MAX phases are a unique class of layered ceramic-metal materials known as ternary carbides and nitrides (𝑀_𝑛+1𝐴𝑋_𝑛), that combine good mechanical properties and thermal stability with metallic machinability, ductility, and high electrical conductivity. Even under high temperatures and in highly corrosive environments, they can be used in bearings, gas-burning nozzles, or high-performance engine components. These materials also serve as precursors for MXenes, with potential applications ranging from energy storage/production to catalysis, biosensing, gas sensing, and conductive inks. The synthesis of MAX phases is critical and requires proper characterisation and understanding, as the synthesis conditions directly influence their properties and performance [1].

Given their highly desirable properties and growing library of MAX phases, we have decided to investigate the synthetic process in greater detail to better elucidate the reaction mechanism. Such insights would enable us to apply additional morphological and other modifications during synthesis. As a target phase, we have selected Ti₃AlC₂, one of the most studied and well-characterised MAX phases, for in situ synthesis under scanning electron microscopy (SEM), which imposes fewer constraints on sample preparation than transmission electron microscopy (TEM). By improving our understanding of the synthesis mechanisms, we aim to apply targeted morphological and property modifications during the process.

Several sample-preparation approaches were evaluated for the method, including simple drop casting of a precursor mixture (Ti, Al, and C powder elements in  3:1.1:2 [2], [4] and 3:1.2:1.8 stoichiometric ratios) in an ethanol suspension. The dried mixture was pressed into pellets to provide good contact between precursor elements (same stochiometric ratio as the powder mix) and polished using broad ion beam to ensure sufficient flatness of surface [1], [3] for SEM observation and TEM lamella preparation. This wide variety of approaches enables comprehensive, all-angle characterisation of the synthesis.

The synthesis was conducted using a localised heat source on one side of the sample. Electron backscatter diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDS) were selected as the primary analytical methods due to their ability to fully characterise the distribution of elements and the presence of phases, even at high temperatures, within relatively short time intervals. Additionally, EBSD is comparable to the traditional powder X-ray diffraction (PXRD) method, enabling direct comparison of data from bulk-synthesised material reported in the literature and from experiments conducted in our work.