Origin of high dielectric performance in fine grain-sized CaCu3Ti4O12 materials

We report on high dielectric constant (8.3 × 10 3 , 10 4  Hz), low dielectric loss (0.029, 10 4  Hz) as well as fine grain size (∼840 nm) achieved in pure CaCu 3 Ti 4 O 12 (CCTO) ceramics through a combination of sol–gel method, spark plasma sintering and annealing process. By adjusting the sintering temperature and annealing conditions, the composition variations, valence states and microstructures of CCTO ceramics are systematically studied, which provide direct clues in understanding the origin of their excellent dielectric response. Through the studies on the dielectric, impedance, modulus and conductivity properties of CCTO ceramics, a modified brick-layer model based on two interfacial polarizations originating from sub-grain boundary and grain boundary barriers is proposed to explain their dielectric behaviors. The high dielectric constant of CCTO ceramics is mainly dominated by the sub-grain contribution; and the reduced dielectric loss is attributed to the decreases of electrical conductivity and relaxation loss.