Electrical Thermal Conductivity Research Articles

Luminescence and Transport Behavior in Incommensurately Modulated CaGd2(MoO4)4:Yb/Er.

The phenomenon of thermal quenching of luminescence can significantly compromise the efficiency of luminescent materials, a process accompanied by the generation of substantial phonon populations. While plenty of models for elucidating this behavior have been proposed, the crucial role of phonon transport has largely been neglected, particularly in the enigmatic incommensurate scheelite structure with good luminescence performance. In this study, we delve into the thermal quenching dynamics of the near-infrared emission in the incommensurately modulated CaGd2(MoO4)4:Yb/Er system. Our comprehensive investigation reveals distinct evolutionary patterns in electrical conductivity, luminescence intensity, thermal conductivity, and Raman scattering at varying temperature regimes. Notably, we have determined that thermally induced ion migration, occurring above ∼300 °C, serves as a pivotal trigger for the activation of all phonons and the enhancement of phonon-defect scattering within this incommensurate framework. This phenomenon not only diminishes the thermal conductivity but also accelerates the multiphonon relaxation of the Er3+ emission levels, culminating in a marked thermal quenching of luminescence. This work illuminates the thermal quenching mechanism of luminescence by focusing on phonon scattering dynamics, providing critical insights for the design of thermally robust near-infrared luminescent materials, which are essential for the advancement of optical amplification systems.

Scrutinizing the electronic structure, magnetic, mechanical, thermodynamic, optical and thermoelectric properties of lead-free hafnium based Hf2VP (P = Si, Sn) full Heusler alloys

The study of energy harvesting and thermoelectric materials has drawn more attention in the last several years. The great thermal stability of these materials is advantageous for thermoelectric devices, in addition to their structural capacity for showcasing and incorporating diverse novel concepts to augment the thermoelectric figure of merit. In the current study, we have predicted the physical properties of Hf2VP (P = Si, Sn) Heuslers using density functional theory in conjunction with the Boltzmann transport scheme. The strength and ductility of these materials are ascertained by simulating elastic characteristics The exchange correlation potential is handled via the modified Becke–Johnson potential (mBJ) and the generalized gradient approximation of Perdew, Burke, and Ernzerhof (GGA-PBE). Near the Fermi level, the band profiles for Hf2VSi and Hf2VSn Heuslers were found to be n-type indirect band-gap respectively. The thermodynamic stability of these materials is approved by the formation and cohesive energy. The relationships between different transport parameters are predicted using the band occupation and density of states in the post DFT treatment. Slack’s equation has identified the most significant lattice component of heat conductivity with great precision. These materials are likely to find use in the design of memory devices and future thermoelectric and energy harvesting materials due to their half-metallic nature and efficient thermoelectric parameters, such as electrical conductivity, Seebeck coefficient, thermal conductivity, power factor, and ZT.

Symmetric sandwich–like rubber composites for “green” electromagnetic interference shielding and thermal insulation

Electromagnetic interference (EMI) shielding rubber composites with thermally insulating properties are necessary for some specific sealing fields, but their fabrication is challenging because it is difficult to realize a balance between high electrical conductivity and low thermal conductivity. Herein, symmetric sandwich–like rubber composites composed of an unfoamed core sandwiched by two foamed layers were prepared using a layer-by-layer vulcanization procedure. Importantly, a segregated Fe3O4@carbon nanotube (Fe3O4@CNT) network was constructed within the entire composite. This structure improved the shielding effectiveness (SE) and decreased the thermal conductivity of Fe3O4@CNT/rubber composites. When the density of the foamed layers was 0.60 g/cm3, the thermal conductivity, electrical conductivity, and SE of the resultant composites were 0.14 W/m K, 21.5 S/m, and 40.7 dB, respectively, and their green index (gs) was 2.13, implying that the prepared materials were “green” EMI-shielding composites. This study provides directions on fabricating EMI shielding materials with thermally insulating performance.

Polyethylene microplastic pollution changes the electrical resistance and thermal conductivity of loess soil.

