Debye Temperature Research Articles

Insight into the Physical Properties of the Chalcogenide XZrS3 (X = Ca, Ba) Perovskites: A First-Principles Computation

AbstractThis study investigates the structural, mechanical, optical, thermal, and electronic properties of the ionic semiconducting materials XZrS3 (X = Ca, Ba) within the framework of density functional theory (DFT). Here, the elastic constants, modulus (bulk, shear, Young's), ratios (Pugh, Poisson) and elastic anisotropy for XZrS3 (X = Ca, Ba) are studied. Furthermore, the electronic, optical, and thermal properties for XZrS3 (X = Ca, Ba) are regenerated and designed using the values obtained with Cambridge Serial Total Energy Package (CASTEP) software. The calculated lattice parameters show excellent agreement with theoretical and experimental values. The elastic stiffness constants confirm the mechanical stability of both compounds. Although XZrS3 (X = Ca, Ba) is elastically anisotropic, it has little optical anisotropy. The electronic band structures of the material exhibit direct-bandgap semiconducting behavior, with values of 1.3 eV (CaZrS3) and 1.1 eV (BaZrS3) using the generalized gradient approximation (GGA), respectively, which is ideal for solar cell (0.9–1.56 eV) and optoelectronic device applications. Bandgap values of 1.9 eV and 1.6 eV are found for CaZrS3 and BaZrS3, respectively, using the Heyd–Scuseria–Ernzerhof HSE06 functional, which is consistent with previous theoretical and experimental bandgap results. The optical properties including dielectric function, refractive index, absorption coefficient, reflectivity, and loss function are characterized using the GGA of Perdew–Burke–Ernzerhof (GGA-PBE) and HSE06 methods and are discussed in detail. Because of the relatively low Debye temperature (D), thermal conductivity of the lattice (kph), and minimum thermal conductivity (Kmin), the studied materials can be used as thermal barrier coating (TBC) materials. The capacity of heat, Debye temperature, and thermal coefficient of expansion are all computed.

Research on the Thermal Aging Characteristics of Crosslinked Polyethylene Cables Based on Polarization and Depolarization Current Measurement

Although XLPE cables are widely used in power transmission and distribution systems, their insulating properties are susceptible to degradation due to thermal aging. In order to clarify the influence law of the thermal aging process on the structural and dielectric properties of XLPE cables, this paper investigates the thermal aging characteristics of XLPE cables by using polarization and depolarization current measurement. Results show that when the XLPE cable is aged at 140 °C, the crystallinity of the insulation layer appears to increase and then decrease. With the increase in aging time, micron-sized microvoids appear on the surface of the XLPE. At the same time, the DC conductivity and 0.1 Hz dielectric loss factor of the insulating layer increase with the aging time. The average DC conductivity increased from 2.26 × 10−16 S/m for new cables to 4.47 × 10−16 S/m after aging for 432 h, while the dielectric loss increased from 0.11% to 0.42%. The polarization characteristics of thermal-aged cables were further analyzed using the extended Debye model. Results indicate that the time constant of the third branch of the model increased significantly with increasing aging time. A correspondence between this parameter and the thermal aging time of the cable was established. Thermal aging can damage the crystalline structure of XLPE, so that the number of interfaces between the crystalline and amorphous regions of the material increases, resulting in structural damages and a decline in the dielectric properties of the cable insulation.

Insights into optoelectronic, thermodynamic, and thermoelectric properties of novel GePtCh (Ch = S, Se, Te) semiconductors: first-principles perspective

Ternary chalcogenides are often studied for their remarkable heat resistance and flexible optical properties. We used density functional theory and examine complicated connections between the various physical features of the exclusive GePtCh (Ch = S, Se, and Te) ternary chalcogenides. The valence band is formed by the hybridization of the Ge-s/p/d, Pt-s/p/d, S-p, Se-p, and Te-p orbitals in the energy range of −6.0 eV to 0 eV. The materials under consideration are confirmed as indirect bandgap materials with estimated energy gaps of 1.29 eV, 0.86 eV, and 0.48 eV, respectively. By substituting Se and Te for S reduced the bandgap in these materials. The complex dielectric function’s components, absorption coefficients, real optical conductivity, energy loss functions, refractive index, reflectivity, and extinction coefficient, are studied and examined to identify their potential use in optoelectronic applications. The thermodynamic parameters of these ternary systems are calculated by employing the quasi-harmonic Debye model. The materials are suitable for thermoelectric devices, as evidenced by their considerable and outstanding thermoelectric features. The GePtTe possessed the highest absorption, indicating that it is a suitable material for the use in optoelectronic applications.

