Development of two-dimensional layered ZnSb-based thermoelectric materials via alkali metal alloying

Two-dimensional (2D) layered Zintl compounds have emerged as promising candidates for thermoelectric applications due to their favorable electronic structures, efficient charge transport pathways, and loosely bound cations. In this study, we engineered 2D-layered structures in polycrystalline ZnSb through alkali metal (A = Li, Na, K) alloying, inducing a bonding transition from sp³ to sp² hybridization that promotes the formation of layered structures. Structural analysis confirmed the formation of layered phases, with increasing texturing fractions from Li to K. Electrical transport measurements revealed that LiZnSb exhibited high electrical conductivity (∼6561 S cm⁻¹) due to a high carrier concentration, while NaZnSb showed moderate conductivity (∼213 S cm⁻¹) with a carrier concentration close to the theoretical value (7.38 ×10¹⁸ cm⁻³). In contrast, KZnSb demonstrated extremely low conductivity, hindering reliable carrier concentration analysis. As a result, NaZnSb achieved a maximum ZT of 0.079 at 375 K, which is significantly higher than that of LiZnSb. The single parabolic band (SPB) model suggests that NaZnSb may be further optimized through extrinsic doping at the Zn site, whereas LiZnSb remains limited by intrinsic cation deficiencies. These results demonstrate that alkali metal-induced bonding transitions offer a viable strategy for engineering 2D structures in Zintl compounds to enhance thermoelectric performance.