CAREER: Fundamentals and synthesis of new compositions and shapes/microstructures of 3D and 2D carbides, nitrides and carbonitrides (MAX phases and MXenes)

CAREER: Fundamentals and synthesis of new compositions and shapes/microstructures of 3D and 2D carbides, nitrides and carbonitrides (MAX phases and MXenes) CAREER: Fundamentals and synthesis of new compositions and shapes/microstructures of 3D and 2D carbides, nitrides and carbonitrides (MAX phases and MXenes) Overview The central goal of this proposal is to synthesize new members as well as new shapes and microstructures of the three- and two-dimensional layered compounds that belong to the families of MAX phases and MXenes. The main target materials are: (i) (Carbo)nitrides, because they are much less explored than the respective carbides, yet, hold promise for improved mechanical stability (solid solution strengthening) and higher conductivities (additional electron of the nitrogen) and (ii) Cr-, Mn- and Mo-containing phases, because of intriguing magnetic (Cr, Mn) and catalytic behavior (Mo) whose investigations are still in their infancy. The distinguishing factor is this proposals strong focus on wet chemical-assisted techniques which (i) benefit from intimate mixing of the precursors on the atomic/molecular scale and with that typically reduced reaction times and temperatures (this leads to MAX phase particles instead of the typical bulky structures and can also stabilize metastable phases), and (ii) allow for advanced processing of the liquid/gel precursor mixture into additional shapes, e.g. wires and hollow microspheres, that would not be possible with powders used in solid-state reactions. To evaluate their stability/degradation and functional properties, the materials will be subject to mechanical testing (nanoindentation) and thermoanalysis as well as electronic/magnetic transport and catalytic measurements. Intellectual Merit The preliminary data that this proposal is based on demonstrate the strengths of the wet chemistry (liquid ammonia and sol-gel) that is used to prepare (mostly amorphous) precursor mixtures that are subsequently annealed, either by conventional or microwave heating, to form the crystalline target compounds. The precursors obtained in liquid ammonia are carbon-free and ensure synthesis of high-quality nitride MAX phases (and MXenes after exfoliation) without any carbon impurities. In the sol-gel process, the gel composition is variable in terms of the (transition) metal ions and the carbon and nitrogen source. This enables expansion to further MAX phase members and tuning of the C/N ratio in carbonitrides. Adding a (bio)polymer leads to a gel that can manually be pulled into MAX phase wires, that have never been prepared before. Being able to manipulate the shape and microstructure of these 3D and 2D layered materials is particularly exciting since it paves the way to new fields of applications due to enhanced processability (that is missing in conventional solid-state chemistry). While the fundamentals between synthesis conditions, structure, morphology and properties will be developed for 3D and 2D layered compounds, they can transcend into the syntheses of new versions of other types of materials, such as borides and oxides. Broader Impacts The outcome of this proposal will be the synthesis of entirely new types of structural and functional materials and will lay the groundwork for various application-based areas, such as construction (self-healing materials, refractory materials), energy technologies (magnetocalorics, catalysts, sensing), consumer electronics (coatings) and electronic textiles (smart/functional fabrics). Concurrently, a strong outreach and educational program will be developed that addresses different aspects of materials science and diverse local, Arizona- and worldwide target groups. This program will be a platform for (i) outreach and recruiting (MateriAlZ Seminars, together with different campus communities at ASU, such as the Society of Women Engineers), (ii) teaching and mentoring (MateriAlZ Buddies pairing ASU and local high school students), (iii) education and discussions (MateriAlZ Winter Schools, organized yearly with the University of Arizona), (iv) networking and promoting (@RealTimeMateriAlZ twitter account reaching an international audience and forging connections to scientific institutes as well as the general public).