scholarly journals Phonon Lifetimes and Thermal Conductivity of the Molecular Crystal α-RDX

MRS Advances ◽  
2019 ◽  
Vol 4 (40) ◽  
pp. 2191-2199 ◽  
Author(s):  
Gaurav Kumar ◽  
Francis G. VanGessel ◽  
Daniel C. Elton ◽  
Peter W. Chung
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Disordered Systems ◽  
Molecular Crystal ◽  
Amorphous Materials ◽  
Phonon Scattering ◽  
Large Degree ◽  
Crystalline Materials ◽  
Boltzmann Model ◽  
Transfer Properties

ABSTRACTThe heat transfer properties of the organic molecular crystal α-RDX were studied using three phonon scattering based thermal conductivity models. It was found that the widely used Peierls-Boltzmann model for thermal transport in crystalline materials breaks down for α-RDX. We show this breakdown is due to a large degree of anharmonicity that leads to a dominance of diffusive-like carriers. Despite being developed for disordered systems, the Allen-Feldman theory for thermal conductivity actually gives the best description of thermal transport. This is likely because diffusive carriers contribute to over 95% of the thermal conductivity in α-RDX. The dominance of diffusive carriers is larger than previously observed in other fully ordered crystalline systems. These results indicate that van der Waals bonded organic crystalline solids conduct heat in a manner more akin to amorphous materials than simple atomic crystals.

scholarly journals Reduction of Lattice Thermal Conductivity in PbTe Induced by Artificially Generated Pores

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Jae-Yeol Hwang ◽  
Eun Sung Kim ◽  
Syed Waqar Hasan ◽  
Soon-Mok Choi ◽  
Kyu Hyoung Lee ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Pore Structure ◽  
Transport Properties ◽  
Thermoelectric Materials ◽  
Thermal Transport ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Phonon Modes ◽  
Thermal Transport Properties

Highly dense pore structure was generated by simple sequential routes using NaCl and PVA as porogens in conventional PbTe thermoelectric materials, and the effect of pores on thermal transport properties was investigated. Compared with the pristine PbTe, the lattice thermal conductivity values of pore-generated PbTe polycrystalline bulks were significantly reduced due to the enhanced phonon scattering by mismatched phonon modes in the presence of pores (200 nm–2 μm) in the PbTe matrix. We obtained extremely low lattice thermal conductivity (~0.56 W m−1 K−1at 773 K) in pore-embedded PbTe bulk after sonication for the elimination of NaCl residue.

Annealing Studies of Re Doped AlPdMn Quasicrystals

2001 ◽  
Vol 691 ◽  
Author(s):  
Donny W. Winkler ◽  
Terry M. Tritt ◽  
Robert Gagnon ◽  
J. Strom-Olsen
Keyword(s):  
Thermal Conductivity ◽  
Electrical Resistivity ◽  
Transport Properties ◽  
Thermal Transport ◽  
Amorphous Materials ◽  
Annealed Sample ◽  
Annealing Conditions ◽  
Thermal Transport Properties ◽  
The Relationship

ABSTRACTQuasicrystals have properties associated with both crystalline and amorphous materials. These properties appear to be sensitive to both composition and annealing conditions. Therefore, it is important to investigate the influence of the microstructure on the electrical and thermal transport properties of quasicrystals. AlPdMn quasicrystal samples were prepared with various levels of Re substituted for the Mn (Al70Pd20Mn10−XReX) and then subjected to different annealing conditions. Electrical resistivity, thermopower and thermal conductivity were measured on each as grown and annealed sample over a broad range of temperature, 10 K < T < 300 K. The relationship between the electrical and thermal transport properties and microstructure will be presented and discussed.

scholarly journals Thermal transport in nanocrystalline Si and SiGe by ab initio based Monte Carlo simulation

