Beyond phase-change materials: Pseudo-binary (GeTe)n(Sb2Te3)m alloys as promising thermoelectric materials

Exploring new materials with complex structures and excellent transport properties has always been a fascinating topic in thermoelectrics. Recently, (GeTe)n(Sb2Te3)m-based compounds (GSTs), a well-known family of phase-change materials, are found to be promising thermoelectric candidates. Rooted in but different from the parent GeTe and Sb2Te3 binary compounds, these pseudo-binary alloys exhibit special structures and good transport properties. Here in this review, we demonstrate some fundamental knowledge and recent progress on these GST materials for thermoelectric applications. The operation principle of phase-change memory, crystal structure, as well as the special metavalent bonding mechanism are introduced at first. Then the electrical and thermal transport properties are illustrated, which are associated with material structures and bonding features. Several strategies are discussed to enhance the thermoelectric performance of hexagonal GSTs. Then, this review extends to discuss a larger family of (AC)n(B2C3)m thermoelectric materials (A = Si, Ge, Sn, Pb; B = As, Sb, Bi; C = S, Se, Te), which share similar crystal structures and transport properties with hexagonal GSTs. Finally, some possible research directions are proposed for the future study on thermoelectric GSTs.