Pressure Effects on the Thermal Properties of Graphite

In this paper, the thermal properties of graphite under external pressure were systematically investigated based on first-principles calculations and Boltzmann transport equation (BTE). This method is relatively simple and general to any other crystals. It was found that a compressive pressure can significantly increase the interaction between the layers in graphite and increase the phonon group velocity, the phonon mean free paths, thus the cross-plane thermal conductivity decreases. The effects of pressure on the in-plane thermal conductivity are much weaker than those on the cross-plane value. Our results indicate that the thermal properties of graphite can be strongly modulated by pressure engineering. Moreover we extracted the phonon dispersion and phonon lifetime of graphite under or without external pressure. And changes in the density of states and the cumulative thermal conductivity under 12GPa pressure are analyzed by comparing with no pressure. Our investigation here provides a physical insight into the modulation and heat transfer mechanism of graphite theoretically, which can help the design of graphite-like materials in experiment and practical application.

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Highly Anisotropic Thermal Transport in LiCoO2

10.26434/chemrxiv.8874404.v2 ◽

2019 ◽

Author(s):

Hui Yang ◽

Jia-Yue Yang ◽

Christopher Savory ◽

Jonathan Skelton ◽

Benjamin Morgan ◽

...

Keyword(s):

Thermal Conductivity ◽

Lithium Ion Batteries ◽

Phonon Dispersion ◽

Lithium Ion ◽

Boltzmann Transport ◽

Heat Management ◽

Positive Electrodes ◽

Anharmonic Lattice ◽

Anharmonic Interactions ◽

The Impact

<div>LiCoO2 is the prototype cathode in lithium ion batteries. It adopts a crystal structure with alternating Li+ and CoO2- layers along the hexagonal <0001> axis. It is well established that ionic and electronic conduction is highly anisotropic; however, little is known regarding heat transport. We analyse the phonon dispersion and lifetimes of LiCoO2 using anharmonic lattice dynamics based on quantum chemical force constants. Around room temperature, the thermal conductivity in the hexagonal ab plane of the layered cathode is ≈ 6 times higher than that along the c axis based on the phonon Boltzmann transport. The low thermal conductivity (< 10Wm-1K-1) originates from a combination of short phonon lifetimes associated with anharmonic interactions between the octahedral face-sharing CoO2- networks, as well as grain boundary scattering. The impact on heat management and thermal processes in lithium ion batteries based on layered positive electrodes is discussed.</div>

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Thermal Properties of Nanotubes and Nanowires With Acoustically Stiffened Surfaces

Volume 4: Energy Systems Analysis, Thermodynamics and Sustainability; Combustion Science and Engineering; Nanoengineering for Energy, Parts A and B ◽

10.1115/imece2011-65365 ◽

2011 ◽

Author(s):

Michael F. P. Bifano ◽

Vikas Prakash

Keyword(s):

Thermal Conductivity ◽

Thermal Properties ◽

Specific Heat ◽

Phonon Dispersion ◽

Thermal Conductance ◽

Frequency Equation ◽

Outer Diameter ◽

Phonon Confinement ◽

Maximum Increase ◽

Acoustic Tuning

A core-shell elasticity model is employed to investigate the effect of a nanowire and nanotube’s increased surface moduli on specific heat, ballistic thermal conductance, and thermal conductivity as a function of temperature. Phonon confinement is analyzed using approximated phonon dispersion relations that result from solutions to the frequency equation of a vibrating rod and tube. The results indicate a maximum 10% decrease in lattice thermal conductivity and ballistic thermal conductance near 160 K for a 10 nm outer diameter nanotube with an inner diameter of 5 nm when the average Young’s Modulus of both the inner and outer free surfaces is increased by a factor of 1.53. In the presence of the acoustically stiffened surfaces, the specific heat of the nanotube is found to decrease by up to 20% at 160 K. Near room temperature, changes in thermal properties are less severe. In contrast, a 10 nm outer diameter nanowire composed of similar material exhibits up to a 12% maximum increase in thermal conductivity at 600 K, a 25% increase in ballistic thermal conductance at 400 K, and a 48% increase in specific heat at 470 K when its outer free surface is acoustically stiffened to the same degree. Our simplified model may be extended to investigate the acoustic tuning of nanowires and nanotubes by inducing surface stiffening or softening via appropriate surface chemical functionalization and coatings.