Investigation on the hydrogen storage properties, electronic, mechanical properties, debye temperature of H24AlXO20S2 (X=Na, Rb, Cs, K) hydrides

The stability and lattice vibration of H24AlXO20S2 (X = Na, Rb, Cs, K) hydrides are predicted by calculating the crystal structure and energy. The formation enthalpy proves the structural stability and the dynamic stability of the hydride is predicted by the phonon dispersion diagram. Meanwhile, the optical and mechanical properties are analyzed by using the quasi-Debye model. The elastic constants and modulus prove H24AlXO20S2 (X = Na, Rb, Cs, K) mechanical stability. By the value of B/G and Poisson's ratio, it inferred that H24AlNaO20S2, H24AlRbO20S2 and H24AlKO20S2 are brittle. Only H24AlCsO20S2 is ductile and has the lowest hardness. H24AlRbO20S2 has the largest shear modulus and Young's modulus, so it has the highest hardness. In addition, by calculating the anisotropy index of the hydrides, it is proved that they are anisotropic. H24AlKO20S2 has the strongest anisotropy and the value of AU is 0.2477. The anisotropy of the hydride is further studied by calculating the Debye temperature and sound velocity of H24AlXO20S2 (X = Na, Rb, Cs, K) hydrides. The energy band and state density analysis reveal their electronic transitions and bonding.

First-principles study on the structural, elastic, electronic, optical and thermophysical properties of NaNO3 and K-doped NaNO3

Abstract The present work represents the structural, electronic, elastic, and thermophysical properties of pure and K-doped NaNO3 obtained using DFT calculations. The estimated structural properties of NaNO3 correspond well with the existing reported values. Electronic characteristics such as band structure and density of statesof pure and doped NaNO3 are analyzed where the calculated band gaps for pure and K-doped NaNO3 are found to be 3.05 eV and 2.90 eV, respectively. The Berry–phase calculations carried out on both systems showed the existence of ferroelectric polarization, where an enhanced spontaneous polarization value of 36 μC/cm2 for K-doped NaNO3, as compared to 20 μC/cm2 for intrinsic NaNO3. The thermophysical properties such as bulk modulus (B0), Debye temperature (θD), and specific heat capacity (Cv) were calculated over a wide temperature range from 0K to 800 K. The linear optical properties namely the dielectric constant, refractive index, absorption coefficient, extinction coefficient and electron energy loss function are calculated in wide energy range from 0 to 30 eV and discussed in detail.

Investigating stress-induced effects on the multifaceted properties of cubic NaTaO3 perovskite oxide: prospects for advanced applications

This study explored the structural, optoelectronic, elastic, mechanical, and thermodynamic behaviour of NaTaO3 cubic perovskite oxide, under varying stress levels. Geometric property analysis reveals a decrease in lattice constants from 4.1 Å to 3.7 Å and cell volume from 71.1–53.4 Å3 as stress increases from 0 to 100 GPa. X-ray diffraction analysis indicated the stable cubic phase with slight peak shifts, demonstrating the material's structural flexibility. Electronic properties revealed an initial increase in the band gap (1.698 eV to 1.936 eV) with applied stress up to 60 GPa, which could be attributed to complex interactions within the material's electronic structure. Optical property analysis suggested that NaTaO3 possessed high optical absorption and conductivity, along with low reflectivity. Furthermore, elastic constants meeting the Born-stability condition (C11 – C12 > 0, C11 + 2C12 > 0, and C44 > 0) confirm the material's mechanical stability. Additional characteristics like the Poisson ratio, Cauchy pressure, and Frantsevich ratio highlighted the ductile and anisotropic nature of NaTaO3. Thermodynamic and phonon dispersion analysis suggested that NaTaO3 can withstand high-stress levels, evidenced by its elevated Debye temperature, indicating superior mechanical stability and increased resistance to thermal degradation. Based on these findings, NaTaO3 proposed as a potential candidate for photovoltaic and thermoelectric devices.

