Experiments were performed using electron spin resonance of Cu2+ in polycrystalline samples of CaCu3Ti4O12; post-annealed in various atmospheres. Following synthesis via solid-state reaction, pellets of CaCu3Ti4O12 were annealed (24h, 1000C) in air, Ar or O2. The temperature-dependent electron spin resonance data revealed a nearly temperature-independent g-value, 2.15, and line-width for T >> TN ≈ 25K. However, the values of the electron spin resonance line-width were strongly affected by the O content of the sample. Thus Ar post-annealed samples exhibited a much larger line-width than did O2- or air post-annealed samples. This broadening was attributed to an increase in the dipolar homogeneous broadening of the Cu2+ electron spin resonance lines due to the presence of O vacancies, which induced an S=1/2 spin within the TiO6 octahedra. A correlation between a systematic dependence of the electron spin resonance line-width upon the O content, and a high dielectric constant of these materials, was considered.

Role of Oxygen Vacancies in the Magnetic and Dielectric Properties of the High Dielectric Constant System CaCu3Ti4O12 - an Electron-Spin Resonance Study. M.A.Pires, C.Israel, W.Iwamoto, R.R.Urbano, O.Agüero, I.Torriani, C.Rettori, P.G.Pagliuso, L.Walmsley, Z.Le, J.L.Cohn, S.B.Oseroff: Physical Review B, 2006, 73[22], 224404 (7pp)