Effect of spin-orbit coupling on the elastic, mechanical, and thermodynamic properties of Bi-Sb binaries

TL;DR

This study uses first principles calculations to analyze how spin-orbit coupling influences the elastic, mechanical, and thermodynamic properties of Bi-Sb binaries, revealing SOC-induced elastic softening and significant auxetic behavior in certain structures.

Contribution

It provides a comprehensive theoretical analysis of Bi-Sb binaries, highlighting the effects of spin-orbit coupling on their physical properties, which was not thoroughly explored before.

Findings

SOC causes elastic softening in most structures

Three monoclinic structures exhibit large auxeticity

Debye temperature decreases with increasing Bi concentration

Abstract

Using first principles calculations, we systematically study the elastic stiffness constants, mechanical properties, elastic wave velocities, Debye temperature, melting temperature, and specific heat of several thermodynamically stable crystal structures of Bi$_{x}$Sb$_{1-x}$ ($0 < x < 1$) binaries, which are of great interest due to their numerous inherent rich properties, such as thermoelectricity, thermomagnetic cooling, strong spin-orbit coupling (SOC) effects, and topological features in the electronic bandstructure. We analyze the bulk modulus ($B$), Young's modulus ($E$), shear modulus ($G$), $B/G$ ratio, and Poisson's ratio ($\nu$) as a function of the Bi concentration in Bi$_{x}$Sb$_{1-x}$. The effect of SOC on above mentioned properties is further investigated. In general, we observe that the SOC effects cause elastic softening in most of the studied structures. Three monoclinic structures of Bi-Sb binaries are found to exhibit significantly large auxeticity. The Debye temperature and the magnitude of the elastic wave velocities monotonically decrease with increasing Bi-concentration. We also discuss the specific heat capacity versus temperature data for all studied binaries. Our theoretical results are in excellent agreement with the existing experimental and theoretical data. The comprehensive understanding of the material properties such as hardness, mechanical strength, melting temperature, propagation of the elastic waves, auxeticity, and heat capacity is vital for practical applications of the studied binaries.