posted on 2021-03-17, 20:05authored byKishor
Kumar Johari, Ruchi Bhardwaj, Nagendra S. Chauhan, Sivaiah Bathula, Sushil Auluck, S. R. Dhakate, Bhasker Gahtori
ZrNiSn-based
half-Heusler (HH) alloys are well-established alloys
for n-type mid-temperature thermoelectric applications because of
their chemical and thermal stability and narrow band gap driven semiconducting
behavior. Here, we observed a high figure of merit, ZT ∼ 1, at 873 K in aliovalent Nb-doped composition Zr1–xNbxNiSn (x = 0–0.035) for x = 0.03 HH alloy prepared
by employing a combination of arc-melting and spark plasma sintering.
The high figure of merit is attributed to synergistic enhancement
of the power factor with thermal conductivity reduction. Further,
the enhancement of the power factor is correlated with the improved
weighted mobility and reduction in thermal conductivity is analyzed
in the framework of the model based on the theories of Callaway, Slack,
and Abeles. The results are corroborated theoretically to establish
the efficacy of Nb doping in ZrNiSn within semimetallic regimes for ZT enhancement. The synthesized Hf-free HH alloys establish
Nb as an effective dopant for attaining high-ZT and
cost-efficient HH-based n-type TE material in a mid-temperature regime
for power generation application.