Synthesis of (V 0.2 Cr 0.8 ) 2 (Ga 0.5 Ge 0.5 )(C 0.6 N 0.4 ), a Triple-Site Solid Solution MAX Phase

MAX phases are an extremely versatile family of layered compounds that usually consist of an early to-mid transition metal ( M -element), a main group element (mainly groups 13–15) or late transition metal ( A -element) and carbon and/or nitrogen ( X -element). It is therefore not too surprising that in addition to the roughly 70 compounds with 211 stoichiometry, there exist many solid solutions with mixed elements on the M - and A -site, respectively. Much less common are solid solution phases with mixed elements on both M - and A -site simultaneously (double-site solid solutions), as well as solid solutions on the X -site (carbonitride MAX phases). Challenging these restrictions in the chemical composition space, we present here for the first time (V 0.2 Cr 0.8 ) 2 (Ga 0.5 Ge 0.5 )(C 0.6 N 0.4 ) as a new carbonitride member of the MAX phase family, containing solid solutions on all three lattice sites simultaneously. This triple-site solid solution MAX phase is synthesized by high-temperature solid-state methods, and we demonstrate that it is possible to use two different nitrogen-containing precursors (VN and Cr 2 N), respectively. Structure, morphology and chemical composition are characterized by X-ray powder diffraction (XRD), electron microscopy (SEM/TEM), secondary ion mass spectrometry (SIMS), and X-ray photoelectron spectroscopy (HAXPES).