While plastics provide convenience, they also endanger the safety of the natural environment. Microplastic pollution caused by plastic aging has become an urgent concern in public places. In order to study the effects of microplastics on soil physical properties, the electrical resistance and thermal conductivity of soils containing different polyethylene and moisture content were tested. The results show that polyethylene have two effects on soil electrical resistance: one is that the plastic particles increase electrical resistance, and the other is that the electrostatic field carried by the plastic particles reduces electrical resistance. The effect of the two factors is balanced by the content of polyethylene at 6-8%. When the polyethylene content of the soil was 6% and 10%, the coefficients of electrical resistance variation were 0.89, 0.67, 0.85, 0.96, 0.97, 0.99 and 0.95, 0.68, 0.71, 0.93, 0.95, 0.96, respectively. Polyethylene alters soil properties by affecting water distribution through hydrophobicity. The water content gradually increases to 10%, the liquid conduction area inside the soil increases, and the higher the soil's ability to conduct electricity and heat. The results can provide theoretical reference for evaluating and controlling soil microplastic pollution.

Applications of Graphene Materials in Optoelectronic Devices

Graphene is a groundbreaking material at the forefront of material science and nanotechnology area. Graphene exhibit special qualities, including great mechanical strength, strong electrical conductivity and thermal conductivity. Consequently, the optical property of graphene is focused in this work. The excellent optical properties of graphene make it a good candidate material for optoelectronic devices. In recent years, a great deal of research has been conducted on the use of graphene for optoelectronic devices. Therefore, conducting research in this field is of great significance. In this work, researches are analyzed and studied to gain new insights into this area. In addition, a summary of the prevalent synthesis methods utilized for the production of graphene is provided, accompanied by a detailed examination of the merits and demerits associated with each technique. Finally, the applications of graphene materials in optoelectronic devices are discussed in depth to further understand the development status of graphene materials. This work seeks to generate new ideas and directions for the future development of optoelectronic technology.

Study on Mechanical Properties of Basalt Fiber and its Composite Materials

With the development of civil engineering industry, the use of new composite materials has become an inevitable trend. This paper mainly focuses on the mechanical properties and development status of Basalt Fiber (BF) and its fiber composites which is called Basalt Fiber Reinforced Polymer (BFRP). The raw material of BFRP, the basalt ore and the preparation of blast furnace are discussed. Then, the preparation method of BFRP is introduced. In the process of research, it is found that when the preparation of BFRP is completed, the types of BFRP can be roughly divided into mixed reinforcement type and basic profile type. Subsequently, the factors affecting the mechanical properties of blast furnace are studied, which are mainly divided into interface modification and interface aging. In the aspect of interface modification, four modification methods such as acid-base etching modification, plasma surface treatment, silane coupling agent treatment and nanoparticle modification are introduced in detail. Finally, comparing BF with carbon fiber (CF), polyester fiber (PF) and glass fiber (GF), it is found that BF has better plasticity, toughness, good electrical insulation and low thermal conductivity. However, there are still many difficulties to be solved in the production, preparation, modification and application of BF and BFRP

Free‐Standing, Multifunctional Thermoelectric and Acoustic Absorbing Nanocomposite Foams

AbstractThermoelectric materials are potential energy harvesting technologies that enable direct, clean conversion between thermal and electrical energy. The efficacy of thermoelectric energy conversion is influenced by the electrical conductivity, thermal conductivity, and Seebeck coefficient. Flexibility, manufacturability, and cost‐effectiveness are also important factors. Polymeric nanocomposites offer advantages in these respects. However, the development of conductive‐polymer thermoelectric materials is limited to an in‐plane architecture, which does not resemble common real‐world scenarios. Moreover, existing works have low thermoelectric properties or rely on additives for performance improvement. In this work, a free‐standing thermoelectric nanocomposite foam is fabricated via the integration of thermally activated microspheres. Due to the microstructure, a thermal conductivity as low as 0.03 W m−1 K−1 is achieved, which is lower than reported for aerogels fabricated via freeze‐drying methods. Additionally, the nanocomposite foam can reach a maximum electrical conductivity of 1.13 S cm−1, power factor of 0.12 µW m−1 K−2, and thermoelectric figure of merit of 3.0 × 10−4. The study also evaluated the compressive stiffness and demonstrated the potential for sound absorption. With the unique combination of the thermoelectric, sound absorption, and mechanical behavior, these nanocomposite foams would offer versatile solutions to address the next generation energy harvesting and acoustic absorption applications.

