Transport properties of the SnBi₂Te₄-PbBi₂Te₄ solid solution

We report on the electrical and thermal transport properties of the Sn_1-xPb_xBi₂Te₄ series and we discuss the potential of these materials for thermoelectric conversion applications. From the evolution of the XRD patterns, we can confidently conclude that a complete solid solution exists between SnBi₂Te₄ and PbBi₂Te₄, with no miscibility gap. A crossover from p-type conduction in Sn-rich samples to n-type conduction in Pb-rich ones has been observed, with a transition between x=0.3 and 0.4. A concomitant increase of the electrical resistivity and of the Seebeck coefficient has been observed in the solid solution, which leads to almost constant values of the thermoelectric power factor. Moreover, the thermal conductivity is slightly reduced in the solid solution. The best figure of merit ZT values at room temperature have been observed for p-type Sn_0.8Pb_0.2Bi₂Te₄ with ZT=0.25 and for n-type Sn_0.3Pb_0.7Bi₂Te₄ with ZT=0.15.