Mid-temperature thermoelectric performance of zone-melted Sb2(Te,Se)3 alloys near phase transition boundary

Abstract

(Bi,Sb)2(Te,Se)3 alloys are widely used commercial thermoelectric (TE) materials for solid-state refrigeration around room temperature. The composition-induced structural phase transition could be realized by varying the compositions in these alloys, which may largely alter the electronic structure and phonon dispersion. Among them, the Se-alloyed Sb2Te3 accompanied with structural transition is seldom reported. Herein, the interrelations of Se-alloying induced changes in structural phase transition, band structure and TE properties of p-type zone-melted Sb2Te3-xSex (x = 1.5–2.4) alloys near phase transition boundary are systematically investigated. The results demonstrate that Sb2Te3-xSex shows a structural transition from a rhombohedral phase to mixed structure at x = 2.0. The carrier concentration and bandgap at room temperature of Sb2Te3-xSex (x = 1.5–2.4) constantly decrease with increasing Se contents x. The zT peak of the Sb2TeSe2 matrix is improved and shifted to higher temperature by optimizing carrier concentration via Ag doping. A maximum zT of ∼0.4 is obtained at 680 K in Sb1.97Ag0.03TeSe2 alloy, about 100% enhancement compared with the undoped sample.