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.

Effects of lattice instability on the thermoelectric behavior of kagome metal ScV6Sn6

Kagome metal ScV6Sn6 has been a subject of interest due to the emergence of a first-order structural phase transition with intriguing charge density wave behavior below the transition temperature Tc ∼ 92 K. To explore the thermoelectric properties and provide experimental insights into the nature of the phase transition, we have carried out a combined study by means of the electrical resistivity, Seebeck coefficient, and thermal conductivity measurements on single crystalline ScV6Sn6. Pronounced features near Tc have been characterized by all measured physical quantities. In particular, the Seebeck coefficient exhibits a marked reduction as lowering temperature across Tc, attributed to an imbalance of the contribution from different type of carriers induced by the structural phase transition. From the examination of the electronic and lattice thermal conductivities, we obtained a confirmation that the observed enhancement at Tc is essentially caused by the change of the lattice thermal conductivity, demonstrating the primary importance of lattice distortions for the heat transport of ScV6Sn6. In addition, the lattice thermal conductivity above Tc was found to increase monotonically with temperature. We associated the peculiar phenomenon with lattice fluctuations, highlighting the essence of structural instability in the kagome lattice ScV6Sn6. These results add to the knowledge about the thermal transport properties in kagome materials with a hexagonal HfFe6Ge6-type structure.

Analysis of Thermoelectric Properties of Hot-deformed Bismuth Telluride Sintered Materials

Bismuth telluride (Bi2Te3)-based alloys are widely used for thermoelectric cooling and power generation at low temperatures, and they are the only commercially available materials for thermoelectric applications below 500 K. The rhombohedral unit cell with a large c/a lattice constant ratio consisting of - Te-Bi-Te-Bi-Te- stacked layers inevitably brings about a large anisotropy in transport properties, which is why texturing is very important in polycrystalline Bi2Te3</sub alloys for maximum performance. In this report, p and n-type polycrystalline Bi2Te3</sub alloys were synthesized and hot-deformed to investigate the effects of texturing on thermoelectric properties. Hot deformation (HD) induces the strong alignment of (001) orientations along the compression direction, and a remarkable increase in the orientation factor F of (001) orientations is observed after HD in both p and n-type materials. All of the hot-deformed polycrystalline samples showed increased electrical conductivity (σ), power factor (PF), and thermal conductivity (k) in the in-plane (IP) direction, and vice versa in the out-of-plane (OOP) direction, which makes the IP direction of the hot-deformed bodies more favorable for module fabrication in terms of power factor, for both p and n-type Bi2Te3</sub-based alloys. However, due to the different degree of anisotropy of k and σ, the figures of merit (zT) were maximized in the OOP direction in the p-type materials after HD, whereas the zTs of the n-type materials were higher in the IP direction. This occurs because the anisotropy factor of electron conduction is higher than that of hole conduction, which more than offsets the advantage of the smaller k in the c-direction of n-type Bi2Te3</sub. The maximum zT of 1.33 (OOP) and 0.90 (IP) were obtained after HD from the p and n-type Bi2Te3 alloys, respectively, which were 9.3% and 18.4% higher than those of as-sintered materials.

Current, core channel radius, and related parameters of channel plasma in artificially triggered lightning

Based on plasma physics methods, the relationship among the channel current (i), core channel radius (rcc), and other related parameters including electrical conductivity (σ), thermal conductivity (λe), and thermal diffusion coefficient (DeT) was investigated and strong interdependence was found among these parameters. Then, these dependent relationships together with the measured electron temperature (Te) and electron density (ne), derived from spectral diagnostics, were applied to determine the measured results on the i, rcc, σ, λe, and DeT of channel plasma in artificially triggered lightning along with their measured accuracies. Good accordance can be found with the aid of comparisons with other measurements of the artificially triggered lightning [L. Cai et al., J. Electrost. 109, 103537 (2021)].

