Unveiling the microscopic origins and thermoelectric performance of full-Heusler compounds K2RbSb and Rb2KSb

Abstract

This study systematically investigates the thermal transport properties of the full-Heusler compounds K₂RbSb and Rb₂KSb using self-consistent phonon theory and the Boltzmann transport equation. The results show that the strong anharmonicity and four phonon scattering of alkali metal atoms result in extremely low lattice thermal conductivity (κ_L) for these compounds. Considering the interaction between phonons and electrons, we obtained a reasonable electron relaxation time by analyzing ADP, POP, IMP, PIE and MFP scattering mechanisms. Under high-temperature conditions (700 K), we achieved excellent thermoelectric performance for p-type K₂RbSb and Rb₂KSb, with zT values of 0.81 and 1.28, respectively. These findings reveal the importance of chemical bonding in achieving ultra-low κ_L and excellent TE performance, and they elucidate the microscopic origins of the ultra-low κ_L in these compounds. These results not only aid in understanding the fundamental physical properties of the materials but also provide theoretical support for their potential applications in thermal management and thermoelectric applications.