First‐Principles Prediction of a New Family of Layered Topological Insulators

Abstract

Dozens of layered V2IV2VI6 (V=P, As, Sb, Bi; IV=Si, Ge, Sn, Pb; VI=S, Se, Te) materials are investigated, several of which have been successfully synthesized in experiment. Among them, nine strong topological insulators (TIs), two strong Z2 topological metals (TMs), and nearly twenty trivial insulators are predicted at their equilibrium structures. The TIs are in the (1;111) topological class, with energy gaps ranging from 0.04 to 0.2 eV. The strong Z2 TMs and the trivial insulators belong to the (1;111) and (0;000) topological classes, respectively. Small compressive strains easily turn some of the trivial insulators into strong TIs. This study enriches not only the family of topological materials but also the family of van der Waals layered materials, providing promising candidates for the future spintronic devices.

Comparative Study of Thermoelectric Properties of Sb2Si2Te6 and Bi2Si2Te6

“…Furthermore, the DFTcalculated band gaps of Sb 2 Si 2 Te 6 and Bi 2 Si 2 Te 6 are 0.15 and 0.07 eV, respectively. 38 These results confirm that both materials have a narrow band gap, which ranges from 0.2 to 0.4 eV. This is consistent with the electronic property measurement results, according to which Bi 2 Si 2 Te 6 exhibits bipolar conduction, while Sb 2 Si 2 Te 6 does not.…”

“…density functional theory (DFT) calculations. 38 The measured value for Sb 2 Si 2 Te 6 is almost identical to that reported previously. 37 Moreover, the lattice parameter of Bi 2 Si 2 Te 6 was slightly higher compared with that of Sb 2 Si 2 Te 6 .…”

“…Moreover, although Si and Te nanoprecipitates were also present, their contents were extremely low since related peaks could not be observed in the XRD patterns. Table lists the experimentally measured lattice parameters of Sb 2 Si 2 Te 6 and Bi 2 Si 2 Te 6 and compares them with those determined by density functional theory (DFT) calculations . The measured value for Sb 2 Si 2 Te 6 is almost identical to that reported previously .…”

“…Similar to Sb 2 Si 2 Te 6 , Bi 2 Si 2 Te 6 is expected to have a layered crystal structure but a slightly smaller band gap compared with that of Sb 2 Si 2 Te 6 . 38 In terms of thermal properties, Bi 2 Si 2 Te 6 is expected to exhibit a lower κ latt value than that of Sb 2 Si 2 Te 6 owing to the substitution of Sb by heavy Bi atoms, which may also result in high zT values. However, the electronic and thermal transport properties of polycrystalline Bi 2 Si 2 Te 6 have not been investigated experimentally.…”

“…The existence of its chemical family, Bi 2 Si 2 Te 6 , has already been predicted by first-principles calculations. Similar to Sb 2 Si 2 Te 6 , Bi 2 Si 2 Te 6 is expected to have a layered crystal structure but a slightly smaller band gap compared with that of Sb 2 Si 2 Te 6 . In terms of thermal properties, Bi 2 Si 2 Te 6 is expected to exhibit a lower κ latt value than that of Sb 2 Si 2 Te 6 owing to the substitution of Sb by heavy Bi atoms, which may also result in high zT values.…”