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Lina Yang ◽  
Austin J. Minnich
Keyword(s):  
Thermal Conductivity ◽  
Monte Carlo ◽  
Ab Initio ◽  
Grain Boundaries ◽  
Thermal Transport ◽  
Phonon Scattering ◽  
Phonon Dispersion ◽  
Computational Study ◽  
Phonon Transport ◽  
Nanocrystalline Si

Abstract Nanocrystalline thermoelectric materials based on Si have long been of interest because Si is earth-abundant, inexpensive, and non-toxic. However, a poor understanding of phonon grain boundary scattering and its effect on thermal conductivity has impeded efforts to improve the thermoelectric figure of merit. Here, we report an ab-initio based computational study of thermal transport in nanocrystalline Si-based materials using a variance-reduced Monte Carlo method with the full phonon dispersion and intrinsic lifetimes from first-principles as input. By fitting the transmission profile of grain boundaries, we obtain excellent agreement with experimental thermal conductivity of nanocrystalline Si [Wang et al. Nano Letters 11, 2206 (2011)]. Based on these calculations, we examine phonon transport in nanocrystalline SiGe alloys with ab-initio electron-phonon scattering rates. Our calculations show that low energy phonons still transport substantial amounts of heat in these materials, despite scattering by electron-phonon interactions, due to the high transmission of phonons at grain boundaries, and thus improvements in ZT are still possible by disrupting these modes. This work demonstrates the important insights into phonon transport that can be obtained using ab-initio based Monte Carlo simulations in complex nanostructured materials.

scholarly journals Effect of Phase Transition on the Thermal Transport in Isoreticular DUT Materials

2021 ◽  
Author(s):  
Penghua Ying ◽  
Jin Zhang ◽  
Zheng Zhong
Keyword(s):  
Phase Transition ◽  
Thermal Conductivity ◽  
Transport Property ◽  
Thermal Transport ◽  
Phonon Scattering ◽  
Transition Process ◽  
Thermal Transport Property ◽  
Potential Applications ◽  
Flexible Metal ◽  
Dynamics Simulations

<p></p><p>Soft porous crystals (SPCs) or flexible metal-organic frameworks have great potential applications in gas storage and separation, in which SPCs can undergo phase transition due to external stimuli. Thus, understanding the effect of phase transition on the thermal transport in SPCs becomes extremely crucial, because the latent heat generated in aforementioned applications is needed to be effectively removed. In this paper, taking the isorecticular DUT series as an example, the thermal transport property of SPCs during the phase transition from the large pore (lp) phase to the narrow pore (np) phase is comprehensively investigated by molecular dynamics simulations together with the Green-Kubo method. According to our calculations, all DUT structures exhibit an ultralow thermal conductivity smaller than 0.2 Wm<sup>-1</sup>K<sup>-1</sup>. In addition, we find that the effect of phase transition on the thermal transport property of different DUT materials considered here strongly depends on their porosity. As for DUT-48, its lp phase has a thermal conductivity larger than that of its np phase. However, in other DUT materials, i.e, DUT-47, DUT-49, DUT-50, and DUT-151 the thermal transport property of their lp phase is found to be weaker than that of their np phase. This complicated effect of phase transition on the thermal transport in SPCs can be explained by a porosity-dominated competition mechanism between the increased volumetric heat capacity and the aggravated phonon scattering during the phase transition process.</p><p></p>

scholarly journals Industrial Thermal Insulation Properties above Sintering Temperatures

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4721
Author(s):  
Amalie Gunnarshaug ◽  
Maria-Monika Metallinou ◽  
Torgrim Log
Keyword(s):  
Thermal Conductivity ◽  
Heat Treatment ◽  
Thermal Insulation ◽  
Fire Protection ◽  
Thermal Transport ◽  
Amorphous Materials ◽  
Transport Theory ◽  
Treatment Temperature ◽  
Dimensional Changes ◽  
Passive Fire Protection

