Thermal transport in silicate glasses. II. Extended phonons

Abstract

In this paper we present measurements of the thermal diffusivities of five glasses between 100 and 500 K. These glasses have composition 0.15(Na20)0. 15(MO)0.05(Eu203)0.65(SiO~), where M is a divalent network modifier Mg, Ca, Sr, Ba, or Zn. The thermal transport is represented by a two-carrier model of conventional phonon-gas transport by extended phonons and thermally activated hopping of phonons whose eigenvectors are localized in the disordered network of the glass. The later contribution is required to explain the increase in the thermal diffusivity at temperatures above room temperature. The extended phonons produce a transport that is a decreasing function of temperature between 100 and 250 K in these glasses. Using the boson peak from Raman scattering as a measure of the phonon mobility edge, agreement with the temperature and frequency dependence of the two-localized-one-extendedphonon anharmonic process studied by Jagannathan et al. is obtained for both the localized and the extended phonons. The model is also applied to fused silica to account for results between 100 and 1100K, with the modification that the limiting process for the extended states does not explicitly depend on temperature.

Plasmon-Assisted Chemical Vapor Deposition

“…In the quasi-diffusive transport regime we simply reduce k ∞ by a factor of 10, (to 0.15 W/m·K) and in both cases, we set K abs = 1.5. A reduction in the heat transfer is expected because the average radius of the nanoparticles is comparable to literature values of Λ for amorphous SiO 2 at 300 K (0.8−8) nm , and further because the nanoparticles are resting on the surface and are not fully embedded in the substrate. These numbers are all approximate and affected by a number of additional factors but are presented here only to illustrate that temperature rises of the order required to explain our deposition results are quite likely.…”

Heat conduction in conducting polyaniline nanofibers

“…It is interesting that this value is pretty close to that observed for silicate glasses $1.4 Â 10 13 s À1 . 24,36 So far our analysis implies that the peak observed in j ph at low T reflects the crystalline nature of the present PANI system, while the quasilinear part above 100 K reflects the amorphous nature of the material. These observations have led us to conclude that the present system consists of crystalline regions separated by the amorphous regions, i.e., the proposed heterogeneous model 37 is very much valid in present nanofibers.…”

Improved thermal properties of borosilicate glass composite containing single walled carbon nanotube bundles

“…Phonons are dominating in thermal transport process both for glass 28,29 and carbon nanotubes. 30 Moreover, above room temperature the mechanism is fully controlled by the localized phonons in glass.…”

“…30 Moreover, above room temperature the mechanism is fully controlled by the localized phonons in glass. 29 However, a frequency mismatch takes place between the phonons of dissimilar materials in case of the composite which can be one of the reasons for the boundary resistance in thermal conduction. This type of difficulty in different composites was comprehensively reviewed by Swartz and Pohl in their report.…”