Debye Temperature Research Articles

First-principles calculations of electronic, vibrational, and thermodynamic properties of nitrogen-rich salt of 3,6-dinitramino-1,2,4,5-tetrazine [(DAG)2(DNAT)·H2O

In recent years, nitrogen-rich salts as green and efficient energetic materials have garnered widespread attention. This study focuses on a novel green synthesized salt, (DAG)2(DNAT)·H2O, which obtained through DNAT synthesis. Employing first-principles calculations, we conducted theoretical investigations to elucidate the electronic structure, vibrational, and thermodynamic properties of (DAG)2(DNAT)·H2O. Our computed lattice parameters align with experimental values from literature data. Analysis of the band structure and electronic states of atoms within the compound was performed. Vibrational modes for each peak in the infrared and Raman spectra were meticulously described, accompanied by phonon dispersion curves and phonon density of states plots for phonon contribution analysis. Thermochemical functions including enthalpy (H), heat capacity at constant volume (CV), Helmholtz free energy (F), Debye temperature (θ), and entropy (S) were computed based on vibrational characteristics, providing essential references for future research endeavors.

A comparative study of magnetic behaviours in bulk and ribbon samples of PrMn2Ge2 compound

The magnetic properties of PrMn2Ge2 samples in both the as-cast bulk and melt-spun ribbon forms have been investigated in detail by a comprehensive set of x-ray and neutron powder diffraction, magnetic and heat capacity measurements and corresponding sets of data analyses. Thermal expansion measurements indicate the presence of magnetoelastic coupling effects around all transition temperatures in the bulk sample. The bulk modulus K0 = 42.0 GPa and its first derivative K0’ = 18.7 have been derived from the pressure-volume data. The Curie temperature from the intralayer antiferromagnetism (AFl) of PrMn2Ge2 to a canted spin structure (Fmc) is TCinter = 332 K for the bulk sample, decreasing to TCinter = 320 K for the ribbon sample. The critical components γ, β and δ of this second order magnetic transition as determined from Kouvel-Fisher analyses, indicate long range magnetic interactions around TCinter. Based on these critical exponents the magnetization, field and temperature data around TCinter collapse onto two curves obeying the single scaling equation M(H,ε)=εβf±(Hεβ+γ). The Debye temperatures and the density of states at the Fermi level are θD=306K and N(EF)=3.47state/eVatom for the bulk sample and θD=320K and (EF)=2.18state/eVatom for the ribbon sample with the nuclear specific heat coefficient for bulk PrMn2Ge2 derived from the splitting of the nuclear hyperfine levels as CN = 517 mJ mol−1 K−1. With a field change of ΔB = 5 T, the maximum values of the magnetic entropy changes -ΔSmax in the region around TCinter are -ΔSmax = 3.00 J/kg K and 2.35 J/kg K for the bulk and ribbon samples respectively, while the relative cooling power (RCP) for the ribbon-spun sample, RCP = 135.9 J/kg, is significantly higher than the value of RCP = 116.6 J/kg for the bulk sample. These findings indicate that PrMn2Ge2 could be a promising candidate for magnetic refrigeration applications in the room temperature region.

Anisotropic Klemens model for the thermal conductivity tensor and its size effect

With the constraint from Onsager reciprocity relations, here we generalize the Klemens model for intrinsic phonon-phonon scattering from isotropic to anisotropic. Combined with the anisotropic Debye dispersion, this anisotropic Klemens model leads to analytical expressions for heat transfer along both ab-plane (κab) and c-axis (κc), suitable for both layered and chainlike materials with any anisotropy ratio of the dispersion and the scattering. This combination of dispersion and scattering is further applied to the equation of phonon radiative transfer to model heat conduction across anisotropic thin films. The model is compared to experimental κab and κc of bulk graphite at high temperatures (T≥0.1×max(θD,ab,θD,c), where θD,ab and θD,c are the two Debye temperatures), leading to best-fit scattering parameters that capture the harmonic and anharmonic nature of the intra- and inter-layer bonding of graphite. With no further adjusting of these parameters, the anisotropic scattering model performs at least 9 times better than the isotropic one at explaining the experimental κc of graphite thin films. This size effect is further justified by comparing the accumulation function of κc.

