Recent progress and future challenges on thermoelectric Zintl materials

Zintl phases are good thermoelectric materials due to their complex structures and bonding, which leads to highly tunable properties, such as exceptionally low, glass-like lattice thermal conductivity. The potential of thermoelectric Zintl materials for further research has been demonstrated thus far through several Zintl families with unique and diverse anionic frameworks, ranging from isolated moieties (14-1-11) to one-dimensional (1D) chains of tetrahedra or frames of ribbons (e.g., 11-6-12, 5-2-6, 3-1-3) to 2D layered structures (e.g., 9-4-9, 1-2-2, 1-1-4), etc., and especially by the most recent exciting development in achieving high ZTs in n-type Zintls (1-2-2). In the low-to-middle temperature range, the Zintl 1-2-2 family displays the best properties among both p-type and n-type families, while at 975-1275 K, the 14-1-11 compounds outperform other reported p-type Zintl families.