Critical size of the phase transition from cubic to tetragonal in pure zirconia nanoparticles

Pure (unstabilized) zirconia nanoparticles in the fluorite-type cubic phase are observed by transmission electron microscopy. Microscopic observations at a pressure of 5 x 10(-5) Pa suggest that the phase transition from the cubic to tetragonal phase arises for particles near 2 nm in diameter. First principles computer simulations of large zirconia clusters show that the critical size of the transition could occur for a diameter of 2.05 +/- 0.15 nm, which is in good agreement with the experimental value.