Enhancement of thermoelectric figure of merit in β-Zn₄Sb₃ by indium doping control

We demonstrate the control of phase composition in Bridgman-grown β-Zn₄Sb₃ crystals by indium doping, an effective way to overcome the difficulty of growing very pure β-Zn₄Sb₃ thermoelectric material. The crystal structures are characterized by Rietveld refinement with synchrotron X-ray diffraction data. The results show an anisotropic lattice expansion in In-doped β-Zn₄Sb₃ wherein the zinc atoms are partially substituted by indium ones at 36f site of R-3c symmetry. Through the elimination of ZnSb phase, all the three individual thermoelectric properties are simultaneously improved, i.e., increasing electrical conductivity and Seebeck coefficient while reducing thermal conductivity. Under an optimal In concentration (x = 0.05), pure phase β-Zn₄Sb₃ crystal can be obtained, which possesses a high figure of merit (ZT) of 1.4 at 700 K