First principle study of X2GaAgCl6 (X = Cs, Rb) double perovskites: structural, mechanical, vibrational, electronic, optical, SLME, thermoelectric, and thermodynamic properties for solar cell applications.

The structural, mechanical, vibrational, electronic, optical, SLME, thermoelectric, and thermodynamic properties of X2GaAgCl6 (X = Cs, Rb), a double perovskite material, were computed by employing Density Functional Theory (DFT). CASTEP and Quantum ESPRESSO were used to perform first-principles calculations. X2GaAgCl6 possesses a cubic structure with the space-group symmetry Fm-3m. The lattice parameters of Cs2GaAgCl6 and Rb2GaAgCl6 were optimized using the energy-volume curves, resulting in values of 7.357Å and 7.365Å, respectively. The population analysis confirmed the charge transfer among transition metals and halogen atoms. The stability of crystal X2GaAgCl6 (X = Cs, Rb) is effectively demonstrated by analyzing phonon dispersion curves with no negative frequencies. The band structure calculations indicated the semiconducting nature of compounds with energy gaps of 0.96eV and 0.88eV for Cs2GaAgCl6 and Rb2GaAgCl6, respectively. The optical characteristics results confirm that the examined materials are suitable for devices working, primarily in the electromagnetic spectrum's visible region. SLME results showed that Cs2GaAgCl6 has 30% and Rb2GaAgCl6 has 27% efficiency, respectively, suggesting their use in photovoltaics. The thermoelectric properties of X2GaAgCl6 (X = Cs, Rb) were calculated by using the BoltzTraP code in the temperature range of 300 to 800K. The quasi-harmonic Debye model was applied to calculate the thermodynamic characteristics.

Phase stability and physical behaviour of Fe3Pd, FePd and FePd3 binary intermetallic compounds

The FP-LAPW method is used to examine the physical properties of Fe–Pd binary intermetallic compounds. The calculated formation enthalpies indicate that FePd and FePd3 compounds are thermodynamically stable in L10 and L12 phases, respectively, and the ferromagnetic Fe3Pd can be formed in a tetragonal Z1 structure with a small negative formation enthalpy. The elastic coefficients and their related parameters show that all compounds are mechanically stable and ductile in nature. The FePd-L10 is the harder compound and Fe3Pd-Z1 exhibits the highest anisotropy. The band structure, the TDOS profile and the charge density distribution show that these compounds are ferromagnetic with a metallic character and covalent-metallic bonds. The PDOS shows that the Pd-4d and Fe-3d states are dominant, and the asymmetry of Fe-3d states is behind the system strong spin polarization. The calculated magnetic moments agree well with previous theoretical results. The thermodynamic parameters are determined using the quasi-harmonic Debye model.

Computational investigation of the structural, elastic, electronic, and thermodynamic properties of chloroperovskites GaXCl3 (X = Be, Ca, or Sr) using DFT framework

In this study, we employed the pseudopotential plane wave approach to examine the influence of the X atom (X = Be, Ca, or Sr) on the physical properties of isostructural chloroperovskites GaXCl3. The GGA-PBEsol functional was employed to simulate the exchange–correlation interactions. The computed equilibrium lattice parameters exhibit a high level of concordance with the existing theoretical findings. The cohesion energy and enthalpy of formation were computed to verify the energetic stability of the materials under consideration. The determined values of the single-crystal elastic constants (Cij) indicate that GaBeCl3 remains mechanically stable up to a hydrostatic pressure of 18 GPa. Similarly, GaCaCl3 preserves its stability up to 5 GPa, while GaSrCl3 remains mechanically stable up to 1.25 GPa. The projected Cij values were used to estimate several elastic moduli and related properties, including the shear and bulk moduli, sound wave speeds, Young’s modulus, Poisson’s ratio, and Debye temperature. The energy band structures of the studied compounds, as predicted by the HSE06 functional, demonstrate their wide bandgap semiconductor nature. Specifically, GaBeCl3 demonstrates an indirect bandgap of 3.828 eV, while GaCaCl3 reveals an indirect bandgap of 4.612 eV and GaSrCl3 has an indirect bandgap of 4.405 eV. The quasiharmonic Debye approach was employed to examine various thermal parameters, including the temperature dependence of the unit cell volume, bulk modulus, expansion coefficient, Debye temperature, isochoric and isobar heat capacities, Grüneisen parameter, and entropy function. It has been shown that GaBeCl3 demonstrates a lower thermal expansion coefficient and a higher Debye temperature in comparison to GaCaCl3 and GaSrCl3.

