Effect on Thermoelectric and Mechanical Properties of Interstitial Void Filling by Cu in ZrNiSn HH Alloy

Widely explored ZrNiSn half-Heusler (HH) alloy has an interpenetrating fcc cubic crystal structure with four vacant positions in the unit cell, where the elemental substitution at these voids by off-stoichiometric composition could play an imperative role in the optimization of electronic transport by tuning the band structure and band gap, as well as it can reduce the phonon transport by interstitial point defect scattering. In the present study, off-stoichiometric compounds are synthesized opting a fast and facile route of arc melting and spark plasma sintering by surplus Cu in ZrNiSn system to fill the available voids at 4d (¾, ¾, ¾,) in the HH unit cell. Here, 0-4% Cu excess was used to easily occupy the vacant site which can improve the thermoelectric properties. The XRD results reflect that up to 2% Cu partially occupied the vacant site. The electronic transport enhances with the Cu excess by increased carrier density due to shifting of fermi level as reflected by reduced chemical potential. Further, this Cu excess of upto 2% significantly reduces the thermal conductivity due to interstitial point defect phonon scattering. The figure-of-merit <i>ZT </i>enhances ~ 45% with the peak value 0.81 at 775 K which is the result of interstitial filling of 2% Cu in ZrNiSn. The mechanical properties also improved upto 2% Cu excess, confirming interstitial filling strengthen the mechanical properties.