Debye Temperature Research Articles

Dielectric Terahertz Characterization of Microwave Substrates and Dry Resist

Microwave fabrication and design techniques are commonly employed in the terahertz (THz) domain. However, a characterization of commercially available microwave dielectric materials is usually lacking at sub-THz and THz frequencies. In this work, we characterized four substrates by Rogers and an Ordyl dry resist between 0.2 and 2 THz, in terms of relative permittivity and loss tangent. The reflectance spectra of the investigated materials were retrieved by means of THz time-domain spectroscopy in reflection mode and post-processed according to a transmission-line model in which the materials’ parameters are fit by means of the Havriliak–Negami variation of the Debye model. The relative permittivity of the investigated materials showed negligible frequency dispersion in the sub-THz and in the THz range. In terms of the loss tangent, the Rogers substrates revealed a more pronounced frequency-dispersive behavior among different materials, as dictated by the Havriliak–Negami model. The Ordyl resist was dispersive in the 0.2–1.2 THz range and presented a nearly constant loss tangent value between 1.2 and 2 THz. These results may represent a reference for the development of innovative components for THz and sub-THz emerging applications.

Debye Temperature Evaluation for Secondary Battery Cathode of α-SnxFe1-xOOH Nanoparticles Derived from the 57Fe- and 119Sn-Mössbauer Spectra.

Debye temperatures of α-SnxFe1-xOOH nanoparticles (x = 0, 0.05, 0.10, 0.15 and 0.20, abbreviated as Sn100x NPs) prepared by hydrothermal reaction were estimated with 57Fe- and 119Sn-Mössbauer spectra measured by varying the temperature from 20 to 300 K. Electrical properties were studied by solid-state impedance spectroscopy (SS-IS). Together, the charge-discharge capacity of Li- and Na-ion batteries containing Sn100x NPs as a cathode were evaluated. 57Fe-Mössbauer spectra of Sn10, Sn15, and Sn20 measured at 300 K showed only one doublet due to the superparamagnetic doublet, while the doublet decomposed into a sextet due to goethite at the temperature below 50 K for Sn 10, 200 K for Sn15, and 100 K for Sn20. These results suggest that Sn10, Sn15 and Sn20 had smaller particles than Sn0. On the other hand, 20 K 119Sn-Mössbauer spectra of Sn15 were composed of a paramagnetic doublet with an isomer shift (δ) of 0.24 mm s-1 and quadrupole splitting (∆) of 3.52 mm s-1. These values were larger than those of Sn10 (δ: 0.08 mm s-1, ∆: 0.00 mm s-1) and Sn20 (δ: 0.10 mm s-1, ∆: 0.00 mm s-1), suggesting that the SnIV-O chemical bond is shorter and the distortion of octahedral SnO6 is larger in Sn15 than in Sn10 and Sn20 due to the increase in the covalency and polarization of the SnIV-O chemical bond. Debye temperatures determined from 57Fe-Mössbauer spectra measured at the low temperature were 210 K, 228 K, and 250 K for Sn10, Sn15, and Sn20, while that of α-Fe2O3 was 324 K. Similarly, the Debye temperature of 199, 251, and 269 K for Sn10, Sn15, and Sn20 were estimated from the temperature-dependent 119Sn-Mössbauer spectra, which were significantly smaller than that of BaSnO3 (=658 K) and SnO2 (=382 K). These results suggest that Fe and Sn are a weakly bound lattice in goethite NPs with low crystallinity. Modification of NPs and addition of Sn has a positive effect, resulting in an increase in DC conductivity of almost 5 orders of magnitude, from a σDC value of 9.37 × 10-7 (Ω cm)-1 for pure goethite Sn (Sn0) up to DC plateau for samples containing 0.15 and 0.20 Sn (Sn15 and Sn20) with a DC value of ~4 × 10-7 (Ω cm)-1 @423 K. This non-linear conductivity pattern and levelling at a higher Sn content suggests that structural modifications have a notable impact on electron transport, which is primarily governed by the thermally activated via three-dimensional hopping of small polarons (SPH). Measurements of SIB performance, including the Sn100x cathode under a current density of 50 mA g-1, showed initial capacities of 81 and 85 mAh g-1 for Sn0 and Sn15, which were larger than the others. The large initial capacities were measured at a current density of 5 mA g-1 found at 170 and 182 mAh g-1 for Sn15 and Sn20, respectively. It is concluded that tin-goethite NPs are an excellent material for a secondary battery cathode and that Sn15 is the best cathode among the studied Sn100x NPs.

