EPR study of defects in as-received, γ-irradiated and annealed monoclinic HfO2 powder

Electron paramagnetic resonance reveals the presence of several paramagnetic centres in monoclinic HfO2 powders. Three labeled H1, H2, H3 have g//=1.940+/-0.003, g=1.970 +/- 0.001 for H1, gxx=2.003+/-0.003, gyy=2.000+/-0.003 and gzz=1.994+/-0.001 for H2 and gxx=2.014+/-0.002, gyy=2.013+/-0.003 and gzz=2.006+/-0.002 for H3. Irradiation with gamma rays causes the population of H2 and H3 to initially rise and then level off; H1 is unaffected by irradiation. H2 and H3 begin to anneal out at or below 100 deg C in air whereas the population of H1 increases at about 400 deg C. Models are suggested for these centres.