Wet-chemical assisted synthesis of nitride and carbonitride MAX phases
KUBITZA N. 1, BIRKEL C. 1,2
1 Technische Universitšt Darmstadt, Darmstadt, Germany; 2 Arizona State University , Tempe, United States
The exceptional materials class of so-called MAX phases is defined as hexagonally layered ternary transition metal carbides and (carbo)nitrides. Their general formula is Mn+1AXn with M = early-to-mid transition metal, A = main group element, mostly from groups 13 and 14, and X = C and/or N (n = 1-4). So far, more than 150 MAX phase compounds are known, however, only low percentages are nitrides (7 %) and even less carbonitrides (1%).  These low numbers can be attributed to the more demanding synthesis procedure due to the high stability and low diffusion rate of nitrogen-containing compounds. However, intriguing materials properties (e.g. superconductivity or magnetism), that are predicted for new MAX phase compositions, drive experimentalist to push for innovative synthesis strategies.
By combining non-conventional wet-chemical based methods, such as the so-called “urea-glass method” , as well as the “liquid ammonia method” , with conventional solid-state preparation techniques, we have developed an alternative two-step process to further expand the hardly investigated field of MAX phase nitrides and carbonitrides by V2GaN and the hitherto unknown carbonitride phases V2GaC1-xNx  and Cr2GaC1-xNx.
For the new carbonitride phases, the mixed carbon/nitrogen character was proven by means of X-ray powder diffraction, Electron energy loss spectroscopy, and X-ray photoelectron microscopy. SEM micrographs reveal the morphology of the samples, consisting of partly typical anisotropic layered MAX phase structures, as well as needle- and drop-like particles covering the surface. Furthermore, magnetic measurements of the Cr2GaC1-xNx were conducted to gain new insights of the influence of the mixed C/N character. This synthesis method has the potential to open the path to further hitherto unknown nitride and carbonitride MAX phases as well as similar ceramic compounds with interesting properties.
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