Influence of the M- and A-Elements on the Oxidation Stability of Solid Solution MAX Phases V2Ga1–xGexC and Cr2Ga1–xGexC

MAX phase carbides have attracted much attention due to their unique combination of metallic and ceramic properties, making them promising materials for high-temperature applications. Understanding how the materials fail is a crucial step in working toward implementing them into devices outside of the laboratory setting. Their stability toward oxidation at high temperatures, while also being electronically and thermally conductive, sets MAX phases apart from other materials. Some aluminum-containing compounds form a protective alumina layer that contributes to the oxidation resistance of the respective MAX phase. However, a broader understanding of how other MAX phases, especially those with M-elements beyond titanium and A-elements beyond aluminum, oxidize is lacking. Therefore, we synthesized two A-site solid solutions (gallium and germanium as the A-elements) based on chromium and vanadium as M-elements by high-temperature solid-state syntheses. Their composition, structural properties, and bonding characteristics are investigated by synchrotron powder X-ray diffraction, electron microscopy with elemental analysis, and Raman and X-ray photoelectron spectroscopy. Thermal analysis reveals the influence of the M- and A-elements on the oxidation behavior: phases with Cr on the M-site have higher oxidation stability than with V, and solid solutions Cr₂Ga_1–xGe_xC have improved oxidation resistance compared to the individual phases Cr₂GaC and Cr₂GeC.