The charge carrier density modulation in off-stoichiometric ZrNiSn leads to enhanced thermoelectric performance

Abstract

The off-stoichiometry i.e., ZrNi1+δSn (0<δ<1), and carrier modulation are the two approaches that have separately been found effective mainly to reduce thermal conductivity and improve power factor. This work explores the combined effect of both of these approaches by tuning the carrier density by varying the Sb-concentration in off-stoichiometric ZrNi1.04Sn, which shifts the Fermi level towards the conduction band as confirmed by the band structure calculations. The maximum thermoelectric figure-of-merit ZT∼0.95 at ∼873 K was achieved in the optimum composition ZrNi1.04Sn0.975Sb0.025. For evaluating the device applicability of the synthesized materials, the cumulative temperature dependence (CTD) model was applied, predicting the single leg maximum efficiency ∼8.6% at ΔT ∼ 546 K. A series of calculations have been performed to predict electronic band structure and electronic transport properties to unearth the underlying physics. The microhardness and fracture toughness were determined to ensure that the enhanced thermoelectric performance is not deteriorating mechanical robustness.