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 (V0.2Cr0.8)2(Ga0.5Ge0.5)(C0.6N0.4) 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 Cr2N), 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).
Huck et al. (Mon,) studied this question.