Ultrahigh Thermal Conductivity Research Articles

Ultrahigh thermal conductivity and strength in direct-gap semiconducting graphene-like BC6N: A first-principles and classical investigation

In recent years, graphene-like boron carbide and carbon nitride nanosheets have attracted remarkable attentions, owing to their semiconducting electronic nature and outstanding mechanical and heat transport properties. Graphene-like BC6N is an experimentally realized layered material and most recently has been the focus of numerous theoretical studies. Interestingly, the most stable form of BC6N monolayer remains unexplored and limited information are known concerning its intrinsic physical properties. Herein, on the basis of density functional theory (DFT) calculations we confirm that the most stable form of BC6N nanosheet shows a rectangular unitcell, in accordance with an overlooked experimental finding. We found that BC6N monolayer is a semiconductor with 1.19 eV HSE06-based direct gap and yields anisotropic and excellent absorption of visible light. First-principles results highlight that BC6N nanosheet exhibits anisotropic and ultrahigh tensile strength and lattice thermal conductivity, outperforming all other fabricated 2D semiconductors. We moreover develop classical molecular dynamic models for the evaluation of heat transport and mechanical properties of BC6N nanomembranes. The presented results in this work not only shed light on the most stable configuration of BC6N nanosheet, but also confirm its outstandingly appealing electronic, optical, heat conduction and mechanical properties, extremely motivating for further theoretical and experimental endeavors.

Flexible Electrothermal Laminate Films Based on Tannic Acid-Modified Carbon Nanotube/Thermoplastic Polyurethane Composite

Carbon nanomaterials are ideal fillers in composites for electrothermal applications due to their ultrahigh electrical conductivity, thermal conductivity, and excellent mechanical property. In this study, high-performance electrothermal laminate films were prepared by a layer-by-layer process, which used tannic acid-functionalized multiwalled carbon nanotubes as filler and thermoplastic polyurethane as substrate. The prepared electrothermal laminate films exhibit excellent mechanical property, electrical heating property, and high electrothermal performance, which can reach steady-state temperature in about 120 s. Additionally, the maximum steady-state temperature can reach ∼150 °C at 20 V. During 10 different cycles of experiments and 5 h aging time, no significant change in temperature was observed. Moreover, from the results, it is clear that the performance of the samples is related to the amount of filler added and the applied voltage, and we can precisely control the sample performance by regulating the amount of filler addition and applied voltage. We believe that these electrothermal laminate films could be widely used in wearable heating cotton fabric, controllable electric heating module, floor heating, and deicing devices.

The graphite foam/erythritol composites with ultrahigh thermal conductivity for medium temperature applications

The mesophase pitch derived graphite foams with low bulk density (L-GF) and high bulk density (H-GF) were spontaneously infiltrated by erythritol to prepare graphite foam/erythritol (GF/erythritol) phase change materials (PCMs) with ultrahigh thermal conductivity for medium temperature thermal energy storage applications. Results of thermophysical properties indicated that thermal diffusivity of the GF/erythritol PCMs can be enhanced by 66 and 117 times as compared with that of pristine erythritol in solid (0.36 mm2/s). This enhancement resulting from three-dimensional ordered network of graphite foam can significantly reduce the charging and discharging time of the PCM storage system. Although H-GF as a matrix can obtain a higher thermal conductivity (68.71 W/(m·K)) than L-GF (40.52 W/(m·K)), the smaller porosity cannot allow more erythritol to be absorbed, and its melting enthalpy (178.4 J/g) is lower than L-GF (266.6 J/g). In addition, the enhancement of thermal conductivity and the increase of interfacial surface area caused by graphite foam structure strongly suppresses the supercooling of erythritol, which can be reduced from 86.0 °C to 53.2 °C. The obtained results demonstrated that the GF/erythritol PCM as a stable PCM is a promising material for medium temperature thermal energy storage applications.

