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

Abstract

The conventional thinking of designing materials with low lattice thermal conductivity κL 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 κL 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 κL. 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.