Effects of Bi doping on the thermoelectric properties of Β-Zn ₄ Sb₃

The thermoelectric properties of Bi-doped compounds (Zn_1-x Bi_x)₄ Sb₃ (x=0,0.0025,0.005,0.01) were studied experimentally as well as theoretically. The results indicate that low-temperature (T<300 K) thermal conductivity of moderately doped (Zn _0.9975 Bi_0.0025)₄ Sb₃ reduces remarkably as compared with that of Zn₄ Sb₃ due to enhanced phonon scattering of impurity (dopant). Electrical resistivity and Seebeck coefficient increase monotonically with increase in the Bi content resulting mainly from decrease in carrier concentration. Moreover, first-principle calculations were performed on the occupation options of Bi atoms in Β-Zn₄ Sb₃, which show that Bi will preferentially occupy the Zn sites and not Sb sites and act as donors, being consistent with the experimental observations. In addition, the lightly doped compound (Zn_0.9975 Bi_0.0025)₄ Sb₃ exhibits the best thermoelectric performance due to the improvement in both its thermal conductivity and Seebeck coefficient, whose figure of merit, Z _T, is about 1.5 times larger than that of Β -Zn₄ Sb₃ at 300 K.