Ab-initio insights into the physical properties of XIr3 (X = La, Th) superconductors: A comparative analysis

Here we report the structural, elastic, bonding, thermo-mechanical, optoelectronic and superconducting state properties of recently discovered XIr3 (X = La, Th) superconductors utilizing the density functional theory (DFT) using two different exchange-correlations functionals. The elastic, bonding, thermal and optical properties of these compounds are investigated for the first time. The calculated lattice and superconducting state parameters are in reasonable agreement to those found in the literature. In the ground state, both the compounds are mechanically stable and possess highly ductile character, high machinability, low Debye temperature, low bond hardness and significantly high melting point. The thermal conductivities of the compounds are found to be very low which suggests that they can be used for thermal insulation purpose. The population analysis and charge density distribution map confirm the presence of both ionic and covalent bonds in the compounds with ionic bond playing dominant roles. The calculated band structure and DOS profiles indicate metallic character of XIr3 compounds. It is also found from the DOS profile that the Ir 5d-states dominate near the Fermi level. Unlike the significant anisotropy observed in elastic and thermal properties, all the optical constants of XIr3 compounds exhibit almost isotropic behavior. The optical parameters’ profiles correspond very well with the electronic band structure and DOS features. We have estimated the superconducting transition temperature (Tc) of XIr3 compounds in this work. The calculated values of Tc for LaIr3 and ThIr3 compounds are 4.91 K and 5.01 K, respectively. We have compared and contrasted all the physical properties of XIr3 (X = La, Th) compounds in this study.

Size Matters: Unraveling the Nanoscale World of Actinide-Based High Entropy Alloys through Ab Initio Methods

Ab initio computational studies of size-dependent Actinide-based High Entropy Alloys (HEAs) nanomaterials (AHEANMs) have emerged as a powerful tool to unravel the fundamental properties and behaviors of these complex systems. AHEAs have demonstrated remarkable mechanical, thermal, and radiation-resistant characteristics making them promising candidates for advanced technological applications. In this context, the size-dependent properties like cohesive energy, melting temperature, Debye temperature, Gibbs free energy of mixing, Heat of mixing, entropy of mixing, etc., have been studied.

Negative dielectric constant and multi-visible photolumenses emissions of Cd(1-x)CoxO nanocomposites with (0.00 ≤ x ≤ 1.00)

We report the photolumenses (PL) and dielectric measurements of Cd(1-x)CoxO nanocomposites with (0.00 ≤ x ≤ 1.00). It is found that an increase in x correlates with a significant change in crystallite size, particle size, porosity, Debye temperature, Young's modulus, q-factor, binding energy, impedance of grains and their boundaries. The samples with x = 0.50 or 0.60 show an adverse change in the behavior of these parameters. We could not evaluate any shift in the wave length of PL emissions, although they are different in intensities. The samples of x = 0.40 and 1.00 show more visible emission colors at 640, 678, 716, and 791 nm. The x = 0.00 sample shows a negative dielectric constant (ε\\), but it crossovers to positive for the other values of x. ε\\ was gradually decreased as frequency increased up to 10 KHz, after which it nearly saturated except x = 0.80, in which it linearly decreased and never saturated. The ac conductivity decreased gradually against x such that the type of conduction is dependent on the chosen x. The Cole-Cole plot shows a straight line for x = 0.00 and arcs for x = 0.20 and 0.60, and a complete semicircular for x = 0.40, 0.50, 0.80 and 1.00. Furthermore, the effective capacitance was 9260 μF for x = 0.00, but it drops to 0.013 μF for x = 0.40, whereas the vice is true for bulk resistance. These results lend a reasonable certainty to the assertion that Co substitutes for Cd and make them potential prospects for devices such as diodes that emit light, cathode-luminescence displays, integrated circuits, Li-battery and supercapacitors.