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Strain engineering of phonon thermal transport properties in monolayer 2H-MoTe2

Physical Chemistry Chemical Physics ◽

10.1039/c7cp06065c ◽

2017 ◽

Vol 19 (47) ◽

pp. 32072-32078 ◽

Cited By ~ 30

Author(s):

Aamir Shafique ◽

Young-Han Shin

Keyword(s):

Thermal Conductivity ◽

First Principles ◽

Lattice Thermal Conductivity ◽

Boltzmann Transport Equation ◽

Strain Engineering ◽

First Principles Calculations ◽

Boltzmann Transport ◽

Phonon Group Velocity ◽

Phonon Lifetime ◽

Phonon Properties

The effect of strain on the phonon properties such as phonon group velocity, phonon anharmonicity, phonon lifetime, and lattice thermal conductivity of monolayer 2H-MoTe2is studied by solving the Boltzmann transport equation based on first principles calculations.

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Highly Anisotropic Thermal Transport in LiCoO2

10.26434/chemrxiv.8874404 ◽

2019 ◽

Author(s):

Hui Yang ◽

Jia-Yue Yang ◽

Christopher Savory ◽

Jonathan Skelton ◽

Benjamin Morgan ◽

...

Keyword(s):

Thermal Conductivity ◽

Lithium Ion Batteries ◽

Phonon Dispersion ◽

Lithium Ion ◽

Boltzmann Transport ◽

Heat Management ◽

Positive Electrodes ◽

Anharmonic Lattice ◽

Anharmonic Interactions ◽

The Impact

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Spectral Detail of Phonon Conduction and Scattering in Graphene

ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, MEMS and NEMS: Volume 1 ◽

10.1115/ipack2011-52243 ◽

2011 ◽

Author(s):

Dhruv Singh ◽

Jayathi Y. Murthy ◽

Timothy S. Fisher

Keyword(s):

Thermal Conductivity ◽

Phonon Scattering ◽

Interatomic Potential ◽

Phonon Dispersion ◽

Transition Probabilities ◽

Transition Probability ◽

Phonon Transport ◽

Temperature Perturbation ◽

Boltzmann Transport ◽

Wide Range

This paper examines the thermodynamic and thermal transport properties of the 2D graphene lattice. The interatomic interactions are modeled using the Tersoff interatomic potential and are used to evaluate phonon dispersion curves, density of states and thermodynamic properties of graphene as functions of temperature. Perturbation theory is applied to calculate the transition probabilities for three-phonon scattering. The matrix elements of the perturbing Hamiltonian are calculated using the anharmonic interatomic force constants obtained from the interatomic potential as well. An algorithm to accurately quantify the contours of energy balance for three-phonon scattering events is presented and applied to calculate the net transition probability from a given phonon mode. Under the linear approximation, the Boltzmann transport equation (BTE) is applied to compute the thermal conductivity of graphene, giving spectral and polarization-resolved information. Predictions of thermal conductivity for a wide range of parameters elucidate the behavior of diffusive phonon transport. The complete spectral detail of selection rules, important phonon scattering pathways, and phonon relaxation times in graphene are provided, contrasting graphene with other materials, along with implications for graphene electronics. We also highlight the specific scattering processes that are important in Raman spectroscopy based measurements of graphene thermal conductivity, and provide a plausible explanation for the observed dependence on laser spot size.

