Substantial enhancement in thermoelectric figure-of-merit of half Heusler ZrNiPb alloys

TL;DR

This study demonstrates a significant increase in the thermoelectric figure-of-merit (ZT) of ZrNiPb-based half Heusler alloys by compositional tuning and phase engineering, achieving ZT of 1.3 at 773 K, promising for thermoelectric applications.

Contribution

The paper introduces a novel compositional tuning method that enhances ZT in ZrNiPb alloys by incorporating minor phases of full Heusler, leading to improved thermoelectric performance.

Findings

Achieved ZT of 1.3 at 773 K in ZrNi1.03Pb0.38Sn0.6Bi0.02 alloy.

Enhanced ZT due to increased power factor and reduced thermal conductivity.

Estimated thermoelectric device efficiency of 13.6% for the best sample.

Abstract

Ternary half Heusler alloys are under intense investigations recently towards achieving high thermoelectric figure-of-merit (ZT). Of particular interest is the ZrNiPb based half Heusler (HH) alloy where an optimal value of ZT = 0.7 at 773 K has been achieved by co-doping Sn and Bi at Pb site. In this work, we identify an excellent ZT of 1.3 in ZrNi1+xPb0.38Sn0.6Bi0.02 (x= 0.03, at 773 K) composite alloy. This is achieved by synergistic modulation of electronic as well as thermal properties via introduction of minor phase of full Heusler (FH) in the HH matrix through compositional tuning approach. These Ni-rich ZrNi1+xPb0.38Sn0.6Bi0.02 alloys were synthesized via Arc melting followed by consolidation via Spark Plasma Sintering (SPS). These alloys were characterized by XRD and SEM that shows formation of nanocomposites comprising of HH matrix phase and FH secondary minor phases. Enhancement in ZT is mainly attributed to a synchronized increase in power factor and about 25% decrease in its thermal conductivity. The thermoelectric compatibility factor (S) is also calculated for all samples. The theoretically calculated thermoelectric device efficiency of best performing sample ZrNi1.03Pb0.38Sn0.6Bi0.02 is estimated to be 13.6%. Our results imply that controlled fine tuning in HH compounds through compositional tuning approach would lead to novel off-stoichiometric HH phases with enhanced ZT value for efficient thermoelectric device fabrication.