Improvement of Electrical and Thermal Properties of Carbon Nanotube Sheets by Adding Silver Nanowire and Mxene for an Electromagnetic-Interference-Shielding Property Study.

Hybrid carbon nanotube (CNT) sheets were fabricated by mixing CNTs with silver nanowires (AgNWs) and MXene to study their electromagnetic-interference (EMI)-shielding properties. CNT/AgNW and CNT/MXene hybrid sheets were produced by ultrasonic homogenization and vacuum filtration, resulting in free-standing CNT sheets. Three different weight ratios of AgNW and MXene were added to the CNT dispersions to produce hybrid CNT sheets. Microstructure characterization was performed using scanning electron microscopy, and the Wiedemann-Franz law was used to characterize transport properties. The resulting hybrid sheets exhibited improved electrical conductivity, thermal conductivity, and EMI-shielding effectiveness compared to pristine CNT sheets. X-band EMI-shielding effectiveness improved by over 200%, while electrical conductivity improved by more than 1500% in the hybrid sheets due to a higher charge-carrier density and synergistic effects between nanomaterials. The addition of AgNW to CNT sheets resulted in a large improvement in electrical conductivity and EMI shielding; however, this may also result in increased weight and sample thickness. Similarly, the addition of MXene to CNT sheets may result in an increase in weight due to the presence of the denser MXene flakes.

Determination of the elemental composition and changes in thermal and electrical conductivity of “Hanford” and low-ash medium-grained graphite’s grade graphites depending on the fast neutrons fluence

Studying the properties of graphite recovered from operating nuclear reactors is vital for predicting the properties and integrity of graphite as part of assessing the continued operation and life extension of nuclear reactors. The purpose of the study is to determine the electrical conductivity and thermal conductivity of low-ash medium-grained graphite’s grade graphite in the thermal column masonry of the VVR-SM research reactor in the measurement temperature range corresponding to the conditions of normal operation of the reactor to determine the service life. In this work, the change in thermal conductivity and electrical conductivity of GMZ graphite was studied, as well as for comparison of Hanford grade graphite depending on the fluence of fast neutrons and the measurement temperature. The dependence of electrical conductivity and thermal conductivity on dose and temperature has been established. It has been shown that the greater the neutron fluence, the more both the thermal conductivity and electrical conductivity of the material decreases. The service life of the thermal column has been determined.

Nanoscale Electron Beam Patterning of PEDOT:PSS Free‐Standing Films for Enhanced Thermoelectric Performance

The growing demand for flexible, lightweight, and highly processable electronic devices makes high‐functionality conducting polymers such as poly (3,4‐ethylene dioxythiophene): polystyrene sulfonate (PEDOT:PSS) an attractive alternative to conventional inorganic materials for various applications including thermoelectrics. However, considerable improvements are necessary to make conducting polymers a commercially viable choice for thermoelectric applications. This study explores nanopatterning as an effective and unique strategy for enhancing polymer functionality to optimize thermoelectric parameters, such as electrical conductivity, Seebeck coefficient, and thermal conductivity. Introducing nanopatterning into thermoelectric polymers is challenging due to intricate technical hurdles and the necessity for individually manipulating the interdependent thermoelectric parameters. Here, array nanopatterns with different pattern spacings are imposed on free‐standing PEDOT:PSS films using direct electron beam irradiation, thereby achieving selective control of electrical and thermal transport in PEDOT:PSS. Electron beam irradiation transformed PEDOT:PSS from a highly ordered quinoid to an amorphous benzoid structure. Optimized pattern spacing resulted in a remarkable 70% reduction in thermal conductivity and a 60% increase in thermoelectric figure of merit compared to non‐patterned PEDOT:PSS. The proposed nanopatterning methodology demonstrates a skillful approach to precisely manipulate the thermoelectric parameters, thereby improving the thermoelectric performance of conducting polymers, and promising utilization in cutting‐edge electronic applications.