Ultrahigh current density and fatigue stability in flexible energy harvester by designing delivery paths

Flexible piezoelectric energy harvesters that efficiently convert mechanical energy into electrical energy have been extensively studied due to their great application potential in low-power wearable electronics and self-powered sensors. However, the low current output and poor thermal fatigue resistance severely restrict their practical applications. Here, we propose a new strategy to simultaneously improve the current density and thermal conductivity of the flexible piezocomposites (PCs) by designing delivery paths. High-quality (Ba0·85Ca0.15) (Ti0·90Zr0.10)O3/copper nanorods/polydimethylsiloxane (BCZT/Cu NRs/PDMS) PCs with a novel co-chained structure prepared using a well-suited technique of dielectrophoresis were reported for the first time. The BCZT particles and Cu NRs aligned in same chains throughout PDMS matrix results in an efficient delivery path both for induced charge transfer and heat dissipation, thus leading to ultrahigh current density (4.7 μA/cm2) and thermal conductivity (0.31 W/(m · K)). Further, a faster charging speed and a dramatically fatigue stability were realized in the co-chained PCs. Our work is expected to provide a potential solution for simultaneously enhancing current density and heat dissipation for a variety of composites in the field of flexible energy harvesting.

Facile Construction of a Flexible Film with Ultrahigh Thermal Conductivity and Excellent Flame Retardancy for a Smart Fire Alarm

Design and development of intelligent fire warning materials with rapid response capabilities has always been an urgent need for the safety of many flammable materials in their applications. Herein...

Density Functional Theory Investigation of Thermal Conductivity in α-CN and α-CP Monolayers: Implications for Thermal Management of Electronic Devices

This work presents the density functional theory based investigations of two-dimensional carbon pnictides α-CX (X = N and P). Despite being from the group of the pnictide family, there are significant differences in the trends of the electronic and vibrational properties of both systems. The calculated electronic band gaps are 3.77 eV and 1.79 eV for α-CN and α-CP, respectively. The direct nature and moderate gap magnitude of α-CP indicate its applicability in the field of optoelectronic and photovoltaic device applications, which is confirmed by the calculated absorption spectra of the system. Distinguished phonon dispersion curves of both systems show a highly anisotropic trend. The diverse and steep nature of the acoustic phonon modes together with high phonon group velocity, low phonon anharmonicity, and high phonon mean free path (MFP) leads to a pronounced magnitude of thermal conductivity in the case of α-CN. In contrast to α-CN, α-CP owing to the lower gap between the optoacoustic phonon modes, lower MFP, and high anharmonicity possesses a remarkably lower thermal conductivity of 292 W m–1 K–1. The thermoelectric performance of the system is assessed by calculating the figure-of-merit ZT in the case of α-CP, which is 0.36 at 300 K that further attains > 0.7 at higher temperatures; whereas, for α-CN, the ZT value remains < 0.1 due to its ultra-high thermal conductivity. The present study paves the pathway toward exploration of carbon-based low-dimensional materials for high mobility and high thermal conductivity-based nanoelectronic device applications.

A Review of Polymer Composites Based on Carbon Fillers for Thermal Management Applications: Design, Preparation, and Properties.

With the development of microelectronic devices having miniaturized and integrated electronic components, an efficient thermal management system with lightweight materials, which have outstanding thermal conductivity and processability, is becoming increasingly important. Recently, the use of polymer-based thermal management systems has attracted much interest due to the intrinsic excellent properties of the polymer, such as the high flexibility, low cost, electrical insulation, and excellent processability. However, most polymers possess low thermal conductivity, which limits the thermal management applications of them. To address the low thermal conduction of the polymer materials, many kinds of thermally conductive fillers have been studied, and the carbon-based polymer composite is regarded as one of the most promising materials for the thermal management of the electric and electronic devices. In addition, the next generation electronic devices require composite materials with various additional functions such as flexibility, low density, electrical insulation, and oriented heat conduction, as well as ultrahigh thermal conductivity. In this review, we introduce the latest papers on thermally conductive polymer composites based on carbon fillers with sophisticated structures to meet the above requirements. The topic of this review paper consists of the following four contents. First, we introduce the design of a continuous three-dimensional network structure of carbon fillers to reduce the thermal resistance between the filler–matrix interface and individual filler particles. Second, we discuss various methods of suppressing the electrical conductivity of carbon fillers in order to manufacture the polymer composites that meet both the electrical insulation and thermal conductivity. Third, we describe a strategy for the vertical alignment of carbon fillers to improve the through-plane thermal conductivity of the polymer composite. Finally, we briefly mention the durability of the thermal conductivity performance of the carbon-based composites. This review presents key technologies for a thermal management system of next-generation electronic devices.

