Dielectric Properties Of CaCu3Ti4O12 Ceramics Research Articles

Microstructure, dielectric and ferroelectric properties of CaCu3-xZnxTi4-xCexO12 ceramics prepared via semi-wet route

In this work, the effect of bi-substitution of Zn and Ce at Cu and Ti sites on microstructure and dielectric properties of CaCu3Ti4O12 ceramics was investigated. The doped CaCu3-xZnxTi4-xCexO12 (CCZTC-x) powders (where x = 0.1, 0.2 and 0.3) were successfully synthesized via semi-wet route and the corresponding ceramics were obtained by sintering at 950 ?C for 14 h in air. The presence of major cubic CaCu3Ti4O12 phase along with minor secondary CuO phase was observed by X-ray diffraction analysis. Scanning electron microscopy analyses confirmed microstructure consisting of cubic-shaped grains and grain sizes of 0.76, 0.87 and 0.98 ?m, for the ceramics with x = 0.1, 0.2 and 0.3, respectively. The high value of relative dielectric constant of 1500 at 100Hz was found for the sample with x = 0.3, which may be regarded as having semiconducting grains surrounded by insulating grain boundaries. In addition, conductivity of the sintered samples decreases with doping concentrations and the activation energies of the samples with x = 0.1, 0.2 and 0.3 are 0.93, 0.76 and 0.74 eV, respectively.

Improvement of the Nonlinear and Dielectric Properties of CaCu3Ti4O12 Ceramics by Nickel Doping

Improvement of the Nonlinear and Dielectric Properties of CaCu3Ti4O12 Ceramics by Nickel Doping

Microwave dielectric properties of CaCu3Ti4O12 ceramics: A clue to its intrinsic dielectric response

CaCu3Ti4[Formula: see text] (CCTO) is a potential dielectric material with giant permittivity, good stability over the wide temperature and frequency range. However, the dielectric responses of CCTO-based ceramics are mainly investigated in the frequency of 10 2–106 Hz, which is far low to clarify the intrinsic dielectric feature. So, microwave dielectric properties have been investigated for the CCTO porous ceramics sintered at low temperature ([Formula: see text]1000[Formula: see text]C). Good microwave dielectric properties of permittivity [Formula: see text] = 62.7, quality factor Qf = 3062 GHz and temperature coefficient of the resonant frequency [Formula: see text][Formula: see text] = 179 ppm/[Formula: see text]C are achieved for the CCTO ceramics sintered at 1000[Formula: see text]C, the dielectric loss significantly decreases two orders to 0.002 compared to that of CCTO ceramics sintered at critical temperature of 1020[Formula: see text]C confirmed by differential scanning calorimetry (DSC). This clue indicates that giant permittivity and high loss is not intrinsic for CCTO ceramics, but derives from composition segregation, liquid phase and defects associated with internal barrier layer capacitor (IBLC). It suggests that CCTO-based ceramics is a promising microwave dielectric materials with high permittivity.

Giant dielectric properties of CaCu3Ti4O12 ceramics synthesized by solid state reaction route

CaCu3Ti4O12 (CCTO) ceramics were prepared by solid-state reaction route, calcination at 1050?C for 4 h and sintering at 1050 and 1100?C for 8 h. X-ray diffraction and Raman studies of the CCTO powders and sintered samples confirmed the formation of single phase cubic structure with small amount of CuO in the sintered ceramics. Scanning electron microscope study revealed the average grain size between ~6 ?m to ~29 ?m in the CCTO ceramics sintered at 1100?C. Room temperature giant dielectric constant (?r) of the order of ~105 with relatively low dielectric loss at 100Hz frequency was obtained in the CCTO ceramics sintered at 1100?C. The present study has revealed that grain size plays an important role in enhancing the dielectric properties of CCTO ceramics.

Optimize the dielectric properties of CaCu3Ti4O12 ceramics by adjusting the conductivities of grains and grain boundaries

Reduction of dielectric loss for CCTO ceramics is a prerequisite for their applications. Considering internal barrier layer capacitance effect, improving the capacitance and grain boundary resistance is an effective way to reduce dielectric loss. Therefore, more conductive Ti3+ and Cu+ ions were introduced to grains by adding carbon to ceramic bodies, improving the permittivity of CCTO ceramics. Annealing was performed to increase the grain boundary resistance. The dielectric loss of the CCTO ceramics thus prepared, which maintain a giant permittivity, is significantly reduced. Specifically, the CCTO ceramic with carbon addition, which was sintered at 1080 °C for 8 h and air annealed at 950 °C for 2 h, exhibits a giant permittivity of about 2.50(5)×104 and a low dielectric loss of less than 0.050(2) from below 20 Hz to 50 kHz at room temperature. Meanwhile, its dielectric loss at 1–10 kHz is less than 0.050(2) from below room temperature to about 100 °C.