Achieving excellent mechanical and antioxidant properties in MoAlB ceramics through spark plasma sintering-high-frequency (SPS-HF) sintering

A fully dense MoAlB ceramic was synthesized utilizing MoAlB powder through SPS-HF technology. The Vickers hardness, fracture toughness and bending strength of the MoAlB ceramic reached 14.08 GPa, 6.70 MPa m1/2 and 407 MPa, respectively. The electrical conductivity and thermal conductivity of the MoAlB ceramic at room temperature were measured to be 3.20 × 106 S m−1 and 23.50 W m−1 K−1, respectively. The ceramic exhibited excellent high-temperature oxidation resistance at 800–1200 °C for up to 64 h. Even after 64 h of oxidation at 800 °C and 1000 °C, the thickness of the oxide layer was only 2.09 µm and 2.20 µm, respectively. The oxidation behavior was controlled by a diffusion process. The rapid formation of a continuous and dense Al2O3 oxide layer effectively inhibited the inward diffusion of oxygen and the oxide layer is well bonded to the matrix.

Mean-field homogenization of liquid metal elastomer composites: comparative study and exact dilute solution of core–shell inclusion

Liquid metal-elastomer composites (LMECs) have gathered significant attention for their potential applications in various functional stretchable devices, with inclusion sizes ranging from micrometers to nanometers. These composites exhibit exceptional properties, such as high electric permittivity and thermal conductivity, surpassing those of the elastomer matrix, thus enabling a broader range of applications without compromising the material's stretchability. To investigate the diverse effective elastic and functional properties of LMECs, micromechanics-based homogenization method based on Eshelby's inclusion solution are invaluable. However, the extreme contrast in elastic constants among the phases in LMECs, particularly for nanosized inclusions where a considerable amount of stiff metal oxide forms around the inclusions, can lead to critical failure in predicting effective properties if inadequate homogenization approach is employed. In this study, we present multiple mean-field homogenization approaches applicable to LMECs with core-shell morphology, namely: (i) multi-phase, (ii) sequential, (iii) pseudo-grain, and (iv) direct approaches. We compare the accuracy of the models concerning effective elastic, thermal, and dielectric properties, evaluated against numerical homogenization results and compared with reported experimental data. Specifically, we highlight homogenization scheme utilizing exact field solutions of dilute core-shell inclusion, emphasizing the importance of accurately capturing the field in the micromechanics of LMECs. Furthermore, we demonstrate that widely utilized interphase model could not properly resolve the core-shell morphology and thus should be avoided. This comprehensive assessment provides critical insights into the proper homogenization strategies for designing advanced LMECs with precise prediction of effective properties.

A Study on the Relationship between the Thermoelectric Properties and Infrared Emission Performance of ZnO/SrTiO3 Composite Materials.

The thermoelectric properties and infrared emissivity of materials may seem unrelated, but both are influenced by electrical conductivity and thermal conductivity. The photothermal effect of SrTiO3 can establish a connection between the Seebeck coefficient and infrared absorption in the 8-14 μm range. However, there is currently limited research on the relationship between thermoelectric performance and infrared emissivity. In this study, ZnO/SrTiO3 composites were prepared using a hydrothermal method combined with spark plasma sintering. The intrinsic relationship between the thermoelectric and infrared emission performance of the composites was investigated by varying the ZnO content. As the ZnO content increased, the grain boundary barrier of the samples changed, affecting both electrical and thermal conductivities. The infrared emissivity initially decreased and then increased with increasing ZnO content, which contrasted with the trend observed in electrical conductivity, in accordance with the Hagen-Rubens relationship. The ZT value and infrared emissivity exhibited opposite trends, with the ZnO-5 sample having the highest thermoelectric performance and the lowest infrared emissivity, making it the most representative sample. The relationship between the thermoelectric performance and infrared emissivity of SrTiO3 is of significant importance for developing multifunctional materials with both thermoelectric and infrared properties.