Ultrahigh thermal conductivity of epoxy composites based on curling bioinspired functionalized graphite films for thermal management application

Unsatisfactory thermal conductive network (TCN) and poor heat conduction interface have limited thermal conductivity (TC) enhancement in the polymeric composites. In this study, inspired by mussels and a Chinese delicacy called the Hanamaki, a facile and environmental strategy is developed to prepare hierarchically ordered graphite film strips@polydopamine/epoxy (GFs@PDA/EP) composites. Organized TCNs and an optimized interface were constructed and thus an ultrahigh TC of GFs/EP (899.44 ± 18.51 W m−1 K−1) in perpendicular direction was obtained. Structural analysis and heat-transfer passages model suggests that superior TCNs were constructed and the designed structure is conducive for heat conduction in the perpendicular direction. Moreover, the interfacial bonding of GFs@PDA with EP matrix contributes to the remarkable enhancement of TC with increasing of PDA coverage. A decrease of ~43 °C in the thermal management experiment of LED chips indicated that it most likely becomes a good candidate in electronic device-cooling application.

Application of lightweight magnesium alloy in satellite antenna products

Combined with the actual work, the new metal matrix composite has the characteristics of light weight, low thermal expansion (CTE), ultra-high thermal conductivity, high specific strength, specific stiffness, good damping, etc. which is the key to realize the requirements of miniaturization, lightweight, long life and high reliability of aerospace products. This paper introduces the selection analysis and practical application of magnesium alloy in satellite antenna products. Antenna products based on magnesium alloy will be more and more widely used in aerospace field.

Constructing zebra skin structured graphene/copper composites with ultrahigh thermal conductivity

Heat sink materials with superior thermal conductivity and excellent mechanical strength with low cost, are desirable for electronic packaging and thermal management in electronic and electrical engineering systems. In this work, the graphene paper (GP)/copper (Cu) composites were prepared by using a vacuum hot pressing. A zebra skin structure was constructed for improving the thermal transportation performance of GP/Cu composites. In virtue to its unique zebra skin structure, the ultrahigh thermal conductivity of 968 W m-1 K-1 was achieved for the GP/Cu composite at 70 vol% graphene loading. Furthermore, the GP/Cu composite retains high flexural strength (88 MPa) due to the good interface compatibility between the surface chemical treated GP and Cu paper. Our work provides a new method to significantly improve the in-plane thermal conductivity of thermal management materials.

Phonon-engineered extreme thermal conductivity materials.

Materials with ultrahigh or low thermal conductivity are desirable for many technological applications, such as thermal management of electronic and photonic devices, heat exchangers, energy converters and thermal insulation. Recent advances in simulation tools (first principles, the atomistic Green's function and molecular dynamics) and experimental techniques (pump-probe techniques and microfabricated platforms) have led to new insights on phonon transport and scattering in materials and the discovery of new thermal materials, and are enabling the engineering of phonons towards desired thermal properties. We review recent discoveries of both inorganic and organic materials with ultrahigh and low thermal conductivity, highlighting heat-conduction physics, strategies used to change thermal conductivity, and future directions to achieve extreme thermal conductivities in solid-state materials.

An Integrated Approach to Design and Develop High-Performance Polymer-Composite Thermal Interface Material.

A computational framework based on novel differential effective medium approximation and mean-field homogenization is used to design high-performance filler-laden polymer thermal interface materials (TIMs). The proposed design strategy has the capability to handle non-dilute filler concentration in the polymer matrix. The effective thermal conductivity of intended thermal interface composites can be tailored in a wide range by varying filler attributes such as size, aspect ratio, orientation, as well as filler–matrix interface with an upper limit imposed by the shear modulus. Serval potential polymers and fillers are considered at the design stage. High-density polyethylene (HDPE) and thermoplastic polyurethane (TPU) with a non-dilute concentration (~60 vol%) of ceramic fillers exhibit high thermal conductivity (4–5 W m−1 K−1) without compromising the high compliance of TIMs. The predicted thermal conductivity and coefficient of thermal expansion are in excellent agreement with measured data of various binary composite systems considering HDPE, TPU, and polypropylene (PP) loaded with Al2O3 and AlN fillers in varying sizes, shapes, and concentrations, prepared via the melt-mixing and compression-molding route. The model also validates that manipulating filler alignment and aspect ratio can significantly contribute to making heat-conducting networks in composites, which results in ultra-high thermal conductivity.