Microstructure and dielectric properties of CaCu3Ti4O12 ceramics by lanthanum/europium co-doping

Microstructure and dielectric properties of CaCu3Ti4O12 ceramics by lanthanum/europium co-doping

Microstructure and dielectric properties of CaCu3Ti4O12 ceramics with high breakdown field strength prepared via polymer pyrolysis

Although polymer pyrolysis has been proven to be an excellent method for synthesising advanced functional ceramics, a detailed preparation process has rarely been reported. It is well known that the mass ratio of initiator to monomer (x value) and the molar ratio of monomer to cation (y value) are key factors in polymerisation. To introduce these two crucial parameters and obtain high-performance dielectric ceramics with high breakdown field strength, pure CaCu3Ti4O12 (CCTO) ceramic samples with different x values and then with different y values (at x = 0.5%) were prepared via polymer pyrolysis in this study. The effects of x and y on the microstructure and dielectric performance of the CCTO ceramics were systematically investigated. The results show that CCTO ceramics with y = 2.0 simultaneously exhibited high breakdown field strength (8.71 kV/cm), large dielectric constant (14,892), and low dielectric loss (0.030). The results also demonstrate that a moderate amount of initiator can promote complete polymerisation, and that an appropriate monomer is favourable for strengthening ionic bonding between metal ions and carboxylic acid ions in polymer chains. We believe that this work can provide a guide for the synthesis of CCTO-based and other matrix ceramics with excellent dielectric performance using the polymer pyrolysis method.

Differences between La substitution and doping strategies in dielectric properties of CaCu3Ti4O12 ceramics with low loss

Differences between La substitution and doping strategies in dielectric properties of CaCu3Ti4O12 ceramics with low loss

Critical Sintering Temperature and Microwave Dielectric Properties of Cacu3ti4o12 Ceramics

Critical Sintering Temperature and Microwave Dielectric Properties of Cacu3ti4o12 Ceramics

Dielectric properties of CaCu3Ti4O12 ceramics doped with aluminium and fluorine

The ceramics СaСu3Тi4–xAlxО12–0.5x–yFy were prepared using solid-state reactions technique and pre-synthesized CaTiO3. It was found that the resistances of both the grain boundary RGB and the interface between sample and electrode RSE increase at the combined introduction of Al3+ and F– ions. At 1100 °С, a decrease in dielectric properties after 12 h of sintering time due to copper losses was observed. The samples with x/y = 0.04/0.04 sintered for 10 h at 1 kHz are characterized by the following dielectric parameters: ε′ ≈ 72,000 and tan δ ≈ 0.047. In the sample x/y = 0.04/0, the lowest dielectric loss (tan δ ≈ 0.044) were found.

Mg2+ Doping Effects on the Structural and Dielectric Properties of CaCu3Ti4O12 Ceramics Obtained by Mechanochemical Synthesis.

In this study, ceramic CaCu3Ti4O12 (CCTO) and CaCu3−xMgxTi4O12 solid solutions in which 0.1 ≤ x ≤ 0.5 were prepared by the mechanochemical method, realized by a high-energy ball milling technique. The effects of the Mg2+ ion concentration and sintering time on the dielectric response in the prepared ceramics were investigated and discussed. It was demonstrated that, by the use of a sufficiently high energy of mechanochemical treatment, it is possible to produce a crystalline product after only 2 h of milling the mixture of the oxide substrates. Both the addition of magnesium ions and the longer sintering time of the mechanochemically-produced ceramics cause excessive grain growth and significantly affect the dielectric properties of the materials. The X-ray diffraction (XRD) analysis showed that all of the as-prepared solid solutions, CaCu3−xMgxTi4O12 (0.0 ≤ x ≤ 0.5), regardless of the sintering time, exhibit a cubic perovskite single phase. The dielectric study showed two major contributions associated with the grains and the grain boundaries. The analysis of the electric modules of these ceramics confirmed the occurrence of Maxwell–Wagner type relaxation, which is dependent on the temperature.

