Phonon drag of electrons in Ag2S

The temperature dependences of the heat-conductivity coefficient χ and the thermopower 6h of Ag2S are investigated in the range of 4.2–300 K. It is found that the value of 6h sharply increases (6h ∞ T-3) with decreasing T at T < 100 K and passes through a maximum at 16–18 K. The heat-conductivity coefficient passes through a maximum at ≈30 K. The sharp increase in 6h is found to be caused by the effect of long-wavelength-phonon drag of electrons. It is shown that the shift of the 6h and χ peaks, as well as the temperature dependence of the phonon thermopower 6hph ∞ T-3, agrees with the Herring theory.