Dielectric Properties Of CCTO Research Articles

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.

Microstructural and Dielectric Responses of Calcium Copper Titanate Added Soda-Lime Glass for High Frequency Devices

The microstructures and dielectric responses of calcium copper titanate (CCTO) ceramics with soda-lime glass addition was investigated. The addition of soda lime glass was varied from 0-5 wt.% by solid-state reaction. The dielectric properties of CCTO indicated that dielectric constant was increased while dielectric loss was decreased after glass addition. The SEM micrographs showed the grain size of CCTO was decreased while the grain boundaries area of CuO + glass were increased after the addition of soda-lime glass. Both XRD patterns of CCTO and CCTO-soda lime glass sintered samples showed the formation of CCTO phase with minor peaks of CuO phase, respectively. These results indicated that soda-lime glass addition gave a significant effect on the microstructural and dielectric responses of CCTO ceramics.

Dielectric Properties of Al<sub>2</sub>O<sub>3</sub>/CaCu<sub>3</sub>Ti<sub>4</sub>O<sub>12</sub> Composite at High Frequency Range

The dielectric properties of CCTO with addition Al2O3 prepared via solid state reaction investigated and reported at 1 GHz. With addition Al2O3 from 20 wt% to 80 wt%, secondary phase starts appear in XRD analysis such as copper dialuminium oxide (CuAl2O4), calcium titanate (CaTiO3) and titanium oxide (TiO2). These secondary phases show great influence on morphology and grain size of Al2O3/ CCTO composites. Hence, the addition of only 20 wt% Al2O3, the dielectric constant of CCTO reduce almost 50% and tangent loss is in between 0.0028 to 0.0630 which is very low and this characterization is suitable to use in electronic application in high frequency range.

Structural and Dielectric Properties of Lanthanum Doped CaCu<sub>3</sub>Ti<sub>4</sub>O<sub>12</sub> for Capacitor Application

CaCu3Ti4O12 (CCTO) is a novel material with high relative dielectric constant and low loss tangent, CCTO belongs to a family of oxides of the type ACu3Ti4O12 (A=Ca, Cd, Sr, Na, Th). CaCu3Ti4O12 was first reported by Subramanian et al., to have an unusually high dielectric constant (~10,000) at 1 kHz. It is well known that dielectric properties of CCTO are strongly dependent upon the processing conditions as well as on doping. Semi-wet route was used to synthesise samples of CaCu3Ti4O12 and Ca(1-3x/2)LaxCu3Ti4O12 (x=0.01). Analytical grade chemicals, Ca(NO3)2.4H2O, La(NO3)3.6H2O, Cu(NO3)2.3H2O, titanium dioxide and citric acid having purity better than 99.95% were used as starting materials. The formation of single-phase solid solutions was confirmed by the absence characteristic lines of constituent’s oxides in the XRD patterns. Dielectric measurement of undoped and La doped CCTO has been performed using four probe novocontrol set up (ZG4) in a wide range of temperature starting from the room temperature. With La doping in CCTO there is an increase in the value of dielectric constant in comparison to undoped CCTO.

Dielectric Properties of Eu-Doped CaCu3Ti4O12 with Different Compensation Mechanisms

To get a better understanding of the influence of rare-earth element doping, CaCu3Ti4O12 (CCTO) samples with a partial substitution of Ca with Eu with different compensation mechanisms were designed and prepared by solid-state reaction. All the ceramics were single phase, while the dielectric constants and thermally activated energy values for dielectric relaxation in Eu-doped ceramics were both lower than those of CCTO. Ca0.875Eu0.1Cu3Ti4O12 (CECT1) exhibited a slight decrease in both the permittivity and electric resistance of grain boundaries compared with CCTO, while Ca0.85Eu0.1Cu3Ti4O12 (CECT2) underwent a sharp decrease in permittivity associated with an abnormally large resistance. The different dielectric behavior indicates that the dielectric properties of CCTO are sensitive to the valence states of cations and defects. The variation of permittivity is related to the localization of carriers, which, according to the XPS results, should be caused by the presence of oxygen vacancies. The formation of defect complexes between cations and oxygen vacancies leads to the increase in resistance and prevents the hopping between Cu+ and Cu2+, which is an important source of the polarization in grain boundaries.

Enhanced extrinsic dielectric response of TiO2 modified CaCu3Ti4O12 ceramics

TiO2 modified CaCu3Ti4O12 (CCTO) has been synthesized via a facile sol–gel precipitation process followed by solid state sintering. The influence of the precipitated TiO2 crystallites on the microstructure, phase composition, and dielectric properties of CCTO has been investigated. The morphology and chemistry of grain boundaries in CCTO ceramics can be significantly tailored by the initial TiO2 crystallites, which results in enhanced barrier layer capacitor structures. The formation mechanism of barrier layers based on the instability of Cu ions has been discussed. A new bimodal brick layer mechanism has been proposed to explain the effect of TiO2 modification. The optimized TiO2 modified CCTO sample exhibits stable dielectric permittivity which is twice as high as the unmodified one, and shows relatively low dielectric loss over the frequency range from 102 to 105Hz. Such enhancement is deemed to arise from the modified and bimodal internal barrier layer capacitor effect.

