Electronic and phonon contributions to the Thermoelectric properties of newly discovered half-Heusler alloys XHfPb (X= Ni, Pd, and Pt)

Abstract

In this work we calculate the thermoelectric figure of merit of XHfPb (X= Ni, Pd, and Pt) by computing the both the power factor and the lattice thermal conductivity by first principles. We make reasonable approximations: we use the Constant Relaxation Time Approximation (CRTA) to compute the electron transport contribution and the modified Debye-Callaway model to calculate the thermal lattice conductivity. We also report the dielectric properties of these semiconductors and the mode Gr\"uneisen parameters. Not surprisingly we find that the average Gr\"uneisen coefficient correlates with the tehrmal conductivity. Next, we consider a realistic relaxation time $\tau$ and carrier concentration $n$ from experimental data on ZrHfPb and obtain the figure of merit $ZT$ as a function of temperature. Our main finding is that despite the Pt is isoelectronic with Ni and Pd, the $ZT$ of PtHfPb is larger and behaves differently from the other two materials, suggesting that PtHfPb is better suited for high temperature thermoelectric generators.