Effect Of Fe And Mg Mixing On CCTO Ceramic Properties

Since 2000,a new type of high-dielectric-constant material has attracted wide attentions from domestic and foreign scholars.The dielectric constant of this material is not only up to 10⁴,but also maintains a stable state over a wide range of frequencies（20-10⁵ Hz）and temperatures（30-180^℃）.Because of its good dielectric properties,CCTO can play an important role in the applications of supercapacitors and energy storage for new energy vehicles,which has attracted a large number of scholars to study it.The dielectric properties of CCTO is varied at different frequencies,in the low frequency range（<10³ Hz）,the dielectric constant is high,and the dielectric loss is low,and in the high frequency range（>10⁵ Hz）,the dielectric constant decreases rapidly,and the dielectric loss increases dramatically.In this regard,an IBLC model was introduced to explain this phenomenon.The model considers that there are crystal grains and insulating grain boundaries in the ceramics.In this paper,pure CCTO phase can be prepared by using NaC l as molten salt at800^℃ for 2 h.In order to explore the mechanism of the dielectric properties of CCTO ceramics,Fe and Mg elements are used to prepare composite ceramics in order to increase the dielectric constant and reduce the dielectric loss.1.The Fe-mixed experiment shows that the ceramics with the mixing amount of0.01 have higher dielectric constant than other mixed ceramics sintered for 10 h.The dielectric loss of the composite ceramic s is lower than the pure CCTO ceramic in the high frequency range,but the dielectric constant is lower than the pure CCTO ceramic.In order to increase the dielectric constant,the sintering time is extended to 20 h.It is found that ceramics with 0.01 mixing has a dielectric constant value of 3×10⁴ in the low frequency range and a dielectric loss of less than 0.1,which is better than pure CCTO ceramic.Using scanning electron microscopy,X-ray diffractometry and Raman spectroscopy,the mechanism of the influence of the amount of Fe-mixed on the dielectric properties of the ceramic was investigated.The results show that a certain amount of Fe element can inhibit the grain growth,decrease the grain boundary thickness,and increase the dielectric constant.Further Fe increase make the grain growth inhibition become weak,and even promotes the growth of the grain.The grain size increases,and the grain boundary thickese decreases,so the dielectric constant decreases.The Fe element has an effect on the stretching vibration of O-Ti-O in the ceramic TiO₆,resulting in eccentric displacement of the Ti ion,which causes local lattice stretching to make polarization easier and result in a high dielectric constant.2.The Mg-mixed experiment shows that the ceramic with a mixing amount of0.05 sintered for 10 h can have a dielectric constant of 9×10⁴,and the dielectric loss value can be less than 0.1.with a certain Mg-mixed amount,the grain growth is inhibited,the grain boundary becomes thin,and the dielectric constant increases.