Electron paramagnetic resonance investigation of polycrystalline CaCu3Ti4O12

Electron paramagnetic resonance (EPR) measurements on pure polycrystalline CaCu3Ti4O12 have been performed and are discussed within a crystal-field approach. A symmetric signal centred at g = 2.15 is observed for T > 25 K, with no evidence of hyperfine structure. At this temperature an antiferromagnetic transition is observed as confirmed by static magnetization data. Cu defective and 2% doped (V, Cr, Mn, La) samples were also prepared and considered, mainly to understand the nature of the observed paramagnetic centre. Substitutions in the octahedral sites, causing variations of the configuration in CuO4-TiO6-CuO4 complexes, change the magnetic and EPR features. To justify the EPR response a strong copper-hole delocalization is suggested.