Native point defects from stoichiometry-linked chemical potentials in cubic boron arsenide

The presence of a point defect typically breaks the stoichiometry in a semiconductor. For example, a vacancy on an A-site in an AB compound makes the crystal B-rich. As the stoichiometry changes, so do the chemical potentials. While the prevalent first-principles methods have provided significant insight into characters of point defects in a transparent manner, the crucial connection between crystal stoichiometry and chemical potentials is usually not made. However, ad hoc choices for chemical potentials can lead to nonphysical negative formation energies in some Fermi level ranges, along with questions about charge balance. Herein, we formulate a canonical framework describing how the chemical potential of each element is directly linked to the composition of the crystal under (off-)stoichiometric conditions instead of the ad hoc assumption that the chemical potential is the elemental limit under a certain growth condition. Consequently, the chemical potential changes with the Fermi level within the bandgap and the formation energies are positive. Using such an approach, we present ab initio results for native point defects in BAs, a semiconductor with ultrahigh room-temperature thermal conductivity. We find that antisites are the constitutional defects in off-stoichiometric material, while BAs antisites and B vacancies dominate in the stoichiometric material. We further discuss the thermodynamic equilibrium and charge neutrality point in BAs in light of our stoichiometry-determined chemical potentials. As discussed, our work offers a more applicable and accessible approach to tackle defect formation energies in semiconductors, especially the ones with wide gap where negative formation energies are commonly seen.

Recent advances in novel aerogels through the hybrid aggregation of inorganic nanomaterials and polymeric fibers for thermal insulation

AbstractAerogel is a nanoporous solid material with ultrahigh porosity, ultralow density, and thermal conductivity, which is considered to be one of the most promising high‐performance insulation materials today. However, traditional pure inorganic aerogels (i.e., silica aerogel) exhibit inherent structural brittleness, making their processing and handling difficult, and their manufacturing costs are relatively high, which limits their large‐scale practical use. The recently developed aerogel based on polymer nanofibers has ultralow thermal conductivity and density, excellent elasticity, and designable multifunction. More importantly, one‐dimensional polymer nanofibers are directly used as building blocks to construct the network of aerogels via a gelation‐free process. This greatly simplifies the aerogel preparation process, thereby bringing opportunities for large‐scale aerogel applications. The aggregation of inorganic nanomaterials and polymer nanofibers is considered to be a very attractive strategy for obtaining highly flexible, easily available, and multifunctional composite aerogels. Therefore, this review summarizes the recent advances in novel aerogels through the hybrid aggregation of inorganic nanomaterials and polymeric fibers for thermal insulation. The main processing routes, porous microstructure, mechanical properties, and thermal properties and applications of these aerogels are highlighted. In addition, various future challenges faced by these aerogels in thermal insulation applications are discussed in this review.

Ab initio determination of ultrahigh thermal conductivity in ternary compounds

Discovering new materials with ultrahigh thermal conductivity has been a critical research frontier and driven by many important technological applications ranging from thermal management to energy science. Here we have rigorously investigated the fundamental lattice vibrational spectra in ternary compounds and determined the thermal conductivity using a predictive ab initio approach. Phonon transport in B-X-C (X = N, P, As) groups is systematically quantified with different crystal structures and high-order anharmonicity involving a four-phonon process. Our calculation found an ultrahigh room-temperature thermal conductivity through strong carbon-carbon bonding up to 2100 W/mK beyond most common materials and the recently discovered boron arsenide. This study provides fundamental insight into the atomistic design of thermal conductivity and opens up opportunities in new materials searching towards complicated compound structures. DOI: 10.1103/PhysRevB.103.L041203

Effect of isotope disorder on the Raman spectra of cubic boron arsenide

Boron arsenide (c-BAs) is at the forefront of research on ultrahigh thermal conductivity materials. We present a Raman scattering study of isotopically tailored cubic boron arsenide single crystals for 11 isotopic compositions spanning the range from nearly pure c-$^{10}$BAs to nearly pure c-$^{11}$BAs. Our results provide insights on the effects of strong mass disorder on optical phonons and the appearance of two-mode behavior in the Raman spectra of mixed crystals. Strong isotope disorder also relaxes the one-phonon Raman selection rules, resulting in disorder-activated Raman scattering by acoustic phonons.

