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 A5M2Sb6 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 (Eg ∼ 0.3 eV) and the other from a lower valence band manifold to the conduction band edge (Eg ∼ 0.55 eV). Sr5In2Sb6 exhibits nondegenerate p-type semiconducting behavior with low carrier concentration (∼4 × 1018 h+ cm-3 at 300 K). Charge carrier tuning was achieved by Zn2+ substitution on the In3+ site, increasing carrier concentrations to up to 1020 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 Sr5In1.9Zn0.1Sb6.
ASJC Scopus subject areas
- Renewable Energy, Sustainability and the Environment
- Materials Science(all)