Thermoelectric properties of Ag2Se

Abstract

To obtain information on the temperature and concentration dependence of thermoelectric quality factor Z and to clarify the nature of scattering in Ag2Se a study was made of electrical conductivity σ, thermo-emf α, and thermal conductivity ϰ in silver selenide over the temperature range T=80–450°K at concentration levels of 2–43·1024 m−3. It is shown that in Ag2Se the Lorentz number L, determined experimentally from the electronic fraction of the thermal conductivity, is less than the Sommerfeld number Lo. Calculation of L/Lo(n) performed with a theory considering inelastic scattering of carriers, shows that the inelasticity is produced by electron interaction. Comparison of experimental data on the temperature dependence of lattice thermal conductivity with theory permits the conclusion that in Ag2Se in range 80–300°K the basic role in phonon scattering is played by three-phonon Umklapp processes. It is shown that with increase in T and decrease in n the thermoelectric quality factor of silver selenide increases. The highest value of Z was achieved in a specimen with electron concentration n=2·1024 m−3 at T=320°K. The rapid decrease in Z upon phase transition is related to discontinuous decrease in α and σ at this point.