Enhanced thermoelectric properties of Sr_5In_2Sb_6 via Zn-doping

Abstract

Zintl phases exhibit inherently low thermal conductivity and adjustable electronic properties, which are integral to designing high-efficiency thermoelectric materials. Inspired by the promising thermoelectric figure of merit of optimized A_5M_2Sb_6 Zintl phases (A = Ca or Sr, M = Al, Ga, In), Zn-doped Sr_5In_(2−x)Zn_xSb_6 (x = 0, 0.025, 0.05, 0.1) compounds were investigated. Optical absorption measurements combined with band structure calculations indicate two distinct energy transitions for Sr_5In_2Sb_6, one direct (E_g ~0.3 eV) and the other from a lower valence band manifold to the conduction band edge (E_g ~0.55 eV). Sr_5In_2Sb_6 exhibits nondegenerate p-type semiconducting behavior with low carrier concentration (~4 × 10^(18) h+ cm^(−3) at 300 K). Charge carrier tuning was achieved by Zn^(2+) substitution on the In^(3+) site, increasing carrier concentrations to up to 10^(20) h+ cm^(−3). All samples displayed relatively low thermal conductivities (~0.7 W m^(−1) K^(−1) at 700 K). The Zn-doped samples exhibited significantly higher zT values compared to the undoped sample, reaching a value of ~0.4 at 750 K for Sr_5In_(1.9)Zn_(0.1)Sb_6.

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