Computational understanding and prediction of 8-electron half-Heusler compounds with unusual suppressed phonon conduction

The conventional thinking of designing materials with low lattice thermal conductivity ?(L) is usually associated with chemical and structural complexity. Here, we proposed a new strategy for establishing the interaction strength between the nested cation and the anionic framework as a control knob for tuning ?(L) in two orders of magnitude in isostructural half-Heusler compounds. A synthesized cubic and light-weight 8-electron half-Heusler compound, namely, MgCuSb, exhibits glass-like thermal conductivity in both magnitude and temperature dependence that seems to contradict common understanding while common 18-electron counterparts are known for high ?(L). Our studies reveal that both the native strong anharmonicity induced by the tension effect of atomic filling and a low-energy shearing vibration mode triggered by weak Mg-Cu bonding are responsible for the unusual suppressed phonon conduction in MgCuSb. Finally, an analytic model is constructed by machine learning method to predict phonon conduction of both 8- and 18-electron half-Heusler compounds in a unified way, which demonstrates that the interaction between cations and anions is universal by means of adjusting the thermal conductivity of this material family.

Automated summary

In this study, a new strategy for tuning the lattice thermal conductivity (L) in isostructural half-Heusler compounds by adjusting the interaction strength between nested cations and the anionic framework is proposed. Through experiments and analysis, it is found that a synthesized 8-electron half-Heusler compound, MgCuSb, exhibits glass-like thermal conductivity despite common understanding for high L in 18-electron counterparts. The unusual suppressed phonon conduction in MgCuSb is attributed to native strong anharmonicity induced by atomic filling and a low-energy shearing vibration mode triggered by weak Mg-Cu bonding.