Papers by Keyword: CaCu₃Ti₄O₁₂ (CCTO)

Abstract: Current research efforts toward achieving ceramic/polymer composites which fulfill the balance between sufficiently high dielectric constant (ε) and low dielectric loss (tanδ) are presented. In this paper, ceramic/polymer composite films made of CaCu₃Ti₄O₁₂ (CCTO) powder as filler, which is modified by silane coupling agent vinyltrimethoxysilane (A-171), and polyvinylidene fluoride (PVDF) copolymer as matrix were prepared by solution casting method. The morphology and dielectric properties (DP) were studied by transmission electron microscopy (TEM) and impedance analyzer. The effect of pH and ethanol concentration on the dielectric properties of A-171@CCTO/PVDF were studied. The results show that constant could reach 54.17 and loss 0.05 when mass fraction of A-171 is 0.4% at 1 kHz. pH=4 and using anhydrous ethanol are the optimal conditions.

Abstract: In this work, we have proposed a simple model to predicte the dielectric constant of CaCu₃Ti₄O₁₂-SrTiO₃ composite ceramics. The model has been established based on the analysis of composition and microstructure. Two different compositions in the composite ceramics correspond to two different grain sizes, large for CaCu₃Ti₄O₁₂, and small for SrTiO₃, which has been identified by the x-ray diffraction, the scanning electron microscope and the energy spectrum analysis. All specimens have been assumed to be the barrier layer dielectrics in the model, according to the complex impedance spectra. The dielectric constant of serial, parallel, and logarithmic mixture models has been discussed. Compared with the experimental results, the model shows the similar variation tendency as SrTiO₃ content increases.

Abstract: The dielectric properties of Zr substituted CaCu₃Ti₄O₁₂ ceramics have been investigated in detail. Grain size decreases with Zr content increasing. The hetero-electrical microstructures of prepared samples have been confirmed by the impedance spectra. The dielectric loss has been improved by Zr doping because of the enhancement of grain boundary resistivity. A Debye-like boundary relaxation behavior has been observed in the temperature range of 220-600K. As Zr content increases, the relaxation time increases due to the higher grain boundary concentration. This work has provided an additional proof for the origin of giant dielectric response in CaCu₃Ti₄O₁₂ ceramics.

Abstract: CaCu₃Ti₄O₁₂ presents colossal dielectric permittivity within a large temperature and frequency range, which makes it to be a suitable material for technological applications, such as components of capacitive memories and mobile phones. In this investigation, SrTiO₃-doped CaCu₃Ti₄O₁₂ ceramics were prepared by solid-state reaction. The influence of doping on the structures, compositions and dielectric properties of the materials were investigated by X-ray diffraction, scanning electron microscopy and dielectric measurements between 40 Hz and 110 MHz. The material presents colossal response (ε_r~10⁴−10⁵) and the dielectric loss tangent decreased with doping level increase at high frequency. The microstructure analysis showed that the second-phase particles segregated in the doped CaCu₃Ti₄O₁₂ grain edges. Cole-Cole modeling correlated well the effects of this segregation with the relaxation parameters obtained. The extrinsic contributions for the dielectric response were discussed together with the structural and compositional evolution of SrTiO₃-doped CaCu₃Ti₄O₁₂ material. The experimental results indicated that SrTiO₃ doping is a suitable method to optimize the dielectric response and electrical properties of CaCu₃Ti₄O₁₂ for the applications in microelectronic devices.

Abstract: The CaCu_3-xZn_xTi₄O₁₂ (CCZTO) (x=0, 0.06, 0.1, 0.2) ceramics were prepared by Sol–gel method. The XRD pattern shows that crystal structure of the sample with no Zn is basically single-phase. The SEM results indicate that the samples have porous structures and the gain size decreases with the content of Zn increasing. The dielectric properties of CCZTO were analyzed by Agilent 4294A. The experimental results show that the dielectric constants are less than that in other papers reported obviously because of their mesoporous structures. With the little doping amount(x=0.06, 0.1), a sharp decrease happened in the dielectric constant (ε_r). The higher ε_r was found when x=0.2, but its dielectric loss (D) had greatly increased and frequency stability of dielectric property became worse. The uniformity of gains was put forward to explain the results which showed great impact on the dielectric constant.

Abstract: The properties of undoped and La-doped CaCu3Ti4O12 ceramics synthesized via solid state reaction under argon environment had been studied. It was found that La-doped CCTOs gave higher dielectric constant and lower dielectric loss than undoped CCTO. X-ray diffraction (XRD) analysis indicated that all of the sintered samples have single-phase cubic structure (space group ). A minor shifted was observed in the peak positions for La-doped samples, which are attributed to the lattice expansion. The lattice parameter obtained from XRD analysis is 7.348 Å for undoped CCTO and increases to 7.348 – 7.377 Å for La-doped CCTOs. The results proven that La ions have effectively substituted into the Ca site of CCTO.

Abstract: The CaCu3Ti4O12 samples with slight amount of doped bismuth were prepared and tested in this research. No second phase with bismuth was found in the doped samples. It was inferred that the bismuth ions has entered the lattice and take the place of the calcium ions. The grain size was diminished with the increase of the bismuth content. The bismuth atoms can inhibit the grains from growing large, and it could be used to modify the microstructure of CaCu3Ti4O12 ceramic. The reduction of the grain size resulted in the decrease of the relative dielectric constant, according to the “internal barrier layer capacitance (IBLC)” theory. The impedance measurements showed that the doped samples have less conductivity and lower potential barrier at the grain boundaries, and the substitution of the bismuth ions on the calcium cites might be the reason for it. As a result of the lowered potential barrier, the non-ohmic I-V property of the CaCu3Ti4O12 ceramic almost disappears in the doped ones.

Abstract: The cooling rate effect on the grain boundaries of the CaCu3Ti4¬O12 ceramic was investigated in this research. The resistance at the grain boundaries is found to be reduced as the cooling rate rises. The activation energies at the grain boundaries do not change with the cooling rate, suggesting that the conduction mechanism keeps the same in different cooling conditions. There is no significant difference in the permittivity of the samples. The dielectric loss can be lowered by using a smaller cooling rate. These results give clues to comprehend the conductive mechanism of the CCTO ceramic. The variation of the cooling rate may affect the re-oxidation process and cause the changes in electric properties.

Abstract: CaCu3Ti4O12 ceramics were prepared by the traditional solid-state reaction method and the dielectric properties were investigated, the activation energy and relaxation time factor of the samples were calculated. Debye relaxation theory was attempted to analyze the experimental datum, the static and high-frequency dielectric constants were obtained according to Cole-Cole spectra. The temperature dependence of the dielectric constant of CaCu3Ti4O12 were fitted by computer and the theoretical results nearly agree with experimental results.

Abstract: CaCu3(Ti1-xZrx)O12 ceramics (x = 0.02, 0.04, 0.06, 0.08) were prepared by the conventional solid-state reaction method. Phase compositions, microstructure and dielectric properties were examined by XRD, SEM and impedance spectroscopy, respectively. The experimental results indicated that there is no obvious effect on microstructure characteristic by substituting Zr4+ for Ti4+. It was found that the values of the dielectric constant for all of the samples dropped into the order of 102, which is significantly lower than the order of 105 that of normally reported in the literature. It was suggested that the presence of impurity phases played an important role for the degeneracy of dielectric properties.