Study Of Thermal Transport Properties Research Articles

Thermal Conductivity of MoS2 and Graphene/MoS2 Heterojunction

With the development of the miniaturization of electronic devices, controlling heat dissipation has become a key factor, which affects the service life of devices and energy utilization efficiency. Therefore, it is particularly important to study the heat conduction mechanism of nanomaterials inside microelectronic devices. Herein, the thermal conductivity of MoS2 and graphene/MoS2 heterojunctions using the bond‐order–length–strength theory and the local bond average method is quantitatively analyzed; the functional relationship between the thermal conductivity and the number of layers, temperature, and pressure is established; and the variation trend of thermal conductivity of materials with these factors is studied. The results show that the thermal conductivity of MoS2 and graphene/MoS2 heterojunctions is inversely proportional to the number of layers and temperature, proportional to the pressure. The work provides a simple and effective method for the study of thermal transport properties of 2D materials and heterojunction systems from the perspective of chemical bonding changes at the atomic level.

Molecular dynamics study of thermal transport properties across covalently bonded graphite-nanodiamond interfaces

The groundbreaking experiment [Luo et al. Nature 2022, 607 (7919) 486–491] recently led to the development of new ultrastrong Carbon/Carbon composites, in which graphene and nanodiamond are strongly connected via covalent bonding. This covalently bonded interface endows the composites with spectacular high strength and other exceptional properties. Herein, non-equilibrium molecular dynamic simulations are conducted to examine the interfacial thermal conductance of graphite-diamond structures by considering the effects of size, environmental temperature, interfacial atomic structures, and tensile strain. Further insight into the microscopic heat transport mechanism of various effects is obtained by analyzing the phonon vibration modes, structural deformation and atomic stress distribution. The variations of interfacial thermal conductance at various temperatures and interfacial configurations are explained qualitatively by the phonon coupling factor. Interestedly, our findings indicate that the interfacial thermal conductance is nearly independent of the graphene size, while it is dependent on the length of the diamond in the direction of heat transport. Furthermore, our study reveals that the interfacial structure retains its heat transport properties even subject to large tensile strain due to interface propagation. Our research provides valuable insights into the heat transport properties of these newly developed Carbon/Carbon composites.

First-principles study of thermal transport properties in ferroelectric HfO2 and related fluorite-structure ferroelectrics.

The discovery of ferroelectricity in the fluorite-structure HfO2 has attracted much interest in various applications including electro-optic devices and nonvolatile memories. Doping and alloying not only induce ferroelectricity in HfO2, but also significantly impact the thermal conduction which plays an essential role in the heat dissipation and thermal stability of ferroelectric devices. To understand and regulate the heat transfer in ferroelectric HfO2, it is crucial to investigate the thermal conduction properties of related fluorite-structure ferroelectrics so as to establish the structure-property relationship. In this work, using first-principles calculations, we investigate the thermal transport in twelve fluorite-structure ferroelectrics. We find an overall satisfactory agreement between the calculated thermal conductivities and those predicted by the simple theory of Slack. Among the family of fluorite-structure ferroelectrics, the transition-metal oxides HfO2 and ZrO2 have the highest thermal conductivities due to the strong interatomic bonding. We demonstrate that the spontaneous polarization, a feature specific to ferroelectrics, is positively correlated with the thermal conductivity, namely, the larger the spontaneous polarization, the larger the thermal conductivity. This is of chemical origin, namely, both the spontaneous polarization and the thermal conductivity are positively correlated to the "ionicity" of the ferroelectrics. We further find that the thermal conductivity is several times lower in the ferroelectric solid solution Hf1-xZrxO2 than in its pure counterparts, especially in the thin films where the finite size effect further suppresses thermal conduction. Our findings suggest the spontaneous polarization as a specific criterion for identifying ferroelectrics with desired thermal conductivities, which may promote the design and application of ferroelectrics.

Study of Thermal Transport Properties of Carbon Based NFPCM (Graphene) For Space Cooling Applications

This examination is planned to research the hardening conduct of water scattered with Graphene nano particles in a circular holder during cementing. The examinations were directed with unadulterated water and nanofluid stage change materials (NFPCMs) with GNP mass grouping of 0.35 %, 0.7 % and 1.05 %. The NFPCM was set up by scattering graphene nanoparticles and a nucleating specialist in the base PCM (stage change material). Nanoparticle’s (GNP) go about as a nucleating specialist to help the quick development of precious stones in cementing processes. The expansion of GNPs came about with an apparent decrease in the sub cooling of water from - 12 °C to - 2.5 °C alongside decrease of 25 % in cementing time attributable to its high warm conductivity and bigger explicit surface region. The expansion of the Nucleating operator lessens the serious situation of sub-cooling in the PCM, all things considered, which improves the exhibition of evaporator in a refrigeration framework. In addition, NFPCM with upgraded heat move rate and without sub-cooling can be valuable in numerous CTES (Cool Thermal Energy Storage) applications. The beginning of hardening progressed on account of NFPCM because of higher cooling rate in the sub cooling district for some random driving potential. The quickened method of vitality charging happened during 78 % of all out cementing time.

On the Influence of Rare Earth Dopants on Thermal Transport in Thermoelectric Bi2Te3 Compounds: An Ab Initio Perspective

AbstractA density functional theory (DFT) study of thermal transport properties of rare earth (RE) doped Bi2Te3 compounds (RE = Y, La, Eu, Gd, and Lu) is reported. The calculations reveal strong nonmonotonous concentration dependence of the lattice thermal conductivity (κL) with local minimum in the region of 2–3 at.% dopant concentration for all dopants in the series except Eu. This behavior is associated with the presence of impurity phonon modes in the frequency range of 0–2 THz. The low‐frequency parts of the phonon spectra vary substantially for different divalent and trivalent RE dopants, which results in different phonon scattering events for different dopants. The concentration dependence of κL correlates with both Grüneisen parameter (γ) and sound velocity (v). This provides us with a simple and powerful predictive tool assessing thermal transport in RE‐doped Bi2Te3 compounds.