Dielectric properties of microwave flash combustion derived and spark plasma sintered CaCu3Ti4O12 ceramic: role of reduction in grain boundary activation energy

CaCu3Ti4O12 nanocrystals have been synthesized by the microwave flash combustion technique. The calcined powders were spark plasma sintered at 1050 °C for 10 min. The surface morphology of sintered samples was studied by SEM. The effects of grain boundary activation energy on dielectric properties of CCTO were investigated by collecting the dielectric data in the frequencies of 30 Hz–8 MHz at temperatures of 20–100 °C under dc bias of 0–6 V. The potential energy barrier at grain boundary has been examined by dc bias experiments. It is observed that, with an increase in dc bias from 0 to 6 V, the grain boundary activation energy decreases from 0.532 to 0.463 eV. The reduction in such grain boundary activation energy results in the decrease in dielectric constant. It is noticed that CCTO ceramic at room temperature under zero dc bias has a colossal dielectric constant of 20,000 (at 100 Hz). Using the cole–cole plot, grain and grain boundary resistance are calculated to be 13 and 52,100 Ω, respectively.

Mechanochemical Processing of CaCu3Ti4O12 with Giant Dielectric Properties

The dielectric properties of CaCu3Ti4O12 (CCTO) ceramic prepared by mechanochemical synthesis (MCS) were investigated. The effect on dielectric properties of ball-to-powder weight ratio and milling time was investigated and compared to the behavior of CCTO prepared by conventional solid state reaction (CSSR). CCTO ceramic was partially obtained after 6h of the milling process, while complete transformation was obtained during the sintering step of milled powders. It was shown that the dielectric properties of CCTO processed by MCS are dramatically improved compared with samples prepared by CSSR.

Effect of Sintering Temperature on Dielectric Properties of CaCu<sub>3</sub>Ti<sub>4</sub>O<sub>12 </sub>Ceramics Prepared by Mechanochemical Process

CaCu3Ti4O12 (CCTO) is well known to have colossal dielectric constant in the range of 105.It is widely accepted that this phenomenon may be attributed to internal layer barrier capacitance (IBLC) model. The dielectric properties of CCTO were reported to be strongly dependent on the processing conditions and grain size. In this work, CCTO samples with different grain sizes were produced by varying sintering temperature in order to investigate IBLC effect on dielectric properties of CCTO. The samples were sintered at four different temperatures, (T=1100°C, 1050°C, 1000°C and 950°C). Dielectric measurements were carried out for the samples in the frequency range of 102 – 106Hz using impedance spectrometer. Electron micrographs showed that increasing temperature promoted the grain growth of CCTO while sintering. The internal crystalline defects are seen to play major role by increasing the grain conductivity in dipole formation and increased the dielectric constant of the samples.

Preparation and Structural Characterization of CaCu<sub>3</sub>Ti<sub>4</sub>O<sub>12</sub> Doped with Nickel, Ferrite, Manganese and Cobalt

Transition metal oxide-doped CCTO (CaCu3Ti4O12) ceramics were prepared by a conventional solgel synthesis method and the effects of pure CCTO and CCTO doped with Mn, Fe, Co, Ni to the crystal structure, microstructures and dielectrical properties of samples were investigated. The phase composition and microstructure were studied by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD analysis reveals that all samples exhibited multiphases with the pseudo-perovskite cubic CCTO phase with space group Im-3 as the main phase in undoped and doped CCTO samples. Peaks of monoclinic CuO and peroveskite CaTiO3 could also be seen in all samples which indicate that solid solution of CuO in CaTiO3 lattice was incomplete.SEM results show that doping effectively enhanced densification. SEM micrographs also suggested that the morphologies of doped CCTO ceramics had showed a matrix consisting of large grains wherein the small grains were embedded between the larger grains. Dielectric properties of pure and doped CCTO were investigated in a broad frequency range of the dielectric constant reached a value as high as εr = 29.4 at room temperature for CCTO doped with Ni at frequency (1000 Hz). Besides the sintering conditions, the microstructure and the dielectric properties of the CCTO are strongly influenced by type of doping elements.

Microstructure, dielectric and pyroelectric properties of CaCu3Ti4O12 ceramics fabricated by tape-casting method

CaCu3Ti4O12 (CCTO) ceramics were prepared by tape-casting method. All the ceramics exhibited body-centered cubic structure. A homogeneous microstructure with clear grain boundaries was obtained by tuning the sintering temperature. The dielectric properties of CCTO were investigated in a temperature range of −100 to +300°C. A relaxation has been observed in the frequency range higher than 100kHz, the activation energy was found to be 0.07eV, close to that of the activation energy for dc conductivity (0.08eV) at low temperatures. It suggests that the polarons induced by oxygen vacancies are responsible for the conduction and relaxation process. The high-temperature dependence of the dc conductivity associated with oxygen vacancies. Also, the hysteresis loop and pyroelectric properties have been measured and the incidence of the pyroelectric effect associated with the temperature dependence of pyroelectric coefficient implies that CCTO has a vast potential in the field of high-temperature pyroelectric thermal detectors.

