Colour centre production in yttria-stabilized zirconia by X-ray and electron irradiations: Effect of yttria content

Yttria-stabilized zirconia (YSZ) single crystals (for 9.5 and 18 mol% yttria) were irradiated at room temperature (RT) by X-rays (W white spectrum) and 2.5-MeV electrons. The growth curves of the so-called T-centre (for trigonal centre, i.e. Zr3+sitting in a trigonal symmetry site) were studied as a function of absorbed dose, or irradiation time, by UV-visible optical absorption (OA) spectroscopy and X-band electron paramagnetic resonance spectroscopy. The defect concentration at saturation and the production rate are increased by a factor around two for 18 mol% yttria with respect to 9.5 mol%. Defect decay was then followed after irradiation by OA spectroscopy as a function of ageing time at RT. Growth and decay curves of the T-centre are modelled on the basis of rate equations of charge-exchange reactions with the zirconium lattice ions. Increase in yttrium content is thought to decrease hole trapping on Zr3+ions, thereby enhancing T-centre formation.