Influence of Nb and Zr co-doping on the structural, morphological and dielectric properties of CaCu3Ti4O12 ceramics

In this work, CaCu3Ti3.8-xNb0.2ZrxO12 (where x=0.0, 0.05, 0.1, 0.2) ceramics were made using the normal solid-state reaction method to assess the influence of Nb5+ & Zr4+ codoping on the structure, morphology and electrical properties of CaCu3Ti4O12 ceramics. Reitveld refinement by Fullprof package was done to achieve the structural information. No phase transformation was observed upon doping. The CCTNZO ceramics occupied a finegrained microstructure with grain sizes ranges from 0.26-0.33 μm. Furthermore, grain size uniformity was enhanced with gradual doping of Zr4+ ion. within the meantime, the CCTNZO ceramics unfolds extensive durability of dielectric constant over a good range of frequency and also shows a lower loss factor. Doping resulted during a gradual decrease in grain sizes and a dielectric loss at low and high frequency. It had been found that 10% of Zr doped CCTNZO ceramics has the very best dielectric constant (3655) at 0.1 kHz. Meanwhile, rock bottom dielectric loss of 0.241 at 0.1 kHz was observed for 20% Zr doped CCTNZO ceramics.

Effect of minor phase (CuO) on sinterability, grain size, and dielectric properties of CaCu3Ti4O12 ceramics

CaCu3Ti4O12 (CCTO) electro ceramic was prepared by a solid-state reaction technique. The formation of CCTO was confirmed by X-ray diffraction (XRD). Pellets of calcined powder were sintered at different temperatures for two different durations, i.e., 2 and 10 h (h). The morphology and grain size of the samples were observed using scanning electron microscopy (SEM). SEM images showed that the minor phase (CuO) plays an important role in the growth of grain size. It seems that higher sintering temperatures led to change in the oxidation states of Cu and Ti, which increase the volume fraction of the CuO minor phase. Dielectric studies show that the dielectric constant is increasing with increasing sintering temperature, holding time, and presence of the CuO phase. The highest dielectric constant of ~ 41,000 was observed for CCTO samples sintered at 1100 °C for 10 h. The present samples find application in the energy storage devices.

Cu2O addition and sintering temperature dependence of structural, microstructural and dielectric properties of CaCu3Ti4O12 ceramics

This study is aimed in the replacement of commonly used (CuO) by Cu2O in the synthesis of perovskite CaCu3Ti4O12 (CCTO) phase by the solid-state reaction method. The XRD analysis of powder calcined at 1100 °C and ceramics sintered at different temperatures show that the CCTO phase was well crystallized with the presence of small quantities of additional phases. The SEM/EDS analysis of prepared pellets show that the formation of Cu2O/CuO phase occurs above 950 °C, resulting in enhanced densification at 1050 °C (>96%). However, it is found that the Cu2O-based CCTO begins to degrade around 1090 °C. The densification after sintering at 1050 °C reaches 96%, meanwhile dielectric constant and loss tangent values are optimum in the low frequency range (<103 Hz); i.e. 13378 and 0.177, respectively. This favors the use of Cu2O instead of CuO in CCTO ceramics for applications at low frequencies.

Significantly improving the giant dielectric properties of CaCu3Ti4O12 ceramics by co-doping with Sr2+ and F- ions

Improved dielectric properties of CaCu3Ti4O12 ceramics were produced by co-doping with Sr2+/F- cation/anions. The grain sizes of the Ca1-xSrxCu3Ti4O12-xFx ceramics were considerably decreased, producing a large amount of insulating grain boundary (GB) layers. Optimized dielectric properties with a high dielectric permittivity of ε′∼6.44 × 104 and a low loss tangent (tanδ∼0.030) were produced. The non-Ohmic properties also improved. The Schottky barrier height (ΦB) of the GBs increased by co-doping with Sr2+/F- ions. The electrical properties of the semiconducting grains changed slightly. Accordingly, the increase in the total GB resistance (Rgb) significantly decreased the tanδ and increased the breakdown electric field. The increased Rgb resulted from the improved intrinsic properties of the GBs (that is, ΦB increased) and the controlled microstructure (that is, the insulating GB layers increased). The macroscopic giant dielectric and electrical properties were described using an internal barrier layer capacitor model related to the Schottky barrier height at the GBs.

