Transition metal carbo chalcogenides: A novel family of 2D solid lubricants

Two-dimensional (2D) layered materials such as transition metal dichalcogenides (e.g., MoS₂, WS₂) and MXenes (e.g., Ti₃C₂T_x), as well as hybrids of these materials are the focus of current research in solid lubrication due to their outstanding performance. Transition metal carbo-chalcogenides (TMCCs), consisting of an MXene core and a TMD-like surface, represent an inherent combination of TMDs and MXenes without the need to construct hybrids out of the individual layers. Due to their layered structure and surface chemistry, favorable tribological properties can be expected from these novel materials. Here, multilayer Ta₂S₂C and Nb₂S₂C TMCCs are deposited solely as a powder onto a steel substrate and their tribological properties under linear sliding against different counterbodies, i.e., Al₂O₃, SiC, 100Cr6, and polytetrafluoroethylene (PTFE) are discussed. Advanced materials characterization techniques are used to detect the presence of TMCCs inside the wear tracks and to reveal their 2D structure within the tribofilm. Finally, density functional theory (DFT) simulations are used to unravel the easy shearability of TMCCs at the nanoscale. The results demonstrate the great potential of this new 2D material family, which also offers many possibilities for defined tuning of the solid-solid interface.