Comprehensive investigation of half Heusler alloy: Unveiling structural, electronic, magnetic, mechanical, thermodynamic, and transport properties

This study employs density functional theory (DFT) using Wien2k to comprehensively analyze the essential properties of two half-Heusler alloys, KCrSi and KCrGe. Our findings demonstrate that the ferromagnetic Type 2 configuration exhibits superior stability over non-magnetic and antiferromagnetic states for all KCrZ (Z = Si, Ge) alloys. These alloys exhibit complete spin polarization and half-metallic character, with calculated magnetic moments of 3 μB for both KCrSi and KCrGe. The Curie temperature (TC) is determined using the mean field approximation. Mechanical stability is assessed through second-order elastic constants (SOECs), and electronic properties are analyzed using local spin density approximation (LSDA), Perdew-Burke Generalized Gradient Approximation (PBE-GGA), and Tran-Blaha modified Becke-Johnson (TB-mBJ) schemes, confirming the retention of the half-metallic nature. The negative enthalpy of formation (ΔH) suggests material stability. The use of semi-classical Boltzmann theory, incorporated through the sophisticated scheme of BoltzTraP, explores transport coefficients. High pressures and temperature discrepancies in thermodynamics are considered by implementing the quasi-harmonic Debye approximation to illustrate stability. Finally, optical properties are summarized to assess the applicability of this alloy for optoelectronic applications. The overall characteristics of these particular alloys suggest potential applications in sustainable thermoelectric and optoelectronic features.

Analytic solutions of Eliashberg gap equations at superconducting critical temperature

We perform simple mathematical analysis of the Eliashberg gap equations, and derive the analytic expression at the superconducting critical temperature. In order to perform exact summation of LTc=∑λm12m−1, we use the Einstein and Debye models for the Eliashberg spectral function. This quantity is in good agreement with data derived from experimental and DFT data. To the leading-term approximation, the analytic expression of the superconducting critical temperature is of the form Tc=2eγ−1πωxexp−1+μ*ln4eγmcλ, where ωx=ω2 or ωln. The frequencies ω2 and ωln come out naturally from the models. These equations contain mc as an adjustable parameter. There are no other free parameters and no empirical formula involved. We compare the results of these equations with the celebrated Allen-Dynes modified McMillan equation together with the data from experiments and DFT calculations. The data show strong correlation between our analytic expression and the celebrated Allen-Dynes equation.

First-principles calculation of P-type Mg3Sb2 thermoelectric performance modification by Ge and Si doping

Mg3Sb2 has been considered a highly promising thermoelectric material for mid-temperature applications. Optimizing the properties of the material is crucial for accelerating its commercial use. In this work, first-principles molecular simulations of P-type Mg3Sb2 doped with the carbon group elements Ge and Si have been carried out. Results indicate that doping with Ge and Si enhances the thermodynamic stability and electrical conductivity of the material. This improvement is achieved by decreasing the bandgap, increasing the local and peak density of states, flattening the band structure, and elevating the relative mass of carriers. Additionally, doping with Ge and Si decreases the phonon velocity and Debye temperature, which weakens the thermal transport properties of the material. These findings suggest that Ge and Si doping is an effective method for improving the thermoelectric properties of the material. At the same doping concentration, the Si single-doped system possesses the smallest bandgap value with the highest peak density of states and forms an indirect bandgap, leading to the best electrical transport properties; the Ge single-doped system has the lowest phonon velocity and Debye temperature, which has the most significant effect in attenuating the thermal transport properties of the material; and the Ge–Si co-doped system has the highest relative mass of carriers, which is conducive to the enhancement of Seebeck coefficient. The results offer theoretical guidance for experimentally analyzing the effects of Ge and Si doping on the thermoelectric properties of Mg3Sb2.

