Phonon scattering

The third term in Eq. 7, K, is the contribution to the basal plane thermal resistance due to defect scattering. Neutron irradiation causes various types of defects to be produced depending on the irradiation temperature. These defects are very effective in scattering phonons, even at flux levels which would be considered modest for most nuclear applications, and quickly dominate the other terms in Eq. 7. Several types of in-adiation-induced defects have been identified in graphite. For irradiation temperatures lower than 650°C, simple point defects in the form of vacancies or interstitials, along with small interstitial clusters, are the predominant defects. Moreover, at an irradiation temperatui-e near 150°C [17] the defect which dominates the thermal resistance is the lattice vacancy. 

Keywords layered cobaltites, Co3+ ion spin state, Raman light scattering, phonon... 

Discontinuities in the lattice such as vacancies, impurities, or grain boundaries also act to scatter phonon propagation, hence a lower thermal conductivity is expected in solids containing these defects at cryogenic temperatures. Whichever mecha-... 

Figure 2. The SWAP the abclssa Is number of unit cells a, electron density b, force on lattice by electron c, lattice displacement d, Incident phonon e, scattered phonon. (Reproduced with permission from reference 5. Copyright 1985 Nljhoff.)...

Thermal conductivity of irradiated SiC decreases due to the accumulation of point defects that effectively scatter phonons in SiC. In the 500-800 C range of interest, the thermal conductivity of conventional SiC/SiC composites at 1 dpa could be in the range required for the FCI As the point defects accumulate, meeting the requirement of low conductivity becomes much easier. So as far as the FCI application is concerned, the critical time for SiC/SiC composites is the beginning of... 

S" and S denote the diffusion thermopower of a non-magnetic RI compound and a magnetic RI compound, respectively. So, Sph, and Sspd are the contributions to the thermopower due to impurity scattering, phonon scattering, and spin-disorder scattering, respectively, p, po, Pph, and Pspd represent the total resistivity, and residual resistivity, the phonon resistivity, and the spin-disorder resistivity, respectively. 

Tin anionic clathrates exhibit low values of thermal conductivity in the range of 0.6-2 Wm K . This is lower than the values for anionic Si- and Ge-containing clathrates with similar framework compositions and the same cations. This indicates that clathrate framework atoms play an important role in the scattering of heat-carrying phonons. Thus, the frameworks with heavier Sn atoms scatter phonons more effectively. 

In addition, the interface disorder can scatter phonons at grain boundaries or interfaces between similar materials [51]. Thus, it may be expected that materials with high interfacial densities should reduce the thermal conductivity of TBCs. For instance, a multilayered W/AI2O3 film could give rise to a thermal conductivity of 0.6 W.m K [51]. For EBPVD coatings, the introduction of interfaces into each column, which are parallel to the ceramic/metal interface, can reduce the thermal conductivity by 37-45% compared to state-of-the art EBPVD TBCs (Fig.8) [9, 52]. 

Thermal Conductivity. The thermal conductivity of superconductors is not nearly as spectacular as the electrical conductivity. From the explanation of thermal conductivity of normal metals one can show that the thermal conductivity of superconductors can either increase or decrease. Superconducting electrons can neither accept heat nor scatter phonons. (Heat cannot be accepted in amounts less than the energy gap amounts. Heats greater than the energy gap reduce superconducting electrons to the normal state.)... 

Keywords. Lattice dynamics, neutron scattering, phonon density of states... 

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