Intrinsic and radiation defects in ZrO2 powders: EPR study

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Abstract
Defect transformations in tetragonal and monoclinic ZrO2 stimulated by high-energy electron irradiation were studied by electron paramagnetic resonance (EPR) method. The undoped and Y-doped ZrO2 powders prepared by co-precipitation approach and annealed at different temperatures as well as their commercial counterparts were used. Both ZrO2 powders and commercial ZrO2 consisted of two phases - monoclinic (m-ZrO2) and tetragonal (t-ZrO2), while Y-doped ZrO2 was of tetragonal phase. In the EPR spectra of ZrO2, the signal caused by Zr3+ centers located in m-ZrO2 and t-ZrO2 phases with parameters g⊥=1.9755, g||=1.9635 and g⊥=1.9755, g||=1.9590, correspondingly, was identified. The concentration of Zr3+ centers is much larger in t-ZrO2, which implies that tetragonal phase is more favorable for the existence of Zr3+ centers. Electron irradiation of ZrO2 decreases the amount of Zr3+ centers, and leads to formation of two singly ionized oxygen vacancies, VO+, in both ZrO2 phases and hole trapped at oxygen atom, O-, in monoclinic phase. The parameters of corresponding EPR centers are: g⊥=2.0029, g||=2.0006 (VO+ in m-ZrO2), g⊥=2.004, g||=2.002 (VO+ in t-ZrO2), and gx=2.0125, gy=2.0113, gz=2.0046 (O- in m-ZrO2). The EPR signal with the parameters g⊥=2.0024 and g||=2.0110 observed in irradiated Y-doped ZrO2 was assigned to O- in tetragonal phase. In the EPR spectra of irradiated commercial ZrO2 powders an additional EPR signal with the parameters g||= 2.000, g⊥=2.001, A||=1265×10-4 cm-1, A⊥=1075×10-4 cm-1 was revealed and ascribed to PZr4+ defects in the Zr sublattice of the m-ZrO2 phase. From the analysis of DFT simulations the radiation-induced defect reactions in ZrO2 were proposed. The EPR data of intrinsic and radiation-induced centers in ZrO2 were systematized and updated.

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