Synthesis and characterization of graphene on copper foil via atmospheric pressure chemical vapor deposition method and its impact on electrical properties

Copper, prized for its exceptional electrical conductivity, thermal conductivity, and mechanical strength, is a staple in electronic applications. The ongoing quest for enhanced performance in miniaturized technologies has led to exploring copper-graphene composites, particularly those integrating bilayer graphene (BLG). This study investigates the enhancement of electrical conductivity in copper through the incorporation of BLG via atmospheric pressure chemical vapor deposition (APCVD). The research highlights the APCVD method's ability to grow high-quality BLG on high-purity oxygen-free copper foil, demonstrating significant improvements in electrical properties. Detailed characterization reveal that the graphene growth process induces structural changes in the copper, promoting ideal crystallographic orientations and larger grain sizes. This process achieves nearly complete graphene coverage and results in a copper/graphene (Cu/GR) composite with minimal defects. The electrical conductivity of the Cu/GR composite significantly increased to 59.32 × 10⁶ S·m⁻1, a 7.83 % improvement over the pristine copper foil. This enhancement is attributed to the increased carrier density and mobility within the composite. These advancements suggest the potential of APCVD-grown graphene for various high-performance electronic applications, providing a promising pathway for further development and optimization of graphene-copper composites.

Influence behavior and mechanism of double-layer Gr stacking configuration on mechanical strength and thermoelectric transport properties of Cu/Gr composites

The mechanical strength, electrical conductivity, and thermal conductivity of Cu/graphene (Gr) composites with Cu (111)/double-layer Gr/Cu (111) structure were investigated by using density functional theory and semi-classical Boltzmann transport theory. The results indicate that, the chemical bonds were generated between the two layers of Gr film, and the maximum charge densities of Gr-Top stacking configuration and Gr-Hollow stacking configuration are 0.104 and 0.118 e/Å3, respectively. Gr-Hollow stacking configuration has the larger mechanical strength and plasticity than Gr-Top stacking configuration. Although the covalent characteristic for the two stacking configurations is identical, the ionic characteristic of Gr-Top stacking configuration is stronger than Gr-Hollow stacking configuration. Therefore, the electron localization of Gr-Top stacking configuration is much stronger, leading to the smaller number of free electrons. The electrical conductivity and thermal conductivity of Gr-Hollow stacking configuration are 2.55 times and 1.63 times those of Gr-Top stacking configuration was achieved. Moreover, as the external longitudinal strain from 0 % to 15 % applied on Cu (111)/double-layer Gr/Cu (111) structure, the thermoelectric transport properties of Gr-Hollow stacking configuration are greater than Gr-Top stacking configuration, while as the strain are 20 % and 25 %, Gr-Top stacking configuration has the larger electric conductivity and thermal conductivity instead.

Induction Coil Design Considerations for High-Frequency Domestic Cooktops

The use of wide band gap (WBG) semiconductor switches in power converters is increasing day by day due to their superior chemical and physical properties, such as electrical field strength, drift speed, and thermal conductivity. These new-generation power switches offer advantages over traditional induction cooker systems, such as fast and environmentally friendly heating. The size of passive components can be reduced, and the decreasing inductance value of induction coils and capacitors with low ESR (equivalent series resistance) values contributes to total efficiency. Other design parameters, such as passive components with lower values, heatsinks with low volumes, cooling fans with low power, and induction coils with fewer turns, can offset the cost of WBG power devices. High-frequency operation can also be effective in heating non-ferromagnetic materials like aluminum and copper, making them suitable for heating these types of pans without complex induction coil and power converter designs. However, the use of these new generation power switches necessitates a re-examination of induction coil design. High switching frequency leads to a high resonance frequency in the power converter, which requires lower-value passive components compared to conventional cookers. The most important component is the induction coil, which requires fewer turns and magnetic cores. This study examines the induction heating equivalent circuit, discusses the general structure and design parameters of the induction coil, and performs FEM (finite element method) analyses using Ansys Maxwell. The results show that the induction coil inductance value in new-generation cookers decreases by 80% compared to traditional cookers, and the number of windings and magnetic cores decreases by 50%. These analyses, performed for high-power applications, are also performed for low-power applications. While the inductance value of the induction coil is 90 μH at low frequencies, it is reduced to the range of 5 μH to 20 μH at high frequencies. The number of windings is reduced by half or a quarter. The new-generation cooker system experimentally verifies the coil design based on the parameters derived from the analysis.