Bonding profiling of gapless ceramic V₂GaC/N MAX phases: a spectroscopic and dual theoretical approach

The family of MAX phases is growing faster than ever, resulting in more than 340 reported members so far. Even though the variety of different M- and A-elements is overwhelming, the X-site of MAX phases is still mainly dictated by solely carbide-based materials, while nitrogen-based materials, such as nitrides and (carbo)nitrides account for below 10% in total. It follows that more profound studies comparing those three classical MAX phase groups are rare in the literature, particularly in terms of combining computational considerations with high-resolution spectroscopic experiments. Here, we report the electronic properties of three vanadium-based MAX phases: V₂GaC, V₂GaN, and the (carbo)nitride phase V₂GaC₁₋ₓNₓ. This investigation is carried out for C/N K-edge and the V L-edge using soft X-ray absorption (XAS) and emission spectroscopy (XES). We determine the x value to be 0.6 in the (carbo)nitride V₂GaC₁₋ₓNₓ phase. Additionally, we determine V²˙²⁺ as the formal oxidation state in all three phases using ligand field multiplet theory (LFMT) calculations. Our density functional theory (DFT) calculations indicate the presence of carbon vacancies in the V₂GaC phase. DFT and LFMT theoretical methods confirm that the V₂GaC has a higher degree of covalency than the V₂GaN phase. Also, Gallium interactions are the weakest with C/N and are entirely metallic.