Minimum Thermal Conductivity Research Articles

Investigation on Mechanical Shock Wave Protective and Thermodynamic Properties of SiO2-Aerogel-Modified Polyurea

In recent years, industrial explosion accidents are frequent, causing serious negative influences on society. Mechanical shock waves, as a typical destructive factor in explosion accidents, can cause serious personal injury and building damage. In addition, actual explosion accidents usually involve heat sources, harming protective materials and personnel. In this study, we designed SiO2-aerogel-modified polyurea and studied the effects of manufacturing pressure process and the concentration of SiO2 aerogel on the mechanical shock wave mitigation and thermodynamic properties of the modified polyurea. The results show that the addition of SiO2 aerogel can improve the mechanical shock wave mitigation performance of polyurea. The maximum peak overpressure and acceleration mitigation rate of the material has reached 17.84% and 62.21%, respectively. The addition of SiO2 aerogel helps to reduce the thermal conductivity of materials and improve the thermal insulation performance, and the atmospheric pressure process is more conducive to improving the thermal insulation performance of materials. The minimum thermal conductivity of the material has reached 0.14174 W/m·K, which is 45.65% lower than that of pure polyurea. The addition of SiO2 aerogel has different effects on the limiting oxygen index (LOI) of polyurea. Using a vacuum process, the LOI value increased with the increase in the SiO2 aerogel concentration, while using atmospheric pressure, the LOI value increased but is always lower than 21% and lower than pure polyurea. Thermogravimetric analysis showed that the addition of SiO2 aerogel under the vacuum process was helpful to improve the thermal stability of materials. However, atmospheric pressure would disrupt the thermal stability, manifested in a decrease in peak degradation temperature, an increase in peak degradation rate, and a decrease in residual mass.

Realizing synergistic optimization of electrical and thermal transport properties in BiCuSeO ceramics via multi-element doping

In this study, the design of high-entropy alloys (multi-element substitution, Al3+/La3+/Sb3+/Y3+) was used to increase material entropy and improve heat scattering to further reduce thermal conductivity. Concurrently, Ca2+ ion hole doping was used to improve its electrical conductivity. Therefore, a series of Bi0.92−xAl0.02La0.02Sb0.02Y0.02CaxCuSeO (x = 0, 0.02, 0.06, 0.10, and 0.14) ceramics was prepared using a combination of high-energy ball milling and cold isostatic pressing. The multi-element substitution of Al0.02La0.02Sb0.02Y0.02Ca0.02 in the Bi site resulted in a minimum thermal conductivity of 0.35 Wm−1K−1, which is one-third of that of intrinsic BiCuSeO. Simultaneously, the conductivity increased up to 10–20 times that of intrinsic BiCuSeO, proportional to the amount of Ca2+ doping. Furthermore, the optimum component Bi0.82Al0.02La0.02Sb0.02Y0.02Ca0.10CuSeO exhibited an extremely high power factor of 568.55 μWm−1K−2 at 773 K, significantly higher than that of pure BiCuSeO (148.7 μWm−1K−2). Consequently, a peak ZT value of approximately 1.12 was achieved at 773 K, which was 4.48 times higher than that of the pristine BiCuSeO specimen (approximately 0.25). Our findings provide a novel strategy to optimize the thermoelectric properties of BiCuSeO and other materials.

The Structural, Elastic, and thermodynamic properties of Sr2P7Br Double Zintl salt with heptaphosphanortricyclane configuration

