scholarly journals Phonon localization in heat conduction

2018 ◽  
Vol 4 (12) ◽  
pp. eaat9460 ◽  
Author(s):  
M. N. Luckyanova ◽  
J. Mendoza ◽  
H. Lu ◽  
B. Song ◽  
S. Huang ◽  
...  
Keyword(s):  
Heat Conduction ◽  
Thermal Transport ◽  
Room Temperature ◽  
Diffusive Transport ◽  
Wave Localization ◽  
Wave Nature ◽  
Phonon Localization ◽  
Localization Behavior ◽  
Classical Size ◽  
Thermal Conductivities

Nondiffusive phonon thermal transport, extensively observed in nanostructures, has largely been attributed to classical size effects, ignoring the wave nature of phonons. We report localization behavior in phonon heat conduction due to multiple scattering and interference events of broadband phonons, by measuring the thermal conductivities of GaAs/AlAs superlattices with ErAs nanodots randomly distributed at the interfaces. With an increasing number of superlattice periods, the measured thermal conductivities near room temperature increased and eventually saturated, indicating a transition from ballistic to diffusive transport. In contrast, at cryogenic temperatures the thermal conductivities first increased but then decreased, signaling phonon wave localization, as supported by atomistic Greenșs function simulations. The discovery of phonon localization suggests a new path forward for engineering phonon thermal transport.

Electrohydrodynamic Flow in Thick Liquid Crystal Cells

1989 ◽  
Vol 177 ◽  
Author(s):  
David H. Van Winkle ◽  
Jit Gurung ◽  
Rand Biggers
Keyword(s):  
Thermal Conductivity ◽  
Liquid Crystal ◽  
Thermal Transport ◽  
Room Temperature ◽  
Liquid Crystal Cell ◽  
Optical Observations ◽  
Constant Voltage ◽  
Maximum Enhancement ◽  
Flowing Liquid ◽  
Crystal Cells

ABSTRACTThe thermal transport across a thick (0.66 cm) liquid crystal cell has been measured versus applied ac voltage and frequency. These measurements are correlated with the optically observed onset of flow and turbulence in cells as identical as practicable to those used for the thermal transport measurements. In addition, the measurements are compared with reported observations in thin cells. The thermal transport across the liquid crystal is characterized by an effective thermal conductivity Kf. It was found that Kf increases with increasing frequency, at constant voltage, to a maximum enhancement at about 40 Hz at room temperature. Optical observations on thick cells indicate that dynamic columnar domains of flowing liquid crystal are the primary mode of heat transport, as determined by correlating the structure and characteristic lifetime of such domains as a function of voltage and frequency. Optical observations at low voltages suggest that Williams Domains do not exist in these thick cells, and that all observed responses are functions of electric field strength, not applied voltage (as in thin Williams Domain cells).

scholarly journals Substitution Versus Full-Heusler Segregation in TiCoSb

Metals ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 935 ◽  
Author(s):  
Maryana Asaad ◽  
Jim Buckman ◽  
Jan-Willem Bos
Keyword(s):  
Powder Metallurgy ◽  
Power Factor ◽  
Thermoelectric Materials ◽  
Room Temperature ◽  
The Difference ◽  
P Type ◽  
Full Heusler ◽  
Thermal Conductivities

Half-Heuslers (HHs) are promising thermoelectric materials with great compositional flexibility. Here, we extend work on the p-type doping of TiCoSb using abundant elements. Ti0.7V0.3Co0.85Fe0.15Sb0.7Sn0.3 samples with nominal 17.85 p-type electron count were investigated. Samples prepared using powder metallurgy have negative Seebeck values, S ≤ −120 µV K−1, while arc-melted compositions are compensated semiconductors with S = −45 to +30 µV K−1. The difference in thermoelectric response is caused by variations in the degree of segregation of V(Co0.6Fe0.4)2Sn full-Heusler and Sn phases, which selectively absorb V, Fe, and Sn. The segregated microstructure leads to reduced lattice thermal conductivities, κlat = 4.5−7 W m−1 K−1 near room temperature. The largest power factor, S2/ρ = 0.4 mW m−1 K−2 and ZT = 0.06, is observed for the n-type samples at 800 K. This works extends knowledge regarding suitable p-type dopants for TiCoSb.

Elastic properties and phonon conductivities of Ti3Al(C0.5,N0.5)2 and Ti2Al(C0.5,N0.5) solid solutions

2008 ◽  
Vol 23 (6) ◽  
pp. 1517-1521 ◽  
Author(s):  
M. Radovic ◽  
A. Ganguly ◽  
M.W. Barsoum
Keyword(s):  
Elastic Properties ◽  
Solid Solutions ◽  
Room Temperature ◽  
Elastic Moduli ◽  
Unit Cell ◽  
Young’S Moduli ◽  
Temperature Shear ◽  
End Members ◽  
Cell Volumes ◽  
Thermal Conductivities

Herein we compare the lattice parameters, room temperature shear and Young’s moduli, and phonon thermal conductivities of Ti2AlC0.5N0.5 and Ti3Al(C0.5, N0.5)2 solid solutions with those of their end members, namely Ti2AlC, Ti2AlN, Ti3AlC2, and Ti4AlN2.9. In general, the replacement of C by N decreases the unit cell volumes and increases the elastic moduli and phonon thermal conductivities. The increase in the latter two properties, however, is sensitive to the concentrations of defects, most likely vacancies on one or more of the sublattices.