Revealing magnetic and physical properties of TbFe4.4Al7.6: experiment and theory

We report on the magnetic, electrical transport, caloric and electronic structure properties of TbFe4.4Al7.6 polycrystalline alloy using experiment and theory. The alloy crystallizes in tetragonal structure with I4/mmm space group with lattice parameters a = b = 8.7234(5) Å and c = 5.0387(6) Å. It is ferrimagnetic with a compensation temperature of Tcmp∼ 151 K, Curie–Weiss temperature θCW∼ 172.11 K and an effective magnetic moment μeff = (2.37±0.07) μB /f.u with Z = 2. At low temperatures, kinetic arrest-like first-order phase transition is realized through the thermal hysteresis between field-cooled cooling and field-cooled warming curves of M(T) and virgin curves of M(H) and ρ(H) which are outside the hysteresis loops with metamagnetic transition. The high magnetic field suppression of multiple transitions and reduced coercive field Hcoer and remnant magnetization Mrem with increasing temperature are reported. Hcoer and Mrem cease to exist above the compensation temperature Tcmp . A correlation between the isothermal magnetization and resistivity is discussed. Specific heat C(T) analysis reveals a Sommerfeld parameter of γ = 0.098 J⋅mol−1⋅K−2 and a Debye temperature of θD∼351.2 K. The sample is metallic as inferred from the ρ(T) behavior and Sommerfeld parameter. The magnetoresistance of the alloy is low and negative which indicates the suppression of weak spin-fluctuations. This alloy avoids the tricritical point despite first-to-second order phase transition. The electronic and magnetic structure calculations, by making use of full potential linearized augmented plane wave method, suggest metallic ferrimagnetic ground state of TbFe4.4Al7.6 with Tb atoms contributing ferromagnetically (5.87 μB ) and Fe atoms with antiferromagnetic contribution (2.67 μB ), in close agreement with the experimental observation.

Tuning the thermoelectric and optoelectronic attributes of lead-free novel fluoroperovskites Cs2BB'F6 (B = Rb, In, Na and B'=Ir, As, Rh): A first-principles investigation

Cesium-based double perovskite materials have generated significant interest because of their fascinating prospects in various optoelectronic and thermoelectric uses. In this manuscript, the physical characteristics of Cs2BB'F6 (B = Rb, In, Na and B' = Ir, As, Rh) are investigated in detail. Volume optimization curves, negative formation energies, tolerance factor and octahedral tilting are used to evaluate the structural stability. Pugh's ratio, Cauchy pressure and Poisson's ratio endorses the ductile character of all studied perovskites. Debye temperature shows that Cs2NaRhF6 is a stiffer material in comparison to Cs2InAsF6 and Cs2RbIrF6. The electronic bandgap and total density of states of Cs2InAsF6, Cs2RbIrF6, and Cs2NaRhF6 reveal a direct band gap of 2.76 eV, 3.78 eV and 3.6 eV, respectively. Furthermore, Kramer-Kronig equations are used to examine the interaction of studied double perovskites with electromagnetic radiation. The optical parameters reveal the absorption in UV region, which show their potential for laser and UV-shields applications. In Addition, thermoelectric characteristics are calculated using the semi-classical Boltzmann theory, extending the investigation up to 800 K. The large ZT value of 0.92 is achieved for Cs2RbIrF6 at 800K, while Cs2InAsF6 and Cs2NaRhF6 exhibit 0.76 and 0.82 at 800K, respectively. Their high ZT values and electrical conductivity enhance their suitability for use in renewable energy devices.

