ESR centers in reduced stabilized zirconia

Stabilized zirconia, when exposed at high temperature to a reducing atmosphere, becomes colored, and a pronounced room-temperature ESR signal appears. The concentration of the color centers was determined by optical absorption in the uv--visible range, and the concentration of the paramagnetic centers was determined by electron paramagnetic resonance in the X band. We found that the concentrations of the centers causing the two effects have the same P(O₂{)}^{{{-}}1/4}$ dependence on the oxygen pressure, a dependence that agrees with a simple model; however, the ESR signal varies strongly from crystal to crystal. We conclude from these results that both effects are caused by the same center, most probably an impurity with a total concentration of 10^-3 mol, which has captured an electron. From the ESR results the level of this electron state is {}1.60 eV below the conduction band. The oscillator strength for optical absorption was found to be fO{}0.01.