Influence of pressure on the structural, elastic, hardness and thermodynamic behavior of Al-rich region TMAl12-type (TM=Mo, W and Cr) alloys

Although transition metal (Mo, W and Cr) aluminides are regarded as the promising alloys, the high pressure behavior of the Al-rich region TMAl12 alloys is entirely unclear. Similar to MoAl12 and WAl12, the structure, mechanical and thermodynamic properties of CrAl12 are also unknown. To solve these problems, here, the structural stability, mechanical and thermodynamic properties of three TMAl12 alloys under pressure are studied by the first-principles calculations. The calculated results show that one novel cubic CrAl12 is firstly predicted. It is found that three TMAl12 alloys are thermodynamic stability under high pressure (<100 GPa). Importantly, the calculated bulk modulus of three TMAl12 alloys increases linearly with increasing pressure. In particular, the calculated bulk modulus under high pressure follows the order of WAl12>MoAl12>CrAl12. Naturally, the high bulk modulus of three TMAl12 alloys is that the pressure enhances the localized hybridization between TM atom and Al atom, which is confirmed by the bond strength of TM-Al bond. However, the shear modulus and Young's modulus of MoAl12 and WAl12 become smaller when the pressure is bigger than 70 GPa. The calculated hardness of three TMAl12 decreases with increasing pressure. I think that the high pressure maybe damaged the crystal structure of MoAl12 and WAl12. Importantly, the pressure results in the brittle-to-ductile transition of three TMAl12 alloys. In addition, the change of Debye temperature of three TMAl12 alloys is similar to the change of shear modulus and Young's modulus.

Stable lead free double perovskites Cs2XAu(Br/I)6 (X = Y, Sc) as an emerging aspirant for solar cells and thermoelectric applications

In present article, the electronic, optical, mechanical, and thermoelectric characteristics of Cs2XAu(Br/I)6, where X = Y, Sc are addressed comprehensively. The Born stability criteria ensure the mechanical stability, whereas the structural, thermodynamic, and lattice stabilities are calculated from tolerance factor, formation energy, and phonons dispersion band structures. The ductility, hardness, lattice thermal conductivity, melting, and Debye temperatures are discussed in terms of elastic constants. The direct band gaps 1.90/1.35 eV Cs2ScAu(Br/I)6, and 2.23/1.74 eV for Cs2YAu(Br/I)6 fall the absorption of light energy in visible to near ultraviolet regions. The Cs2ScAuI6 has ideal band gap (1.35 eV) for solar cells because broad absorption band in visible region. Finally, thermoelectric behavior has been studied by Seebeck coefficient, electrical conductivity, power factor, and thermal conductivity in the temperature range 200 K–600 K. The highest figure of merit (1.0 at 300 K) for Cs2YAuBr6 increases demand for thermoelectric generators.

Study of electronic, mechanical, thermoelectric, and optical aspects of K2AlAg(Br/I)6 for solar cells, and energy storage applications

Double perovskite materials exhibit considerable potential in addressing global energy challenges and advancing renewable energy technologies. This study focuses on K2AlAg(Br/I)6 and employs a comprehensive DFT approach to explore its structural, mechanical, thermodynamic, optical, and thermoelectric properties. The structural and thermodynamic stabilities of K2AlAg(Br/I)6 are accurately examined through tolerance factor (τF) and formation energy analysis. The mechanical stability and ductile characteristics are affirmed by studying elastic constants, Passion's, and Pugh's ratios. Additionally, insights into hardness, Debye temperature, as well as transverse and longitudinal sound velocities contribute to a deeper understanding of the material's thermodynamic response. The band gap of K2AlAgBr6 is identified as 2.71 eV, which undergoes a reduction to 1.17 eV when Br is substituted with I, attributed to the pd-hybridization of cations and anions. Exploring optical properties reveals valuable information through dielectric constants ε(ω), refractive index (n(ω)), absorption (α(ω)), and reflectivity (R(ω)). Notably, absorption in both visible and ultraviolet ranges underscores the material's significance for solar cell applications. Furthermore, the computed ultralow lattice thermal conductivity and higher figure of merit are noteworthy outcomes, driven by the substantial Seebeck coefficient and electrical conductivity of the material. These results collectively highlight the exclusive and promising characteristics of K2AlAg(Br/I)6 in the area of renewable energy materials.

