| Abstract
| - In the literature two intrinsic paramagnetic centers have been identified by EPR in pure zirconia: Zr3+ ions,yielding an axial signal (g∥ = 1.958 and g⊥ = 1.979) and electrons trapped in oxygen vacancies (VȮ). In thisstudy we investigated by quantitative-EPR pure and doped ZrO2 heated in air and redox treated at varioustemperatures. In pure and in doped zirconia the axial signal has similar spectral features, including the satelliteline due to the most intense component of 53Cr hyperfine structure, and the signal intensity yielded the sameredox trend. In doped zirconia the concentration of the species yielding the axial signal was a constant fraction(about 50%) of the total chromium content. In pure zirconia samples, the concentration determined by EPRwas also about 50% of the Cr impurity level determined by GFAAS. These findings attribute this signal tothe extrinsic center, Cr5+ ion, arising from chromium impurity. In reduced zirconia a signal of Lorentzianshape (g = 2.002; ΔHpp = 4−5 G) arises from the only intrinsic defect detected by EPR in zirconia bulk,namely VȮ center. This signal could easily be confused with another having the same g value, but a differentline width (ΔHpp = 0.5−1 G) and line shape that forms in some vacuum-activated zirconia samples andarises from an extrinsic center, carbon paramagnetic impurity.
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