Quasi-two-dimensional GeSbTe compounds as promising thermoelectric materials with anisotropic transport properties

Pseudo-binary GeSbTe alloys, best known as phase-change materials, are quasi-two-dimensional semiconductors in their stable trigonal phases with high electrical conductivity and low thermal conductivity, but their thermoelectric properties have not been systematically investigated. Here, in this letter, we prepared polycrystalline Ge2Sb2Te5, GeSb2Te4, and GeSb4Te7 bulk materials and studied the thermoelectric transport properties. Large anisotropy in Seebeck coefficient as well as in electrical conductivity is observed, which is not commonly reported in polycrystalline thermoelectric materials. Combining experimental study and theoretical calculations, one can find that this phenomenon is attributed to the asymmetry of a material's band structure. Maximal zT values of 0.46–0.60 are achieved at 750 K, indicating that GeSbTe-based compounds are promising thermoelectric materials for mid-temperature applications.