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

Abstract

We have used electron paramagnetic resonance to study the thermal annealing of colourcentres induced in cubic yttria-stabilized zirconia by swift electron and heavy ionirradiations. Single crystals were irradiated with 1 or 2 MeV electrons, and 200 MeV127I or200 MeV 197Au ions. Electron and ion beams produce the same colour centres, namely (i) anF+-like centre, (ii) theso-called T-centre (Zr3+ in a trigonal oxygen local environment), and (iii) a hole centre. Isochronal annealing wasperformed up to 973 K. Isothermal annealing was performed at various temperatures onsamples irradiated with 2 MeV electrons. The stability of paramagnetic centres increaseswith fluence and with a treatment at 1373 K under vacuum prior to the irradiations.Two distinct recovery processes are observed depending on fluenceand/or thermal treatment. The single-stage type I process occurs forF+-like centres at low fluences in as-received samples, and is probably linked toelectron–hole recombination. T-centres are also annealed according to a single-stageprocess regardless of fluence. The annealing curves allow one to obtain activationenergies for recovery. The two-stage type II process is observed only for theF+-like centres in as-received samples, at higher fluences, or in reduced samples. These centresare first annealed in a first stage below 550 K, as in type I, then transform into newparamagnetic centres in a second stage above 550 K. A simple kinetics model is proposedfor this process. Complete colour centre bleaching is achieved at about 1000 K.