On the Application of Fractional Derivative Operator Theory to the Electromagnetic Modeling of Frequency Dispersive Media

Fractional derivative operators are finding applications in a wide variety of fields with their ability to better model certain phenomena exhibiting spatial and temporal nonlocality. One area in which these operators are applicable is in the field of electromagnetism, thereby modelling transient wave propagation in complex media. To apply fractional derivative operators to electromagnetic problems, the operator must adhere to certain principles, like the trigonometric functions invariance property. The Grünwald–Letnikov and Marchaud fractional derivative operators comply with these principles and therefore could be applied. The fractional derivative arises when modelling frequency-dispersive dielectric media. The time-domain convolution integral in the relation between the electric displacement and the polarisation density, containing an empirical extension of the Debye model, is approximated directly. A common approach is to recursively update the convolution integral by approximating the time series by a truncated sum of decaying exponentials, with the coefficients found through means of optimisation or fitting. The finite-difference time-domain schemes using this approach have shown to be more computationally efficient compared to other approaches using auxiliary differential equation methods.

Study of electronic, mechanical, thermodynamic, optical, and thermoelectric properties of CdLa2X4 (X = S, Se, Te) chalcogenides for solar cells and energy applications

Spinels chalcogenides are an emerging aspirant for renewable energy which attained huge potential from the last decade. Therefore, the electronic structure, and mechanical properties are discussed by DFT approach. The Born stability criteria, and formation energies (−2.0, −1.98, −1.93) eV have been computed to assure mechanical, and thermodynamic stabilities. The ductile nature (υ > 0.26, and B/G > 1.75), hardness, Debye temperature, and lattice thermal conductivities are addressed in terms of elastic constants, and elastic modulus. The band gaps (2.0, 1.7, 0.85) eV for CdLa2X4 (X = S, Se, Te) have been calculated from band structures. The polarization of light, absorption bands in visible regions, refractive index, and reflection of light energy have made them significantly important materials for solar cells. Furthermore, transport characteristics are revealed by Seebeck coefficient, electrical & thermal conductivities, and figure of merit (ZT). The ZT has values 1.0, 0.80, and 0.66 at room temperature for CdLa2X4 (X = S, Se, Te) which increases their significance for thermoelectric devices.

Oxysulfide perovskites: reduction of the electronic band gap of RbTaO3 by sulfur substitution

In this study, the effects of sulfur substitution on the structural, mechanical, electronic, optical, and thermodynamic properties of RbTaO3−x S x have been investigated using the WIEN2k code in the framework of density functional theory (DFT). The cubic phase of RbTaO3 transforms to tetragonal for RbTaO2S and RbTaOS2; the latter transforms again to a cubic phase with added sulfur for RbTaS3. The results show that substituting S for O anions in RbTaO3 effectively decreased the band gap [calculated using TB-mBJ functional] from 2.717 eV to 1.438 eV, 0.286 eV, and 0.103 eV for the RbTaO3, RbTaO2S, RbTaOS2, and RbTaS3 compounds, respectively. The optical constants such as dielectric constant, refractive index, absorption coefficient, photoconductivity, reflectivity, and loss function have been calculated and analyzed. The elastic constants and moduli and their anisotropic nature were also investigated. Finally, the Debye temperature, thermal conductivity, melting temperature, specific capacities, and thermal expansion coefficients were computed and analyzed using established formalisms. The reduced band gap (1.438 eV) and high absorption coefficient (∼106 cm−1) of RbTaO2S, make it suitable for solar cell applications and for other visible light devices. Both ordered structure and super-cell have been used to cross-check results for RbTaO2S and RbTaOS2 compositions.

Structural, mechanical, electronic and thermodynamic properties of YBC, YB2C, YB2C2, Y2B3C2 intermetallics

Transition metal diboride and transition metal boron-carbon intermetallics have attracted extensive attention. In this work, we adopted the first-principles method to reveal the structural stability, elastic behavior, anisotropy and electronic structures of transition metal boron-carbon intermetallics (YBC, YB2C, YB2C2, Y2B3C2). The formation enthalpy suggests that YB2, YBC, YB2C, YB2C2 and Y2B3C2 are thermodynamically stable. The calculated results of elastic constants indicates that all five intermetallics exhibit the mechanical stability. The band structures and density of states indicate that YB2, YBC, YB2C, YB2C2 and Y2B3C2 possess metallic properties. According to v and G/B, these intermetallics exhibit the brittleness. The 3D and 2D maps display the anisotropic properties. Moreover, the Debye temperature θD of YB2, YBC, YB2C, YB2C2 and Y2B3C2 at high temperatures obeys the order of YBC> YB2C2> YB2C > Y2B3C2 > YB2.

