Crystal Growth and Real Structure Effects of the First Weak 3D Stacked Topological Insulator Bi₁₄Rh₃I₉

Abstract

A detailed account of the crystal-growth technique and real structure effects of the first 3D weak topological insulator Bi 14 Rh 3 I 9 = [(Bi 4 Rh) 3 I][BiI 4 ] 2 is given. As recently shown, this compound features decorated-honeycomb [(Bi 4 Rh) 3 I] 2+ sheets with topologically protected electronic edge-states and thereby constitutes a new topological class. Meticulous optimization of the synthesis protocol, using thermochemical methods, yielded high-quality crystals of Bi 14 Rh 3 I 9 suitable for the experimental characterization of the structural as well as topological properties. Insightful information about the crystal structure, its pseudosymmetry, and the thereby caused stacking disorder and twinning phenomena, obtained by X-ray diffraction and TEM studies, is crucial for an adequate theoretical modeling of coupling between the topologically nontrivial sheets. As demonstrated here, Bi 14 Rh 3 I 9 is not an exotic anomaly, but a stable, structurally well-defined bulk material, which can be used for gaining experimental knowledge about the yet poorly investigated class of weak 3D topological insulators. It could equally foster the synthesis and understanding of related compounds with the bismuth-based decorated-honeycomb sheets.