Potential for High Thermoelectric Performance in n-type Zintl Compounds: A Case Study of Ba Doped KAlSb4

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 un while maintaining the low thermal conductivity KL 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 un (50 cm2 V-1 s-1) coupled with a near minimum KL (0.5 W m-1 K-1) at 370 degrees C. Together, these properties yield a zT of 0.7 at 370 degrees C for the composition K0.99Ba0.01AlSb4. 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.