| CaCu3Ti4O12 (CCTO) is dielectric material with high dielectric constantεr of about 104, and good temperature stability, as in recent years the academic focus of attention. On the other hand, CCTO ceramics with a high dielectric loss (tanδ-0.1) affects its application.In this paper, the phase structure, microstructure and dielectric properties of CaCu3Ti4O12 ceramics were studied through different preparation methods (solid-phase synthesis method, molten salt method and semi-chemical method), different conditions, and then further study on this basis the B variant, A-substituted on CaCu3Ti4O12 ceramic to accommodate the high dielectric constant and lower dielectric loss.Firstly, systematically the affect of under different conditions on dielectric properties of CaCu3Ti4O12 ceramics was studied. The results show that precalcined at 900℃, sintering temperature of 1070℃-1110℃sintering of the ceramics has good dielectric properties. When the calcining temperature is 900℃, the ceramics obtain a pure perovskite the structure, clearly grain boundary, lesser porosity, higher density and larger grain size, plump grain. the average grain size are about 100μm. At 1 kHz at room temperature, the preheat temperature of 900℃ceramic has the best dielectric properties, the dielectric constant of about 6.14×104, the dielectric loss of 0.044. Room temperature in the 40 Hz-105 Hz frequency range,1070℃-1110℃sintering temperature range of sintered ceramic can be huge dielectric constant, the dielectric constant are more than 6.0 x 104, the dielectric loss values is less than 0.48.Secondly, the microstructure, dielectric constant and dielectric loss effects of the CaCu3Ti4O12 ceramics by prepared the system of the solid phase, NaCl molten salt method, CaCl2 molten salt method and the semi-chemical method was studied. The results showed that the CCTO ceramics by prepared solid-phase has greater grain, more clearly the grain boundary, Closely arranged grains, good density. In the 40-105 Hz frequency range, the dielectric constant of CCTO ceramics of by prepared solid state, NaCl molten salt method, semi-chemical synthesis are more than 104, especially the dielectric constant of the CCTO ceramics prepared by solid-phase is up to 6.0×104 more, the highest dielectric constant of CCTO ceramics by prepared CaCl2 molten salt is only 1.5×104. At-50-55℃temperature range, the frequency of 10 kHz, dielectric constant of CCTO ceramics prepared by the the solid phase is up to 3.1×104, its dielectric loss is less than 0.04, and it also has good temperature stability. However, the dielectric loss of CCTO ceramics by prepared the NaCl flux method, semi-chemical method, CaCl2 molten salt is up to 0.12,0.13,0.39, respectively. This shows that CCTO ceramics prepared by solid phase has high dielectric constants and low dielectric loss.Thirdly, the effect of Ti content on the phase structure, microstructure and dielectric properties of CaCu3TixO12 ceramics was discussed. The X-ray diffraction patterns showed that there was a second phase (Cu2O) when x<4.00, and a pure phase was obtained when x≥4.00. SEM and EDX analysis showed that a large number of copper-rich phase (Cu2O) was found at the grain boundary region of ceramics with x<4.00. Impedance spectroscopy analysis showed that, with the Ti content increasing, the grain resistance Rg and the grain boundary resistance Rgb decrease at first, minimum values(1.48 Q.cm and 94.5 kΩ.cm, respectively) were obtained at x=4.00, and then increased. From room temperature dielectric frequency spectrum, it was found that the dielectric constant of the ceramics with x=4.00 are more than 5.50×104 in the frequency range of 40 Hz to 105 Hz, and at 1 kHz, dielectric constant value is as follows:εr=6.15×104 tanδ=0.044.Lastly, the effects of Sr content on the phase structure, microstructure and dielectric properties of CSCTO ceramics were discussed. A pure structure without any impurity phases can be confirmed by the X-ray diffraction patterns. Scanning electron microscopy analysis illuminate that the grains of CSCTO (x=0.10) ceramics are greater than that of CCTO. And then the grains of CSCTO (x>0.10) ceramics gradually decrease as x increasing. It is found that the CSCTO (x= 0.10) ceramics have the higher permittivity (71153) and the lower dielectric loss (0.022) at 1 kHz at room temperature. In the range of-50-100℃, the dielectric constant of the CSCTO (x=0.10) is no less than 65000 and the dielectric loss is no more than 0.05 at 1 kHz. The results indicate that the CSCTO (x=0.10) display lower dielectric loss and good temperature stability. The current-voltage nonlinear behavior of CSCTO ceramics is also investigated. The effects of alkaline earth metals (Mg, Ba, Sr) substituted on the microstructure, dielectric constant and dielectric loss of Ca0.9A0.1Cu3Ti4O12 ceramics were discussed. The results showed that the grain of Ca0.9Sr0.1Cu3Ti4O12 ceramics is bigger and the grain boundary of it is thinner than that of Ca0.9Mg0.1Cu3Ti4O12, Ca0.9Ba0.1Cu3Ti4O12, CaCu3Ti4O12 ceramics. Room temperature in the frequency range of 40 Hz-105 kHz, the dielectric constant of Ca0.9Sr0.1Cu3Ti4O12 ceramics is higher than that of pure CCTO ceramics, Ca0.9Mg0.1Cu3Ti4O12 and Ca0.9Ba0.1Cu3Ti4O12, ceramics. The dielectric loss of Ca0.9Sr0.1Cu3Ti4O12. ceramics is lower than than of pure CCTO ceramics. |
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