Thermal annealing study of swift heavy-ion irradiated zirconia

TL;DR

This study investigates phase transformations in zirconia induced by swift heavy-ion irradiation and their reversal through thermal annealing, revealing kinetic parameters and underlying mechanisms using XRD, Raman, and EPR techniques.

Contribution

It provides new insights into the phase transition thresholds, kinetic modeling of back-transformation, and the effects of annealing on irradiated zirconia.

Findings

Phase transition to tetragonal zirconia occurs at high fluence.

Back-transformation begins around 500 K and completes by 973 K.

Activation energy for back-transformation is approximately 1 eV.

Abstract

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 (approx 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 "cross-cut" 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 EPR spectroscopy is discussed. Effects of crystallite size evolution and oxygen migration upon annealing are also addressed.