scholarly journals First Principles Investigation of Anomalous Pressure-Dependent Thermal Conductivity of Chalcopyrites

Materials ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 3491
Author(s):  
Loay Elalfy ◽  
Denis Music ◽  
Ming Hu
Keyword(s):  
Thermal Conductivity ◽  
Phonon Dispersion ◽  
Negative Thermal Expansion ◽  
Building Blocks ◽  
Boltzmann Transport ◽  
Energy Devices ◽  
Acoustic Modes ◽  
Group I ◽  
Dispersion Data ◽  
Phonon Relaxation Time

The effect of compression on the thermal conductivity of CuGaS2, CuInS2, CuInTe2, and AgInTe2 chalcopyrites (space group I-42d) was studied at 300 K using phonon Boltzmann transport equation (BTE) calculations. The thermal conductivity was evaluated by solving the BTE with harmonic and third-order interatomic force constants. The thermal conductivity of CuGaS2 increases with pressure, which is a common behavior. Striking differences occur for the other three compounds. CuInTe2 and AgInTe2 exhibit a drop in the thermal conductivity upon increasing pressure, which is anomalous. AgInTe2 reaches a very low thermal conductivity of 0.2 W·m−1·K−1 at 2.6 GPa, being beneficial for many energy devices, such as thermoelectrics. CuInS2 is an intermediate case. Based on the phonon dispersion data, the phonon frequencies of the acoustic modes for CuInTe2 and AgInTe2 decrease with increasing pressure, thereby driving the anomaly, while there is no significant pressure effect for CuGaS2. This leads to the negative Grüneisen parameter for CuInTe2 and AgInTe2, a decreased phonon relaxation time, and a decreased thermal conductivity. This softening of the acoustic modes upon compression is suggested to be due to a rotational motion of the chalcopyrite building blocks rather than a compressive oscillation. The negative Grüneisen parameters and the anomalous phonon behavior yield a negative thermal expansion coefficient at lower temperatures, based on the Grüneisen vibrational theory.

scholarly journals Highly Anisotropic Thermal Transport in LiCoO2

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>LiCoO<sub>2</sub> is the prototype cathode in lithium ion batteries. It adopts a crystal structure with alternating Li<sup>+</sup> and CoO<sub>2</sub><sup>-</sup> 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 LiCoO<sub>2</sub> 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<sup>-1</sup>K<sup>-1</sup>) originates from a combination of short phonon lifetimes associated with anharmonic interactions between the octahedral face-sharing CoO<sub>2</sub><sup>-</sup> 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>

scholarly journals Highly Anisotropic Thermal Transport in LiCoO2

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>LiCoO<sub>2</sub> is the prototype cathode in lithium ion batteries. It adopts a crystal structure with alternating Li<sup>+</sup> and CoO<sub>2</sub><sup>-</sup> 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 LiCoO<sub>2</sub> 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<sup>-1</sup>K<sup>-1</sup>) originates from a combination of short phonon lifetimes associated with anharmonic interactions between the octahedral face-sharing CoO<sub>2</sub><sup>-</sup> 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>

Spectral Detail of Phonon Conduction and Scattering in Graphene

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.

Heat Conduction of a Porous Material

2012 ◽  
Vol 134 (5) ◽  
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.

scholarly journals Thermoelectric Properties of Hexagonal M2C3 (M = As, Sb, and Bi) Monolayers from First-Principles Calculations

Nanomaterials ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 597 ◽  
Author(s):  
Xue-Liang Zhu ◽  
Peng-Fei Liu ◽  
Guofeng Xie ◽  
Wu-Xing Zhou ◽  
Bao-Tian Wang ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Density Functional ◽  
Optical Absorption Coefficient ◽  
Boltzmann Transport ◽  
Low Thermal Conductivity ◽  
Phonon Group Velocity ◽  
Optical Modes ◽  
Potential Applications ◽  
High Seebeck Coefficient ◽  
Phonon Relaxation Time

Hexagonal M2C3 compound is a new predicted functional material with desirable band gaps, a large optical absorption coefficient, and ultrahigh carrier mobility, implying its potential applications in photoelectricity and thermoelectric (TE) devices. Based on density-functional theory and Boltzmann transport equation, we systematically research the TE properties of M2C3. Results indicate that the Bi2C3 possesses low phonon group velocity (~2.07 km/s), low optical modes (~2.12 THz), large Grüneisen parameters (~4.46), and short phonon relaxation time. Based on these intrinsic properties, heat transport ability will be immensely restrained and therefore lead to a low thermal conductivity (~4.31 W/mK) for the Bi2C3 at 300 K. A twofold degeneracy is observed at conduction bands along Γ-M direction, which gives a high n-type electrical conductivity. Its low thermal conductivity and high Seebeck coefficient lead to an excellent TE response. The maximum thermoelectric figure of merit (ZT) of n-type can approach 1.41 for Bi2C3. This work shows a perspective for applications of TE and stimulate further experimental synthesis.

scholarly journals Effect of Phonon Dispersion on Thermal Conduction Across Si/Ge Interfaces

