Potential for high thermoelectric performance in n-type Zintl compounds: a case study of Ba doped KAlSb4

Abstract

High-throughput calculations (first-principles density functional theory and semi-empirical transport models) have the potential to guide the discovery of new thermoelectric materials. Herein we have computationally assessed the potential for thermoelectric performance of 145 complex Zintl pnictides. Of the 145 Zintl compounds assessed, 17% show promising n-type transport properties, compared with only 6% showing promising p-type transport. We predict that n-type Zintl compounds should exhibit high mobility μ_n while maintaining the low thermal conductivity κ_L typical of Zintl phases. Thus, not only do candidate n-type Zintls outnumber their p-type counterparts, but they may also exhibit improved thermoelectric performance. From the computational search, we have selected n-type KAlSb₄ as a promising thermoelectric material. Synthesis and characterization of polycrystalline KAlSb₄ reveals non-degenerate n-type transport. With Ba substitution, the carrier concentration is tuned between 10¹⁸ and 10¹⁹ e⁻ cm⁻³ with a maximum Ba solubility of 0.7% on the K site. High temperature transport measurements confirm a high μ_n (50 cm² V⁻¹ s⁻¹) coupled with a near minimum κ_L (0.5 W m⁻¹ K⁻¹) at 370 °C. Together, these properties yield a zT of 0.7 at 370 °C for the composition K_0.99Ba_0.01AlSb₄. Based on the theoretical predictions and subsequent experimental validation, we find significant motivation for the exploration of n-type thermoelectric performance in other Zintl pnictides.