| The giant dielectric and nearly stable with temperature change of CaCu3Ti4O12 make it become supercapacitor potential medium materials. The CaCu3Ti4O12 (CCTO) is a well known non-ferroelectric material with high and nearly stable dielectric constant (from 25℃to 300℃) at 1 kHz. It is being widely used in the electronic industries to manufacture electronic components such as multilayer capacitor and microwave devices. The high permittivity of CaCu3Ti4O12 depends upon the powder morphology. The morphology of CaCu3Ti4O12 powder depends on the different synthesizing methods, temperature, heating rate, et al. In this paper, the high performance CCTO powders were prepared by oxalate co-precipitation and sol-gel auto-combustion method. The powders particles prepared by wet-chemical method were smaller and have higher activity. The oleic acid (OA) was used as surfactant during sol-gel auto-combustion method to prepare CCTO powder and their ceramic. Then the CCTO powders coated with Al2O3 was prepared in order to reduce the dielectric loss and enhance the dielectric constant. The decomposition of the precursor, the microstructure and morphology of ceramics were characterized by thermogravimetry-Differential Scanning Caborimetry(TG-DSC), X-ray diffraction(XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) method.The main contents of this paper include the following three aspects.1. The CCTO powders were synthesized by oxalate co-precipitation method and their ceramics were prepared at the same time. When the CCTO powders were prepared in a solution with the pH value of 3.0 and calcined at 850℃, their ceramics sintered at 980℃showed a higher dielectric constant. The results indicated that the grain size diminished and the sintering temperature reduced by using oxalate co-precipitation method. The perfect composition of the mixing solution for preparation of CCTO powders was Ca:Cu:Ti (mol)=1.10:2.95:4.05. which was beneficial to obtain the pure CCTO phase. The dielectric constant at room temperature of its ceramics reached to 1.3 x104, with a dielectric loss of 0.1.2. The CCTO powders and ceramics were prepared using oleic acid (OA) as a surfactant by sol-gel auto-combustion method. The amount of the surfactant on the effect of morphology and phase composition of CCTO powders was investigated. The dielectric properties were also measured and the effect of auto-combustion and sintering temperature was also studied. The ceramic with a [Ti(OBu)4]/[OA] (mol) ratio of 4/1 that was combusted at 400℃and then sintered at 1120℃for 4 h had the room-temperature dielectric constant (3.7x104), and dielectric loss (0.07).3. The Al2O3-coated CCTO (CCTO@A12O3) was synthesized, whose CCTO was prepared via oxalate co-precipitation method and sol-gel auto-combustion method, respectively. The effect of the AliO3-coated on the CCTO and the methods of preparing morphology and phase composition of CCTO ceramics were investigated. The dielectric properties were also measured. The results indicated that CCTO powders prepared by oxalate co-precipitation, the dielectric properties of the CCTO ceramics was enhanced by coating Al2O3 of 4.0 wt% and the dielectric loss decreased, the dielectric constant at room temperature of ceramics sintered at 1100℃for 4 hours reached to 25000, with a dielectric loss of 0.07. But for sol-gel auto-combustion method, the CCTO coated Al2O3 of 2.0 wt% showed the dielectric constant of 12000, with a dielectric loss of 0.05. Both of the two samples suggested that the Al2O3 coating played an important role in reducing the dielectric loss. |
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