Application of an axial next-nearest-neighbor Ising model to the description of Mn+1AXn phases
Résumé
We show that some important features characterizing the M(n+1)AX(n) phases, a family of hexagonal-structure ternary carbides and nitrides (X) including a transition metal (M) and an A-group element (A), can be reproduced by modifying the spin model known as the axial next-nearest-neighbor Ising model into a form where pseudospin inversion changes the system energy and requires the inclusion of single- and three-spin products. We describe the various MAX phases in terms of M-A or M-X bilayer stacking along the c axis. We discuss the dependence of the cohesive energy and phase stability on coupling parameters which characterize the first-and second-neighbor interactions between those bilayers. We also address the case of "hybrid" MAX phases.