Optoelectronic and transport properties of Lead-Free halide based Na2AgTlZ6 (Z = Cl, Br, I) double perovskites for energy harvesting applications

The bandgap engineering and deliberate band edge manipulation of perovskites make them potential candidates for the photovoltaic industry. Here we theoretically investigate the structure, density of states, and photovoltaic and thermoelectric characteristics of Na2AgTlZ6 (Z = Cl, Br, I) using WIEN2k code. The incorporation of Br and I at the Cl site caused the increase in lattice constant which leads to the decrease in bulk modulus and Debye temperature. The computed values of Poisson (<0.26) and Pugh (<1.75) ratio verified their brittle nature. The bandgap analysis reveals direct bandgap nature and bandgap value lie in the visible region for parent composition and infrared and far infrared when Cl is replaced with Br and I. The density of state plots uncovers the shifting of energy states in valence and conduction bands towards the Fermi level with the increasing number of electrons in the halogens. The increase in the value of dielectric constant, refractive index, and shifting of peaks towards lower energy value is witnessed with atomic number of halogen atoms. The viability of these compositions for thermoelectric devices is further confirmed when electrical conductivity and Seebeck coefficient dependent Figure of merit and power factor are evaluated in the temperature range of 200–800 K. In addition, the anisotropic nature of studied compositions is explored through the computation of the modulus of elasticity including Young’s modulus, Shear modulus in addition to compressibility, and Poisson’s ratio.

Sound velocities, elasticity and thermal properties of cBN composite with AlN binder at high pressure

Cubic boron nitride (cBN) has been used as a tool material for several decades due to its high hardness and thermal stability. Various binders are commonly added to cBN to synthesise cBN composites for better cutting performance. However, most studies have only investigated properties such as hardness and bulk modulus, without comprehensively studying elastic properties through experiments. In this study, the sound velocities and elastic properties of cBN with AlN binder were determined by using the ultrasonic interferometry technique. The bulk and shear moduli with their pressure dependence were determined as B0 = 351(3) GPa, G0 = 344(3) GPa, = 4.32(4) and = 1.74(2) using the finite strain equation-of-state approaches. Elasticity-related thermal properties, such as Debye temperature, Grüneisen parameter, thermal conductivity and coefficient of thermal expansion were also estimated. The results show that the elastic properties of the cBN composite with vol. 8.8% AlN-binder are comparable to the pure cBN compact. Additionally, the thermal conductivity and coefficient of thermal expansion have little effect on cBN composite with AlN binder compared to pure cBN.

Increase in interplanar distances and formation of amorphous shear bands in deformed diamond

Amorphous transformation-deformation bands have been observed in diamond under cyclic loading (at planetary ball milling) near the graphite-diamond equilibrium line at temperatures below the Debye temperature. The maximum stresses and temperature in the diamond do not exceed 6 GPa and 420 K, respectively. These bands add to the set of plastic deformation mechanisms in diamond. TEM methods and conventional X-rays were used to investigate the mechanisms of plastic deformation of diamond. The observed mechanisms include amorphous deformation bands, bond breaking, twin formation, and phase transitions of diamond-lonsdaleite and diamond-onions. The increased interplanar distances provide evidence of the plastic deformation mechanism due to bond breaking. The distances of 0.222 and 0.255 nm are significantly larger than the initial value of 0.206 nm, which is characteristic of d111 diamond. This increase in distance cannot be attributed to lattice expansion caused by point defects, but rather to the breakage of interatomic bonds.

