Dynamical stabilization of cubic ZrO2 by phonon-phonon interactions: Ab initio calculations

Cubic zirconia exhibits a soft phonon mode (X-2(-)) which becomes dynamically unstable at low temperatures. Previous ab initio investigations into the temperature-induced stabilization of the soft mode treated it as an independent anharmonic oscillator. Calculations presented here, using the self-consistent ab initio lattice-dynamical method to evaluate the phonons at 2570 K, show that the soft mode should not be treated independently of other phonon modes. Phonon-phonon interactions stabilize the X-2(-) mode. Furthermore, the effective potential experienced by the mode takes on a quadratic form.