Study On The Preparation Of CaCu₃Ti₄O₁₂ Giant Dielectric Materials And The Improving Dielectric Properties With K⁺,Zr⁴⁺ Doping CaCu₃Ti₄O₁₂

With the development of microelectronics technology,the electronic device with low performance or large size can’t satisfy people’s needs anymore.Therefore,the devices with high-performance and miniaturization have drawn lot attentions,such as the high dielectric material,which can be used in the resonator,capacitors,filters,memories.In the last decade,the giant dielectric material CaCu₃Ti₄O₁₂（CCTO）have brought more and more attentions,since CCTO owns high dielectric constant and dielectric stability is very good in a very wide frequency range and temperature range.So,it can be expected to become a new generation of high dielectric ceramic materials.However,the excessive dielectric loss limited its application in practice.Hence,the theoretical and experimental research work of CCTO is still needed.It is widely accepted that the dielectric properties of CCTO are closely related with extrinsic factors such as the grains and grain boundaries,hence,we prepared pure CCTO and K⁺,Zr⁴⁺ doping CCTO by the sol-gel method and optimize the experimental conditions,and then the structure,dielectric properties and the influencing mechanism were studied.Firstly,pure CCTO ceramic samples were synthesized.The microstructures and dielectric properties were then investigated.The samples of x-ray powder diffraction analysis indicated no second phase occurred.The dielectric constant（ε’）of CCTO only changed slightly while the sintering temperature was above 1040 oC and the frequency was below 400 kHz.The loss tangent（tanδ）was below 0.05 in a relatively wide frequency range in some samples.Meanwhile,a very low tanδ 0.028 was observed for the sample sintered at 1100 oC for 16 h with ε’=1.82×104 at 1 kHz.Secondly,CCTO ceramic materials with Zr⁴⁺ doping at the Ti⁴⁺ site(CaCu₃Ti₄-xZrxO₁₂,x = 0,0.05,0.1 and 0.2)were prepared by sol-gel method in order to change the CCTO microstructures and then the dielectric properties can be expected to be imporved.We found that the main grain size increased and the ε’（>2×104）also increased obviously for the CaCu₃Ti₃.95Zr_0.05O₁₂（CCTZO）ceramics in a wide frequency range（20 Hz-400 kHz）at room temperature,and the fluctuation of ε’ is less than ±20% measured at 200 kHz and temperature range from 20 oC to 180 oC.Meanwhile the tanδ was below 0.05 with frequency rang from 2 kHz to 50 kHz.The tanδ and ε’ of CCTZO sintered 1100 oC for 16 h are about 0.026 and 2.35×104 measured at 10 k Hz,respectively.These results indicated that dielectric properties of CCTO can be advanced by Zr⁴⁺ doping.And then,CaCu₃Ti₄O₁₂ ceramics doped by K⁺at Ca²⁺ site(Ca₁-xKxCu₃Ti₄O₁₂-δ)were prepared by the same method and sintered from 1040 oC to 1100 oC.The microstructures and dielectric properties of Ca₁-xKxCu Ti₄O₁₂-δ ceramics were investigated.All of X-ray diffraction patterns indicated a typical cubic structure and no the formation of second phase.Scanning electron microscopy（SEM）found that the grain size as well as the dielectric constant（ε’）increase obviously with the increasing sintering temperature.A low tanδ value about 0.039 was observed in the Ca_0.99K_0.01Cu₃Ti₄O₁₂-δ sample sintered at 1060 oC for 8 h at room temperature and 1 kHz.Dielectric relaxations were observed in（ε′/tanδ）-T curves.In summary,the dielectric properties of CCTO can be improved by optimizing the preparation method,sintering conditions and K⁺,Zr+ doping.The experimemtal results showed that the dielectric properties of CCTO were closely related with its microstructures,therefore,we will continue to study the influncing mechanism of the microsctructures of CCTO in detail in the future,and we intend to synthesize CCTO / ferrites composites in order to extend the application prospect of CCTO.