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Thermal Properties for Bulk Silicon Based on the Determination of Relaxation Times Using Molecular Dynamics

Journal of Heat Transfer ◽

10.1115/1.3211853 ◽

2009 ◽

Vol 132 (1) ◽

Cited By ~ 33

Author(s):

Javier V. Goicochea ◽

Marcela Madrid ◽

Cristina Amon

Keyword(s):

Thermal Conductivity ◽

Molecular Dynamics ◽

Thermal Properties ◽

Total Energy ◽

Normal Mode ◽

Relaxation Times ◽

Dispersion Relations ◽

Boltzmann Transport ◽

Mode Decomposition ◽

The Impact

Molecular dynamics simulations are performed to estimate acoustical and optical phonon relaxation times, dispersion relations, group velocities, and specific heat of silicon needed to solve the Boltzmann transport equation (BTE) at 300 K and 1000 K. The relaxation times are calculated from the temporal decay of the autocorrelation function of the fluctuation of total energy of each normal mode in the ⟨100⟩ family of directions, where the total energy of each mode is obtained from the normal mode decomposition of the motion of the silicon atoms over a period of time. Additionally, silicon dispersion relations are directly determined from the equipartition theorem obtained from the normal mode decomposition. The impact of the anharmonic nature of the potential energy function on the thermal expansion of the crystal is determined by computing the lattice parameter at the cited temperatures using a NPT (i.e., constant number of atoms, pressure, and temperature) ensemble, and are compared with experimental values reported in the literature and with those computed analytically using the quasiharmonic approximation. The dependence of the relaxation times with respect to the frequency is identified with two functions that follow the functional form of the relaxation time expressions reported in the literature. From these functions a simplified version of relaxation times for each normal mode is extracted. Properties, such as group and phase velocities, thermal conductivity, and mean free path, needed to further develop a methodology for the thermal analysis of electronic devices (i.e., from nano- to macroscales) are determined once the relaxation times and dispersion relations are obtained. The thermal properties are validated by comparing the BTE-based thermal conductivity against the predictions obtained from the Green–Kubo method. It is found that the relaxation times closely resemble the ones obtained from perturbation theory at high temperatures; the contribution to the thermal conductivity of the transverse acoustic, longitudinal acoustic, and longitudinal optical modes being approximately 30%, 60%, and 10%, respectively, and the contribution of the transverse optical mode negligible.

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THE EFFECT OF SPONTANEOUS AND PIEZOELECTRIC POLARIZATION ON THERMAL CONDUCTIVITY OF InN

International Journal of Modern Physics B ◽

10.1142/s0217979213500318 ◽

2013 ◽

Vol 27 (09) ◽

pp. 1350031 ◽

Cited By ~ 3

Author(s):

BIJAYA KUMAR SAHOO ◽

SUSANT KUMAR SAHOO ◽

SUKDEV SAHOO

Keyword(s):

Thermal Conductivity ◽

Thermal Properties ◽

Group Velocity ◽

Room Temperature ◽

Phonon Scattering ◽

Polarization Property ◽

Optical And Electrical Properties ◽

High Quality ◽

Phonon Group Velocity ◽

Debye Frequency

The spontaneous (SP) and piezoelectric (PZ) polarization present in the wurtzite III nitrides influence the optical and electrical properties of these materials. The effects of SP and PZ polarization on thermal properties of III nitrides have yet to be investigated. Here we have investigated the SP and PZ effects on thermal conductivity of InN . Inclusion of polarization property modifies the group velocity of phonons. The combined phonon scattering rates and thermal conductivity k of InN are calculated using modified phonon group velocity, Debye frequency and Debye temperature. Without SP and PZ polarization, the room temperature thermal conductivity of InN is found to be 132.55 W/m.K. Inclusion of SP and PZ polarization property enhances the room temperature thermal conductivity from 132.55 to 134.32 W/m.K. Our predicted thermal conductivity values are closer to the recent experimental value 120 W/m.K measured by Levander et al. for a high quality irradiated InN films at room temperature.

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Heat Conduction of a Porous Material

Journal of Heat Transfer ◽

10.1115/1.4005709 ◽

2012 ◽

Vol 134 (5) ◽

Cited By ~ 7

Author(s):

Koji Miyazaki ◽

Saburo Tanaka ◽

Daisuke Nagai

Keyword(s):