Enhancement of breakdown electric field and dielectric properties of CaCu3Ti4O12 ceramics by Sr doping

In order to enhance the breakdown electric field (Eb) and dielectric properties of CaCu3Ti4O12 ceramics, Ca1-xSrxCu3Ti4O12 ceramics with different Sr doping concentration were fabricated by modified sol–gel method. It was found that the dielectric properties of Ca1-xSrxCu3Ti4O12 ceramics greatly depended on the Sr doping concentration, and Ca0.5Sr0.5Cu3Ti4O12 ceramics behaved high Eb of ~52.50 kV/cm, low dielectric loss (tanδ) of ~0.066, and high dielectric constant (εr′) of ~3902 at 1 kHz and room temperature, simultaneously. Moreover, it was proved that the enhanced Eb can be attributed to both the increasing amount of grain boundaries and higher Schottky barrier height. All the results indicated that Ca0.5Sr0.5Cu3Ti4O12 ceramics were very promising materials for practical applications.

Dielectric properties of CaCu3Ti4O12 ceramics doped by La3+

Abstract XRD, SEM, EDS and XPS were used to study the influence of La3+ on phase structure, microstructure, cationic distribution and cationic oxidation state of CaCu3Ti4O12 ceramics. It was found that donor doping is formed by preferential substitution of La3+ for Ca2+. The concentration of O in the grain is increased and the segregation of Cu into the grain boundary is suppressed effectively by La3+ doping, leading to the decrease and uniform distribution of gain size. The influence of La3+ on dielectric properties of CaCu3Ti4O12 ceramics were investigated also by Novocontrol broadband dielectric spectrometer. It was found that oxygen vacancy-related dielectric relaxation at medium frequency region is suppressed and the corresponding dielectric loss is significantly reduced also. At the same time, high frequency dielectric relaxation is increased obviously, which results in a significant increase of dielectric constant from about 5 × 103 to 2 × 104. The study in this paper shows that donor doping is an effective way to modulate intrinsic point defects, microstructure and then dielectric properties of CaCu3Ti4O12 ceramics.

The effects of sintered sample thickness on the dielectric properties of CaCu3Ti4O12 ceramics prepared at 1000–1100 °C in air

Abstract In this study, the relationship between dielectric properties and sintered sample thickness (d) (0.41–2.74 mm) of CaCu3Ti4O12 (CCTO) ceramics prepared at 1000–1100 °C in air was investigated. Compacted green ceramic bodies in varying weights and sintered at different temperatures were prepared to obtain ceramics with varying thicknesses. The samples were evenly polished on either surface, electroded and measured by a precision LCR meter at 20 Hz–1 MHz. The results showed that the e′ increased monotonically with increasing sintering temperature and indicated a linear relationship with d for samples sintered at ≥1040 °C, while the e′ for samples sintered at ≤1030 °C was barely affected. Complex impedance analysis showed that the ρgb was nearly constant with the change of d. The inverse effect of e′ and ρgb with d can also be observed for the gradual thickness reduction sample sintered at 1040 °C, confirming that the grain boundary plays a key role in the variation of dielectric properties for CCTO ceramics.

Influence of sintering conditions and CuO loss on dielectric properties of CaCu3Ti4O12 ceramics

Phase structures, morphology and dielectric properties of prepared CaCu3Ti4O12 ceramics were investigated to better understand the origin of giant dielectric constant in CCTO system. It was found that the samples' dielectric properties obviously vary with sintering conditions and the corresponding dielectric constant can reach more than 5 × 104 by sintering at 1100 °C for 8˜10 h. XPS results revealed that the ratios of Cu2+/Cu+ and Ti4+/Ti3+on the surface are apparently higher than that in the interiors, showing CuO segregation and oxidation process on the surface of CCTO ceramics during sintering in air. Therefore, it is significant for CCTO to achieve giant permittivity by properly controlling sintering conditions. According to defect chemistry, the mechanisms of defect formation and recombination are proposed to explain the influence of CuO loss on electrical properties of CCTO-base materials.

Effect of different pH values adjusted by ammonia on the dielectric properties of CaCu3Ti4O12 ceramics prepared by a sol-gel method

To investigate the effect of different pH values (pH = 1, 3, 5, 7) of a solution used to prepare CaCu3Ti4O12 (CCTO) ceramics on the microstructure and dielectric properties of the resultant ceramics, the acid regulator in the solutions was replaced with an alkaline regulator, ammonia water, and CCTO ceramics were prepared through a sol-gel method. The data show that the dielectric constants of the as-prepared samples maintained relatively high values in the frequency range from 1 to 107 Hz. In addition, the dielectric loss decreased to 0.028 at 103 Hz for the sample prepared at pH = 5. Moreover, the results reveal that the grain size, porosity and content of the CuO phase at the grain boundaries of the CCTO ceramics varied with the pH value. Our results indicate that using an alkaline regulator to adjust the pH value of the synthesis solution is an effective method for reducing the dielectric loss of CCTO ceramics.