Entropy engineering induced low thermal conductivity in medium-entropy (Zr, Ti, Hf)CoSb triple half-Heusler compounds

This study proposes a new concept to realize a low thermal conductivity in half-Heusler (HH) compounds and develop triple HH compounds via entropy engineering. The n-type medium-entropy M1-xNxCoSb ( M = Zr, Ti, Hf; N = V , Ta, equimolar) triple HH compounds are prepared via levitation melting and spark plasma sintering. Entropy engineering induced Zr-site disorder is characterized via the Raman spectroscopy. Subsequently, the thermal conductivity of the n-type M0.9N0.1CoSb triple HH compound (4.1 Wm(-1)K(-1)) at 323 K is less than-67.5% that of the ZrCoSb HH compound (12.6 Wm- 1K- 1). Furthermore, the Zr-site donor doping considerably improved the power factor, affording a peak figure of merit of ~0.18 for the M0.9N0.1CoSb HH compound at 923 K. This approach proposes a new pathway to lower the thermal conductivity of HH compounds, establishing a high standard for developing high-performance HH compounds.