Porous\nThermoelectric Zintl: YbCd₂Sb₂

Abstract

The\nsimultaneous reduction of the lattice thermal conductivity\nand maintenance of the electrical conductivity are great challenges\nfor porous thermoelectric materials in achieving superior thermoelectric\nperformance. Herein, by taking advantage of the low melting temperature\nof the inevitable impurity in a YbCd₂Sb₂ Zintl\ncompound, a porous structure (∼11%) with varying sizes, irregular\nshape, and oriented pores was investigated by controllable annealing.\nEspecially, a high density of strain lines was introduced and incorporated\nwith porous structures to achieve a dramatic reduction of lattice\nthermal conductivity (∼40% @ 673 K). Moreover, the carrier\nconcentration was doubled by annealing, which resulted in the involvement\nof low-lying valence bands for charge transport and enhancing the\npower factor. This porous YbCd₂Sb₂ realizes\nthe highest on record figure of merit (<i>zT</i>) (higher\nthan unity @ 673 K) and average <i>zT</i> (0.61 in the range\nof 323–673 K) among pristine p-AB₂C₂ (A\n= Eu, Yb, Mg, Ca, Sr, and Ba; B = Mn, Mg, Zn, and Cd; C = Sb and Bi)\nZintls.