Processing highly flammable products, the oil and gas (O&G) industry can experience major explosions and fires, which may expose pressurized equipment to high thermal loads. In 2020, oil fires occurred at two Norwegian O&G processing plants. To reduce the escalation risk, passive fire protection may serve as a consequence-reducing barrier. For heat or cold conservation, equipment and piping often require thermal insulation, which may offer some fire protection. In the present study, a representative thermal insulation (certified up to 700 °C) was examined with respect to dimensional changes and thermal transport properties after heat treatment to temperatures in the range of 700 °C to 1200 °C. Post heat treatment, the thermal conductivity of each test specimen was recorded at ambient temperature and up to 700 °C, which was the upper limit for the applied measurement method. Based on thermal transport theory for porous and/or amorphous materials, the thermal conductivity at the heat treatment temperature above 700 °C was estimated by extrapolation. The dimensional changes due to, e.g., sintering, were also analyzed. Empirical equations describing the thermal conductivity, the dimensional changes and possible crack formation were developed. It should be noted that the thermal insulation degradation, especially at temperatures approaching 1200 °C, is massive. Thus, future numerical modeling may be difficult above 1150 °C, due to abrupt changes in properties as well as crack development and crack tortuosity. However, if the thermal insulation is protected by a thin layer of more robust material, e.g., passive fire protection to keep the thermal insulation at temperatures below 1100 °C, future modeling seems promising.

Optimized Design of Composite Materials for Heat Transport Applications

2011 ◽  
Author(s):  
Babak Kouchmeshky ◽  
Peter Kroll ◽  
Ibukun Olubanjo
Keyword(s):  
Thermal Conductivity ◽  
Composite Materials ◽  
Thermal Transport ◽  
Elevated Temperatures ◽  
Phonon Scattering ◽  
Optimized Design ◽  
Individual Contributions ◽  
Non Equilibrium Molecular Dynamics ◽  
Dynamics Simulations ◽  
The Individual

Careful design of composite materials offers a chance for engineering phonon band gaps and controlling phonon scattering. Taking advantage of this strategy, we study properties of SiC composite materials for engineering applications in which the control of thermal transport is important. In particular, knowledge of the individual contributions of phonons on thermal transport provides us the necessary information to focus on most significant phonon frequencies. In our study, we select a series of candidate model geometries and use a virtual testing method for elevated temperatures to support the design process. Integrating atomistic non-equilibrium molecular dynamics simulations to determine thermal conductivity we provide a proof-of-concept study and deliver best design scenarios of SiC composite materials with very low-thermal conductivity.

Theoretical Analysis of Thermal Conductivity in Amorphous Inter-layer Dielectrics

2006 ◽  
Vol 914 ◽  
Author(s):  
Manu Shamsa ◽  
Patrick Morrow ◽  
Shriram Ramanathan
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Thermal Transport ◽  
High Frequency ◽  
Thermal Conduction ◽  
High Performance ◽  
Amorphous Materials ◽  
Disordered Materials ◽  
Semiconductor Processing ◽  
Hopping Model

AbstractUnderstanding thermal conduction in interlayer dielectrics (ILDs) is important for the optimal design of interconnect layers in backend semiconductor processing for future high-performance nano-scale devices. Reduced thermal conductivity of porous ILDs for example can adversely affect the temperature rise in the embedded metal lines leading to un-desirable reliability issues and design constraints. In this paper, we report results of our theoretical and experimental investigation of thermal transport in amorphous and porous dielectrics. A phonon-hopping model has been adapted to calculate the thermal conductivity in disordered materials. The value of hopping integral has been calculated by comparing the modeling results with experimental data for various amorphous and porous materials. The model shows reasonable agreement with experimental data for various amorphous materials including SiO2 and other glasses over a wide temperature range from 50K – 300K. The model suggests that the hopping of localized high frequency phonons is a dominant thermal transport mechanism in such material systems.

