Halogen substitution, that is, bromine for iodine, in the series of topological BinTeI (n = 1, 2, 3) materials was conducted in order to explore the impact of anion exchange on topological electronic structure. In this proof-of-concept study, we demonstrate the applicability of the modular view on crystal and electronic structures of new Bi2TeBr and Bi3TeBr compounds. Along with the isostructural telluroiodides, they constitute a family of layered structures that are stacked from two basic building modules, ∞2[Bi2] and ∞2[BiTeX] (X = I, Br). We present solid-state synthesis, thermochemical studies, crystal growth, and crystal-structure elucidation of Bi2TeBr [space group R3̅m (no. 166), a = 433.04(2) pm, c = 5081.6(3) pm] and Bi3TeBr [space group R3m (no. 160), a = 437.68(3) pm, c = 3122.9(3) pm]. First-principles calculations establish the topological nature of Bi2TeBr and Bi3TeBr. General aspects of chemical bonding appear to be similar for BinTeX (X = I, Br) with the same n, so that alternation of the global gap size upon substitution is insignificant. The complex topological inversion proceeds between the states of two distinct modules, ∞2[Bi2] and ∞2[BiTeBr]; thus, the title compounds can be seen as heterostructures built via a modular principle. Furthermore, highly disordered as well as incommensurately modulated ternary phase(s) are documented near the Bi2TeBr composition. Single-crystal X-ray diffraction experiments on BiTeBr and Bi2TeI resolve some discrepancies in prior published work.

This work was supported by the German Research Foundation (DFG) in the framework of the Special Priority Program (SPP 1666) Topological Insulators and by the ERANET-Chemistry Program. We acknowledge support by Academic D. I. Mendeleev Fund Program of Tomsk State University (Project 8.1.01.2018), by St. Petersburg State University (Project 15.61.202.2015), by Ministry of Education and Science of the Russian Federation within the framework of the governmental program Megagrants (State Task 3.8716.2017/P220 or 3.8716.2017/9.10), by Russian Science Foundation 18-12-00169 (for surface electronic structure within tight-binding method), by Spanish Ministry of Science and Innovation (Grants FIS 2013-48286-C02-02-P, FIS 2013-48286-C02-440-01-P, and FIS 2016-75862-P).

Peer reviewed