Electronic and thermal properties of Nb2CCl2 MXenes

The molten salt synthesis has recently opened up new opportunities to functionalize two-dimensional MXenes with uniform halogen terminations. In this work, we synthesize Nb2CCl2 MXenes by etching the Al layer from the Nb2AlC precursor in the melt of CuCl2 Lewis acid. In Cl-terminated MXenes, intercalation of water is negligible, so that MXenes get closer to ideal, ordered van der Waals solids. We identify the preferential atomic stacking arrangement, which is of the AB type, as opposed to the AA stack assumed in previous works. We combine X-ray absorption near edge spectroscopy with density functional theory to clarify the local chemical environment of Cl atoms. Using vibrating sample magnetometry and specific heat measurements, we confirm that Nb2CCl2 MXenes are superconducting with a transition temperature of 6.0 K and find a Debye temperature of 320 K. We further show that the transition temperature slightly decreases with applied isostatic pressure.

A leap-frog nodal discontinuous Galerkin method for Maxwell polynomial chaos Debye model

The Maxwell polynomial chaos Debye model uses the parameter distribution in the Debye model to represent the Cole-Cole dispersive mechanism. In this paper, a leap-frog nodal discontinuous Galerkin (DG) method is studied for solving this model. Under the Courant-Friedrichs-Lewy (CFL) condition, the stability of the fully discrete DG scheme is demonstrated and its error estimate is derived. Numerical examples are provided for supporting the correctness of the theoretical analysis and the effectiveness of our proposed method.

Temperature-Dependent Structural and Elastic Properties of CdS, CdSe, and CdTe Compounds Studied by Statistical Moment Method

The statistical moment method has been applied to investigate the temperature effects on the lattice parameters and elastic properties of the zinc-blende CdX (X = S, Se, Te) compounds. The analytical expressions of thermal-induced atomic displacement, lattice constant, elastic moduli (Young’s modulus, bulk modulus and shear modulus) and elastic constants (including C11,C12 and C44) of the zinc-blende compounds have been derived. We have pointed out that the temperature effects on the elastic properties of CdS and CdSe are almost the same. And the elastic quantities of CdS and CdSe are more strongly dependent on temperature than those of CdTe semiconductor. This phenomenon is caused by the weaker coupling force of Cd-Te bonds compared to those of Cd-S and Cd-Se bonds. Furthermore, from the calculated Debye temperatures of CdX (X = S, Se, Te) compounds we conclude that CdS has higher phonon thermal conductivity and is therefore more thermally conductive among the three semiconductor compounds. The calculations of present work can be used as an appropriate reference for the experiments in future.

Mechanical and thermal response of XFe2O4 (X = Zn, Ag and Co) spinel ferrites via IR-spectroscopy and first-principles calculations

The lack of comprehensive literature on the all-important aspect of the elasticity of spinel ferrites led to the hydrothermal synthesis of different (Co, Zn, Ag) spinel ferrites. IR spectroscopy revealed the characteristic absorption bands of metal-oxygen in all three compositions. The shifting of tetrahedral and octahedral bending vibrations towards higher frequencies owes to changes in inter-atomic and inter-ionic distances. Elastic parameters, wave velocities, and Debye temperature have been calculated using IR spectroscopy data. Elastic parameters have been higher for Co ferrites than Zn and Ag ferrites. The Poisson ratio seems to be consistent for different spinel ferrites. Shear wave velocity has been found to be higher than longitudinal wave velocity because perpendicular particle vibrations take higher energy than parallel vibrations. Wave velocities have been found to be higher in Ag ferrites than in the other two compositions. Debye temperature follows the same trend as elastic parameters. Additionally, we have confirmed the mechanical stability of the Co, Zn, and Ag ferrites using the first-principles calculations in the density functional theory (DFT) approach framework. Interestingly, the Co/Zn/Ag ferrites exhibit semiconducting nature with a band gap of 3.96/3.66/0.71 ev. Our study could pave the way for next-generation spintronic devices.