Investigation of Structural, Magnetic, Mechanical, Electronic and Thermal properties of new quaternary Heusler: KMgNZ (Z=O or S)

The structural stability as well as the mechanical, magnetoelectronic and thermal properties of the quaternary Heusler KMgNZ (Z=O or S) were studied using first principles approach based on the DFT implemented in Wien2k code. The exchange-correlation potential is treated by PBE-GGA. The calculated negative formation energies for both materials corroborate their thermodynamic stability. Moreover, the derived elastic constants support the mechanical stabilities of the latter compounds. On the other hand, the density of states of the studied materials shows that both compounds are half-metallic ferromagnets. The total magnetic moments for both compounds are mainly originated from N atom, and its integer value followed the Slater-Pauling rule. The calculated half-metallic gaps are found for two systems. The three-dimensional plots of different mechanical moduli exhibit that the bulk modulus is isotropic, whereas Young's modulus, Poisson's ratio and shear modulus of both compounds are highly anisotropic. The effects of temperature and pressure on the heat capacity, thermal expansion coefficient and Debye temperature are also studied.

The structure, magnetism and mechanical properties of L21-type full-Heusler alloy Cr2ZrSi: a first-principles study

Heusler alloy is a widely studied spintronic material in recent years, which has played a huge role in the field of spintronic devices due to its high spin polarization and high Curie temperature. Using first-principles calculation to predict the basic properties of Heusler alloy can not only save experimental costs and time but also provide a reliable theoretical basis for experimental research. This study used a first-principles calculation to study the magnetic and mechanical properties of full-Heusler alloy Cr2ZrSi with an L21-type structure. The research results indicate that the alloy is a half-metallic ferromagnetic material with a theoretical value of 100% spin polarization. The magnetism mainly comes from the asymmetric spin contribution of d-orbital electrons of transition metal atoms and their hybridization. At the same time, this complex hybridization coupling process is also a possible reason for the half-metallic band gaps. In terms of mechanical properties, the Cr2ZrSi alloy exhibits good ductility and anisotropy, with a Debye temperature of 303.848K. Our theoretical research results provide more choices and theoretical basis for subsequent experimental research.

Investigation of anharmonic EXAFS parameters of Ag using anharmonic correlated Debye model under the effect of thermal disorders

Investigation of anharmonic EXAFS parameters of Ag using anharmonic correlated Debye model under the effect of thermal disorders

Elastic, Electronic, Dynamic and Thermodynamic Properties of YbPdH3

A comprehensive computational investigation has been carried out for YbPdH3 via first principles calculations for the first time. Structural, electronic and thermodynamic properties are obtained. The obtained lattice constant of YbPdH3 is in a good agreement with the existing literature. Subsequently, the elastic constants are obtained and used to compute several parameters such as anisotropy, hardness, Cauchy pressure, shear and Young modulus, machinability index and Poisson’s ratio. According to Born stability criteria, YbPdH3 is mechanically stable material. Cauchy pressure and Poisson’s ratio indicates ductile nature. The anisotropy factor indicates anisotropic nature almost in every direction for Young modulus, shear modulus, linear compressibility and Poisson’s ratio. The machinability index (B/C44) is found to be 2.88 whereas Vickers hardness of YbPdH3 is computed via Chen’s model as 2.965. The electronic band structure of YbPdH3 demonstrates metallic characteristics since there is no band gap between valence and conduction band. The thermodynamic properties such as Debye temperature, Debye vibrational energy, vibrational free energy, entropy, heat capacity and melting temperature of YbPdH3 are also obtained. The heat capacity seems to reach its Dulong-Petit limit at about 300 K.

Pressure dependent physical properties of a potential high-TC superconductor ScYH6: Insights from first-principles study

Cubic ScYH6 is elastically and thermodynamically stable within the pressure range considered. Moreover, the compound is brittle. The elastic anisotropy of ScYH6 is low and the machinability index is moderate which increases gradually with rising pressure. It is a hard material. The electronic band structure shows weakly metallic character with low density of states at the Fermi level. The Debye temperature of the compound is high and increases with increasing pressure. The Grüneisen parameter of ScYH6 is low and the phonon thermal conductivity is high at room temperature. The compound is a very efficient reflector of infrared radiation. ScYH6 is also an efficient absorber of visible and ultraviolet light. We have investigated the pressure induced changes in the predicted superconducting state properties. The superconducting transition temperature is found to increase slowly with increasing pressure.