A new differential scheme for the development of thermally conductive polymer-composites with non-dilute filler concentrations

The recent approach for enhancing the thermal conductivity of polymer-composites is to generate an interconnecting network of thermally conductive fillers. However, the existing models for effective thermal conductivity of composites are, generally, based on effective medium theory and valid for dilute filler concentration (low volume fraction), which leads to inaccurate predictions with non-dilute and percolating filler concentrations. In this work, the model is developed focusing on non-dilute filler concentrations, which is more practical for the recent approach towards thermally conductive polymer-composites. The existing model for dilute filler concentrations is modified based on Bruggeman's differential scheme wherein the ‘non-dilute concentrations’ are obtained by integrating the effect of adding ‘dilute concentrations’ in small increments. The proposed model can handle particulate fillers of variable geometry. The proposed model is validated by producing different polymer matrix composite systems with ceramic fillers. Using Al2O3 or AlN as filler, and high-density polyethylene or polypropylene as matrix, different binary composite systems were processed with volume fractions up to 0.5. From the parametric studies, conducted to establish the understandings of the model, the aspect ratio of filler particles is found the most critical. The proposed model is expected to be the mathematical ground for the industry and researchers to produce computationally designed polymer composites with tailorable ultrahigh thermal conductivity in corrosive environment-heat transfer applications such as polymeric heat exchangers for seawater desalination.

Preparation, Properties and Mechanisms of Carbon Fiber/Polymer Composites for Thermal Management Applications.

With the increasing integration and miniaturization of electronic devices, heat dissipation has become a major challenge. The traditional printed polymer circuit board can no longer meet the heat dissipation demands of microelectronic equipment. If the heat cannot be removed quickly and effectively, the efficiency of the devices will be decreased and their lifetime will be shortened. In addition, the development of the aerospace, automobiles, light emitting diode (LED{ TA \\1 “LED; lightemitting diode” \\s “LED” \\c 1 }) and energy harvesting and conversion has gradually increased the demand for low-density and high thermal conductive materials. In recent years, carbon fiber (CF{ TA \\1 “CF; carbon fiber” \\c 1 }) has been widely used for the preparation of polymer composites due to its good mechanical property and ultra-high thermal conductivity. CF materials easily form thermal conduction paths through polymer composites to improve the thermal conductivity. This paper describes the research progress, thermal conductivity mechanisms, preparation methods, factors influencing thermal conductivity and provides relevant suggestions for the development of CF composites for thermal management.

Ultra-high thermal conductivities of tetrahedral carbon allotropes with non-simple structures.

Pursuing high thermal conductivity is of great significance to enhance the performance and working stability of microelectronics in terms of efficient heat dissipation. Traditionally, ultra-high thermal conductivity is thought to exist only in simple crystals with few atoms in the primitive cell, such as diamond and boron arsenide, where the phonon-phonon scattering is weak. In this study, we report an innovation from conventional knowledge based on state-of-the-art first-principles calculations. It is found that the thermal conductivities of three carbon allotropes of C32, C36, and C94 with non-simple structures can be as high as 1152.75, 1075.70, and 860.07 W m-1 K-1, respectively, despite a large number of atoms in the primitive cell. Through comparative analysis, it is revealed that there exist certain competitive mechanisms, where the weak phonon anharmonicity is found to dominate the high thermal conductivity. Our study not only uncovers excellent carbon-based candidates with ultra-high thermal conductivity for enhancing heat dissipation with potential applications in electronics, but also provides insights into the thermal transport, which will shed light on future studies.

Synthesis of centimeter-scale high-quality polycrystalline hexagonal boron nitride films from Fe fluxes.

High-quality hexagonal BN (hBN) crystals, owing to their irreplaceable roles in new functional devices such as universal substrates and excellent layered insulators are exceedingly required in the field of two-dimensional (2D) materials. Although large-scale monolayer hBN crystals have been successfully grown on catalytic metals, the synthesis of large-area continuous hBN films with thickness in microns is challenging, hindering their applications at the mesoscopic level. Herein, we report the single-metal flux growth of centimeter-large, micron-thick, and high-quality continuous hBN films by balancing the grain size and coverage. The as-grown films can be readily exfoliated and transferred onto arbitrary substrates. Isotopically engineered hBN crystals can be obtained as well by the method. The narrow Raman line widths of the intralayer E2g mode peak (2.9 cm-1 for h11BN, 3.3 cm-1 for h10BN, and 7.9 cm-1 for hNaBN) and ultrahigh thermal conductivity (830 W m-1 K-1 for 4L h11BN) demonstrate high crystal quality and low defect density. Our results provide the foundation for the cost-efficient and lab-achievable synthesis of high-quality hBN films aimed at its mesoscopic applications.