Abstract:

Benefiting from the unique “Phonon-Glass, Electron-Crystal” (PGEC) characteristic, Zintl phases have been considered as a kind of promising thermoelectric materials. For the typical AM₂X₂ compounds with the CaAl₂Si₂-type structure, YbMg₂Bi₂ has shown competitive thermoelectric performance recently. Nevertheless, the optimization of YbMg₂Bi₂ compounds is primarily focused on the substitution on Yb or Mg site. Herein, the Bi site is substituted by isoelectric Sb and the effect on the thermoelectric transport behavior is investigated. The partial substitution reduces the carrier concentration and induces the lattice deformation caused by the different atomic radius and mass between Bi and Sb, further leading to the decreased power factor and thermal conductivity. Fortunately, the reduction extent of the thermal conductivity outperforms that of power factor. Finally, the Sb substitution successfully results in a better thermoelectric performance compared with that of the pristine YbMg₂Bi_1.98. Especially, the calculated energy conversion efficiency (η) of YbMg₂Bi_1.88Sb_0.1 which also possesses a relatively high output power density reaches the maximum value of 9.8 % when T_h = 873 K, and T_c = 300 K, respectively. This work demonstrates that the idea of substitution on anionic site should be a new strategy to achieve better ZT values for AM₂X₂ compounds.

Key words: Zintl phase, YbMg2Bi2, Anionic substitution, Thermoelectric properties