Ternary p-type half-Heuslers: another perspective bulk thermoelectrics

By employing the nanocomposite approach, we have achieved peak ZT of 0.8 at 700 $^{\circ}$C for p-type Hf$_{0.5}$Zr$_{0.5}$CoSb$_{0.8}$Sn$_{0.2}$. A larger difference in atomic mass and size of Hf and Ti than Hf and Zr in the crystal structure has produced a peak ZT of $\sim $1.1 at 800 $^{\circ}$C for p-type Hf$_{0.8}$Ti$_{0.2}$CoSb$_{0.8}$Sn$_{0.2}$. However the ZT peak is on the high temperature side. A ternary combination of Ti, Zr, and Hf at M site (MCoSb) has given rise to higher ZT in n-type MNiSn system. Will ternary on the M site yield better ZT for p-type? In this report, we will present our recent achievement of 10-25{\%} ZT improvement for temperature range 25-700 $^{\circ}$C without sacrificing the peak ZT value of 1.1 at 800 $^{\circ}$C.