Lattice Dynamics Study of Anisotropic Heat Conduction in Superlattices

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.

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

2013 ◽  
Vol 27 (09) ◽  
pp. 1350031 ◽  
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.

Umklapp collisions and thermal conductivity

2021 ◽  
pp. 309-321
Author(s):  
Geoffrey Brooker
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Heat Flow ◽  
Group Velocity ◽  
Thermodynamic Equilibrium ◽  
Reciprocal Lattice ◽  
Reciprocal Lattice Vector ◽  
Momentum Balance ◽  
Lattice Vector ◽  
Phonon Group Velocity

“Umklapp collisions and thermal conductivity” deals with heat conduction in a dielectric solid. Collisions of phonons are divided into Umklapp and normal according as a reciprocal lattice vector is or is not involved in the phonon momentum balance. A local temperature is defined by appeal to local thermodynamic equilibrium. An equilibrium phonon distribution can be off-centred, yet non-decaying, if the only collisions are “normal”, conserving the total phonon momentum. Then heat flow does not decay, even if a representative collision reverses the phonon group velocity. Conversely, in an Umklapp collision it is the non-conservation of phonon momentum that causes heat flow to decay.

Effect of Parameters on Lattice Thermal Conductivity in Germanium Nanowires

2013 ◽  
Vol 832 ◽  
pp. 33-38 ◽  
Author(s):  
S.M. Mamand ◽  
M.S. Omar
Keyword(s):  
Thermal Conductivity ◽  
Low Temperatures ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Intrinsic Properties ◽  
Phonon Confinement ◽  
Germanium Nanowires ◽  
Transverse Modes ◽  
Experimental Values ◽  
Electron Phonon Scattering

Modified Callaway's theory was used to calculate lattice thermal conductivity (LTC) of Germanium nanowires. Results are compared to those of experimental values of the temperature dependence of LTC for nanowire diameters of 62, 19, and 15nm. In this calculation, both longitudinal and transverse modes are taken into account. Scattering of phonons is assumed to be by nanowire boundaries, imperfections, dislocations, electrons, and other phonons via both normal and Umklapp processes. Effect of parameters, phonon confinement and imperfections in limiting thermal conductivity for the nanowires under considerations are investigated. The suppression in thermal conductivity of these nanowires is arise from electron-phonon scattering and phonon-boundary scattering at low temperatures, while at high temperatures is due to imperfections and intrinsic properties.

Modeling of Strain-Induced Phonon Thermal Conductivity Reduction in Thermoelectric Nanocomposites

2008 ◽  
Author(s):  
Yaoyao Xu ◽  
Gang Li
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Lattice Dynamics ◽  
Tensile Strain ◽  
Phonon Scattering ◽  
Mean Free Path ◽  
Nanocomposite Material ◽  
Phonon Thermal Conductivity ◽  
Strain Effects ◽  
Strain Dependent

In this paper, we study strain effects on the phonon thermal conductivity of 2-D Si/Ge nanocomposites. Lattice dynamics is employed for the calculation of the phonon scattering properties as a function of strain. Cauchy-Born rule is used to model the deformed configuration of the atoms. The effective thermal conductivity of the nanocomposite material is modeled by using a modified effective medium approximation (EMA) approach. The strain effects are incorporated into the modified EMA through the strain dependent phonon mean free path. The effective thermal conductivity of the strained nanocomposite material is calculated for different characteristic lengths of the Si component. The results show that a 2% tensile strain can reduce the effective thermal conductivity by more than 10%.

The Effects of Material Composition on the Thermal Conductivity of Zeolite MFI

2007 ◽  
Author(s):  
Abraham M. Greenstein ◽  
Yeny C. Hudiono ◽  
Samuel Graham ◽  
Sankar Nair
Keyword(s):  
Thermal Conductivity ◽  
Relaxation Time ◽  
Pore Structure ◽  
Point Defect ◽  
Lattice Dynamics ◽  
Phonon Scattering ◽  
Material Composition ◽  
Boundary Scattering ◽  
Upper Limit ◽  
Effective Suppression

The thermal conductivity of zeolite MFI is modeled for different silicon/aluminum ratios using lattice dynamics and relaxation time theory. The model uses the actual phonon dispersions, Slack’s model for phonon-phonon scattering, a slightly modified form of Klemens’s model for point defect scattering, and a boundary scattering term. Our results strongly suggest that the upper limit of thermal conductivity is defined by boundary-like scattering associated with the pore structure of the material. Below this limit, silicon substitution with aluminum allows effective suppression of the thermal conductivity by point defect scattering and phonon slowing mechanisms.

