Unravelling the phonon scattering mechanism in half-Heusler alloys ZrCo1-xIrxSb (x=0, 0.1 and 0.25).

Insight about the scattering mechanisms responsible for reduction in the lattice thermal conductivity (κL) in half-Heusler alloys (HHA) is imperative. In this context, we have thoroughly investigated the temperature response of thermal conductivity of ZrCo1-xIrxSb (x= 0, 0.1 and 0.25). For ZrCoSb,κLis found to be ∼15.13 W m-1 K-1at 300 K, which is drastically reduced to ∼4.37 W m-1 K-1in ZrCo0.9Ir0.1Sb. This observed reduction is ascribed to softening of acoustic phonon modes and point defect scattering, on substitution of heavier mass. However, no further reduction inκLis observed in ZrCo0.75Ir0.25Sb, because of identical scattering parameter. This has been elucidated based on the Klemen's Callaway model. Also, in the parent alloy, phonon-phonon scattering mechanism plays a significant role in heat conduction process, whereas in Ir substituted alloys, point defect scattering (below 500 K) and phonon-phonon scattering (above 750 K) are the dominant scattering mechanisms. The minimumκLis found to be ∼1.73 W m-1 K-1(at 950 K) in ZrCo0.9Ir0.1Sb, which is the lowest reported value till now, for n-type Zr based HHA. Our studies indicate that partial substitution of heavier mass element Ir at Co-site effectively reduces theκLof n-type ZrCoSb, without modifying the nature of charge carriers.