High-Temperature-Phase BiRhI: Electronic Localization by Structural Distortion.

The metal-rich compound BiRhI was discovered in a thorough investigation of the Bi-Rh-I phase system. The monoclinic crystal structure was solved via single-crystal X-ray diffraction. It consists of infinite strands of face-sharing distorted square antiprisms [RhBi], which are separated by iodide ions. BiRhI is the high-temperature phase related to the weak three-dimensional topological insulator BiRhI (BiRhI) and forms peritectically at 441 °C, where BiRhI decomposes. The structure of BiRhI is compared with BiRuI and BiRhI, all three sharing a similar intermetallic strand-like structure, although their overall count of valence electrons differs. A chemical bonding analysis of BiRhI via the electron localizability indicator reveals a complex bonding pattern with covalent bonds between rhodium and bismuth, as well as between bismuth atoms and suggests a possible explanation for the formation of this structure type. Band structure calculations indicate a narrow band gap of 157 meV, which was verified by resistivity measurements on a pressed powder pellet and on single crystals. In a broader context, this strandlike structure type accounts for unusual physical phenomena, such as the transition into a charge-density-wave phase.