Ab initio modeling of MAX phase solid solutions using the special quasirandom structure approach.

MAX phases are technologically important materials exhibiting both metallic and ceramic properties. In the present study we propose the use of the special quasirandom structure (SQS) approach as a computationally tractable method to predict the phase stability of disordered MAX phase solid solutions. We have generated 128-atom SQS structures to mimic the 211 MAX phase solid solutions with random distribution of different elements within either the M or the A sublattice. Using DFT-calculated mixing energy and instability energy as predictors, we show that (Zr1-xMx)2AlC (for M = Nb and Ta) and Zr2(Al1-xAx)C (for A = Bi, Pb and Sn) MAX phase solid solutions may be experimentally synthesized. Our predicted results are in agreement with the limited available experimental data and chemical bonding analysis using the crystal-orbital Hamilton population (COHP) technique. The SQS cells reported are transferable and can be employed to model numerous MAX phase solid solutions.