Thermoelectric Power of Dilute Copper Alloys. II

The work of Blatt and Kropschot was extended to dilute CuAg and CuAu alloys; simultaneous measurements of the thermopower and thermal conductivity were made on CuSn alloys. The decomposition of the absolute thermopower of copper into diffusion $S_d$ and phonon drag $S_g$ contributions proposed by Blatt and Kropschot was verified. It is based on the observed quenching of $S_g$ by large-mass solutes due to anisobaric phonon scattering. It was found that $S_g$ is completely suppressed by approximately 1 at.% of Ag or Sn and by 0.4 at.% of Au. In the temperature region ($T\simeq 60°$K) where anisobaric scattering is important in limiting the lattice conduction ${\kappa }_g$, it was observed that ${\kappa }_g$ is reduced considerably less than $S_g$. It is suggested that this is due to the characteristic dispersion of phonons of large wave vector. At low temperatures, where the Debye model holds, comparison of $S_g$ and $S_d$ with specific-heat data leads to the conclusion that the umklapp contribution ${S_g}^U$ is 25% larger in magnitude than the normal contribution ${S_g}^N$. This is in agreement with estimates by Ziman of the relative importance of normal and umklapp processes in copper.