Oxygen vacancy related defect dipoles in CaCu3Ti4O12: Detected by electron paramagnetic resonance spectroscopy

Oxygen vacancy associate defects were studied by electron paramagnetic resonance (EPR) for the perovskite oxide CaCu3Ti4O12 (CCTO), which have a colossal dielectric constant. It is found that the EPR line width of the Cu2+–host signal of CCTO correlates with its permittivity. A new signal was found in the second differential of the Cu2+–host signal, which we think is associated with a specific copper–oxygen vacancy defect. This signal shows a negative g factor shift with temperature, suggesting a contribution to the conduction. Assuming solid state reactions between the various defects and using the mass action law, we offer a more specific relation between permittivity, the content of oxygen vacancy and the new signal, which might be useful for an indirect but fast oxygen vacancy content determination.