Stability and instability of long-period superstructures in binary Cu–Pd alloys: A first principles study

Whereas binary intermetallic compounds often appear as ordered structures with fewer than 10 atoms per cell, large-supercell structures consisting of one- and two-dimensional superstructures have long been observed in CuPd. However, whereas the stability of the ordinary one-dimensional long-period superstructures (1-D LPS) has been previously investigated by first-principles total-energy methods, two-dimensional superstructures were not amenable to such calculations because of their large number of atoms (OO(103) atoms/cell). Using a cluster expansion extracted from a set of first-principles total energy calculations, we show that 2-D LPSs are likely kinetically-stabilized structures which transform into the 1-D LPS ground-state structures at thermodynamic equilibrium.