Phase stability and thermoelectricity in topological Dirac semimetal Na3Bi

Abstract

A vibrant research field in condensed matter is the study of topological materials, which range from topological insulators to Dirac semimetals and Weyl semimetals. Na3Bi is predicted to be Dirac semimetal with a Dirac node near the Fermi level. Hence, to validate the presence of Dirac cone and to check the stability of Na3Bi in cubic and hexagonal phases for its practical applications an ab-initio calculation has been performed. A structural phase transition has been observed from hexagonal to cubic phase at 0.89 GPa pressure for Na3Bi. The computed elastic constants satisfy Born-Huang stability criteria for both phases indicating the mechanical stability of the present compound. But it has been found that the P63/mmc phase of Na3Bi is dynamically unstable at ambient conditions therefore, the thermoelectric properties of c-Na3Bi have been investigated by employing Boltzmann transport theory. The low lattice thermal conductivity (1.89 W/mK) and high value of the figure of merit (0.32) at 1200K suggest a good thermoelectric response of the material at high temperatures. Hence, Na3Bi is a potential material that can be used in quantum electronic and thermoelectric devices.