Exploration of Stacked MXenes as Precursors to Ultra-High Temperature Ceramics

Ultra-high temperature ceramic (UHTC) vacancy-ordered zeta phases are critical for applications over 2000°C due to their high melting temperatures, oxidation resistance, and fracture toughness. However, the synthesis of zeta phase systems typically requires high temperature processing at >1400°C with high pressures, making alternative synthesis pathways to UHTC phases highly desirable. In this work, we investigate the potential of layered 2D MXenes as nanoceramic building blocks for nanolamellar carbide and nitride zeta-like phases. Stacked MXenes can expand the domain of zeta-like phases via their large space of interfacial combinations. We employed density functional theory (DFT) to investigate the thermodynamic stability of stacked MXenes as UHTC precursors, with sequential quasi-random structures to study non-stoichiometric nanolamellar carbides. We identify both stoichiometric and non-stoichiometric nanolamellar carbides below the established convex hull. Furthermore, we use a workflow that combines DFT simulations and machine learning to predict key UHTC features, such as melting temperature and elastic constants. Our findings show that by using stacked MXenes the UHTC domain can be expanded beyond vacancy-ordered zeta phases and traditional UHTC transition metals via a lower-temperature synthesis pathway.