Effect of Annealing in O2 and Mechanisms Contributing to the Overall Loss Tangent of CaCu3Ti4O12 Ceramics

Mechanisms contributing to the overall loss tangent (tan δ) of CaCu3Ti4O12 ceramics were investigated via doping with Yb3+ ions and annealing in an O2 atmosphere. A high tan δ value for CaCu3Ti4O12 ceramics in a low-frequency range was primarily caused by direct-current (DC) conduction. It can be greatly suppressed by annealing in an O2 atmosphere to fill oxygen vacancies at grain boundaries (GBs) and enhance GB resistance. The tan δ value in a middle frequency range originated from oscillation of ionic dipole moments. Ceramics which contain a relatively high atomic mass number (Yb3+-doped CaCu3Ti4O12) generated more dissipated energy compared with undoped ceramics. A rapid increase in tan δ in a high frequency range was attributed to the relaxation of active dipole moments that gave rise to the giant dielectric response. Balancing these factors, while simultaneously retaining high values of dielectric permittivity, is an ideal strategy to effectively improve the dielectric performance of CaCu3Ti4O12-based compounds.