Thermoelectric transport properties of single-crystalline ZrCoBi half-Heusler

Half-Heusler compounds are one of most promising thermoelectric materials for power generation at high temperatures. Recent studies focus on fine-grained polycrystalline samples because of their lower thermal conductivity, and the induced defects are found to play an important role in the thermoelectric transport properties. Here, we report the thermoelectric transport properties of single-crystalline ZrCoBi. Two samples from different batches clarify the same charge carrier concentration of ~1020 cm-3, denoting the robust Fermi level position in the ZrCoBi single crystals. The high electron density is attributed to the Zr interstitial point defects. Moreover, a high power factor of over 3.3 mWm-1K-2 is achieved in the single-crystalline ZrCoBi. By comparing the thermoelectric properties of single-crystalline and fine-grained polycrystalline samples, we reveal the role of grain boundary scattering in reducing the thermal conductivity from ~11.5 Wm-1K-1 to ~9 W/mK at 300 K. The present work declares the significance of defects in tuning the transport properties of ZrCoBi half-Heusler compound.