Thermal Conductivity ◽

Heat Conduction ◽

Porous Material ◽

Boundary Conditions ◽

Periodic Boundary ◽

Phonon Dispersion ◽

Bulk Material ◽

Periodic Boundary Conditions ◽

Boltzmann Transport ◽

Time Space

In this study, we introduce our numerical and experimental works for the thermal conductivity reduction by using a porous material. Recently thermal conductivity reduction has been one of the key technologies to enhance the figure of merit (ZT) of a thermoelectric material. We carry out numerical calculations of heat conduction in porous materials, such as phonon Boltzmann transport (BTE) and molecular dynamics (MD) simulations, in order to investigate the mechanism of the thermal conductivity reduction of a porous material. In the BTE, we applied the periodic boundary conditions with constant heat flux to calculate the effective thermal conductivity of porous materials.In the MD simulation, we calculated the phonon properties of Si by using the Stillinger–Weber potential at constant temperature with periodic boundary conditions in the x, y, and z directions. Phonon dispersion curves of single crystal of Si calculated from MD results by time-space 2D FFT are agreed well with reference data. Moreover, the effects of nanoporous structures on both the phonon group velocity and the phonon density of states (DOS) are discussed. At last, we made a porous p-type Bi2Te3 by nanoparticles prepared by a beads milling method. The thermal conductivity is one-fifth of that of a bulk material as well as keeping the same Seebeck coefficient as the bulk value. However, electrical conductivity was much reduced, and the ZT was only 0.048.

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Lattice Dynamics Study of Anisotropic Heat Conduction in Superlattices

MRS Proceedings ◽

10.1557/proc-626-z8.3 ◽

2000 ◽

Vol 626 ◽

Author(s):

B. Yang ◽

G. Chen

Keyword(s):

Thermal Conductivity ◽

Group Velocity ◽

Lattice Dynamics ◽

Phonon Scattering ◽

Diffuse Interface ◽

Phonon Confinement ◽

Dynamics Model ◽

Phonon Group Velocity ◽

Anisotropic Heat Conduction ◽

The Cross

ABSTRACTPast studies on the thermal conductivity suggest that phonon confinement and the associated group velocity reduction are the causes of the observed drop in the cross-plane thermal conductivity of semiconductor superlattices. In this work, we investigate the contribution of phonon confinement to the in-plane thermal conductivity of superlattices and the anisotropic effects of phonon confinement on the thermal conductivity in different directions, using a lattice dynamics model. We find that the reduced phonon group velocity due to phonon confinement may account for the dramatic reduction in the cross-plane thermal conductivity, but the in-plane thermal conductivity drop, caused by the reduced group velocity, is much less than the reported experimental results. This suggests that the reduced relaxation time due to diffuse interface phonon scattering, dislocation scattering, etc, should make major contribution to the in-plane thermal conductivity reduction.

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Effect of Phonon Dispersion on Transport Properties of Single-Crystalline Dielectrics

Electronic and Photonic Packaging, Electrical Systems Design and Photonics, and Nanotechnology ◽

10.1115/imece2004-62244 ◽

2004 ◽

Cited By ~ 3

Author(s):

Mehdi Asheghi ◽

Wenjun Liu ◽

K. E. Goodson

Keyword(s):

Thermal Conductivity ◽

Phonon Dispersion ◽

Additional Insight ◽

Transverse Modes ◽

Scattering Rate ◽

Magnitude Variation ◽

Silicon And Germanium ◽

Conductivity Modeling ◽

Insight Into ◽

Mass Fluctuation

Thermal conductivity modeling using the Debye approximation can significantly reduce the complexity involved in the evaluation of thermal conductivity integral. Nevertheless, there are several compelling reasons (e.g., inconsistency between the estimations of the density of states used for heat capacity and thermal conductivity) that motivate more detailed modeling of the phonon dispersion in silicon or other diamond-like dielectrics. This manuscript presents closed-form expressions for the dispersion of the longitudinal and transverse modes in diamond-like dielectrics, which are then used to estimate the isotopic scattering rate, phonon spectrum and specific heat. The combinations of the above parameters are then used to predict the thermal conductivity of the bulk silicon and germanium with orders of magnitude variation in the mass fluctuation of isotopes and for the temperature range 2 to 1000 K. While this approach offers an elegant and consistent account of the phonon dispersion in diamond-like materials, however, provides no additional insight into the relative contributions of the longitudinal and transverse phonons to the heat transport.

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