Decoupling thermoelectric transport coefficients of Dirac semimetal Na2AgSb with intrinsically ultralow lattice thermal conductivity

Abstract

Topological semimetals have attracted tremendous attention from the science community owing to their exotic electronic structures. It is generally assumed that metallic or similar systems exhibit rather poor thermoelectric performance due to very small Seebeck coefficients. Here we demonstrate by first-principles calculations and Boltzmann transport theory that the Dirac semimetal Na2AgSb is an exception because of its strong band asymmetry around the Fermi level. In addition, the system shows ultralow lattice thermal conductivity caused by the rattling of the Na atoms in the cage-like framework of Ag and Sb atoms. As a consequence, one can realize certain decoupling of the thermoelectric transport coefficients, and a considerable ZT value of 1.3 can be reached at 300 K in the p-type Na2AgSb. The present work highlights the promising possibility of semimetals or similar systems for high-performance thermoelectric applications.