Preparation And Study Of CaCu₃Ti₄O₁₂ Ceramics With Core-shell Structure

Giant dielectric materials have become increasingly important,as their significant use in high-performance capacitive devices for microelectronic applications and high energy density storage.In recent years,CaCu₃Ti₄O₁₂?CCTO?with perovskite-related structure has attracted much scientific attention because of its unusual giant dielectrical properties.It has the extremely large ?' values over 104 with weak frequency dependence and little temperature dependence over a very wide frequency and temperature range.However,the large low-frequency dielectric loss hinders CCTO ceramics to be actually used in practical applications.To clarify the origin?s?of the unusual giant dielectrical properties,the related electrical properties of CCTO ceramics have been studied extensively.It has been clear that CCTO ceramics are electrically heterogeneous,consisting of semiconducting grains and insulating grain boundaries.On the basis of these results,the internal barrier layer capacitance?IBLC?effect seems to be the most plausible explanation for the giant dielectrical properties of CCTO ceramics.According to IBLC effect explanation,the low-frequency dielectric loss of CCTO ceramics mainly rests with the equation as follow: tan? ? 1/??RgbCp?where ? is the angular frequency,Rgb represents the resistance of insulating grain boundary,and Cp represents the capacitance of the ceramics.According to the equation,increasing the resistance of grain boundary is an effective way to reduce the low-frequency dielectric loss of CCTO ceramics.Fully oxidized MgO has the very good insulation.Here,it is designed to coat the nano MgO powder to the outside of CCTO powder to prepare CCTO/xTiO₂?x=0,0.5,1 and 2?composite ceramics with core-shell structure.Then,make MgO fully oxidized through annealing in oxygen to improve the grain boundaries insulation and reduce the low-frequency dielectric loss of the composite ceramics.In this paper,CCTO/MgO composite ceramics were prepared by sol-gel-like method,and their microstructures and electrical properties were investigated.Also,CCTO/TiO₂?x=0,0.5,1 and 2?composite ceramics were prepared and investigated by the similar method.The results show that CCTO/oxide composite ceramics with core-shell structure were obtained.The low-frequency dielectric loss does not decrease in CCTO/MgO composite ceramics,while the insulating grain boundary resistance of CCTO/xTiO₂?x=1?composite ceramic evidently increases and their low-frequency dielectric loss prominently decreases with lower than 0.05 in a wide frequency range of 20 Hz to 45 kHz at room temperature after annealing in oxygen.