Preparation And Properties Of CCTO Porous Ceramics

Due to the giant dielectric constant (as high as 104). good temperature stability (almost constant of dielectric constant within 100-600K) and good nonlinear voltage-current characteristics, CaCu3Ti4O12 (CCTO) has an important potential application in the high density storage, high-energy capacitor, varistor and so on. Therefore, CCTO materials have been extensively investigated. However, some shortcomings such as high dielectric loss and strong process sensitivity still exist for CCTO. And the dielectric mechanism of CCTO is not clear. It is important to note that CCTO is an n-type semiconductor. So it is expected to be applied in sensitivity field. In order to expand the application field of CCTO, and to reveal the extrinsic properties of CCTO base materials, different sintering process, starch pore-forming method, freezing method had been adopted to prepare CCTO porous ceramics in this thesis. The phase constitutions, microstructure, dielectric properties and the varistor properties had been investigated. And the dielectric mechanism of CCTO ceramics was further discussed.CCTO ceramics had been prepared by different sintering process. And the phase composition, microstructure, dielectric properties and the varistor properties had been investigated. When the sintering temperature is less than 1050℃, the porosity is about 40%. As the sintering temperature is between 1100℃ and 1150℃, the porosity is in the range of 10%-20%. The dielectric constant and dielectric loss of CCTO porous ceramics increase with the increase of the sintering temperature. When the sintering temperature reaches 1100℃, CCTO ceramics exhibits good varistor properties.Different content (0%,5%,10%) of starch was added to the CCTO ceramics powder which calcined at different temperature (950℃,1050℃,1100℃). And CCTO porous ceramics was sintered at low temperature from 800℃ to 950℃. And the structure, dielectric properties and varistor properties of CCTO porous ceramics had been investigated. The porosity of CCTO ceramics increases with the increase of starch content. The porosity is 30-40%,40-49% and 60% for the CCTO porous ceramics with 0%,5%,10% starch, respectively. And the porosity reduces with the increase of the sintering temperature. The resistivity increases with the content starch increases. Dielectric constant increases with elevating of calcining temperature and sintering temperature. But no obvious varistor properties are observed.PVA solution was added into the calcined CCTO ceramics powder. The CCTO porous ceramics were prepared by freezing method and sintering at different temperatures. The porosity of CCTO porous ceramics is as high as 70%. And good dielectric properties had been achieved. The CCTO porous ceramics has the highest dielectric constant of 990 at 1kHz and exhibites good temperature stability. Good varistor characteristics have been observed in the CCTO porous ceramics, which are sintered at 1065℃ or the higher temperature.