Enhanced thermoelectric properties of Sr5In2Sb6 via Zn-doping

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(5)M(2)Sb(6) Zintl phases (A = Ca or Sr, M = Al, Ga, In), Zn-doped Sr5In2-xZnxSb6 (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 Sr5In2Sb6, one direct (E-g similar to 0.3 eV) and the other from a lower valence band manifold to the conduction band edge (E-g similar to 0.55 eV). Sr5In2Sb6 exhibits nondegenerate p-type semiconducting behavior with low carrier concentration (similar to 4 x 10(18) h(+) cm(-3) at 300 K). Charge carrier tuning was achieved by Zn2+ substitution on the In3+ site, increasing carrier concentrations to up to 10(20) h(+) cm(-3). All samples displayed relatively low thermal conductivities (similar to 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 similar to 0.4 at 750 K for Sr5In1.9Zn0.1Sb6.