Built-in-polarization field effect on intrinsic and extrinsic thermal conductivities of AlN/GaN/AlN quantum well

2015 ◽  
Vol 29 (21) ◽  
pp. 1550149 ◽  
Author(s):  
A. Pansari ◽  
V. Gedam ◽  
B. K. Sahoo
Keyword(s):  
Thermal Conductivity ◽  
Relaxation Time ◽  
Quantum Well ◽  
Room Temperature ◽  
Mean Free Path ◽  
Polarization Field ◽  
Polarization Mechanism ◽  
Negative Effect ◽  
Phonon Velocity ◽  
Thermal Conductivities

In this paper, the effect of built-in-polarization field on lattice thermal conductivity of AlN/GaN/AlN quantum well (QW) has been theoretically investigated. The built-in-polarization field at the hetero-interface of GaN/AlN modifies elastic constant, phonon velocity and Debye temperature of GaN QW. The relaxation time of acoustic phonons (AP) in various scattering processes in GaN with and without built-in-polarization field has been computed at room temperature. The result shows that combined relaxation time of AP is enhanced by built-in-polarization field and implies a longer mean free path. The revised intrinsic and extrinsic thermal conductivities of GaN have been estimated. The theoretical analysis shows that up to a certain temperature the polarization field acts as negative effect and reduces the thermal conductivities. However, after this temperature both thermal conductivities are significantly contributed by polarization field. This gives the idea of temperature dependence of polarization effect which signifies the pyro-electric character of GaN. The intrinsic thermal conductivity at room temperature for with and without polarization mechanism is found to be 491 Wm -1 K -1 and 409 Wm -1 K -1, respectively i.e., 20% enhancement. However, the extrinsic thermal conductivity at room temperature for with and without polarization mechanism is found to be 280 Wm -1 K -1 and 245 Wm -1 K -1, respectively i.e., 13% enhancement. The method we have developed may be taken into account during the simulation of heat transport in optoelectronic nitride devices to minimize the self-heating processes and in polarization engineering strategies to optimize the thermoelectric performance of GaN alloys.

scholarly journals Computational Study of In-Plane Phonon Transport in Si Thin Films

2014 ◽  
Vol 4 (1) ◽  
Author(s):  
Xinjiang Wang ◽  
Baoling Huang
Keyword(s):  
Thin Films ◽  
Thermal Transport ◽  
Computational Study ◽  
Isotope Effects ◽  
Phonon Transport ◽  
Phonon Confinement ◽  
Phonon Modes ◽  
Scattering Rate ◽  
Si Films ◽  
Thermal Conductivities

Abstract We have systematically investigated the in-plane thermal transport in Si thin films using an approach based on the first-principles calculations and lattice dynamics. The effects of phonon mode depletion induced by the phonon confinement and the corresponding variation in interphonon scattering, which may be important for the thermal conductivities of ultra-thin films but are often neglected in precedent studies, are considered in this study. The in-plane thermal conductivities of Si thin films with different thicknesses have been predicted over a temperature range from 80 K to 800 K and excellent agreements with experimental results are found. The validities of adopting the bulk phonon properties and gray approximation of surface specularity in thin film studies have been clarified. It is found that in ultra-thin films, while the phonon depletion will reduce the thermal conductivity of Si thin films, its effect is largely offset by the reduction in the interphonon scattering rate. The contributions of different phonon modes to the thermal transport and isotope effects in Si films with different thicknesses under various temperatures are also analyzed.

A Predicting Method for Thermal Conductivity of Functional Carbide Crystals and Ceramic Materials

2007 ◽  
Vol 280-283 ◽  
pp. 1175-1178
Author(s):  
Qing Ren Wu ◽  
Xiao Ping Wang ◽  
Hua Qing Xie ◽  
Tonggeng Xi
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Relative Error ◽  
Ceramic Materials ◽  
Prediction Equation ◽  
Atomic Mass ◽  
New Method ◽  
Relative Atomic Mass ◽  
Thermal Conductivities

A new method for predicting the thermal conductivity of functional carbide crystals and ceramics materials is proposed. The effect of average relative atomic mass and density on thermal conductivities of carbide function crystals and ceramics is considered in the method. Correlations are developed for thermal conductivity with average relative atomic mass and density according to the microscope theories of heat conduction. The thermal conductivities calculated from the prediction equation for many functional carbide crystals and ceramics were compared with the measured dada and found to be agreement. It is show that, for the most of functional carbide crystals and ceramics materials, the relative error between the predicting values and the measuring data is ± 20%. It is discovered in further analysis that the larger the average relative atomic mass and density are, the more accurately the thermal conductivities predict.

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