We investigated the effects of externally applied pressure on the Sr2P7Br compound’s properties, specifically its crystalline structure, elasticity, and thermodynamics. This investigation was carried out using the pseudopotential plane wave method within the framework of density functional theory. We used the well-known PBEsol variant of the exchange–correlation general gradient approximation specifically designed for solid-state analysis. This is the first endeavor to investigate the effects of pressure on the Sr2P7Br material using a theoretical approach. The computed equilibrium structural parameters closely match the relevant experimental counterpart values. The determined elastic constants, obtained under both ambient pressure and hydrostatic pressures up to 18 GPa, satisfy the mechanical stability requirements. Based on the computed Pugh’s ratio, Cauchy pressure, and Poisson’s ratio, it can be concluded that the Sr2P7Br compound exhibits ductile behavior. The polycrystalline elastic moduli, including the isotropic bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio, at ambient pressure and under pressure effects, were derived from the single-crystal elastic constants. Additionally, associated parameters, such as average sound velocity, Debye temperature, minimum thermal conductivity, and Vickers hardness, were examined under pressure influences. The quasi-harmonic Debye approximation was used to investigate the relationship between temperature and some macroscopic physical parameters, such as lattice parameter, bulk modulus, Debye temperature, volume thermal expansion coefficient, and isobaric and isochoric heat capacities, at fixed pressures of 0, 4, 8, 12, and 16 GPa. The results derived from the elastic constants exhibit substantial concordance with those computed using the Debye quasi-harmonic model, thereby validating the reliability of our findings.

A DFT exploration of the stabilities, physical properties, and tensile strength of new synthesized Nb2AC (A=Ni and Co) MAX phases

Based on first-principles calculations, this study explored the structural stability, elastic anisotropy, tensile strength, and the mechanical, electronic, and thermodynamic properties of the newly synthesized MAX phases Nb2NiC and Nb2CoC. It has been found that these compounds are thermodynamically and mechanically stable, exhibit metallic conductivity, and possess ductile nature. The ultimate tensile strengths of Nb2NiC and Nb2CoC depend on their crystallographic directions, specifically [0001] and [112̄0]. In the [0001] direction, Nb2CoC has a tensile strength of about 36.63 GPa at a strain of 26%, compared to Nb2NiC, which has a tensile strength of 31.70 GPa at a strain of 24%. In the [112̄0] direction, Nb2CoC exhibits a tensile strength of around 23.29 GPa at a strain of 12%, while Nb2NiC has a tensile strength of approximately 18.51 GPa at an strain of 8%. Both Nb2CoC and Nb2NiC demonstrate significant elastic deformation before reaching their ultimate tensile strengths, indicating good ductility. It is noteworthy that Nb2NiC is less elastic than Nb2CoC in both the [0001] and [112̄0] directions, as the elastic constants of Nb2CoC are comparatively higher than those of Nb2NiC. Furthermore, the estimated thermal parameters show that these compounds exhibit a relatively low Debye temperature, a high melting point, low minimum thermal conductivity, and thermal expansion coefficient values that are similar to those of well-established thermal barrier coating (TBC) materials such as Al2O3, LaPO4, and TiO2. Consequently, the newly synthesized MAX phases Nb2NiC and Nb2CoC are promising candidates for TBC applications.

Natural fibers as promising core materials of vacuum insulation panels

To reduce energy consumption in buildings, this paper investigates the feasibility of using natural fibers as cost-effective, environmentally sustainable core materials for vacuum insulation panels (VIPs). First, a comprehensive experimental study was conducted for 10 potential natural fiber candidates. The thermal conductivities of the 10 natural fiber mats at various vacuum pressures were measured; their compression and morphology properties were quantified. In addition, an analytical model was used to explore the major factors that influence the thermal conductivity of natural fibers as a function of internal air pressure. Results show that recycled cotton, kapok, and bamboo fibers are ideal candidates for VIP core materials; at <0.05 Pa, their thermal conductivities varied between 2 and 4 mW/(m⋅K). Furthermore, for some fibers, thermal conductivity was inversely proportional to fiber density. For the selection of fiber materials for VIP cores, the ideal fiber candidate has a small fiber diameter and a low fiber mat density. Based on thermal measurements, even though the internal air pressure of 5 Pa was enough to attain the minimum thermal conductivity, obtaining internal air pressure below 5 Pa is recommended for prolonged service life, considering small leaks of VIP package barrier films and potential off-gassing from fibers. The simulation results predicting the effective thermal conductivities matched the experimental results well. These findings indicate that natural fiber–based VIPs have the potential to be a sustainable, inexpensive alternative to the current technologies in building insulation materials.

