Microstructure and dielectric properties of CaCu3Ti4O12 ceramic

CaCu₃Ti₄O₁₂ (CCTO) was prepared by the solid state technique. The sample was calcined at 900 °C/12 h and sintered at 1050 °C/24 h, then subjected to XRD to ensure CCTO formation. The microstructure was observed by SEM. XRD results identified both samples as single phase CCTO, whereas the microstructure shows abnormal grain growth and large pores. Sintering was studied in the temperature range of 950–1050 °C for 3–12 h. Increasing sintering temperature enhances the density and secondary formation of Cu₂O. A clear grain boundary and dense microstructure were observed. The results show that the sample sintered at 1040 °C/10 h yields a clearly uniform grain size with the highest ε_r (33,210).     

Microwave synthesis and sintering characteristics of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript>

CaCu₃Ti₄O₁₂ (CCTO) was synthesized and sintered by microwave processing at 2·45 GHz, 1·1 kW. The optimum calcination temperature using microwave heating was determined to be 950°C for 20 min to obtain cubic CCTO powders. The microwave processed powders were sintered to 94% density at 1000°C/60 min. The microstructural studies carried out on these ceramics revealed the grain size to be in the range 1–7 μm. The dielectric constants for the microwave sintered (1000°C/60 min) ceramics were found to vary from 11000–7700 in the 100 Hz–00 kHz frequency range. Interestingly the dielectric loss had lower values than those sintered by conventional sintering routes and decreases with increase in frequency.     

Abnormal dielectric behaviors in Mn-doped CaCu3Ti4O12 ceramics and their response mechanism

Mn-doped CaCu₃Ti₄O₁₂ (CCTO) polycrystalline ceramics have been prepared by the conventional solid state sintering. Our results indicate that 10% Mn doping can decrease the dielectric permittivity in CaCu₃Ti₄O₁₂ by about 2 orders of magnitude (from 10⁴ to 10²). The grain and grain boundary activation energies show an obvious increase from 0.054 eV to 0.256 eV, and decrease from 0.724 eV to 0.258 eV with increasing the Mn doping concentration, respectively, which may be caused by the variation of Cu and Ti valence states in the CCTO samples evidenced by the X-ray absorption spectra. The similar grain and grain boundary activation energies result in invalidation of the internal boundary layer capacitance effect for the 10% Mn-doped CCTO sample, and thus result in the dramatic decrease of dielectric permittivity.     

Current–voltage nonlinear and dielectric properties of CaCu3Ti4O12 ceramics prepared by a simple thermal decomposition method

In this work, pure-CaCu₃Ti₄O₁₂ was successfully prepared by a simple thermal decomposition method. This can easily be achieved by direct firing of starting raw materials dissolved in an aqueous citric acid solution at 800 °C for 6 h. The results show that sintering conditions have a remarkable influence on the microstructure of the CaCu₃Ti₄O₁₂ ceramics. Interestingly, dense CaCu₃Ti₄O₁₂ ceramic sintered at 1,050 °C for 2 h exhibits a high dielectric constant of ~5.1 × 10³ with low loss tangent of ~0.048 at 30 °C and 1 kHz. The dielectric properties, electrical response of grain boundaries, and related nonlinear current–voltage behavior are found to be associated with the microstructure of CaCu₃Ti₄O₁₂ ceramics.     

The influence of the segregation of Cu-rich phase on the microstructural and impedance characteristics of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics

The influence of sintering conditions on the microstructural features and impedance characteristics of the giant dielectric constant material CaCu₃Ti₄O₁₂ (CCTO) was investigated. The microstructure and impedance characteristics were found to be strongly dependent on the sintering conditions. Sintering of the CCTO ceramics at elevated temperatures (>1100 °C) for prolonged durations resulted in the segregation of Cu-rich phase, mostly confined to the surface, which was in concomitance with the appearance of the additional semicircle at the low frequency end in Impedance (Z*) plots. The absence of this additional semicircle in the Cu-deficient CCTO ceramics and the appearance of the same in Cu-rich CCTO ceramics that were deliberately fabricated corroborated the above observations. Also, La_2/3Cu₃Ti₄O₁₂ (LCTO), a low dielectric constant member of CCTO family, which consisted of small grains without the segregation of Cu-rich phase at the grain boundary, did not reveal the presence of additional semicircle in the Z*plots.     