Thermal Resistance of Silicon/Germanium Interfaces From Lattice Dynamics Calculations

2009 ◽  
Author(s):  
E. S. Landry ◽  
A. J. H. McGaughey
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Energy Conversion ◽  
Silicon Germanium ◽  
Lattice Dynamics ◽  
Phonon Scattering ◽  
Semiconductor Interfaces ◽  
Thermoelectric Energy ◽  
Interface Scattering ◽  
Computer Chips

Phonon scattering at the interface between two materials results in a thermal resistance, R [1]. An ability to accurately predict the thermal resistance of semiconductor interfaces is important in devices where phonon interface scattering is a significant contributor to the overall thermal resistance (e.g., computer chips with high component density). This ability will also lead to improvements in the design of semiconductor superlattices with low thermal conductivity, desirable in thermoelectric energy conversion applications [2].

MeV Si Ions Bombardment Effects on the Thermoelectric Properties of Si/Si+Ge Multi-Layer Superlttice Nanolayered Films

2010 ◽  
Vol 1267 ◽  
Author(s):  
Marcus Pugh ◽  
S. Budak ◽  
Cydale Smith ◽  
John Chacha ◽  
Kudus Ogbara ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Electrical Conductivity ◽  
Seebeck Coefficient ◽  
Thermoelectric Materials ◽  
Phonon Scattering ◽  
Ion Beam ◽  
Absolute Temperature ◽  
Inelastic Interaction ◽  
Before And After ◽  
The Cross

AbstractEffective thermoelectric materials have a low thermal conductivity and a high electrical conductivity. The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT = S2σT/K, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature and K is the thermal conductivity. ZT can be increased by increasing S, increasing σ or decreasing K. MeV ion bombardment caused defects and disorder in the film and the grain boundaries of these nano-scale clusters increase phonon scattering and increase the chance of an inelastic interaction and phonon annihilation. We have prepared 100 alternating layers of Si/Si+Ge nanolayered superlattice films using the ion beam assisted deposition (IBAD). The 5 MeV Si ions bombardments have been performed using the AAMU Pelletron ion beam accelerator to make quantum clusters in the nanolayered superlattice films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. We have characterized the thermoelectric thin films before and after Si ion bombardments as we measured the cross-plane Seebeck coefficient, the cross-plane electrical conductivity, and the cross-plane thermal conductivity for different fluences

Molecular Dynamics Simulations of Thermal Conductivity of Bi2Te3 Nanowires

2009 ◽  
Author(s):  
Bo Qiu ◽  
Lin Sun ◽  
Xiulin Ruan
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Surface Roughness ◽  
Smooth Surface ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Md Simulations ◽  
Interatomic Potentials ◽  
Phonon Confinement ◽  
Dynamics Simulations

In this paper, by employing the previously developed two-body interatomic potentials for bismuth telluride, molecular dynamics (MD) simulations are used to describe the thermoelectric properties, namely the lattice thermal conductivity, of Bi2Te3 nanowires. Cylindrical nanowires with both smooth surface and sawtooth surface roughness are studied, aiming at revealing the effects of phonon confinement in 1-D structures, phonon boundary scatterings and surface roughness on the lattice thermal conductivity of Bi2Te3 nanowires. In the end, the influence of various phonon scattering mechanisms on the nanostructures under study are summarized, possible paths to reduce lattice thermal conductivity in nanostructured Bi2Te3, which is favorable for enhancing thermoelectric performance, are pointed out.

Thermal conductivity of chalcogenide glass phases governed by disparity in phonon group velocity

Scilight ◽  
2019 ◽  
Vol 2019 (28) ◽  
pp. 280002
Author(s):  
Phil Dooley
Keyword(s):  
Thermal Conductivity ◽  
Group Velocity ◽  
Chalcogenide Glass ◽  
Phonon Group Velocity
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