High-Pressure Synthesis of Te-Ge Double-Substituted Skutterudite with Enhanced Thermoelectric Properties.

We synthesized Co4Sb11TexGe1-x (x = 0.5-0.8) using high-pressure, high-temperature conditions at ∼2 GPa and ∼900 K. The microstructure, morphology, and components were characterized via X-ray diffraction, scanning electron microscopy, and electron backscatter diffraction (EBSD). EBSD indicated that the average grain size of Co4Sb11Te0.8Ge0.2 was 1 μm. Electrical conductivity, Seebeck coefficient, and thermal conductivity were measured from 300 to 800 K. The minimum lattice thermal conductivity of Co4Sb11Te0.8Ge0.2 was 0.72 W m-1 K-1, 74% lower than that at 300 K. The introduction of Te and Ge effectively enhanced point effects scattering and location scattering, notably decreasing lattice thermal conductivity. Therefore, the maximum zT value of Co4Sb11Te0.8Ge0.2 was 1.13 at 800 K. These results indicate that high pressure combined with multielement substitution optimized the thermoelectric transport properties of skutterudites.

MAX phase borides, the potential alternative of well-known MAX phase carbides: A case study of V2AB [A = Ge, P, Tl, Zn] via DFT method

This study predicted four new MAX phase borides via the DFT method, with a comprehensive and thorough approach. The stability of the predicted phases has been thoroughly studied using formation energy, phonon dispersion curve (PDC), and elastic constants (Cij). The metallic nature of the studied phases is confirmed through the computation of the electronic band structure and density of states (DOS). Their bonding nature is disclosed using the partial density of states, Mulliken population analysis, and charge density mapping. The mechanical behavior is investigated in depth by calculating elastic constants, elastic moduli, Poisson's & Pugh ratio, machinability index, and Vickers hardness. Different anisotropic indices are also computed to demonstrate the elastic anisotropy. The Debye temperature (ΘD), Grüneisen parameter (γ), phonon thermal conductivity (kph), minimum thermal conductivity (kmin), thermal expansion coefficient (TEC), and melting temperature (Tm) are all calculated, and the suitability of the studied phases as thermal barrier coating (TBC) materials has been discussed. Finally, the optical constants are calculated and analyzed, further certifying the metallic nature of the herein-studied phases. The reflectivity spectra of all the herein selected compounds reveal their potential as coating materials to lessen solar heating. Among the studied phases, V2PB exhibits the best thermo-mechanical properties for potential applications in diverse fields, such as structural components and TBC materials. The potential applications of our findings are vast, and the obtained results reveal that the predicted phases are indeed potential alternatives to their counterpart carbides.

INVESTIGATION OF WETTABILITY, ANTIBACTERIAL ACTIVITY, THERMAL INSULATION, AND MECHANICAL CHARACTERISTICS OF ELASTOMER BLEND ADHESIVES WITH HIGH-DENSITY FIBERBOARD WOOD AND ALUMINUM

