Investigation of novel crystal structures of Bi–Sb binaries predicted using the minima hopping method

Abstract

Semi-conducting alloys BiSb have emerged as a potential candidate for topological insulators and are well known for their novel thermoelectric properties. In this work, we present a systematic study of the low-energy phases of 35 different compositions of BiSb (0 < x < 1) at zero temperature and zero pressure. We explore the potential energy surface of BiSb as a function of Sb concentration by using the ab initio minima hopping structural search method. Even though Bi and Sb crystallize in the same R3[combining macron]m space group, our calculations indicate that BiSb alloys can have several other thermodynamically stable crystal structures. In addition to the configurations on the convex hull, we find a large number of metastable structures which are dynamically stable. The electronic band structure calculations of several stable phases reveal the presence of strong spin-orbit interaction leading to the Rashba-Dresselhaus spin-splitting of bands which is of great interest for spintronics applications. We also find an orthorhombic structure of BiSb in the Imm2 space group which exhibits signatures of type-II Weyl semimetal. Additionally, we have studied the thermoelectric properties of the selected structures. Regarding thermoelectric properties, we find that the compositions which crystallize in the rhombohedral structure exhibit values of the Seebeck coefficient and the power factor similar to that of BiTe at room temperature, while the theoretical maximum figure of merit (ZT) is smaller than that of BiTe. We observe enhancement in the thermopower with the increase in the strength of the Rashba-Dresselhaus spin-splitting effect.

Prediction and control of spin polarization in a Weyl semimetallic phase of BiSb

“…The polarization can be switched by reversing the direction of the polar displacement of Bi-atoms from the ideal rocksalt sites. 27,28 We find that the energy barrier (∆E) to overcome the transition from the paraelectric phase in R3m symmetry 41 (λ = 0) to the ferroelectric phase in R3m symmetry (λ = ±1) is ∆E = 0.141 eV/f.u. (see figure S5).…”

“…We find that E R = 147.3 meV and α R = 10.43 eVÅ for CBB along L-H direction, while E R = 65.9 meV and α R = 4.71 eVÅ for VBT along L-H direction. Further details about the Rashba spin-splitting in this compound can be obtained in Ref 41. In the R3m phase, Bi and Sb atoms are displaced from the ideal rocksalt sites.…”

“…39,40 For all calculations presented in this paper, we used a conventional unit-cell of BiSb (space group 160: R3m), containing 3 atoms of Bi and 3 atoms of Sb. 41 The cell was relaxed, first in the internal coordinates and then in the volume until the total energy difference between two consecutive steps was smaller than 10 −8 eV and the total residual forces were less than 10 −5 eV/Å. Spin-orbit interaction was included for all ionic relaxations.…”

Ab initio density functional theory study of the electronic, dynamic, and thermoelectric properties of the crystalline pseudobinary chalcogenide (GeTe)x/(Sb2Te3)Ibarra-Hernández1, Raty2 2018Phys. Rev. BSelf Cite

“…No comparison with data measured on the stable GST326 phase is possible as Sittner et al [64] evidenced a very large variability in the measured Seebeck coefficient with annealing temperature. The strong variation of the S with the annealing T could be due to changes in the carrier concentration like in the case of Bi-Sb compounds [65].…”

Electronic structure, lattice dynamics, and optical properties of a novel van der Waals semiconductor heterostructure: InGaSe2

“…The non-linear behavior of the lowest energy acoustic phonon modes near Γ is not exclusive to our system. It has also been observed in other layer materials, as in different stacking configurations for Graphene 85 or KC 8 and Rb 8 86 , BiSb layered structure 87 and it is related to the weak forces between layers and the rigid-layer (in-plane layer) that moves as a rigid unit. 88,89 Nevertheless, the non-linear behavior that we observe is not as abrupt as in the previous mentioned examples, since we have bilayers stacking along the c-axis.…”