both patterns except MoSSe, WSSe, WSeTe and WSTe in 1T layout. Direct energy gap is observed for MoSSe, MoSeTe, WSSe, and WSeTe in 2H arrangement. In 1T phase, MoSSe, WSSe and their respective heterostructures exhibit metallic attributes and are suitable for high speed supercapacitors. Remnant heterostructures are indirect band gap semiconductors in both phases. PDOS affirms type-I band alignment of BlackP-MoSSe and BlackP-MoSeTe in 2H and BlackP-WSTe in 1T phase that can be well employed for future IR detectors. Moreover, globally desirable type-II band association is investigated for remaining heterostructures rendering exclusive laser, optoelectronic, photovoltaic and sensing applications. Each system manifests incredible effective masses of charge carriers. Heterostructures present a significant potential drop and work function (Φ). Also, every single heterostructure demonstrates noteworthy charge transfer which is accountable for electrostatic as well as vdW interaction at interface. Furthermore, sophisticated optical properties of all heterostructures are achieved by estimating absorption spectra. Optical responses suggest their eminent optoelectronic device applications like: telecommunication laser, optical fiber, photo diodes and solar cells. In addition, a comprehensive insight into thermoelectric properties of all the systems illustrates their ability for thermoelectric generator. Likewise, these materials are suitable alternative for non-toxic and inexpensive thermoelectric devices for waste heat recovery at ambient temperature. [Display omitted] • Electronic, vibrational, optical and thermoelectric properties of BlackP/Janus vdW heterostructures are analyzed in 2H and 1T phases. • Semiconducting nature of black phosphorene and Janus monolayers fit them best for electronic and multifunctional devices. • 1T-MoSSe and 1T-WSSe are suitable for high speed supercapacitors due to their metallic nature. • Type-I band alignment is worthy for optoelectronic whereas Type-II favors light detection and photovoltaic applications. • Heterostructures show high competency for non-toxic thermoelectric devices. [ABSTRACT FROM AUTHOR]

The analysis of the temperature dependences of the electrical conductivity of thin metal films is performed. It is shown that the size dependence of the effective parameter of the electron-phonon interaction is connected with amplification of high-temperature electron-phonon interaction at the decrease in the film thickness which appears as a result of the shift of the phonon spectrum to higher frequencies. We have found that the slope of the experimental temperature dependences of the resistance for Pd, Pt, and Sc films, as in the case of Mo, Cr, Ag, Au, and PdAu films, according to the data of other authors, increases with the decrease in the thickness. As the film thickness decreases the average phonon energy increases that leads to the increase in the efficiency of the electron-phonon scattering and, finally, to the increase in the resistivity. [ABSTRACT FROM AUTHOR]

Abstract: We study the dispersion characteristics of strained graphene using many-body interatomic potentials and find: (i) borders of the structural stability of a flat graphene in the three-dimensional space of the strain components (ε xx , ε yy , ε xy ); (ii) sound velocities of strained graphene; and (iii) phonon density of states (DOS) of strained graphene. The border of structural stability of flat graphene is also presented in the space of components of normal and shear membrane forces (T x , T y , T xy ). We find that flat graphene is structurally stable under elastic strain up to 0.3–0.4, but it becomes unstable to a shear strain in the absence of tensile components of strain. Also graphene cannot remain flat under compressive membrane forces because its bending stiffness vanishes. We employ the molecular dynamics simulations to study the post-critical behavior of graphene. We demonstrate that ripples with controllable amplitude and orientation can be generated under simultaneous action of shear and tensile membrane forces. Gaps in the phonon DOS are observed when graphene is strained close to the appearance of ripples. Sound velocities of unstrained graphene do not depend on the propagation direction but application of strain makes graphene anisotropic. One of the sound velocities vanishes at the border of the structural stability of graphene meaning that vanishing of sound velocity (or corresponding elastic constant) predicts impending instability. [Copyright &y& Elsevier]

Abstract: The vibrational and thermal properties of small diameter AlN nanowires are investigated using first principles calculations. Upon applying external pressure, the nanowires suffer a stress induced phase transition from a würtzite (WZ) to a graphite-like (GL) phase. The thermal conductance displays a nearly identical behavior for all systems in the temperature regime governed by acoustical modes, while at higher temperatures the conductance is systematically enhanced for nanowires in the GL phase. The heat capacity points out the different phonon group velocities for the acoustical modes in the two structural configurations. Our DFT-based calculations are consistent with experimental data for bulk AlN, in terms of phonon spectrum and temperature dependent heat capacity in the large nanowire limit. [Copyright &y& Elsevier]