Attention has recently been given to finding alternative and sustainable raw material sources for wood and metal adhesives, such as polyvinyl alcohol (PVA), corn starch (CS), arabic gum (AG), and dextrins (D). Modifying polymer dispersion using unique substances, such as modifying reactive elastomer liquid (EL) using PVA, CS, AG, or D results in sufficiently moisture-resistant adhesive joins. In the present study, the physical characteristics of EL/blended with the natural polymers PVA, CS, AG, and D, based on high-density fiberboard (HDF) wood and aluminum (Al) adhesives and coatings, were investigated and compared to those of pure EL. The EL was blended with PVA, CS, AG, or D at a ratio of 60/40 (w/w) to form EL/blends. The chemical structures, surface and interface morphology, adhesion strengths (including shear strength and pull-off strength), surface roughness, wettings, color intensity, and thermal insulation of the prepared EL and EL/blends were investigated. A scanning electron microscopy (SEM) investigation confirmed filler dispersion and adhesion between the blends, and coated HDF wood, or Al. The developed EL/AG blend had a pull-off strength of 144±5 and 102±3 MPa and a shear strength of 771±11, and 52±3 N with HDF wood and Al substrate, respectively. The EL/PVA blend had a maximum surface roughness value 4.57 µm, and its average water contact angle (WCA) was 85.6°. A plasma jet was used to treat the surface roughness and hence the wettability of the pure EL and the EL/blends, for example, plasma treatment decreased the roughness of the EL/AG blend from 4.36 to 3.28 μm. WCA, and hence wettability, was also significantly influenced by plasma treatment, for example, plasma treatment decreased the WCA of the pure EL from 71.7±0.4° to 30.7±0.7°. The lightness value of the EL/blends was less than that of the pure EL, indicating that (the color adhesives have darkened). Similarly, the yellowness-blueness and redness-greenness values of the EL/blends were greater than those of the pure EL,( rendering the blended adhesives more reddish and bluish). The EL/AG blend was found to have a minimum thermal conductivity (of 0.27 W/m.K), indicating maximum insulation.

Theoretical investigation of structural, mechanical, electronic, optical, and thermal properties of ternary compounds of heusler alloy ANiSn (A= TI, TH, U) using first principles calculations

In this study, we investigated the ANiSn (A = Ti, Th, U) half-Heusler materials for various properties, including structural, electronic, mechanical, elastic anisotropic, optical, and thermal properties, using Density Functional Theory (DFT) with the Cambridge Serial Total Energy Package (CASTEP) code. The elastic constants satisfied Born's criteria, confirming the thermodynamic and mechanical stability of the ANiSn compounds. Mechanical stability was further assessed through bulk modulus, shear modulus, and Poisson's ratio. Our analysis revealed that TiNiSn and ThNiSn exhibit ductile behaviour, whereas UNiSn is brittle. The calculated elastic modulus indicated that the compounds we studied are elastically anisotropic. The electronic and optical properties confirmed the semiconducting nature of these materials, with significant absorption and conductivity observed in the ultraviolet region. ANiSn is suitable for manufacturing various optoelectronic devices, such as laser diodes (LDs), photodetectors, LEDs, and UV sensors, due to its high absorption coefficient in the IR to UV regions. Additionally, measured Debye and melting temperatures confirmed that TiNiSn is more thermally conductive and can be used in high-temperature structural substances. The low minimum thermal conductivity suggests that UNiSn may be a more efficient material for thermal barrier coatings (TBC) compared to TiNiSn and ThNiSn.

Computational study of Rubidium-Rb based cubic Rb2TlCoF6 double perovskite material for photocatalytic water degradation applications: A DFT investigations

The fascinating characteristics, such as straightforward and stable crystal structure, and double perovskites are currently popular materials for applications in renewable energy. In our study, we applied CASTEP and DFT, called density functional theory, to theoretically investigate the mechanical, optical, and thermoelectric characteristics of cubic Rb2TlCoF6. Calculations of the compound Rb2TlCoF6's structural, electrical, optical, mechanical, and thermodynamic properties are made using the GGA-PBE exchange correlational functional and the Fm3m with space group no.225 vol and compound lattice constant are 9.08 Å and 748.613 Å3, respectively. For Rb2TlCoF6, the measured energy band gaps are 1.45 eV. The mechanical and elastic constants are calculated to confirm the ductile properties of Rb2TlCoF6. The brittle characteristics have been verified using Passion and Pugh's ratios, which are 1.67 and 0.25, according to elastic constants. Vickers compound hardness Hv and anisotropy factor “A” are 4.19 and 0.77, respectively. The compounds' optical characteristics reveal significant conductivity and absorption. The compound exhibits high-efficiency photocatalytic activity based on its optical characteristics. Based on mechanical stability, such as Debye temperature, melting temperature, minimum thermal conductivity, average sound velocity, free energy, and other variables, the thermodynamic and structural stabilities are calculated. These materials controlled electrical and other properties make them potentially useful in photocatalytic applications. According to the outcomes, Rb2TlCoF6 is appropriate for photocatalytic water-splitting applications and water deterioration.

