Thermoelectric properties of Sr_3GaSb_3 – a chain-forming Zintl compound

Abstract

Inspired by the promising thermoelectric properties in the Zintl compounds Ca_3AlSb_3 and Ca_5Al_2Sb_6, we investigate here the closely related compound Sr_3GaSb_3. Although the crystal structure of Sr_3GaSb_3 contains infinite chains of corner-linked tetrahedra, in common with Ca_3AlSb_3 and Ca_5Al_2Sb_6, it has twice as many atoms per unit cell (N = 56). This contributes to the exceptionally low lattice thermal conductivity (κ_L = 0.45 W m^(−1) K^(−1) at 1000 K) observed in Sr_3GaSb_3 samples synthesized for this study by ball milling followed by hot pressing. High temperature transport measurements reveal that Sr_3GaSb_3 is a nondegenerate semiconductor (consistent with Zintl charge-counting conventions) with relatively high p-type electronic mobility (~ 30 cm^2 V^(−1) s^(−1) at 300 K). Density functional calculations yield a band gap of ~ 0.75 eV and predict a light valence band edge (~ 0.5 me), in qualitative agreement with experiment. To rationally optimize the electronic transport properties of Sr_3GaSb_3 in accordance with a single band model, doping with Zn^(2+) on the Ga^(3+) site was used to increase the p-type carrier concentration. In optimally hole-doped Sr_3Ga_(1−x)Zn_xSb_3 (x = 0.0 to 0.1), we demonstrate a maximum figure of merit of greater than 0.9 at 1000 K.

Files

Additional details