Phonons atom-single-phonon scattering

The thermal conductivity of a pure metal is lowered by alloying, whether the alloy formed is a single phase (solid solution) or multiphase mixture. There are several reasons for this. First, electrons are scattered by crystal imperfections and solute atoms (electron-defect scattering). Second, a substantial portion of the thermal conductivity in alloys, in contrast to that of pure metals, is by phonons, Kph (phonons are the sole contribution in electrically insulating solids) and phonons are also scattered by defects. Finally, electron-phonon interactions limit both Kei and Kp. ... 

The effects of impurities and solid solutions on phonon conductivity in single-phase crystalline ceramics are discussed next. Impurities and solute atoms tend to decrease thermal conductivity. These increase the phonon scattering by way of differences in mass, binding force, and elastic strain field. As the temperature is raised, the scattering increases at low temperatures. At temperatures greater than about half the Debye temperature, it becomes independent of temperature. This is because the average wavelength at these temperatures becomes comparable with or less than the point imperfection. 

A semiconductor material, in an ideal situation, should be a single crystal with a strictly periodic lattice. Electrons or holes travel easily in such a crystal, suffering only from phonon scattering. In a periodic potential held, electron-hole propagation takes place as nearly loss-free transport. In a similar way, heat transport in diamond is conducted by thermal waves. The waves are least scattered when the crystal lattice is periodic. Vibrating atoms in a crystal have potential wells prescribed to them and the minima of these wells form a three-dimensional crystal lattice. 

There are no gas—metal systems for which the dominant loss mechanism has been determined. However, it can be anticipated that developments in angle-resolved inelastic atom beam scattering experiments, exemplified by the recent work of Feuerbacher and Allison [380] with scattering from LiF 100, will make good this deficiency. In cases where single surface phonons are responsible for the inelasticity in He scattering, time-of-flight measurements with the detector scanned away from the molecular beam enable the dispersion curves for surface phonons to be constructed. 

---