Phonon Conductivity ofMg 2
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Abstract:
The two-mode conduction of thermal energy as proposed by Holland has been used to explain the temperature dependence of the phonon conductivity of ${\mathrm{Mg}}_{2}$Sn in the temperature range 4-300\ifmmode^\circ\else\textdegree\fi{}K, especially the change in slope at about 80\ifmmode^\circ\else\textdegree\fi{}K. The elastic part of Kwok's expression for the resonance-scattering relaxation rate for phonons is shown to account for the magnitude near the conductivity maximum. The present work also shows that practically all the transport of thermal energy is due to transverse phonon.Keywords:
Atmospheric temperature range
We report on the Raman analysis of the phonon lifetimes of the A1(LO) (longitudinal optical) and E2(high) phonons in bulk AlN crystals and their temperature dependence from 10 to 1275 K. Our experimental results show that amongst the various possible decay channels, the A1(LO) phonons decay primarily into two phonons of equal energy (Klemens model), most likely longitudinal-acoustic phonons, whereas the E2(high) phonon decays asymmetrically into a high-energy and a low-energy phonon. Possible decay channels of the E2(high) phonon have been shown to include combinations of E2(low) and acoustic phonons. Phonon lifetimes of the A1(LO) phonon and the E2(high) phonon of 0.75 and 2.9 ps, respectively, were measured at 10 K.
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Vibrational relaxation times in pure oxygen have been measured over the temperature range 100°–200°C. An anomalously rapid decrease in the relaxation time is observed for temperatures above 150°C, confirming earlier conclusions based on a comparison of theory and experiment [J. G. Parker, J. Chem. Phys. 41, 1600–1609 (1964)]. This decrease in the vibrational relaxation time may be interpreted as a transition in oxygen from a low-temperature state to a high-temperature state, although the exact nature of the physical mechanism underlying this transition remains obscure.
Vibrational energy relaxation
Atmospheric temperature range
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Atmospheric temperature range
Cole–Cole equation
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Abstract : Contents: Phonons in Mixed Valence Compounds; Phonons in Amorphous and Disordered Systems, Phonon-Phonon Interactions and Non-Linear Lattice Dynamics, Phonons in Superionic Conductors, Phonon Imaging and Phonon Focusing, Phonon Transport, Phonons in Low Dimensional Matter, Phonons in Metals, Phonons in Ferroelectrics, Interaction of Phonons with Other Excitations, General Theoretical Methods of Phonon Physics, Phonons in Molecular and Organic Substances, Phonons in Semiconductors, The Role of Phonons in Phase Transitions, Phonons at Surfaces and Interfaces, Phonon Echoes, and Phonon in Insulators.
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The graded thermal conductivity in nanoscale “hot spot” system is a new phenomenon in nanoscale heat conduction. It is found that the thermal conductivity is no longer uniform, and the thermal conductivity gradually increases from the inside to the outside in the radial direction, which no longer obeys Fourier’s law of thermal conductivity. An in-depth understanding of the mechanism of the graded thermal conductivity can provide a theoretical basis for solving engineering problems such as heat dissipation of nanochip. This paper first reviews the new phenomenon of heat conduction recently discovered in nanosystem, then, focuses on the graded thermal conductivity in the “hot spot” system, and expounds the variation law of the graded thermal conductivity in different dimensional systems. According to the changes of atomic vibration mode and phonon scattering, the physical mechanism of the graded thermal conductivity is explained. Finally, the new challenges and opportunities brought by the graded thermal conductivity characteristics of nano “hot spot” to the heat dissipation of nanodevices are summarized, and the future research in this direction is also prospected.
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Phonon scattering
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Thermal conductivity measurement
Thermal effusivity
Volumetric heat capacity
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Anisotropic solids possess thermal conductivities ranging from among the highest found in nature, as in the in-plane thermal conductivity of graphite, to the lowest, as in the cross-plane thermal conductivity of disordered layered crystals. Though these extremes of thermal conductivity make anisotropic materials attractive for diverse applications such as thermal management and thermal insulation, the microscopic physics of heat conduction in these materials remain poorly understood. In this review article, we discuss the recent advances in our understanding of thermal phonon transport in anisotropic solids obtained using new theoretical, computational, and experimental tools.
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