Reduce Low Frequency Dielectric Loss Of Ca Cu₃Ti₄O₁₂ Ceramics By Constructing High Resistance Phase?grain?boundaries

Materials that can be polarized under the electric field can be calleddielectric materials.They have very wide applications,such as in producing capacitors,resonators,filters,memory and other electronic components.With the rapid development of technology,especially the microelectronics technology,those traditional dielectric materials have been difficult to meet the high performance and miniaturization needs of electronic components.The key to solve this problem is to develop other new type high dielectric materials.CaCu₃Ti₄O₁₂?CCTO?,a high dielectric material with perovskite-like structure,is a potential excellent high dielectric material due to its unusual dielectric properties,such as high room temperature dielectric constant?greater than 10⁴?,good frequency and thermal?100-400 K?stabilities.However,the large low-frequency dielectric loss hinders its practical application.So reducing its low-frequency dielectric loss is always a hot point in the research about CCTO.According to the results of previous researchers,CCTO ceramics consist of semi-conductive grains and insulating grain boundaries.Therefore,the high dielectric properties of CCTO ceramics should originate from the internal barrier capacitance?IBLC?effect.Relevant studies have found that increasing the resistance of CCTO ceramics can effectively reduce its low-frequency dielectric loss,and the grain boundary resistance of CCTO ceramics is much larger than the grain resistance,so the low-frequency dielectric loss of CCTO ceramics can be reduced by constructing high-resistance phase?grain?boundaries around grains.In this paper,the low frequency dielectric loss of CCTO ceramics is reduced by using high insulating oxide CuO,ZnO,Al₂O₃ coated CCTO grains to increase phase boundary resistance,hydrogen peroxide oxidation to reduce oxygen vacancy content of CCTO ceramics,and carbon sintering technology to increase the oxidation degree of grain and grain boundary of CCTO ceramics.In this paper,the author prepared CCTO micron powders with gooddispersability by sol-gel method and mechanical ball milling method.Then the ZnO nano powder was coated to the surface of micron CCTO.After sintering,xZnO/CCTO?x=0,0.02,0.05,0.1?composite ceramics with high resistance phase boundaries were prepared.Characterization test results show that the dielectric constant of ZnO/CCTO composite ceramics sintered for 8 hours at 1020OC increases to 1.3×10⁵ and the dielectric loss is lower than 0.1 in the frequency range of 100 Hz-13 kHz,which indicates that ZnO can improve the dielectric constant of CCTO ceramics.In this paper,xCuO/CCTO?x=0,0.02,0.05,0.1,0.2?composite ceramics were fabricated by the similar method,among them,CuO is transformed into Cu₂O under high temperature and hypoxia environment.It is found that Cu₂O can not only reduce the low-frequency dielectric loss of CCTO ceramics,but also improve the frequency stability.In the frequency range of 30Hz-30 kHz,the dielectric loss of CuO/CCTO composite ceramics is lower than0.05 and the lowest dielectric loss is about 0.015,while the dielectric constant is still high to 9.0×10⁴.xAl₂O₃/CCTO/?x=0,0.02,0.05 and 0.1?composite ceramics were alsoprepared by the similar method.It was found that the copper phase?CuO,Cu₂O?precipitated from CCTO phase,and reacted with part of Al₂O₃ phase to form CuAl₂O₄ at high temperature.Therefore,the actual ceramics samples prepared in this paper are Al₂O₃/CuAl₂O₄/CCTO composite ceramics.CuAl₂O₄ has an excellent insulation.It was found that the dielectric loss of Al₂O₃/CuAl₂O₄ CCTO composite ceramics was less than 0.05 in the frequency range of 20 Hz-6.4 kHz at room temperature and the lowest dielectric loss was only 0.019,and the dielectric constant of Al₂O₃/CuAl₂O₄/CCTO composite ceramics was relatively high?about 3.6×10⁴?.The dielectric constant of Al₂O₃/CuAl₂O₄/CCTO ceramics after being soaked in H₂O₂ is still as high as 3.0×10⁴.The frequency range of low dielectric loss?less than 0.05?expands from 20 Hz-6.4 kHz to 20 Hz-13.7 kHz.At the same time,the frequency stability of composite ceramics is slightly improved.We also prepared a sub-micron?200 nm?CCTO powders with gooddispersability by sol-gel method.After mixing CCTO powder with 2%wt graphite powder,ceramic samples were sintered.It was found that the dielectric loss of the ceramics sintered at 1020OC for 10 h was lower than 0.05 in the frequency range of 20 Hz-137 kHz,especially in the frequency range of 40 Hz-2 kHz,the lowest dielectric loss was lower than 0.0065.However,the dielectric constant of the ceramics sample remains stable in the range of test frequency?20 Hz-2 MHz?while maintaining low dielectric loss,and it is as high as 2.3×10³.The dielectric constant of ceramics sintered at 1080OC for 20 h is as high as 4.2×10⁴ and he dielectric loss of ceramics is lower than 0.05 at 20 Hz-30 kHz with the lowest dielectric loss is about 0.009.