Effects of SrO–B2O3–SiO2 glass additive on the microstructure and dielectric properties of CaCu3Ti4O12

The effect of SrO–B₂O₃–SiO₂ glass additive (SBS) on the microstructure and dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics was investigated. This SBS–added CCTO ceramics were prepared by the solid state reaction. The undesirable impurity phases Ca₃SiO₅ started appearing in the XRD patterns, suggesting a possible chemical reaction between CaTiO₃ and SiO₂ (the devitrification production of SBS glass). The SBS glass additive promoted the grain growth and densification of CCTO ceramics. Cole–Cole plots of conductance suggested that the resistivity grain boundary decreased with increasing amount of SBS glass (when x = 0–2 wt%), then increased (when x = 2–3 wt%). The addition of SBS glass was desirable to increase the dielectric constants (up to 10⁴) and lowered the dielectric losses of CCTO over the frequency range of 450–40 kHz at the relatively lower sintering temperature for relatively shorter sintering time (1,050 °C, 12 h).     

Effects of Kaolinite additions on sintering behavior and dielectric properties of CaCu3Ti4O12 ceramics

Commercial Kaolinite was employed as sintering aid to reduce the sintering temperature of CaCu₃Ti₄O₁₂ (CCTO) ceramics. The effects of Kaolinite content and sintering temperature on the densification, microstructure and dielectric properties of CCTO ceramics have been investigated. The density characterization results show that the addition of Kaolinite significantly enhanced the relative density of CCTO ceramics to about 92 %. X-ray diffraction results show CCTO ceramics with a low amount of Kaolinite exhibited perovskite-like structure, but 1.0 wt% Kaolinite additions resulted in the formation of a secondary phase, CaO–TiO₂–Al₂O₃–SiO₂ glass phase was formed and improved the dielectric constant of ceramics, which was supported by scanning electron microscopy–energy dispersive X-ray results. CCTO ceramic with 1.0 wt% Kaolinite addition possessed well temperature and frequency stability of dielectric constant. It was found that Kaolinite lowered the dielectric loss of the samples.     

Microstructure and dielectric properties of Ca1–3/2xBixCu3Ti4O12 (x = 0, 0.05, 0.10, 0.15 and 0.20) ceramics

Influence of bismuth substitution on calcium site in CaCu₃Ti₄O₁₂ has been investigated. Compositions of Ca_1-3/2xBi_xCu₃Ti₄O₁₂ (x = 0, 0.05, 0.10, 0.15 and 0.20) were fabricated by solid-state sintering method. Crystal structure is remained cubic. X-ray diffraction indicates the presence of secondary phase of CuO in CCTO ceramics. Bismuth doping restrains the formation of CuO phase apparently. The grain size of CaCu₃Ti₄O₁₂ ceramics was greatly decreased by Bi³⁺ doping, resulting from the ability of bismuth to inhibit the grain growth. The dielectric and electric properties of CCTO ceramics were found to be influenced by bismuth doping. The fitting results of the complex impedance spectra showed an increase of the resistance of grain and grain boundary by bismuth substitution. Ca_0.70Bi_0.20Cu₃Ti₄O₁₂ showed the highest dielectric constant in the low frequency range. A modest composition such as Ca_0.85Bi_0.10Cu₃Ti₄O₁₂ expressed the optimized dielectric properties of higher dielectric constant (1.3 × 10⁴) and lower dielectric loss (0.06) than pure CCTO. The low and high temperature dielectric loss spectra demonstrate the interfacial polarization of the initial and secondary oxygen ionization, relating with the grain and grain boundary (the electrode contact for Ca_0.70Bi_0.20Cu₃Ti₄O₁₂) respectively.     

