Sintering effects on structure and dielectric properties of dielectrics CaCu3Ti4O12

Due to the continuous demand for miniaturization of electronics, there is an interest in developing dielectric materials with higher permittivity. Recently, the CaCu3Ti4O12 (CCTO) has been reported [1–3], has a very high permittivity (~10) at room temperature and very small temperature dependence in a broad temperature range. However, it appears that the dielectric properties of CCTO are very sensitive to processing. [4–7] Permittivities from 478 to 300,000 have been obtained for CCTO prepared by different routes. The original work, done by Subramanian et al. [1] and Ramirez et al. [2] using conventional mixed-oxide processing via mortar and pestle, showed that room temperature permittivities ranged from 10,000 to 20,000. Other researchers using the same technique have reported permittivities of 478, 2400 and 18,700 [8–10]. The highest permittivity reported as derived from impedance spectroscopy measurements was 300,000 for CCTO made from powder that was mixed via ball milling and sintered for 24 h at 1100 C [11]. Though different hypotheses have been put forth to explain the high permittivity of CCTO, its origin is still not fully justified. At present, the grain boundary barrier layer capacitance model of extrinsic mechanism is the most favorable one [12–19]. It is believed that insulating surfaces form on semi-conducting grains during the sintering of CCTO ceramics, which results in an electronically heterogeneous material very similar to the nature of internal barrier layers capacitors (IBLC). The dielectric properties of these IBLCS are very sensitive to different processing parameters. In the present work, the CCTO ceramics are prepared by the solid-state reaction method. The sintering effects on the phase evolution, structure and dielectric properties of CCTO ceramics have been investigated.