Multiscale Length Structural Investigation and Thermoelectric Performance of Double-Filled Sr0.2Yb0.2Co4Sb12: An Exceptional Thermal Conductivity Reduction by Filler Segregation to the Grain Boundaries.

Among thermoelectric materials, skutterudites are the most prominent candidates in the mid-temperature range applications. In the multiple-filled Sr0.2Yb0.2Co4Sb12 skutterudite, with Sr and Yb as fillers, we have enhanced the thermoelectric performance of CoSb3 through the reduction of lattice thermal conductivity and the optimization of carrier concentration and electrical conductivity. The high-pressure synthesis of the double-filled derivative promotes filling fraction fluctuation. This is observed by high angular resolution synchrotron X-ray diffraction, showing a phase segregation that corresponds to an inhomogeneous distribution of the filler atoms, located at the 2a positions of the cubic space group Im3̅. In addition, scanning transmission electron microscopy (STEM) combined with EELS spectroscopy clearly shows a segregation of Sr atoms from the surface of the grains, which is compatible with the synchrotron X-ray powder diffraction results. Mean square displacement parameters analysis results in Einstein temperatures of ∼94 and ∼67 K for Sr and Yb, respectively, and a Debye temperature of ∼250 K. The strong effect on resonant and disorder scattering yields a significantly lower lattice thermal conductivity of 2.5 W m-1 K-1 at 773 K. Still, good weighed-mobility values were obtained, with high filling fraction of the Yb and Sr elements. This drives a reduced electrical resistivity of 2.1 × 10-5 Ω m, which leads to a peak zT of 0.26 at 773 K. The analysis and results performed for the synthesized (Sr,Yb)-double filled CoSb3, shed light on skutterudites for potential waste-heat recovery applications.

Investigations on the electronic, optical, thermoelectric and thermodynamic properties of quaternary coinage metal HgSeBr: a DFT study

In the present study, we examine the structural, electronic, optical, thermodynamic, and transport properties of CuHgSeBr, a mercury chalcogenide halide of coinage metals. Employing the FP-LAPW method via first principles calculations in the WIEN2k code, we investigate various properties including band structure, density of states, lattice constants, Debye temperature, and effective mass. CuHgSeBr manifests as an indirect bandgap semiconductor with a measure of 0.808 eV. Optical assessments using dielectric constants reveal its pronounced absorption of photons in the ultraviolet spectrum according to the ε 2 spectra. Furthermore, we present findings on electronic and lattice thermal conductivity, binding energy, and figure of merit. Notably, our calculations indicate a figure of merit of 0.226 at 300 K and 0.556 at 800 K, indicating CuHgSeBr’s potential as a valuable material for thermoelectric devices within industrial applications. Importantly, these detailed properties of CuHgSeBr have not been previously documented, underscoring the significance of this comprehensive research, which could guide future theoretical explorations aimed at identifying alternative materials with similarly intriguing properties.

A Density Functional Theory Insight into Structural, Mechanical, and Optical Properties of Rb2LiTlF6 Double Perovskite

The density functional theory (DFT) is applied to systematically investigate the geometrical structure, electronic, mechanical, vibrational, and optical properties of double perovskite Rb2LiTlF6 in its cubic phase. To the best of one's knowledge, many physical properties of this compound are still not well established or not yet investigated; such as phonon properties, mechanical behavior, thermal properties, and so on. In this work, the stability of Rb2LiTlF6 is explored by looking at its thermodynamical behavior through calculation of formation energy, cohesive energy, Goldschmidt tolerance factor, and phonon dispersion. Its mechanical properties are examined based on various characterization descriptors such as the independent elastic coefficients, bulk, shear, and Young's modulus, ratios such as Pugh and Poisson's, Kleinnman parameter, Zener anisotropy factor, Debye temperature, and melting temperature. Sound velocity in this material is predicted from the values of the bulk and shear modulus obtained. Thermal expansion coefficient at finite temperatures are obtained using the approach of quasi‐harmonic approximation. Its electronic property is also investigated using generalized gradient approximation and also hybrid functionals. At a later stage, its optical behavior upon the effect of light excitation is explored using the many body pertubation theory approximation. Having envisioned this material as a wide band gap semiconductor, it can be useful in numerous applications such as designing the top‐cell of tandem photovoltaic configuration, photodetection, and light emitting diodes. It is strongly believed that this work will provide a helpful guidance for future experimental and theoretical investigations of this material.