Better than linear strength scaling of multifunctional ceramic truss lattice materials

Driven by the goal of creating exceptionally strong and lightweight thermal insulators to enable the operation of a vacuum airship on Venus, conditions where ceramic truss lattice materials provide better than linear scaling of strength with respect to variations in relative density have been found. This enhanced scaling relationship is a consequence of the pressure sensitive shear strength of ceramic materials. A new Gibson-Ashby type scaling relationship is developed between strength and relative density. Elementary analysis is used to formulate theoretical limits for the compressive strength, minimum density, and minimum thermal conductivity for truss lattice materials subjected to hydrostatic pressure loads. Shape optimization using the covariance matrix adopted evolutionary strategy (CMA-ES) and highly resolved finite element models is conducted on silicon carbide Kelvin cells with variable cross-section axisymmetric struts considering three failure modes: buckling, tensile rupture, and shear failure. The optimized designs closely adhere to and validate the newly developed analytical scaling relationship with better than linear strength scaling. These optimized designs are found to withstand the extreme loading conditions on Venus while providing up to 43 kgm3 of buoyancy. The thermal conductivity of the optimized designs are computed and found to be less than 0.5 WmK, with one design outperforming silica aerogels at elevated temperature.

First‐Principles Calculations to Investigate the Structural, Mechanical, Electronic, Optical and Thermal Properties of Disilicides Materials UT2Si2 (T = Ru, Rh, and Pd)

Different physical features of UT2Si2 (T = Ru, Rh, Pd) are investigated using ab initio methods. The examined lattice parameters are closely aligned with the experimental data. The negative cohesive energy ensures the chemical stability of the UT2Si2 (T = Ru, Rh, Pd). The mechanical stability of UT2Si2 (T = Ru, Rh, Pd) is ensured from the positive elastic constants. Very large bulk and Young's moduli of URu2Si2, and URh2Si2 ensures their high resistance to volume and longitudinal deformation. Whereas the lower Young's modulus (E) for UPd2Si2 suggests its heightened capacity to resist thermal shock resistance. The high machinable index of UPd2Si2 compared to URu2Si2 and URh2Si2 confirm its more damage‐tolerant and high elastic behavior and probable industrial applications. All the phases exhibit elastic anisotropy and ductile nature. Metallic features as well as mixture of covalent and ionic bonding are observed from electronic properties. Furthermore, the investigation on optical properties suggests the potential use of UT2Si2 (T = Ru, Rh, Pd) in anti‐reflection coatings, UV detectors, and optoelectronic devices due to their notable peaks in the UV energy range. The thermodynamic parameters such as Debye temperature as well as minimum thermal conductivity indicate the potential utility of these compounds in thermal barrier coating materials.

Effects of Si/Ge superlattice structure with intermixed interfaces on phonon thermal conductivity