Effect of the Synthesis Route on the Microstructure and the Dielectric Behavior of CaCu3Ti4O12 Ceramics

CaCu3Ti4O12 (CCTO) was prepared by a conventional synthesis (CS) and through reaction sintering, in which synthesis and sintering of the material take place in one single step. The microstructure and the dielectric properties of CCTO have been studied by XRD, FE‐SEM, EDS, AFM, and impedance spectroscopy to correlate structure, microstructure, and electrical properties. Samples prepared by reactive sintering show very similar dielectric behavior to those prepared by CS. Therefore, it is possible to prepare CCTO by means of a single‐step processing method.

Dielectric relaxation behaviors of pure and Pr 6O 11-doped CaCu 3Ti 4O 12 ceramics in high temperature range

Pure and Pr 6O 11-doped CaCu 3Ti 4O 12 (CCTO) ceramics were prepared by conventional solid-state reaction method. The compositions and structures were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influences of Pr-ion concentration on dielectric properties of CCTO were measured in the ranges of 60 Hz–3 MHz and 290–490 K. The third phase of Ca 2CuO 3 was observed from the XRD of CCTO ceramics. From SEM, the grain size was decreased obviously with high valence Pr-ion (mixing valence of Pr 3+ and Pr 4+) substituting Ca 2+. The room temperature dielectric constant of Pr-doped CCTO ceramics, sintered at 1323 K, was an order of magnitude lower than the pure CCTO ceramics due to the grain size decreasing and Schottky potential increasing. The dielectric spectra of Pr-doped CCTO were flatter than that of pure CCTO. The loss tangent of Pr-doped CCTO ceramics was less than 0.20 in 2 × 10 2–10 5 Hz region below 440 K. The complex impedance spectra of pure and Pr-doped CCTOs were fitted by ZView. From low to high frequency, three semicircles were observed corresponding to three different conducting regions: electrode interface, grain boundary and grain. By fitting the resistors R and capacitors C, the activation energies of grain boundary and electrode contact were calculated. All doped CCTOs showed higher activation energies of grain boundary and electrode than those of pure CCTO ceramics, which were concordant with the decreasing of dielectric constant after Pr 6O 11 doping.

The Effect of GeO2 and In2O3 Doping on the Dielectric Properties of CaCu3Ti4O12 Ceramics Prepared via Vibro-Milling Method

In this work, effects of GeO2 and In2O3 doping on the dielectric properties of CCTO were investigated. Doping levels range from 0.5 to 2.0 mol%. The vibro-milling method was employed for processing. The dopant addition produced a slightly smaller grain size. A reduction in dielectric constant was observed, but it is still high. The 2.0 mol% GeO2 and In2O3 doped samples exhibited high dielectric constant of about 25,000 and 23,000 and low dielectric loss with 0.06 and 0.05 respectively at room temperature and at 10 kHz. The dielectric measurements showed that the modified samples exhibited a strong dielectric independency of temperature and frequency. In addition, the loss tangent reduced after doping. From this results, it can be incurred that GeO2 and In2O3 doping, processed via vibro-mill are the suitable methods to achieve the stability of high ϵr and low loss ceramics.

Dielectric characteristics and positron annihilation study of Eu 2O 3-doped CaCu 3Ti 4O 12 ceramics

Eu 2O 3-doped CaCu 3Ti 4O 12 ceramics were sintered using traditional solid-state reaction method. The microstructure and dielectric characteristics of samples were measured and their interrelation was analyzed. The results indicate that a small quantity of Eu 2O 3-doped in CCTO can deter the formation of Cu-enriched phase and improve the structure of crystal grains, which is of help to improve the thermal and frequency stability of dielectric properties. Positron annihilation lifetime spectra measurements indicate that a small quantity of Eu 2O 3 doping in CCTO can reduce the defect concentration and thin grain boundary layers in the material. The dielectric characteristics of CCTO have been explained in terms of the defects in the material. It is concluded that the microstructure and the dielectric properties of CCTO can greatly be improved by doping with 0.2 wt% of Eu 2O 3. The ramifications of current study could be very useful in applications of this important material.

Effect of the addition of B 2O 3 and BaO–B 2O 3–SiO 2 glasses on the microstructure and dielectric properties of giant dielectric constant material CaCu 3Ti 4O 12

The effect of the addition of glassy phases on the microstructure and dielectric properties of CaCu 3Ti 4O 12 (CCTO) ceramics was investigated. Both single-component (B 2O 3) and multi-component (30 wt% BaO–60 wt% B 2O 3–10 wt% SiO 2 (BBS)) glass systems were chosen to study their effect on the density, microstructure and dielectric properties of CCTO. Addition of an optimum amount of B 2O 3 glass facilitated grain growth and an increase in dielectric constant. However, further increase in the B 2O 3 content resulted in its segregation at the grain boundaries associated with a reduction in the grain size. In contrast, BBS glass addition resulted in well-faceted grains and increase in the dielectric constant and decrease in the dielectric loss. An internal barrier layer capacitance (IBLC) model was invoked to correlate the dielectric constant with the grain size in these samples.