Even well-known element pairings hold surprises. A team found such surprises when they identified two previously unknown compounds made from bismuth and neodymium or samarium. The materials are thermodynamically stable phases in a materials system that has been well studied. Scientists thought this class of bismuth compounds was fully understood.
Finding such unexpected materials illustrates the existence of a potentially vast source of as yet unknown materials. The properties and structure of the new materials suggest that scientists can tune this family of compounds. Such tuning may lead to materials that could capture, for example, waste heat generated during fuel combustion to increase vehicle fuel efficiency.
While research to develop new materials for a wide range of energy technologies increasingly has focused on developing rational design and synthesis approaches, these results demonstrate that serendipity can still play a role in the discovery of materials. Bismuthides are compounds of bismuth and, typically, other metals that are prone to donate their electrons. In comparison to other compounds composed of an element from the same group in the Periodic Table such as nitrides or phosphides, bismuthides are far less explored due to the lower tendency of bismuth to form chemical bonds with other metals. Although scientists have constructed binary phase diagrams containing bismuth for many elements, even thoroughly studied systems may still hold some surprises for researchers as this study demonstrates. Researchers discovered two new binary rare-earth bismuthides, Nd3Bi7 and Sm3Bi7, in seemingly well-known systems where the existence of these phases have never been indicated before, probably due to their limited thermal stability, meaning they can’t be synthesized using high-temperature processes commonly employed with this type of inorganic materials. The crystal structure of these compounds includes extended frameworks of bismuth–bismuth bonds as a result of the bismuth-rich composition. Physical property measurements and theoretical computations reveal metallic properties for Nd3Bi7 and Sm3Bi7. Detailed analysis of the electronic structure suggests that electron-doping, which can be achieved by chemical tuning, will drive these systems toward a semiconducting state. The latter can provide potentially good performance of these new phases as thermoelectric materials.
University of Delaware
This work was supported by the Department of Energy, Office of Science, Basic Energy Sciences.
A. Ovchinnikov, J.P.A. Makongo, and S. Bobev, “Yet again, new compounds found in systems with known binary phase diagrams. Synthesis, crystal and electronic structure of Nd3Bi7 and Sm3Bi7.” Chemical Communications 54, 7089 (2018). [DOI: 10.1039/c8cc02563k]