2009 ◽  
Author(s):  
Dhruv Singh ◽  
Jayathi Y. Murthy ◽  
Timothy S. Fisher
Keyword(s):  
Thermal Conductivity ◽  
Volume Fraction ◽  
Phonon Dispersion ◽  
Boltzmann Transport ◽  
Host Materials ◽  
Wide Range ◽  
Heterogeneous Interfaces ◽  
Silicon And Germanium ◽  
First Time ◽  
Superlattice Period

We report finite volume simulations of the phonon Boltzmann transport equation (BTE) for heat conduction across the heterogeneous interfaces in SiGe superlattices. We employ the diffuse mismatch model with full details of phonon dispersion and polarization. Simulations are performed over a wide range of Knudsen numbers. Similar to previous studies we establish that thermal conductivity of a superlattice is much lower than the host materials for superlattice period in the submicron regime. Details of the non-equilibrium between optical and acoustic phonons that emerge due to the mismatch of phonon spectrum in silicon and germanium are delineated for the first time. Conditions are identified for which this can lead to a significant additional thermal resistance than that attributed primarily to boundary scattering of phonons. We report results for thermal conductivity for various volume fraction and superlattice periods.

Role of Phonon Dispersion in Lattice Thermal Conductivity Modeling

2004 ◽  
Vol 126 (3) ◽  
pp. 376-380 ◽  
Author(s):  
J. D. Chung ◽  
A. J. H. McGaughey ◽  
M. Kaviany
Keyword(s):  
Thermal Conductivity ◽  
Relaxation Time ◽  
Lattice Thermal Conductivity ◽  
Phonon Dispersion ◽  
Phonon Relaxation Time ◽  
Dynamics Simulations ◽  
Transfer Mechanisms ◽  
Conductivity Modeling ◽  
Fitting Parameters

The role of phonon dispersion in the prediction of the thermal conductivity of germanium between temperatures of 2 K and 1000 K is investigated using the Holland approach. If no dispersion is assumed, a large, nonphysical discontinuity is found in the transverse phonon relaxation time over the entire temperature range. However, this effect is masked in the final prediction of the thermal conductivity by the use of fitting parameters. As the treatment of the dispersion is refined, the magnitude of the discontinuity is reduced. At the same time, discrepancies between the high temperature predictions and experimental data become apparent, indicating that the assumed heat transfer mechanisms (i.e., the relaxation time models) are not sufficient to account for the expected thermal transport. Molecular dynamics simulations may be the most suitable tool available for addressing this issue.

Study of thermoelectric properties of InGaN/GaN superlattice

2011 ◽  
Vol 1329 ◽  
Author(s):  
Hung-Hsun Huang ◽  
Yuh-Renn Wu
Keyword(s):  
Thermal Conductivity ◽  
Electrical Properties ◽  
Figure Of Merit ◽  
Phonon Dispersion ◽  
Boltzmann Transport ◽  
Superlattice Structure ◽  
Operation Temperature ◽  
Relaxation Time Approximation ◽  
Thermal And Electrical Properties ◽  
Callaway Model

ABSTRACTAs many reports show that the superlattice structure could greatly enhance the figure of merit ZT value for the thermoelectric application. We studied the thermal and electrical properties of the InGaN/GaN superlattice structure, and further analyze the thermoelectric features with different superlattice period, doping concentration, and operation temperature. The elastic continuum model and Callaway model have been applied to calculate the phonon dispersion relation and the thermal conductivity, respectively. The electrical properties are obtained by the Boltzmann transport equation with the relaxation time approximation. Simulation results indicate that both the reduced thermal conductivity and enhanced power factor would have the contribution to the enhancement of the figure of merit ZT.

Comparison of Scattering Rates and Thermal Conductivity in Diamond Using Dispersion Curve Data

2005 ◽  
Author(s):  
Todd Kalisik ◽  
Pradip Majumdar ◽  
John Shafer
Keyword(s):  
Thin Films ◽  
Thermal Conductivity ◽  
Phonon Scattering ◽  
Vibrational Energy ◽  
Phonon Dispersion ◽  
Symmetry Direction ◽  
Curve Fit ◽  
Polynomial Curve ◽  
Dispersion Data ◽  
Scattering Rates

The understanding of the mechanism of thermal energy transfer in thin films ranging in thicknesses from micro-scale to nano-scale is becoming very important. Thin films must be modeled at the atomic level and this entails treating the heat transfer as vibrations in a crystal lattice. The concept of phonons can be used to model the vibrational energy of the crystal. Phonon scattering rates and thermal conductivity are investigated for Cubic C (diamond). Boundary scattering, Umklapp processes, and Normal processes are the mechanisms considered for heat flow resistance. The normal processes are included due to there indirect effect on resistance (through phonon redistribution). Three symmetry directions [001], [110], [111], and three polarizations for each direction in the first Brillouin zone are considered. The main purpose of the paper is to study the effect of the curvature of the phonon dispersion curves when computing the phonon scattering rates and thermal conductivity. A comparison of thermal conductivity for each polarization and symmetry direction is made between a continuum model, a linear curve fit and a polynomial curve fit of dispersion data. A comparison is also made between the scattering rates for each polarization, symmetry direction as well as the group velocity for each.

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