EPR characterization of defects in monoclinic powders of ZrO2 and HfO2

Electron paramagnetic resonance (EPR) measurements have been made on a variety of commercially available samples of the monoclinic form of the high-dielectric constant (high k) materials ZrO₂ and HfO₂ with the aim of characterizing the defects they contain. All EPR measurements were at about 9.5 GHz and at room temperature. An axially symmetric spectrum with g=1.961(2), g=1.976(2) is observed in most of the ZrO₂ samples and a similar one with g=1.940(3), g=1.970(2) is seen for most of the HfO₂ samples; they are attributed to centres involving Zr³⁺and Hf ³⁺, respectively. Their average concentration lies in the approximate range 10¹⁵–10¹⁷ cm⁻³, depending on the product specification, and, with one exception is unaffected by γ-irradiation. Grinding granules to powder and/or γ-irradiation yields further EPR spectra of defects, some of which are likely to involve oxygen, those are probably in the near surface region.