Thermoelectric, mechanical, and pressure sustained half-metallic properties of BaInO3 perovskite for spintronics applications: DFT computation

Oxide perovskites continue to promote research interest because of their concurrent use in spintronic and thermoelectric applications. The electronic, magnetic, and thermoelectric properties of new half-metallic BaInO3 perovskite are investigated using the density functional theory. The structural and thermodynamic stability of the proposed perovskite is provided by the tolerance factor, octahedral factor, formation energy, and phonon dispersion curves. The structural relaxation curves reveal that the ground state is ferromagnetic. The generalized gradient approximation and mBJ band structure plots show that the half-metallicity exclusively results from the strong exchange splitting of 2p-bands at the Fermi level. Compared with PBE, mBJ depicts highly localized magnetic moments around oxygen along with enhanced half-metallic gaps and band gaps in the spin-up channel. Under a compressive strain, the system undergoes a magnetic phase transition from half-metallic ferromagnet to non-magnetic metal at 30 GPa. The elastic stability at the studied pressure range has been verified from Blackman’s and Every’s diagrams. The material remains ductile and exhibits moderate elastic anisotropy in the studied pressure range. The quasi-harmonic Debye model is employed to study the temperature and pressure effects of thermodynamic parameters. The computed transport properties including the Seebeck coefficient and spin-Seebeck coefficient predict reasonable thermoelectric performance in generating thermally induced spin-polarized current and spin current, respectively. Such a detailed study of this material could open prospects in spintronic as well as waste energy recovery devices.

Structural, electronic, optical, elastic, mechanical, thermodynamic, and thermoelectric properties of lead-free and environmentally friendly CsSnX3 (X = Cl, Br) perovskites

In this study, we systematically examined the physical properties of CsSnX3 (X = Cl, Br) by employing the (FP-LAPW) method within the (GGA) and GGA + mBJ approximations. The investigated compounds exhibit direct bandgap semiconducting with an ionic-covalent mixture in CsSnX3 bonds. Notably, CsSnCl3 and CsSnBr3 exhibit exceptional light absorption and optical conductivity, making them appropriate for a particular application. Elastic constants of compounds and different moduli are determined for the first time. Considering the thermodynamic model, perovskite materials consistently display thermodynamic properties such as heat capacity, Debye temperature, Grüneisen constant for a range of pressures and temperatures. The calculations of transport properties by using BoltzTrap code reveals a high figure of merit close to unity for CsSnX3 (Cl, Br) at room temperature, highlighting their potential for thermoelectric applications. Overall, CsSnX3 (Cl, Br) perovskite exhibit remarkable physical properties and environmental compatibility, positioning them as up-and-coming candidates for optoelectronic and thermoelectric applications.

First-principles calculations to investigate structural, elastic and electronic properties of chloro-perovskite NaMgCl3

In this work, we have investigated the structural, electronic, and optical properties of the halide-perovskite NaMgCl3 by performing first-principles calculations using a mixed basis of the full-potential linearized augmented plane wave (FP-LAPW) approach under the generalized gradient approximation (GGA-PBEsol), a revised Perdew-Burke-Ernzerhof, and the modified Becke-Johnson (TB-mBJ) implemented on the Wien2k package. The obtained results show that NaMgCl3 is more stable in the nonmagnetic phase.The compound is found to be thermodynamically and elastically stable. It is found that there is a good agreement between the calculated lattice constants and the values published in previous studies. The complete set of first-order elastic constants tensor has been calculated, implying mechanical stability. The Young's modulus, shear modulus, Poisson's ratio,Pugh's ratio, and universal anisotropy index have been additionally calculated. The atomic bonds along both x and y axis are stronger than those along the z-axis. The Debye temperature is calculated using the average sound velocity. From electronic band structures, we have found that NaMgCl3 is an insulator with a direct wide band gap ΓV→ΓC. The electronic charge densities were plotted.Analysis of the charge density distribution map reveals that the bondings in NaMgCl3 are ionic. The calculated density of states (DOS) indicates that the valence band is mainly dominated by Cl− anions, the conduction band is mainly dominated by Mg2+ cations, whereas Na+ has a negligible contribution. The optical characteristics, notably the dielectric function tensor, refractive function, reflectivity, absorption coefficient, photo-conductivity and transmittance were plotted and discussed. The optical properties confirm that NaMgCl3 is optically anisotropic in 10–24 eV range .The low transmittance and high absorption coefficient in the far ultra-violet region, between 90 and 250 nm, make this compound a good candidate for use as an ultraviolet shield, in vacuum ultraviolet lenses and in thermoelectric promising features due to his direct wide band gap.Experimental and theoretical data are scarce for this compound in an ilmenite-type structure.