First-principles study of thermal transport properties in the two- and three-dimensional forms of Bi2O2Se.

Recently, an air-stable layered semiconductor Bi2O2Se has been synthesized [Nat. Nanotechnol., 2017, 12, 530; Nano Lett. 2017, 17, 3021]. It possesses ultrahigh mobility, semiconductor properties, excellent environmental stability and easy accessibility. Here, we report on the thermal transport properties in monolayer (ML), bilayer (BL), and bulk forms of Bi2O2Se using density-functional theory and the Boltzmann transport approach. The results show that the ML exhibits better thermal transport properties than the BL and bulk. The intralayer opposite phonon vibrations greatly suppress the thermal transport and lead to an ultralow lattice thermal conductivity of ∼0.74 W m-1 K-1 in the ML, which has a large band gap of ∼2.12 eV, a low value of average acoustic group velocity of ∼0.76 km s-1, low-lying optical modes of ∼0.54 THz, strong optical-acoustic phonon coupling, and large Grüneisen parameters of ∼5.69. The size effect for all three forms is much less sensitive due to their short intrinsic phonon mean free path (MFP).

Thermal Transport in Phosphorene.

Phosphorene, a novel elemental 2D semiconductor, possesses fascinating chemical and physical properties which are distinctively different from other 2D materials. The rapidly growing applications of phosphorene in nano/optoelectronics and thermoelectrics call for comprehensive studies of thermal transport properties. In this Review, based on the theoretical and experimental progresses, the thermal transport properties of single-layer phosphorene, multilayer phosphorene (nanofilms), and bulk black phosphorus are summarized to give a general view of the overall thermal conductivity trend from single-layer to bulk form. The mechanism underlying the discrepancy in the reported thermal conductivity of phosphorene is discussed by reviewing the effect of different functionals and cutoff distances on the thermal transport evaluations. This Review then provides fundamental insight into the thermal transport in phosphorene by reviewing the role of resonant bonding in driving giant phonon anharmonicity and long-range interactions. In addition, the extrinsic thermal conductivity of phosphorene is reviewed by discussing the effects of strain and substrate, together with phosphorene based heterostructures and nanoribbons. This Review summarizes the progress of thermal transport in phosphorene from both theoretical calculations and experimental measurements, which would be of significance to the design and development of efficient phosphorene based nanoelectronics.

Disparate Strain Dependent Thermal Conductivity of Two-dimensional Penta-Structures.

Two-dimensional (2D) carbon allotrope called penta-graphene was recently proposed from first-principles calculations and various similar penta-structures emerged. Despite significant effort having been dedicated to electronic structures and mechanical properties, little research has been focused on thermal transport in penta-structures. Motivated by this, we performed a comparative study of thermal transport properties of three representative pentagonal structures, namely penta-graphene, penta-SiC2, and penta-SiN2, by solving the phonon Boltzmann transport equation with interatomic force constants extracted from first-principles calculations. Unexpectedly, the thermal conductivity of the three penta-structures exhibits diverse strain dependence, despite their very similar geometry structures. While the thermal conductivity of penta-graphene exhibits standard monotonic reduction by stretching, penta-SiC2 possesses an unusual nonmonotonic up-and-down behavior. More interestingly, the thermal conductivity of penta-SiN2 has 1 order of magnitude enhancement due to the strain induced buckled to planar structure transition. The mechanism governing the diverse strain dependence is identified as the competition between the change of phonon group velocity and phonon lifetime of acoustic phonon modes with combined effect from the unique structure transition for penta-SiN2. The disparate thermal transport behavior is further correlated to the fundamentally different bonding nature in the atomic structures with solid evidence from the distribution of deformation charge density and more in-depth molecular orbital analysis. The reported giant and robust tunability of thermal conductivity may inspire intensive research on other derivatives of penta-structures as potential materials for emerging nanoelectronic devices. The fundamental physics understood from this study also solidifies the strategy to engineer thermal transport properties of broad 2D materials by simple mechanical strain.

The magnetic, electrical transport and thermal transport properties of Fe-based antipervoskite compounds ZnCxFe3

The effects of carbon concentration on the crystal structure, magnetic, and electrical/thermal transport properties of ZnCxFe3 (1.0 ≤ x ≤ 1.5) have been investigated systematically. Both the Curie temperature and the saturated magnetization decrease firstly and then reach saturation with increasing x. The investigations of heat capacity and resistivity indicate that ZnC1.2Fe3 displays a strongly correlated Fermi liquid behavior considering its Kadowaki-Woods ratio (∼0.64 a0). Around the ferromagnetic-paramagnetic phase transition (∼358 K), a reversible room-temperature magnetocaloric effect is observed. The relative cooling power (RCP) is ∼164 J/kg (∼385 J/kg) with the magnetic field change ΔH = 20 kOe (45 kOe). Considering the considerable large RCP, inexpensive and innoxious raw materials, ZnC1.2Fe3 is suggested to be a promising candidate for room-temperature magnetic refrigeration. Furthermore, the studies of thermal transport properties indicate that ZnC1.2Fe3 can also be a potential thermoelectric material with the dimensionless figure of merit (ZT = α2T/ρk) reaching its maximum of 0.0112 around 170 K.