Exploring the Cobalt–Carbon System at High Pressures

Metallic carbides are ideal in heavy-duty applications for hypersonic flight and aerospace engineering. In renewable energy research, there is a need for a sustainable permanent magnet that can support technological innovation without being as environmentally taxing as lanthanide rare earth permanent magnets. It has been shown that carbon may have a magnetic pinning effect on carbon, inducing permanent magnetic effects. However, cobalt–carbon only exists as a nanomaterial or thin film, where surface effects can stabilize the metastable compound. We investigated the cobalt–carbon system computationally via random structure searching done with Ab Initio Random Structure Search (AIRSS) interfaced with Castep to perform DFT calculations that generate random structures of cobalt–carbon and adjust them into their local energy minima. We randomly sampled phases of cobalt–carbon at incremental pressures of 5 GPa between 0 and 25 GPa and found a system of 16-atom Pnma-Co3C that became thermodynamically accessible above 7 GPa. We assembled four diamond anvil cells (DACs) containing carbon and cobalt to perform laser heated synthesis at the Argonne National Laboratory.