Unraveling the leverage effect in phases stability and mechanical properties of Al-Zn-Mg-Cu alloy

In order to further improve the comprehensive performance of advanced aluminum (Al) alloys, especially 7xxx Al-Zn-Mg-Cu alloys, tuning the relative ratios between major alloying elements (Zn, Mg, Cu) while maintaining the total alloying amount has been widely adopted. However, the specific influence of these relative element ratios on various properties has yet to be well understood. In this work, the leverage effect of those alloying element pairs (Al:Cu, Mg:Zn, Cu:Mg, and Cu:Zn) on the phase stability and mechanical properties of Al-Zn-Mg-Cu alloy is systematically investigated by means of first-principles calculations, cluster expansion, and quasi-harmonic Debye model. The tradeoffs in formation energy, elastic strength, and anisotropy are unraveled when the element pairs deviate from the equal ratio (1:1), indicating a strong leverage effect in element pairs. Among those element pairs, Al:Cu and Cu:Mg are the major lever in phase stability, in which the stable phase reversed on the two sides of 1:1; while the Mg:Zn lever dominates the elastic strength and anisotropy. Cu:Zn, on the other hand, has less impact on material properties. The underlying mechanism of those leverage effect is analyzed by the bonding electron density and lattice distortion around the major alloying elements. Our results are in good agreement with experimental observations and clarify the controversaries of those element pairs on the material properties. The weight of each lever could provide a practical guidance to the optimization of the alloy composition of 7xxx Al-Zn-Mg-Cu alloys, and also shed lights on the development of other advanced alloy systems.

A DFT study of structural, electronic, optical, thermal and mechanical properties of cubic perovskite KGeX3 (X = Cl, Br) compound for solar cell applications

This study examined the structural, electronic, optical, mechanical, and thermal properties of K-based halide perovskites KGeX3 (X = Cl, Br). All the calculations have been carried out using the DFT-based CASTEP simulation package with an ultra-soft pseudo-potential plane wave and PBE-GGA technique. Both the studied perovskite compounds are stable in terms of mechanical and thermal stability. The calculated electronic properties indicate that both materials have a semiconducting behavior with a direct band gap. The band gap value is 0.92 and 0.62 eV for KGeCl3 and KGeBr3, respectively. The analysis of the electronic properties reveals a notable reduction in the bandgap as chlorine (Cl) is substituted with bromine (Br), decreasing from 0.92 to 0.52 eV. The results of our calculations are in good agreement with the previously reported research. The optical properties analysis reveals that both materials demonstrate high absorption and minimal reflection within the visible spectrum. The determined values for Poisson’s and Pugh’s ratios suggest that studied materials demonstrate a ductile behavior. The obtained values of Debye temperature are 265.25 and 191.62 K for KGeCl3 and KGeBr3, respectively. Based on their appropriate direct band gap and high absorption coefficient, these materials are considered promising candidates for photovoltaic applications, and are proposed as ideal potential materials for solar cells applications.

Effect of magnetic field on impedance characteristics in manganese sulfide Mn0.9S

Manganese sulfide with a lack of manganese cations in the lattice is being studied. Samples that are single-phase and have a cubic structure have been certified. The impedance components were measured over a wide range of frequencies and temperatures without a magnetic field and in a magnetic field. The real and imaginary parts of the impedance as a function of temperature are described in the Debye model. The relaxation time of current carriers is found from the impedance hodograph. The change in impedance components in a magnetic field is described in a model of an inhomogeneous electrical medium.

