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

Abstract

Abstract Insight about the scattering mechanisms responsible for reduction in the lattice thermal conductivity (κ L) in half-Heusler alloys (HHA) is imperative. In this context, we have thoroughly investigated the temperature response of thermal conductivity of ZrCo1−x Ir x Sb (x = 0, 0.1 and 0.25). For ZrCoSb, κ L is found to be ∼15.13 W m−1 K−1 at 300 K, which is drastically reduced to ∼4.37 W m−1 K−1 in 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 in κ L is 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 minimum κ L is 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 the κ L of n-type ZrCoSb, without modifying the nature of charge carriers.