By means of the Monte-Carlo/Molecular Dynamics and the non-equilibrium Molecular Dynamics methods we investigate the cross- and in-plane thermal conductivities of the (001)-, (110)- and (111)-oriented Si/Ge films (2 − 20 nm) and bulk superlattices with an intermixing at interfaces in comparison with the corresponding alloy structures at 300 K. For the first time the anomalous conductivity reduction of the in-plane thermal transport with respect to the film thickness has been revealed. This effect can be caused by interplay of three phonon scattering mechanisms: the phonon-alloy scattering mechanism, which is dominant, and competing phonon-phonon and phonon-surface scatterings due to the phonon depletion and the surface phonon localization, respectively. In general, the estimated minimal in-plane thermal conductivity values are found to be of 1.7 W/(m∙K) for the SiGe alloy thin films. It is established that the cross-plane thermal conductivity in the Si/Ge film superlattices crucially depends on intermixing at interfaces displaying even smaller values (less 1.5 W/(m∙K)) than in the corresponding SiGe alloy structures. We also show Si/SiGe superlattices in comparison with Ge/SiGe ones to provide up to 9 % gain in decreasing of both cross and in-plane thermal conductivities due to specific redistribution of peak weights in phonon density of states, which affect the thermal transport. These results reveal the insights into the application of SiGe-based superlattices and alloys for the cross- and in-plane thermoelectrics from the thermal transport minimization viewpoint.

Optimization of Co4Sb11.5Te0.5 thermoelectric performance through Al filling under high temperature and high pressure

So far, the method of optimizing the thermoelectric properties of skutterudite CoSb3 is usually to achieve a breakthrough in high-properties thermoelectric merit by selecting excellent doping atoms and determining a reasonable percentage of atoms. In this study, we achieved the preparation of small atomic radius Al-filled Co4Sb11.5Te0.5 compounds by high-temperature and high-pressure (HTHP) synthesis methods. The thermoelectric properties of the samples AlxCo4Sb11.5Te0.5 were optimized from two dimensions: synthesis pressures (1.0 GPa, 1.5 GPa, 2.0 GPa) and Al filling concentration (x = 0.1, 0.2, 0.3, 0.5), ultimately achieving effective decoupling of electron-phonon transport properties. The experimental results show that Al doping can optimize the electrical transport properties of materials effectively, rapid synthesis method of HTHP can introduce abundant grain boundaries, diversification of grain sizes, a large number of dislocations and widely distributed nano second phase, etc. These microstructures in bulk materials form a multi-scale phonon scattering network in situ, which can effectively scatter phonons and reduce the lattice thermal conductivity effectively. After optimizing the synthesis pressure and Al filling concentration through orthogonal transformation, the sample Al0.3Co4Sb11.5Te0.5 prepared at a synthesis pressure of 1.5 GPa obtained a minimum lattice thermal conductivity value of 0.88 W m−1 K−1, a maximum power factor of 40.96 μ W cm−1 K−2 and a maximum zT value of 1.18 at 773.15 K.

Effect of Yb3+ on the thermophysical and mechanical properties of gadolinium zirconate ceramics: First-principles calculations and experimental study

Thermal barrier coating materials require high phase stability, low thermal conductivity, and a thermal expansion coefficient that matches the bonding layer. Cation doping is a highly efficient method for enhancing the thermophysical and mechanical characteristics of materials used in thermal barrier coatings. The thermophysical and mechanical properties, as well as the phase stability at high temperatures of ceramic materials doped with Yb3+ in gadolinium zirconate, are examined by utilizing first principles calculations and solid-state reaction methods. As the Yb3+ content increases, the grain average particle size of gadolinium zirconate ceramics first decreases and then increases. Given that a smaller grain size results in more grain boundaries, thereby reducing the thermal conductivity of the material, it can be inferred that Yb0.20 ((Gd0.8Yb0.2)2Zr2O7) with the smallest grain size exhibits lower thermal conductivity. As the Yb3+ content increases, both the calculated and experiment results suggest the Young’s modulus of gadolinium zirconate initially declines to its minimum value when the Yb3+ content is 0.5 and subsequently experiences a little increase. Furthermore, as the concentration of Yb3+ increases, the material initially experiences a drop in both hardness and fracture toughness, followed by a subsequent increase. Both the calculation and experimental results indicate that the thermal conductivity of gadolinium zirconate initially decreases and then increases. Among the different compositions, Gd1.5Yb0.5Zr2O7 demonstrates the minimum thermal conductivity, measuring 1.029 W/(m⸱K) according to the Clark model and 1.152 W/(m⸱K) according to the Cahill model. At a temperature of 1273 K, the experimental results demonstrated that (Gd0.8Yb0.2)2Zr2O7 has the lowest thermal conductivity of 1.415 W/(m·K). Furthermore, both the calculated and experimental thermal expansion coefficients of the material decrease first until the Yb3+ concentration is 0.5 and then increase slightly when the Yb3+ content increases. Moreover, gadolinium zirconate ceramics have demonstrated a consistent single-phase fluorite structure, excellent stability at high temperatures, and remarkable structural integrity during repeated heating and cooling cycles. The calculation results exhibit strong congruence with the experimental data. The objective of this work is to improve the thermophysical and mechanical properties of gadolinium zirconate ceramics for their application as materials for thermal barrier coatings.

