Optimized carrier concentration and enhanced thermoelectric properties in GeSb4-xBixTe7 materials.

As the pseudo-binary alloys between GeTe and Sb₂Te₃, GeSbTe-based compounds are promising thermoelectric materials. Although Ge₂Sb₂Te₅ and GeSb₂Te₄ have widely been studied, the thermoelectric properties of GeSb₄Te₇ have not been well understood yet. In this work, we design a series of GeSb_4-xBi_xTe₇ solid solutions and systematically study the variation in the crystal structure, electrical, and thermal transport properties. Alloying Bi effectively reduces the carrier concentration and, thus, enhances the Seebeck coefficient. Meanwhile, the thermal conductivity is greatly reduced via large mass fluctuations. A maximum zT of 0.69 at 550 K and an average zT value of 0.52 between 300 and 700 K have been achieved for GeSb_1.5Bi_2.5Te₇. These findings will promote the understanding and development of GeSbTe-based thermoelectric materials. [ABSTRACT FROM AUTHOR]