Dielectric properties of Erbium doped CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> prepared by sol–gel self combustion method

The dielectric properties of Erbium doped CaCu₃Ti_(4–x)Er_xO_(12–δ) with x = 0, 0.05, 0.1 were synthesized by the sol–gel self combustion method. XRD (X-ray powder diffraction) analysis confirmed the formation of single-phase material in the samples calcined at 800 °C. Crystal structure does not change on doping with Erbium and it remains cubic in all the three compositions studied. It is found that lattice parameter increases slightly with Erbium doping. The surface morphology of CaCu₃Ti_(4–x)Er_xO_(12–δ) powders sintered at 950 °C in air for 3 h was observed using high resolution—scanning electron microscope and it shows that the grain size is in the range of 1–8 μm for these samples. Energy dispersive X-ray spectroscopy pattern confirmed the presence of Erbium with 1.9 and 4.86 atomic percentages with doping concentration. The dielectric characteristics of CaCu₃Ti_(4–x)Er_xO_(12–δ) were studied by LCR meter in the frequency range (100 Hz–1 MHz) at various temperatures (RT to 500 °C). Interestingly, the dielectric constant increases and dielectric loss had lower values than those of undoped CCTO.     

Chemical solution deposition of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> thin film

CaCu₃Ti₄O₁₂ (CCTO) thin film was successfully deposited on boron doped silica substrate by chemical solution deposition and rapid thermal processing. The phase and microstructure of the deposited films were studied as a function of sintering temperature, employing X-ray diffractometry and scanning electron microscopy. Dielectric properties of the films were measured at room temperature using impedance spectroscopy. Polycrystalline pure phase CCTO thin films with (220) preferential orientation was obtained at a sintering temperature of 750°C. There was a bimodal size distribution of grains. The dielectric constant and loss factor at 1 kHz obtained for a film sintered at 750°C was k ∼ 2000 and tan δ ∼ 0.05.     

Synthesis of the giant dielectric constant oxide CaCu3Ti4O12 via ethylenediaminetetraacetic acid precursor

CaCu₃Ti₄O₁₂ powders were prepared via EDTA route and single-phase CaCu₃Ti₄O₁₂ was obtained at 800 °C for 2 h. DTA/TG and XRD were used to characterize the precursor and derived oxide powders. The dielectric properties of CaCu₃Ti₄O₁₂ ceramics were presented. Increasing sintering temperature leads to the increase in dielectric constant. CaCu₃Ti₄O₁₂ ceramics sintered at 1090 °C for 3 h exhibited giant dielectric constant of up to 2.1 × 10⁵ at room temperature and 100 Hz, which is significantly higher than those obtained from other chemical methods.     

Nanoparticles of the giant dielectric material,calcium copper titanate from a sol–gel technique

The precursor of CaCu₃Ti₄O₁₂ (CCTO) nano particles have been successfully synthesized by sol–gel method at 90 °C. The dried precursor powder was milled and then calcined at 450 °C, 550 °C, 650 °C, 800 °C, 850 °C and 950 °C for 3 h. The phase formation of CCTO was analyzed by step by step using FTIR and XRD. Particle size and shape were evaluated by AFM. The XRD results of the powder calcined at 800 °C indicated the formation of CCTO phase. AFM studies showed that average particle size of the CCTO powder range 90–120 nm. The absorption bands corresponding to vibrations of CaO, CuO and TiOTi were observed at 606, 525 and 463 cm^? 1 using FTIR. The samples sintered at 1040 °C showed the densities as high as 96% of theoretical density. The grain sizes of sintered pellets were determined by FE-SEM. The dielectric properties of prepared samples were studied by LCR meter.     

Low-temperature synthesis of CaCu3Ti4O12 powders, ceramics and thin films via an organic solution

The giant-dielectric-constant material CaCu₃Ti₄O₁₂ (CCTO) was synthesized via an organic solution containing stoichiometric amounts of the metal cations, which is done at lower temperature and shorter reaction time than the conventional solid-state reaction. A stable solution was prepared by dissolving calcium nitrate, copper nitrate, and tetrabutyl titanate in grain alcohol. CCTO powders, ceramics and thin films were synthesized via the solution. The phases, microstructures, and dielectric properties of samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and dielectric spectroscopy. XRD results identify both samples as single phase CCTO. The CCTO ceramics has a low-frequency permittivity of 3.5 × 10⁴. The CCTO thin films has a low-frequency permittivity of 3.1 × 10⁴. Both the CCTO ceramics and CCTO thin films exhibit two dielectric relaxations at room temperature. The low leakage current density of CCTO thin films shows that it is suitable for memory device applications.     