Adiabatic invariance and its application to Wien's complete displacement law of blackbody radiation

We derive the “complete” or “strong” version of Wien's displacement law from two adiabatic invariants: one of a thermodynamic system composed of a finite-sized segment of frequencies taken from the spectrum of blackbody radiation and one of the individual electromagnetic waves that compose this system. By exploiting the algebra of these invariants, we shift the calculational burden of deriving Wien's displacement law toward the methods of classical thermodynamics. These methods also produce a class of displacement laws that constrain both the particles of a classical ideal gas and the acoustic waves of the Debye model of a solid.

Novel approach for modification of graphene oxide using continuous wave-laser obtained from surgical laser diode

The present investigation employs a modified version of Hummer's method to synthesise graphene oxide (GO), which is subsequently subjected to treatment with a continuous-wave (CW) laser derived from surgical laser diodes for the purpose of performing minimally invasive surgery for 30 s to yield laser-modified GO. XRD analysis was used to look at how CWlaser changed the sizes of crystallites, the distance between planes, and the average number of layers. The study examined the FTIR spectra of graphite oxidation and modification using a CW laser. Changes in the G band, D band, and 2D peaks in the Raman spectra showed disorder and multiple layers. The variations in negative zeta potential were used to analyse colloidal stability in graphite, GO, and laser-modified GO. Different types of dynamic light scattering techniques were used to study electrophoretic mobility, Brownian motion, and electrical double layers. The obtained results exhibited a high degree of agreement with the findings derived from the FTIR spectra. This work examined dielectric and impedance spectroscopy to assess relaxation behaviour that deviates from the Debye model. By fitting curves to the data, we evaluated the dielectric constant, loss, and conductivity. Graphite to laser-modified GO via GO lowered the real component of the dielectric constant at any frequency.

First principal calculations for understanding physical properties and possible applications of vacancy ordered double perovskite Cs2ZrI6 (CZI)

First principal calculations are performed to understand structural, elastic, electronic, thermoelectric, thermodynamic and optical properties of inorganic vacancy ordered double perovskite, the Cs2ZrI6 (CZI). Calculated lattice constant of the rock-salt structured CZI shows closeness to that reported in the Materials Project Database. It exhibits mechanical stability, elastic anisotropy, brittleness, dominating ionic bonding, predominant stretching in chemical bonds, fair thermal stability and high melting temperature. It is an indirect band-gap (Γ-X) semiconductor with a band-gap of 2.267eV, which would be suitable for fabricating low-cost tandem solar cells. Calculated thermoelectric properties predicted holes as the majority charge carriers and also shows its thermoelectric efficiency in the higher temperature region. Though, calculated specific heat at constant volume in the very low temperature region obeys the Debye's T3 law, it reaches the Dulong-Petit limit in the very high temperature region. The temperature and pressure dependence of some other thermodynamic parameters are also calculated in the present study. In terms of real and imaginary part of the dielectric function as well as some other auxiliary parameters, we have investigated the optical properties of the CZI and found its high optical absorbance capability in the far UV to extreme UV region of solar spectra.

Thermoelectric properties of two‐dimensional ternary transition metal nitrides HfNF

AbstractThe exceptional electron transfer properties and low thermal conductivity of two‐dimensional layered materials render them a promising choice for thermoelectric applications. In this study, we explore the stability, electronic properties, and thermoelectric characteristics of materials composed of two‐dimensionally layered transition metal nitride HfNF. Our research findings show that the structure of HfNF is stable and exhibits the properties of a direct bandgap semiconductor. Furthermore, we employ the Boltzmann transport theory and Slack model to investigate the thermoelectric properties of HfNF within the temperature range of 300 to 900 K. The HfNF materials exhibit relatively large thermoelectric dominance values ( values), with the ‐type HfNF demonstrating a maximum value of 1.46. Furthermore, utilizing the quasi‐harmonic Debye model, thermodynamic properties such as heat capacity, coefficient of thermal expansion, and bulk modulus within the 6 GPa and 600 K range are estimated. Based on these calculations, it is predicted that two‐dimensional HfNF materials will serve as promising new materials for thermoelectric applications spanning from 300 to 900 K.

