Cell-constrained melt-quench simulation of d-AlCoNi: Ni-rich versus Co-rich structures

Abstract

Complex crystalline ground state structures may be obtained by direct (simulated) quenches from the melt for systems of up to a few hundred atoms, given the constraint of a fixed unit cell, coupled with use of (i) replica-exchange Monte Carlo, and (ii) realistic empirical interaction pair potentials. We applied this procedure to decagonal approximants of Al72Co8Ni20 and Al73Co27, obtaining the best energies seen to date for d-AlCoNi models (respectively +20 meV/atom and +9 meV/atom above the tie-plane of competing phases). We elucidated the reasons why different decagonal structures are associated with the Ni-rich and Co-rich compositions. We found a cell doubling to c = 8 Å due to layer puckering not only in the Co-rich structure, but (locally) in the nominally c = 4 Å Ni-rich structure.