Understanding the role of entropy in designing high-performance thermoelectrics.

The design of high-entropy alloys is effective in lowering thermal conductivity but often reduces carrier mobility, thereby limiting electrical transport properties. Understanding the relationship among configurational entropy, thermal conductivity, and carrier mobility in high-entropy alloys is critical for enhancing thermoelectric performance. We demonstrate that a systematic and substantial increase in configurational entropy in half-Heusler alloys leads to an asymptotic reduction of lattice thermal conductivity. The reduced phonon group velocity and enhanced phonon scattering induced by atomic-scale chemical disorder result in a low lattice thermal conductivity of 2 watts per meter per kelvin at room temperature, with an achievable minimum of about 1.48 watts per meter per kelvin as disorder further increases, approaching the amorphous limit. Single-phase stabilization, along with optimized carrier mobility, is essential to preserve high electrical conductivity. Our results provide fundamental insights into integrating specific strategies with high-entropy design to simultaneously achieve low thermal conductivity and high thermoelectric performance, advantageous for high-temperature thermoelectric power generation applications.