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 (<i>M</i>-element), a main group element (mainly groups 13-15) or late transition metal (<i>A</i>-element) and carbon and/or nitrogen (<i>X</i>-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 <i>M</i>- and <i>A</i>-site, respectively. Much less common are solid solution phases with mixed elements on both <i>M</i>- and <i>A</i>-site simultaneously (double-site solid solutions), as well as solid solutions on the <i>X</i>-site (carbonitride MAX phases). Challenging these restrictions in the chemical composition space, we present here for the first time (V_0.2Cr_0.8)₂(Ga_0.5Ge_0.5)(C_0.6N_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 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).