Effects of silicon addition on thermoelectric properties of bulk Zn ₄Sb₃ at low-temperatures

The thermoelectric properties of Si-doped compounds (Zn _1-xSi_x)₄Sb₃ (x = 0, 0.0025, 0.005, 0.01) have been studied. The results indicate that low-temperature (T < 300 K) thermal conductivity of moderately doped (Zn_0.9975Si _0.0025)₄Sb₃ reduces remarkably as compared with that of Zn₄Sb₃ due to enhanced impurity (dopant) scattering of phonons. Electrical resistivity and Seebeck coefficient are found to increase and then decrease moderately with the increase in the Si content. In addition, first-principles calculations are performed on the occupation options of Si atoms in disordered β-Zn₄Sb₃. The results indicate that Si atoms occupy preferentially the Zn vacancies in normal sites. Subsequently, Si atoms will substitute for interstitial Zn atoms. The lightly doped compound (Zn_0.9975Si_0.0025)₄Sb ₃ exhibits the best thermoelectric performance due to the improvement in both its thermal conductivity and Seebeck coefficient. Its figure of merit, ZT, is about 1.3 times larger than that of pure Zn₄Sb₃ at 300 K.