In view of continuing interest in the parent compound of the recently discovered superconducting iron-oxypnictide (LaO1-xFxFeAs) we present fresh results and analyses of ab-initio calculations of the electronic band structure, lattice dynamical properties, and elastic constants assuming it to be insulating as well as metallic. The total and partial electronic density of states (EDOS) of the undoped LaOFeAs in both states are extracted from the electronic band structure. The phonon dispersion and the phonon density of states (PDOS) are also studied. Possible implications of the band structure, EDOS, and PDOS of LaOFeAs on the eventual appearance of high-Tc superconductivity upon carrier doping are discussed. Our findings reveal that phonons are unlikely to mediate Cooper pairing in RE- OFeAs. In addition, the values of various independent elastic constants of the compound assuming both insulating and metallic states are estimated and discussed. [ABSTRACT FROM AUTHOR]

Abstract: The phonon dispersion curves of the unconventional superconductor PuCoGa5 were studied by inelastic X-ray scattering at room temperature. The experimental data agree well with ab initio lattice dynamics calculations. An accurate theoretical description of the phonon spectrum is obtained only when a local Coulomb repulsion  eV among 5f electrons is taken into account. This implies partial localization of the 5f electrons in this compound. A comparison made with the phonon spectrum of UCoGa5 suggests that the latter compound is better described with a fully itinerant f electrons model. [Copyright &y& Elsevier]

Due to the high lattice symmetry and special three-dimensional crystal channel, sulvanite Cu 3 VSe 4 is predicted to be a new type of thermoelectric material with good performance. In this work, the energy band diagram and phonon spectrum of Cu 3 VSe 4 with sulvanite structure were calculated using density functional theory, and Cu 3 VSe 4 pure phase was experimentally synthesized through the combination of the elements using conventional solid-state reactions. Surprisingly, the thermoelectric characterization reveals that Cu 3 VSe 4 is a semiconductor with electron-hole co-transport feature, which results in the poor thermoelectric performance due to the recombination of electrons and holes at low temperature. While holes gradually dominate with the increase of temperature and Cu 3 VSe 4 possesses a high Seebeck coefficient of 558 μV/K at 571 K. Our results may serve as the groundwork for future research on the structure and thermoelectric properties of Cu 3 VSe 4. • Cubic Cu 3 VSe 4 is a semiconductor with an indirect band gap of 0.84 eV. • Pure Cu 3 VSe 4 was synthesized by traditional solid-state reaction. • Cu 3 VSe 4 is a semiconductor with electron-hole co-transport feature. • The Seebeck coefficients increase from 20 μV/K at 325 K to 558 μV/K at 571 K. [ABSTRACT FROM AUTHOR]

The multi-body system's elasticity and vibrational behavior is an old topic. The conventional method to study this issue is to transform a multi-body system to an abstracted network model consisting of nodes connected by central-force springs. In recent years, abnormal mechanical responses, including negative Poisson ratio, vanishing shear modulus, non-trivial topological characteristics, are discovered in such network systems making this topic be with lasting charms. In this paper, we investigate the vibrational modes of a series of distorted square lattice networks. The distorted degree for this network is only characterized by one parameter, the twisting angle θ. By studying their phonon spectrums, we find a band gap between the two lowest modes of the distorted square lattice. The gap width is linearly correlated to θ , and the gap will be closed when θ reaches a specific value. Our results may find applications in device protection and energy harvesting. • Multi-body system's elasticity and vibrational behavior. • Isostatic network consisting of nodes connected by central-force springs. • There exists a band gap between the two lowest modes of the distorted square lattice. • The band gap' s width linearly decreases with the distorted angle. • The band gap will totally be closed when the distorted angle is larger than a specific value. [ABSTRACT FROM AUTHOR]

In the present work the author describes a method for investigating phonon spectra of thin films of semiconductor solid solutions that is based on reflection-absorption spectroscopy in the far IR region. Analysis of spectra is carried out for two radiation polarizations (of the s- and p-type) and for the following experimental conditions: the spectral region 30–250 cm−1 and an angle of incidence of 45°. By comparing theoretical and experimental spectra for quaternary solid solutions of ZnxCdyHg1−x−yTe (ZCMT), the frequencies of LO- and TO-phonons are found and the three-mode behavior of the phonon spectra of ZCMT is established. [ABSTRACT FROM AUTHOR]