Porous Thermoelectric Zintl: YbCd₂Sb₂

The simultaneous reduction of the lattice thermal conductivity and maintenance of the electrical conductivity are great challenges for porous thermoelectric materials in achieving superior thermoelectric performance. Herein, by taking advantage of the low melting temperature of the inevitable impurity in a YbCd2Sb2 Zintl compound, a porous structure (∼11%) with varying sizes, irregular shape, and oriented pores was investigated by controllable annealing. Especially, a high density of strain lines was introduced and incorporated with porous structures to achieve a dramatic reduction of lattice thermal conductivity (∼40% @ 673 K). Moreover, the carrier concentration was doubled by annealing, which resulted in the involvement of low-lying valence bands for charge transport and enhancing the power factor. This porous YbCd2Sb2 realizes the highest on record figure of merit (zT) (higher than unity @ 673 K) and average zT (0.61 in the range of 323–673 K) among pristine p-AB2C2 (A = Eu, Yb, Mg, Ca, Sr, and Ba; B = Mn, Mg, Zn, and Cd; C = Sb and Bi) Zintls.