First-principles calculations to investigate the structural, electronic, optical, mechanical, and thermodynamic properties of double perovskites Ba2WB′O6 (B′ = Co, Fe, Mn, Ni, and Zn)

We utilized the WIEN2K code within the DFT framework to comprehensively investigate Ba2WBˈO6 (Bˈ = Mn, Fe, Co, Ni, Zn) double perovskite compounds. Structural stability, assessed by Goldsmith's tolerance factor (tG), revealed values close to unity, indicative of stable cubic perovskite structures. The Birch-Murnaghan's equation of state optimization determined ground states, unveiling trends in lattice constant (a0) and bulk modulus (B) for different cations. Structural and phonon stability were confirmed by negative energy formation and real frequencies in phonon calculations. DFPT results affirmed the thermodynamic stability of all compounds. Electronic band structure calculations identified Ba2WMnO6 and Ba2WNiO6 as conductors, while Ba2WCoO6 and Ba2WZnO6 were insulators with 3.7 eV and 3.8 eV band gaps, respectively. Ba2WFeO6 demonstrated semiconducting properties with a 2.37 eV band gap. Density of States (DOS) analysis supported the electronic band structure. Optical conductivity analysis revealed increasing values at higher energy ranges, followed by gradual decreases, differing between conductors and insulators. Absorption coefficient indicated potential suitability for optoelectronic devices, and refractive index analysis highlighted trends in material transparency. To understand fundamental properties, thermodynamic characteristics (thermal expansion coefficient, heat capacities, Debye temperature) were analyzed across a wide pressure (0–30 GPa) and temperature (0–1600 K) range.

Theoretical investigations on the structural, elastic and thermodynamic properties of dysprosium hafnate

The lattice structure and elastic properties of Dy2Hf2O7 at 0 K and 0–40 GPa are calculated by using first-principles methods. The results show that the calculated structural parameters are in good agreement with the experimental values. The elastic constants increase with the increase of pressure, and all the elastic constants satisfy the Born criterion, that is, the Dy2Hf2O7 crystal is kinetically stable within the range of the calculated conditions. In addition, the thermodynamic properties of Dy2Hf2O7 crystal at different temperatures (0–2000 K) and pressures (0–40 GPa) are calculated by using the quasi-harmonic Debye model, and the temperature-pressure dependence of thermodynamic properties, such as the heat capacity, coefficient of thermal expansion, and Debye temperatures, is obtained and compared with the experimental values. We also obtain the melting point and hardness of Dy2Hf2O7 compound by using empirical formulas in the literature.

Assessing Lattice Thermal Conductivity of Topological Insulator Bi2Se3 by Raman Thermometry

Lattice thermal conductivity (κL) of the hexagon‐shaped nanocrystals cluster of Bi2Se3, prepared by the hot‐injection technique using nontoxic solvents, is studied. From the temperature‐dependent Raman spectra of Bi2Se3 nanocrystals, the average Debye temperature (θD) and Gruneisen parameter (γ) are calculated by adopting the bond‐order–length–strength correlation theory. The average room temperature κL of Bi2Se3 nanocrystals evaluated from the Slack model using θD and γ is ≈1.1 Wm−1K−1. The κL of Bi2Se3 nanocrystals is larger than out‐of‐plane κL (≈0.4 Wm−1K−1) but close to the in‐plane κL (≈1.4 Wm−1K−1) simulated using the Boltzmann transport equation for phonon with three‐phonon scatterings. Nanostructuring introduces grain boundaries in the Bi2Se3 that block the long mean free path of phonons physically, reduces the phonon mean free path, and decreases the κL. The anisotropic phonon scattering introduced by the weak van der Waals force between adjacent quintuple layers in the out‐of‐plane direction, in addition to the acoustic–optical phonon scattering and anharmonicity, hinders the efficient transport of thermal energy in the Bi2Se3 and results in a lower κL. By utilizing materials with anisotropic thermal conductivity, thermoelectric devices can be designed to preferentially conduct heat in specific directions while minimizing heat loss in others.

