Phonon Scattering by Lattice Vacancies in Platinum

The change $\Delta S$ of the thermoelectric power of high-purity platinum wire due to quenched-in lattice vacancies was measured between 4.2 and 400°K and was separated into the electronic component $\Delta S^e$ and the phonon-drag component $\Delta S^g$. The vacancy concentration ranged from about 1×${10}^{-2\mathrm{}}$ to 6×${10}^{-2\mathrm{}}$ at.%. Vacancies were found to increase the electronic part and to reduce the phonon-drag part of the thermoelectric power in platinum. From the $\Delta S^g\mathrm{}\left(T\right)\mathrm{}$ curves the phonon-scattering cross section $\sigma$ of vacancies in platinum was estimated. The experimental $\Delta S^g\mathrm{}\left(T\right)\mathrm{}$ curves could not be fitted using for $\sigma$ a pure Rayleightype scattering law. However, a good fit could be obtained, using for $\sigma$ the expression which is valid for resonance scattering of phonons by point defects. The experiments suggest that in the phonon scattering by vacancies in platinum a resonance occurs at about one-third of the Debye frequency.