Free energy and molecular dynamics calculations for the cubic-tetragonal phase transition in zirconia - art. no. 094101

The high-temperature cubic-tetragonal phase transition of pure stoichiometr ic zirconia is studied by molecular dynamics (MD) simulations and within th e framework of the Landau theory of phase transformations. The interatomic forces are calculated using an empirical, self-consistent, orthogonal tight -binding model, which includes atomic polarizabilities up to the quadrupola r level. A first set of standard MD calculations shows that, on increasing temperature, one particular vibrational frequency softens. The temperature evolution of the free-energy surfaces around the phase transition is then s tudied with a second set of calculations. These combine the thermodynamic i ntegration technique with constrained MD simulations. The results seem to s upport the thesis of a second-order phase transition but with unusual, very anharmonic behavior above the transition temperature.