High-Pressure Discovery of Co–Bi Compounds

Many transition metal (TM) and Bi compounds exhibit emergent properties, such as superconductivity and permanent magnetism, driving interest in TM and Bi bond formation. However, there is a paucity of TM–Bi materials due to the limited reactivity between TMs and Bi at ambient pressure. We can use high-pressure conditions to overcome this to synthesize novel TM–Bi compounds. High pressure yielded the first Co–Bi compound, superconducting CoBi₃, at 10 GPa. We aimed to study the Co–Bi system above 10 GPa. Using ab initio random structure searching (AIRSS), we found 5 new predicted Co–Bi structures. In conjunction with our calculations, we performed laser-heated diamond anvil cell experiments and realized 3 of the predicted structures: <b>α</b>-CoBi₂, ß-CoBi, and ß-CoBi₂. Additionally, by using a high-pressure multi-anvil press, we synthesized a 4th compound not predicted by AIRSS, <b>α</b>-CoBi, that forms in a novel structure type not reported in the ICSD. Through examination of these structures, we determine trends in TM and Bi bond formation, such as higher dimensionality and higher bismuth content at higher pressure. Further, these higher-pressure phases are isostructural to other TM–Bi structures. Density of states calculations suggest these materials are non-magnetic, unlike ferromagnetic MnBi and Mn_1.05Bi. These results illustrate how computational methods can enhance the discovery of experimental materials and understanding of the structure-property relationship.