Effects of Ag doping on thermoelectric properties of Zn₄Sb₃ at low temperatures

The thermoelectric properties of Ag-doped compounds (Zn_1-xAg_x)₄Sb₃ (x = 0, 0.0025, 0.005, 0.01) have been studied at the temperatures from 15 to 300 K. The results indicate that low-temperature (T < 300 K) thermal conductivity of the moderately doped (Zn_1-xAg_x)₄Sb₃ (x = 0.0025 and 0.005) reduced remarkably as compared with that of Zn₄Sb₃ due to enhanced impurity (dopant) scattering of phonons. Electrical resistivity and Seebeck coefficient were found to increase first and then decrease obviously with the increase in the Ag content, which could be ascribed to the change of carrier concentration presumably due to different Zn positions occupied by Ag upon increasing doping content. Moreover, the lightly doped compound (Zn_0.995Ag_0.005)₄Sb₃ exhibited the best thermoelectric performance due to the improvement in both its electrical resistivity and thermal conductivity, whose figure of merit (at 300 K), ZT, is about 1.3 times larger than that of β-Zn₄Sb₃ obtained in the present study. Present results suggest that proper Ag doping in Zn₄Sb₃ is a promising way of improving its thermoelectric properties.