Sterically stabilised (Ti,Zr,Nb,Hf,M)2(Al,Sn)C (M=V/Ta) MAX phase solid solutions with enhanced chemical complexity on the M-site

The MAX phases constitute a family of atomically layered ternary carbides/nitrides with hexagonal structure (space group P6 3 /mmc ) applauded for their compositional versatility, which is demonstrated by the easy formation of solid solutions with varying chemical complexity. Intentionally tailoring chemically complex MAX phase solid solutions enables the production of materials with tuneable properties vis-à-vis the requirements of the targeted application(s). This work synthesised high-purity (Ti,V,Zr,Nb,Hf) 2 (Al,Sn)C and (Ti,Zr,Nb,Hf,Ta) 2 (Al,Sn)C MAX phase solid solutions by reactive hot pressing metal hydride-based powder feedstocks at 1450 °C, also elucidating their elemental-diffusion-limited, complex formation mechanism. The hydrogenated, milled, and sieved powder feedstocks facilitated the formation of damage-tolerant ceramics with homogeneous microstructures and minute impurities. Sterically balanced M- and A-site elemental occupancies alleviated lattice distortions, whilst increasing the configurational entropy of the produced MAX phase compounds further enhanced their thermodynamic stability.