Thermophysical properties of Yb3+-doped nonstoichiometric gadolinium zirconate ceramics

Low thermal conductivities and high thermal expansion coefficients are desirable for rare-earth zirconate thermal barrier coating materials. Introduction of cation doping and adjustment of the nonstoichiometry are efficient methods for enhancing the thermophysical characteristics of materials. Herein, the thermophysical properties of Yb3+-doped nonstoichiometric gadolinium zirconate ceramic materials were investigated using first-principles calculations and solid-state reaction techniques. As the Yb3+ content increases, additional cations enter the interstitial spaces (for excess Gd3+ gadolinium zirconate) and form vacancy defects (for excess Zr4+ gadolinium zirconate), which serve as phonon scattering centres to decrease the thermal conductivity. When Yb3+ is doped at the same concentration, gadolinium zirconate with excess Zr4+ exhibits a lower thermal conductivity. Specifically, Gd1.875Yb0.25Zr2.125O7 shows the lowest minimum thermal conductivity of 1.133 W/(m⸱K) (according to the Clark model) and 1.241 W/(m⸱K) (according to the Cahill model). In addition, the experimental results also suggest that the optimal content of Yb3+ is 0.25 excess Zr4+ gadolinium zirconate, which has the lowest intrinsic thermal conductivity of 1.037 W/(m⸱K) at 1300 K. Moreover, the thermal expansion coefficient of the Yb3+-doped excess Gd3+ nonstoichiometric material is greater than that of the doped excess Zr4+ material, this is due to the greater electronegativity difference between Yb3+ and Zr4+ than that between Yb3+ and Gd3+ and the lower binding energy of Gd-O than that of Zr-O. The experimental results and the calculated results are in good agreement. The aim of this work is to enhance the thermophysical characteristics of gadolinium zirconate ceramics for use as thermal barrier coating materials.

Unveiling the DFT perspectives on structural, elastic, electronic, optical and thermal properties of XMn2As2 (X = Ca, Sr)

A comprehensive first-principles investigation of XMn2As2 (X = Ca, Sr) materials using Density Functional Theory (DFT) have used in this study. Variety of physical attributes, including thermal, mechanical, electronic, optical and elastic anisotropic properties are explored. Lattice parameters and crystal structures showed excellent agreement with previous experimental data. The findings reveal that CaMn2As2 and SrMn2As2 exhibit notable elastic anisotropy, and satisfy the Born criteria for mechanical stability. The calculated elastic moduli are consistent with previously published values. The metallic nature of these compounds is demonstrated through band structure and density of states (DOS) analyses. Optical property analyses, including energy loss function, electrical conductivity, reflectivity, dielectric constant, refractive index, and absorption coefficient, highlight the potential of these materials for optoelectronic and photovoltaic applications. Notably, SrMn2As2 displays an exceptionally low minimum thermal conductivity compared to CaMn2As2, indicating its potential as a superior Thermal Barrier Coating (TBC) material.