Rietveld analysis of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> thin films obtained by RF-sputtering

Calcium copper titanate, CaCu₃Ti₄O₁₂, CCTO, thin films with polycrystalline nature have been deposited by RF sputtering on Pt/Ti/SiO₂/Si (100) substrates at a room temperature followed by annealing at 600 °C for 2 h in a conventional furnace. The crystalline structure and the surface morphology of the films were markedly affected by the growth conditions. Rietveld analysis reveal a CCTO film with 100 % pure perovskite belonging to a space group Im3 and pseudo-cubic structure. The XPS spectroscopy reveal that the in a reducing N₂ atmosphere a lower Cu/Ca and Ti/Ca ratio were detected, while the O₂ treatment led to an excess of Cu, due to Cu segregation of the surface forming copper oxide crystals. The film present frequency -independent dielectric properties in the temperature range evaluated, which is similar to those properties obtained in single-crystal or epitaxial thin films. The room temperature dielectric constant of the 600-nm-thick CCTO films annealed at 600 °C at 1 kHz was found to be 70. The leakage current of the MFS capacitor structure was governed by the Schottky barrier conduction mechanism and the leakage current density was lower than 10^?7 A/cm² at a 1.0 V. The current–voltage measurements on MFS capacitors established good switching characteristics.     

Very low loss tangent and giant dielectric properties of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics prepared by the sol–gel process

The pure phase of CaCu₃Ti₄O₁₂ (CCTO) powder can be successfully synthesized by the sol–gel process. CCTO ceramic samples were synthesized at different sintering temperatures of 1015 and 1050?°C and sintering times of 8 and 10 h. X-ray diffraction results indicated a pure phase for all ceramic samples. Rietveld refinements were adopted for the calculation of lattice constants. Scanning electron microscopy micrographs revealed the effect of sintering conditions on the microstructural evolution of ceramic samples. X-ray absorption near edge spectroscopy was performed to determine the oxidation state of Cu and Ti ions in ceramic samples. The dielectric and non-linear current voltage properties of CCTO ceramic samples were systematically investigated. Interestingly, very low loss tangent (tanδ?<?0.017 at 30?°C and 1 kHz) and giant dielectric constant (ε′?～?10,942) with temperature coefficients less than ±15% in a wide temperature range of ?60 to 125?°C were obtained in the CCTO ceramic sample sintered at 1015?°C for 10 h (CCTO1-10). This suggests a potential use for CCTO1-10 sample in capacitor applications. All CCTO ceramic samples display non-linear characteristic with non-linear coefficient (α) and breakdown field (E _b ) values in the range of 5.69–11.02 and 1415–4294, respectively.     

Dielectric properties of iron doped calcium copper titanate,CaCu<Subscript>3</Subscript>Ti<Subscript>3.9</Subscript>Fe<Subscript>0.1</Subscript>O<Subscript>12</Subscript> ceramic

Dielectric properties of iron doped CaCu₃Ti₄O₁₂ (CCTO), viz. CaCu₃Ti_3.9Fe_0.1O₁₂ (CCTFO) prepared by a novel semi-wet route have been investigated. X-ray diffraction of powder sintered at 900 °C show formation of single phase solid solution. Energy dispersive X-ray spectroscopy (EDX) confirmed the presence of CuO rich phase at grain boundaries of CCTFO. Nature of dielectric relaxation observed above room temperature is studied using complex plane impedance analysis and modulus spectroscopy. It has been found that out of the two relaxations reported earlier above room temperature, one occurring at lower temperature is due to grainboundaries interfacial polarization.     

