Strong quartic anharmonicity, ultralow thermal conductivity, high band degeneracy and good thermoelectric performance in Na2TlSb

Abstract

We employ first-principles calculations combined with self-consistent phonon theory and Boltzmann transport equations to investigate the thermal transport and thermoelectric properties of full-Heusler compound Na₂TlSb. Our findings exhibit that the strong quartic anharmonicity and temperature dependence of the Tl atom with rattling behavior plays an important role in the lattice stability of Na₂TlSb. We find that soft Tl-Sb bonding and resonant bonding in the pseudocage composed of the Na and Sb atoms interaction is responsible for ultralow κ_L. Meanwhile, the multi-valley band structure increases the band degeneracy, results in a high power factor in p-type Na₂TlSb. The coexistence of ultralow κ_L and high power factor presents that Na₂TlSb is a potential candidate for thermoelectric applications. Moreover, these findings help to understand the origin of ultralow κ_L of full-Heusler compounds with strong quartic anharmonicity, leading to the rational design of full-Heusler compounds with high thermoelectric performance.