Investigation On The Dielectric Properties Of CaCu₃Ti₄O₁₂ Ceramic

With the development of microelectronic technology, the electronicsindustry is demanding more for the miniaturization, integration andintellectualization of the microelectronic devices such as capacitance-basedcomponents （capacitors, resonators and filters） and memories. Theperovskite-like CCTO has attracted increasing interests because of the giantdielectric constant （of the order of10⁴） with weak frequency and temperaturedependence，and this material is lead-free. These excellent properties of CCTOprovided a good premise condition, but the dielectric loss of this material is large,which is still an inevitable obstacle to the practical applications. However, it isstill a matter of disputation of what is the origin of giant dielectric response. Inorder to optimize the dielectric performance of CCTO and investigate thedielectric mechanism, we carried out the following works. We prepared theCCTO and CCTO-SBS ceramics by the solid state reaction in differentatmosphere. The phase composition, microstructure and dielectric properties ofthese ceramics were investigated in this paper.CCTO ceramics were prepared by a solid state reaction process using thehigh purity materials of CaCO3, CuO and TiO₂，These raw materials werecalcined at950and1000℃for12h in air. During sintering, with the increase ofsintering temperature and sintering time, we could see that the average grain sizeincreased, and the dielectric constant increased relevantly, so the microstructureof CCTO ceramics has a crucial impact on its dielectric perfoemance. Thecubic-like grains of CCTO ceramics piled up by the types of contact such as“plane-vertex”,“plane-arris” and “arris-arris”, and formed the micro defects（voids） inevitably. The diffuse phase transition occurred above450K, it isindicated that CCTO ceramics have the ferroelectric relaxor characteristics inthis temperature range.The additive SBS glass promoted grain growth and densification of CCTOceramics. When additive amount of SBS is0²wt%, the Rgbof CCTO-SBS ceramics decreased from4.4×10⁶cm to2.2×10⁶cm, when SBS was addedto3wt%, the Rgbrise to3.7×10⁶cm again. The Rgof CCTO-SBS ceramicswere maintained in10³0cm. The addition of SBS glass was desirable toincrease the dielectric constants （up to10⁴） and lowered the dielectric losses ofCCTO over the frequency range of450Hz⁴0kHz at the relatively lowersintering temperature for relatively shorter sintering time （1050℃,12h）. CCTOceramics is electrically heterogeneous and consists of semiconducting grainswith insulating grain boundaries, and constructed a model called internal barrierlayer capacitance. The electrically heterogeneous also has a crucial impact on itsdielectric perfoemance.Therefore, focused research on microstructure and electrical properties ofthe grain/grain boundary become the key importance in exploring the dielectricproperties of CCTO ceramics. CCTO ceramics were sintered in the mixed gasesflowing of O₂and N₂with different volume ratios by the solid state reactionmethod, the volume ratios were strictly controlled by a gas mixture proportionerduring sintering. With the increasing of volume fractions of O₂（x）, the averagegrain size decreased, the activation energy of grain boundary increased fromabout0.474to0.937eV, and the Rgbincreases from about2.84×10⁴cm to1.93×10⁶cm. All the samples showed high dielectric constant （≥5×10³） in abroad frequency range from20Hz to100kHz, which decreased gradually from2×10⁴to5×10³with increasing x. IBLC model have a wide range of applications,it can effectively explain a variety of dielectric phenomenons for CCTO ceramics.According to IBLC model, we deduced that the dielectric loss depended in largepart upon the resistivity of insulating layer.