Role of grain boundaries as phonon diffraction gratings in the theory of thermal conductivity

Abstract

The picture of a grain boundary as a periodic array of dislocations implies the occurrence of phonon scattering processes that the Klemens theory of thermal conductivity does not account for. A grain boundary works similar to a diffraction grating, producing diffraction spectra of various orders: each order number n is associated with a class of scattering processes contributing to thermal resistance. The Klemens theory corresponds to nϭ0: it is shown that processes with n 0 are essential to explain the heat transport properties of a specimen containing grain boundaries. The theory is used to explain the behavior of thermal conductivity, both in the range below 5 K and in the region of the conductivity peak, as observed in crystals of lithium fluoride, alumina, and quartz. It is also applied to the conductivity curve of fused silica, in the frame of a model where a glass is pictured as a solid with a high-density distribution of grain boundaries.

Structural, thermal, electrical and magnetic properties of Eurofer 97 steel

“…(9) we find that Eurofer 97 has a lower impurity scattering but a higher phononic scattering. The change of the strength of the scattering mechanisms could be attributed predominantly to that Eurofer 97 has a finer grain structure which has as a result the reduction of the electron and phonon free mean path [24].…”

Polypyrrole Coated PET Fabrics for Thermal Applications

“…The very low thermal diffusivity of polypyrrole films is originated in the lattice structure, in particular from a dominant amorphous character of the chain structure. An amorphous structure strongly reduces the thermal phonon transport, because strong phonon scattering mechanisms appear [27,28].…”

Lattice thermal conductivity in cubic silicon carbide

“…31, the role of grain boundaries in diffracting phonons is much more complex, but the experimental data in the low-temperature region of SiC are really too poor for a reliable comparison.…”