Dielectric Ba(Ti1?xSnx)O3 (x?=?0.13) ceramics, sintered by spark plasma and conventional methods

A two-step sintering approach composed of spark-plasma-sintering (SPS) technique at 1000 °C for 1 min and under a uniaxial pressure of 63 MPa followed by conventional sintering at 1400 °C for 3 h is proposed for synthesis of dense Ba(Ti_0.87Sn_0.13)O₃ ceramics. Starting powders had grain size of about 90 nm and were obtained by co-precipitation. The SPS pellets consist of submicron (300–500 nm) grains. X-ray diffraction analysis of as-prepared Ba(Ti_0.87Sn_0.13)O₃ ceramic shows the occurrence of cubic and tetragonal phase coexistence for the pellets obtained after SPS processing and the presence of only tetragonal phase in the samples after the second (conventional) sintering. Grain uniformity in the final product is high, with average size of ~2 μm. The apparent densities of the sintered pellets at temperature of 1400 °C were ~92% of the theoretical value of Ba(Ti_0.87Sn_0.13)O₃. The ceramics exhibit a high relative dielectric constant of 6,550 and a dielectric loss (tan δ) = 0.078 at Curie temperature of 63 °C and 10 Hz.     

Microstructural and dielectric properties of donor doped (La3+) CaCu3Ti4O12 ceramics

The effect of La³⁺ doping on Ca²⁺ sites in CaCu₃Ti₄O₁₂ (CCTO) was examined. Polycrystalline samples in the chemical formula Ca_(1-x)La_(2/3)x Cu₃Ti₄O₁₂ with x = 0, 0.5, 1 were synthesized via the conventional solid state reaction route. X-ray powder diffraction analysis confirmed the formation of the monophasic compounds and indicated the structure to be remaining cubic with a small increase in lattice parameter with increase in La³⁺ doping. The dielectric and impedance characteristics of Ca_(1-x)La_(2/3)x Cu₃Ti₄O₁₂ were studied in the 100 Hz–10 MHz frequency range at various temperatures (100–475 K). A remarkable decrease in grain size from 50 μm to 3–5 μm was observed on La³⁺ substitution. The dielectric constant of CaCu₃Ti₄O₁₂ decreased drastically on La³⁺ doping. The frequency and temperature responses of dielectric constant of La³⁺ doped samples were found to be similar to that of CaCu₃Ti₄O₁₂. The effects of La³⁺ doping on the electrical properties of CaCu₃Ti₄O₁₂ were probed using impedance spectroscopy. The conducting properties of grain decreased while that of the grain boundary increased on La³⁺ doping, resulting in a decrease of the internal barrier layer effect. A decrease in grain boundary capacitance and stable grain response in La³⁺ doped CCTO ceramics were unambiguously established by modulus spectra studies.     

Dielectric and non-Ohmic properties of CaCu3Ti4O12 ceramics modified with NiO, SnO2, SiO2, and Al2O3 additives

In order to conciliate dielectric and non-Ohmic properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics, NiO, SnO₂, SiO₂, and Al₂O₃ were added as sintering aids to promote the grain growth of CCTO ceramics. Microstructure, dielectric properties, and non-Ohmic behavior of the CCTO ceramics were investigated. Among them, NiO-modified CCTO exhibits good dielectric and non-Ohmic properties (ε = 69833, tanδ = 0.073, α = 3.66 and E _B = 296.7 V/cm), due to NiO is also one of giant dielectric materials. Therefore, it is suitable for applying semiconductor circuits. The relationship between electrical current density (J) and electrical field (E) demonstrated that Schottky barrier should exist at grain boundaries. Non-linear coefficient α was directly proportional to the height of barrier. Depressing barrier width would improve significantly dielectric permittivity but decrease breakdown voltage.     

CaCu3Ti4O12 ceramics from different methods: microstructure and dielectric

CaCu₃Ti₄O₁₂ (CCTO) ceramics were synthesized by methods of sol–gel, traditional solid-state reaction, and thermal decomposition of organic solution. The results exhibit that the microstructures and electric characteristics are affected by the methods of synthesis. The X-ray diffraction patterns show that all samples have a perovskite-like CCTO phase. Moreover, CCTO ceramic from traditional solid-state reaction have the phases of TiO₂ and CuO. The scanning electron microscopy images show that CCTO ceramics from different methods have different grain sizes, grain boundaries, and densities. Dielectric properties of the CCTO ceramics were characterized in a broad frequency range (10–10⁷ Hz) at room temperature. The CCTO ceramics from thermal decomposition of organic solution have the dielectric constant of more than 5 × 10⁴ at 10 Hz. The nonlinear relationship between the current density and the electric field strength can be observed in all the three samples.