Systematic investigation of physical properties of Mg3XO4 (X = Cr, Mn, Fe, Co, Ni); a computational approach

Material development is primarily dependent on their design and theoretical exploration. Density functional theory is a great tool to achieve this goal. Here, Mg3XO4 (X = Cr, Mn, Fe, Co, Ni) are considered in order to reveal their full characteristics using density functional theory. Mg3XO4 (X = Cr, Mn, Fe, Co, Ni) are investigated in terms of their structural, elastic, mechanical, thermodynamic, electronic, and dynamic properties. The formation energies for Mg3XO4 (X = Cr, Mn, Fe, Co, Ni) are found to be negative implying synthesisability and dynamic stability of these materials. The evolution of elastic constants of materials demonstrates that all materials satisfy the Born stability criterion, hence Mg3XO4 (X = Cr, Mn, Fe, Co, Ni) are mechanically stable. Several polycrystalline parameters are derived by using elastic constants and evaluated. All materials are found be brittle, hard (Vickers hardness) and magnetic. They exhibit some degree of anisotropy in Young/Shear modulus and Poisson’s ratio. The electronic band structures for Mg3CrO4, Mg3MnO4 and Mg3FeO4 indicated a semi-metallic nature whereas for Mg3CoO4 and Mg3NiO4 indicated metallic nature because both the majority and minority energy bands cut the Fermi level. The phonon modes are found to be in positive frequencies that confirms dynamical stability. The materials’ free energy, entropy, specific heat capacity, Debye and melting temperatures, minimum thermal conductivity and Grüneisen parameters are also obtained and discussed.

A theoretical investigation on the structure stability, electronic structures, optical properties, and transport properties of Zintl compounds CsZn4P3 and CsZn4As3

The present study investigates the structure stability, electronic structures, and optical properties of Zintl compounds CsZn4P3 and CsZn4As3 by first-principles calculations. An assessment of the phonon dispersion curves and elastic constants indicate both dynamic and mechanical stability for the both compounds. By employing the HSE06 hybrid functional, both compounds display direct bandgap with widths of 0.93 eV for CsZn4P3 and 0.66 eV for CsZn4As3. Furthermore, an analysis of the dielectric constant, refractive index, extinction coefficient, and energy loss as functions of photon energy is conducted to study the optical properties. Based on the semi-classical Boltzmann transport theory and the Slack's equation, a large Seebeck coefficient and minimum lattice thermal conductivity are obtained for CsZn4As3, which result in a figure of merit value of 0.79 at 700 K. These findings underscore the potential of CsZn4As3 as a promising candidate for future research and development in the realm of thermoelectric materials.

Construction of dielectric and magnetic coupling cobalt salt/chitosan derived Co/C hybrid aerogels for high-performance infrared/radar compatible applications

In virtue of mutually exclusive stealth mechanisms, effectively protecting from infrared detection and attenuating microwaves through composition and structure design remains a formidable challenge. To achieve high-efficiency infrared/radar compatible stealth, in this work, 0D magnetic Co nanoparticles were successfully in situ grown onto the renewable biomass chitosan-based 3D porous carbon skeletons via facile liquid reaction, freeze-drying, and calcination method. Herein, the as-prepared Co/C hybrid aerogels exhibit dielectric and magnetic coupling network, and the relevant infrared/radar compatible stealth property can be regulated by adjusting the addition amount of Co salt. The minimum thermal conductivity value reached 0.095 W m−1 K−1 at 60 °C, and the lowest infrared emissivity of 0.717 in the 8–14 μm band was also achieved. Furthermore, the minimum reflection loss (RLmin) value of −44.70 dB at a relatively thin thickness of 1.35 mm and the maximum effective absorption bandwidth (EAB) of 5.45 GHz at only 1.5 mm appeared in the optimal Co/C hybrid aerogel with the most appropriate Co content. Compared with perfect conductive layer (PEC), the simulated radar cross section (RCS) signals of Co/C composites covered PEC have been significantly reduced by 18.44 dB m2 at the scanning angle of 80°. This study inspires the exploration of the elaborate design strategy and facile construction method for environment-friendly infrared/radar compatible hybrid aerogels in the future.