Thermal annealing study of swift heavy-ion irradiated zirconia

Sintered samples of monoclinic zirconia (alpha-ZrO2) have been irradiated at room temperature with 6.0 GeV Pb ions in the electronic slowing down regime. X-ray diffraction (XRD) and micro-Raman spectroscopy measurements showed unambiguously that a transition to the metastable tetragonal phase (beta-ZrO2) occurred at a fluence of 6.5x10(12) cm(-2) for a large electronic stopping power value (approximate to 32.5 MeV mu m(-1)). At a lower fluence of 1.0x10(12) cm(-2), no such phase transformation was detected. The back-transformation from beta- to alpha-ZrO2 induced by isothermal or isochronal thermal annealing was followed by XRD analysis. The back-transformation started at an onset temperature around 500 K and was completed by 973 K. Plots of the residual tetragonal phase fraction deduced from XRD measurements versus annealing temperature or time are analyzed with first- or second-order kinetic models. An activation energy close to 1 eV for the back-transformation process is derived either from isothermal annealing curves, using the so-called crosscut method, or from the isochronal annealing curve, using a second-order kinetic law. Correlation with the thermal recovery of ion-induced paramagnetic centers monitored by electron paramagnetic resonance spectroscopy is discussed. Effects of crystallite size evolution and oxygen migration upon annealing are also addressed. (c) 2006 American Institute of Physics.