Thermal annealing study of swift heavy-ion irradiated zirconia

Abstract

Sintered samples of monoclinic zirconia (α-ZrO2) have been irradiated at room temperature with 6.0GeV 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 (β-ZrO2) occurred at a fluence of 6.5×1012cm−2 for a large electronic stopping power value (≈32.5MeVμm−1). At a lower fluence of 1.0×1012cm−2, no such phase transformation was detected. The back-transformation from β- to α-ZrO2 induced by isothermal or isochronal thermal annealing was followed by XRD analysis. The back-transformation started at an onset temperature around 500K and was completed by 973K. 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 1eV 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.