Martensite-type ε-VC_y′′ high pressure synthesis pathway revealed through in situ x-ray diffraction

High-pressure synthesis is a powerful tool in materials discovery and often uncovers new metastable phases, even in well studied systems such as transition metal carbides. The vanadium–carbon system has been thoroughly studied due to its importance in the steel industry as well as its many high resilience phases used across a range of industrial applications, such as in turbine coatings and catalysis.^1,2 Although this system is well known for strength and resiliency, there are few studies exploring syntheses under high-pressure.³ Here we employ high-pressure synthesis with the multi-anvil press to investigate the relative stability of known and novel vanadium carbides. During high-pressure synthesis, in situ synchrotron XRD data reveals significant volume expansion consistent with carbon incorporating into the metal lattice interstices and provides a time-resolved glimpse into the growth dynamics of the competing phases. Here we present in situ synchrotron XRD data as well as the synthesis and recovery of the novel martensite type ε-VC_y′′ phase between 1.1–5.4 GPa. This discovery of a novel vanadium analogue of the well-known martensite structure demonstrates that high-pressure synthesis may be a rich source for other non-equilibrium carbide materials, and that in situ XRD can reveal the path towards novel materials.