Role of chemically and thermally induced crystal lattice distortion in enhancing the Seebeck coefficient in complex tellurides

Abstract

Composition and crystal structure of complex materials can significantly change the Seebeck effect, i.e., heat to electrical energy conversion, which is utilized in thermoelectric materials. Despite decades of studies of various thermoelectric materials and their application, the fundamental understanding of this effect still is limited. One of the most efficient groups of thermoelectric materials is based on GeTe, where Ge is replaced by [Ag + Sb], i.e., Ag_xSb_xGe_50−2xTe₅₀ alloys, traditionally shown as (GeTe)_m(AgSbTe₂)_100−m (TAGS-m series). Here we report on the discovery of two unique phenomena in TAGS materials attributed to the effects from [Ag + Sb] atoms: (i) a linear relation between the Seebeck coefficient and rhombohedral lattice distortion, and (ii) resonance-like temperature-induced behavior of the contribution to the Seebeck coefficient produced by [Ag + Sb] atoms. Our findings show that heat to electrical energy conversion strongly depends on the temperature- and compositionally-induced rhombohedral to cubic transformation where [Ag + Sb] atoms play a crucial mediating role.