Modular Design with 2D Topological-Insulator Building Blocks: Optimized Synthesis and Crystal Growth and Crystal and Electronic Structures of BixTeI (x = 2, 3)

Structural engineering of topological bulk materials is systematically explored with regard to the incorporation of the buckled bismuth layer [Bi 2 ], which is a 2D topological insulator per se, into the layered BiTeI host structure. The previously known bismuth telluride iodides, BiTeI and Bi 2 TeI, offer physical properties relevant for spintronics. Herewith a new cousin, Bi 3 TeI (sp.gr. R 3 m, a = 440.12(2) pm, c = 3223.1(2) pm), joins the ranks and expands this structural family. Bi 3 TeI = [Bi 2 ][BiTeI] represents a stack with strictly alternating building blocks. Conditions for reproducible synthesis and crystal-growth of Bi 2 TeI and Bi 3 TeI are ascertained, thus yielding platelet-like crystals on the millimeter size scale and enabling direct measurements. The crystal structures of Bi 2 TeI and Bi 3 TeI are examined by X-ray diffraction and electron microscopy. DFT calculations predict metallic properties of Bi 3 TeI and an unconventional surface state residing on various surface terminations. This state emerges as a result of complex hybridization of atomic states due to their strong intermixing. Our study does not support the existence of new stacking variants Bi x TeI with x > 3; instead, it indicates a possible homogeneity range of Bi 3 TeI. The series BiTeI–Bi 2 TeI–Bi 3 TeI illustrates the influence of structural modifications on topological properties.