Thermal recovery of colour centres induced in cubic yttria-stabilized zirconia by charged particle irradiations

TL;DR

This study investigates how colour centres in yttria-stabilized zirconia recover during thermal annealing after being induced by electron and heavy ion irradiation, revealing distinct recovery processes and activation energies.

Contribution

It provides new insights into the thermal annealing mechanisms of irradiation-induced colour centres in cubic yttria-stabilized zirconia, including the identification of two-stage recovery processes and their kinetics.

Findings

Colour centres are stable up to high fluences and temperatures.

Two distinct annealing processes depend on fluence and thermal treatment.

Complete bleaching occurs around 1000 K.

Abstract

We have used electron paramagnetic resonance to study the thermal annealing of colour centres induced in cubic yttria-stabilized zirconia by swift electron and heavy ion-irradiations. Single crystals were irradiated with 1 or 2-MeV electrons, and 200-MeV 127I, or 200-MeV 197Au ions. Electron and ion beams produce the same colour centres: namely i) an F+-like centre, ii) the so-called T-centre (Zr3+ in a trigonal oxygen local environment), and iii) a hole center. Isochronal annealing was performed up to 973 K. Isothermal annealing was performed at various temperatures on samples irradiated with 2-MeV electrons. The stability of paramagnetic centres increases with fluence and with a TCR treatment at 1373 K under vacuum prior to the irradiations. Two distinct recovery processes are observed depending on fluence and/or thermal treatment. The single-stage type I process occurs for F+-like centres at low fluences in as-received samples, and is probably linked to electron-hole recombination. T-centres are also annealed according to a single-stage process regardless of fluence. The annealing curves allow one to obtain activation energies for recovery. The two-stage type II process is observed only for the F+-like centres in as-received samples, at higher fluences, or in reduced samples. These centres are first annealed in a first stage below 550 K, like in type I, then transform into new paramagnetic centres in a second stage above 550 K. A simple kinetics model is proposed for this process. Complete colour centre bleaching is achieved at about 1000 K.