Effect of sintering temperature on structural, elastic, and hyperfine features of nickel ferrite nanoparticles

Temperature is one of the key parameters in the synthesis of a system of magnetic nanoparticles and can affect considerably the arrangement of atoms in the crystal structure. Consequently, the magnetic, elastic, and structural properties are strongly impacted. In the magnetically soft NiFe1.8O4 spinel ferrite, the relative number of Ni and Fe ions in each of the two possible different geometries, tetrahedral (T) and octahedral (O), is of extreme importance. In this work, this material was studied on products of co-precipitation synthesis followed by a temperature dependent sintering. We performed 57Fe Mössbauer spectroscopy (MS), X-ray diffraction (XRD), scanning and transmission electron microscopies (SEM and TEM), X-ray absorption spectroscopy (XAS) using synchrotron radiation at Ni K- and L2-edge, and vibrating sample magnetometry (VSM) measurements. From XAS measurements it was found that Ni atoms prefer an octahedral coordination when the sintering temperature is increased. MS showed that the T-sites are more populated by Fe ions than the O-sites, a fact that can be explained by the presence of Fe ion vacancies in the O- sites. However, as the sintering temperature increases, we found that there is also a migration of Fe atom to the O-sites. Additionally, based on MS measurements in 78–292 K region, we estimated the Debye temperatures of the Fe ions in the tetra- and octahedral geometries and found that the recoiless f-factor depends on the sintering temperature of the nickel ferrite powders. The ratio fO/fT is about 0.98 and 0.95 at room temperature for the samples sintered at 1000 °C and 600 °C, respectively.

Investigating the structural, electronic, magnetic, thermodynamic, and optical properties of rare earth-based halide perovskites CsMCl3 (M = U, Np, Pu)

A detailed study of the physical properties of caesium-based halide perovskites, specifically CsUCl3, CsNpCl3, and CsPuCl3, by full-potential linearized augmented plane wave method has been performed. The stability of the compounds is ensured after energy optimization in two different phases, viz. ferromagnetic and non–magnetic, wherefrom we concluded these perovskites are energetically more stable in the ferromagnetic phase. By adopting the optimized lattice constant, we have determined different electronic, magnetic, thermodynamic, optical, and transport properties. The GGA+ mBJ approximation predicts the half-metallic character of these compounds. The M-sited atom is the foremost contributor to the ferromagnetic nature of these compounds. We have also calculated thermodynamic parameters like thermal expansion, Gruneisen parameter, specific heat capacity, and Debye temperature by employing the quasi-harmonic Debye model. Further optical properties of the compounds are examined in terms of dielectric constant, absorption coefficient, and refractive index. The obtained results from the study signify that these materials are apt for electro-optic and spintronics devices.

Some physical properties of K2TlAsX6 (X = Cl, Br) and CsPbBr3 semiconducting compounds

Some physical properties of K2TlAsX6 (X = Cl, Br) double perovskite compounds have been predicted using the theoretical unit cell parameters and elastic constants computed by Munir et al. (Materials Science and Engineering B 298 (2023) 116830). At equilibrium the Debye temperatures of K2TlAsCl6 and K2TlAsBr6 materials were found to be 193.5 K and 159.6 K, respectively. Furthermore, the mass density, the longitudinal, transverse and mean acoustic wave speeds, the acoustic impedance and the Debye temperature of Cesium Lead Bromide (CsPbBr3) inorganic perovskite compound under high stress up to 15 GPa have been predicted using the theoretical unit cell parameters and elastic constants computed by Junaid Zaidi et al. (Materials Research Express, Vol. 9, No. 12, (2022) 125501). To the best of our knowledge, there is no any data in the literature that can be compared to the findings we’ve achieved on the Debye temperature of K2TlAsX6 (X = Cl, Br) and CsPbBr3 materials.