Thermal Transport in Few-Quintuple Bi2Te3 Thin Films and Nanoribbons

2011 ◽  
Author(s):  
Bo Qiu ◽  
Xiulin Ruan
Keyword(s):  
Thin Films ◽  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Temperature Dependence ◽  
Thermal Transport ◽  
Room Temperature ◽  
Phonon Scattering ◽  
Md Simulations ◽  
Boundary Scattering ◽  
Nanoporous Films

In this work, thermal conductivity of perfect and nanoporous few-quintuple Bi2Te3 thin films as well as nanoribbons with perfect and zig-zag edges is investigated using molecular dynamics (MD) simulations with Green-Kubo method. We find minimum thermal conductivity of perfect Bi2Te3 thin films with three quintuple layers (QLs) at room temperature, and we believe it originates from the interplay between inter-quintuple coupling and phonon boundary scattering. Nanoporous films and nanoribbons are studied for additional phonon scattering channels in suppressing thermal conductivity. With 5% porosity in Bi2Te3 thin films, the thermal conductivity is found to decrease by a factor of 4–6, depending on temperature, comparing to perfect single QL. For nanoribbons, width and edge shape are found to strongly affect the temperature dependence as well as values of thermal conductivity.

scholarly journals Phonon transport in the nano-system of Si and SiGe films with Ge nanodots and approach to ultralow thermal conductivity

Nanoscale ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 4971-4977
Author(s):  
Tatsuhiko Taniguchi ◽  
Tsukasa Terada ◽  
Yuki Komatsubara ◽  
Takafumi Ishibe ◽  
Kento Konoike ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Amorphous Materials ◽  
Phonon Scattering ◽  
Phonon Transport ◽  
Si Films

Ballistic phonon transport was observed in Si films containing Ge nanodots. In SiGe films containing Ge nanodots, thermal conductivity was drastically reduced close to that of amorphous materials due to alloy phonon scattering and nanodot scattering.

scholarly journals Influence of Te Vacancies on the Thermoelectric Properties of n-type Cu0.008Bi2Te2.7-xSe0.3

2020 ◽  
Vol 58 (10) ◽  
pp. 721-727
Author(s):  
Yerim Yang ◽  
TaeWan Kim ◽  
Seokown Hong ◽  
Jiwoo An ◽  
Sang-il Kim
Keyword(s):  
Thermal Conductivity ◽  
Transport Properties ◽  
Point Defect ◽  
Thermoelectric Properties ◽  
Thermal Transport ◽  
Phonon Scattering ◽  
Band Model ◽  
Total Thermal Conductivity ◽  
Thermal Transport Properties ◽  
Callaway Model

In this study, we report the influence of Te vacancy formation on the thermoelectric properties of n-type Cu0.008Bi2Te2.7Se0.3 alloys, including their electronic and thermal transport properties. Te-deficient Cu0.008Bi2Te2.7-xSe0.3 (x = 0, 0.005, 0.01 and 0.02) samples were systematically synthesized and characterized. Regarding electronic transport properties, carrier concentration was increased with Te vacancies, while carrier mobility was maintained. As a result, the electrical conductivity significantly increased while the Seebeck coefficient reduced moderately, thus, the power factor was enhanced from 3.04 mW/mK<sup>2</sup> (pristine) to 3.22 mW/mK<sup>2</sup> (x = 0.02) at 300 K. Further analysis based on a single parabolic band model revealed that the weighted mobility of the conduction band increased, which is favorable for electron transport, as Te vacancies were generated. Regarding thermal transport properties, lattice thermal conductivity decreased with Te vacancies due to additional point defect phonon scattering, however, total thermal conductivity increased due to larger electronic contribution as Te vacancies increased. Analysis using the Debye-Callaway model suggests that the phonon scattering by the Te vacancies is as efficient as the substitution point defect scattering. Consequently, the thermoelectric figure of merit zT increased at all temperatures for x = 0.005 and 0.01. The maximum zT of 0.95 was achieved for Te-deficient Cu0.008Bi2Te2.69Se0.3 (x = 0.01) at 400 K.

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