Experimental and DFT investigation of (Cr,Ti)₃AlC₂ MAX phases stability

Using a synergistic combination of experimental and computational methods, we shed light on the unusual solubility of (Cr,Ti)₃AlC₂ MAX phase, showing that it may accommodate Cr only at very low concentrations (<2 at%) or at the exact Cr/(Cr + Ti) ratio of 2/3, even when the ratio of reactants is far from this stoichiometry (1/2 ≤ Cr/(Cr + Ti) ≤ 5/6). In both phases, Cr exclusively occupies the 4f sites, bridging carbide layers with the Al layer. Despite this, the peculiar stability of (Cr_2/3Ti_1/3)₃AlC₂ is attributed to the formation of strong, spin-polarized Cr–C bonds, which result in volume reduction and a marked increase in c/a ratio.

IMPACT STATEMENT

Solubility of Cr and Ti in (Cr,Ti)₃AlC₂ was investigated using experimental and DFT techniques. It was also determined that (Cr_2/3Ti_1/3)₃AlC₂ owe its remarkable stability to the formation strong Cr–C bonds.