Topological Dirac Semimetal Phase in Bismuth Based Anode Materials for Sodium-Ion Batteries

TL;DR

This study uses advanced density functional theory calculations to explore the topological electronic properties of Na3Bi, revealing a SOC-driven Dirac semimetal state and a topological phase transition in Na3Bi-Sb alloys, with implications for sodium-ion battery anodes.

Contribution

It demonstrates that the SCAN meta-GGA functional provides a more accurate description of Na3Bi's electronic structure and topological phase transitions than GGA, highlighting the importance of SOC effects.

Findings

SCAN yields better agreement with experiments for Fermi velocities and band shifts.

Na3Bi exhibits a SOC-driven Dirac semimetal state with SCAN, unlike GGA predictions.

A topological phase transition occurs in Na3Bi-Sb alloys as SOC strength varies.

Abstract

Bismuth has recently attracted interest in connection with Na-ion battery anodes due to its high volumetric capacity. It reacts with Na to form Na$_3$Bi which is a prototypical Dirac semimetal with a nontrivial electronic structure. Density-functional-theory based first-principles calculations are playing a key role in understanding the fascinating electronic structure of Na$_3$Bi and other topological materials. In particular, the strongly-constrained-and-appropriately-normed (SCAN) meta-generalized-gradient-approximation (meta-GGA) has shown significant improvement over the widely used generalized-gradient-approximation (GGA) scheme in capturing energetic, structural, and electronic properties of many classes of materials. Here, we discuss the electronic structure of Na$_3$Bi within the SCAN framework and show that the resulting Fermi velocities and {\it s}-band shift around the $\Gamma$ point are in better agreement with experiments than the corresponding GGA predictions. SCAN yields a purely spin-orbit-coupling (SOC) driven Dirac semimetal state in Na$_3$Bi in contrast with the earlier GGA results. Our analysis reveals the presence of a topological phase transition from the Dirac semimetal to a trivial band insulator phase in Na$_{3}$Bi$_{x}$Sb$_{1-x}$ alloys as the strength of the SOC varies with Sb content, and gives insight into the role of the SOC in modulating conduction properties of Na$_3$Bi.