Table 3 Impact of atomic size on formation of chemically ordered structures.

Energy difference, ΔE, between the chemically ordered i-MAX phase and the related MAX phase with a disordered distribution of M 1 and M 2 on the M lattice, for (V2/3Zr1/3)2AlC, (Mo2/3Y1/3)2AlC, (Mo2/3Sc1/3)2AlC, and the hypothetical (V2/3Ti1/3)2AlC. The corresponding temperature, Tdisorder, required for decreasing the free energy of the disordered phase to the ordered one through the entropic contribution to Gibbs free energy. The difference in the atomic radius (metallic) and electronegativity between the two metals M1 and M2 is also included.

M1M2ΔE (meV per
atom)
Tdisorder
(K)
Difference between M2 and M1
Atomic
radius* (Å)
Electronegativity
VZr−13649510.25−0.30
MoY−19771920.41−0.94
MoSc−8229990.23−0.80
VTi−124380.12−0.09

*1.35 Å for V, 1.60 Å for Zr, 1.39 Å for Mo, 1.80 Å for Y, 1.62 Å for Sc, and 1.47 Å for Ti.

†1.63 Å for V, 1.33 Å for Zr, 2.16 Å for Mo, 1.22 Å for Y, 1.36 Å for Sc, and 1.54 Å for Ti