Internal Barrier Layer Capacitor Research Articles

Colossal permittivity of Sb and Ga co-doped rutile TiO2 ceramics

Material with colossal permittivity (CP) is important for the miniaturization of electronic devices and fabrication of high-density energy storage devices. However, the unbalanced developments of dielectric constant, dielectric loss and stability preclude its practical applications. In this work, we report that Sb + Ga co-doped TiO2 (SGTO) ceramics exhibit colossal permittivity and low dielectric loss. Especially, a high dielectric permittivity of 3.5 × 104 and a low dielectric loss of 0.06 at 1 kHz are obtained in the optimum composition with x = 0.02. The dielectric property shows high stability in wide temperature (25–130 °C) and frequency (20–106 Hz) range. XPS, complex impedance spectroscopy, I-V curve and frequency dependent dielectric constant under DC bias results indicate that electron-pinned defect-dipoles (EPDD) model, internal barrier layer capacitance (IBLC) effect and electrode effect all contribute to the observed colossal permittivity behavior in (Sb0.5Ga0.5)xTi1-xO2 ceramics.

Dielectric and impedance studies of La and Zn co-doped complex perovskite CaCu3Ti4O12 ceramic

Pure and modified CaCu3Ti4O12 with nominal compositions Ca0.95La0.05Cu3-xZnxTi4O12 (x = 0.01, 0.025, 0.05, 0.10) were synthesized using conventional solid state reaction route. The preliminary pure phase formation of all prepared CaCu3Ti4O12 compositions was confirmed by X-ray diffraction data and further analyzed by Rietveld refinement method. The grain size was found to be remarkably decreased from 15 µm to 3–4 µm on Zn2+ substitution in CCTO lattice. Dielectric spectra shows the presence of two relaxation processes corresponds to grain boundaries and grains in low and high frequency regions. The grain relaxation is more predominating over GBs relaxation process and found to be merged together for Zn rich compositions. The frequency response of ε' for doped compositions were found to be different from pure CaCu3Ti4O12. The dielectric permittivity (ε') values are significantly decreased for doped compositions, but Zn rich (5–10%) compositions still exhibit high ε' (~ 8102) and low dielectric loss (tan δ ≤ 0.10) over a wide range of frequency (102–106 Hz). Impedance measurement revealed that grain resistance enhanced with enhancement in Zn content to CaCu3Ti4O12 lattice and approached to grain boundary resistances. The overlapping of grain and grain boundary relaxation processes for Zn rich compositions attributed to the similar relaxation times of both contributions and indentified by Modulus analysis. Both formalism suggested that the electrical microstructure destroyed the Internal barrier layer capacitor (IBLC) formation that produces high dielectric permittivity in CaCu3Ti4O12 ceramic.

Existence of internal domains in (Bi0.5La0.5FeO3)(1-x)–(Ba0.7Sr0.3TiO3)x solid solution and their effects on magnetic and dielectric behaviour

A significant experimental effort has been undertaken to evaluate the doping effect of La3+at Bi-site in solid solutions of BiFeO3 (BFO) and Ba0.7Sr0.3TiO3 (BST) through various techniques like x-ray diffraction, magnetic measurements, and frequency and/or temperature dependent impedance spectroscopy. The magnetic isotherm at room temperature in La doped BFO (BLFO)-BST solid solution indicates weak ferromagnetism due to improvement in the homogeneous canted spin structure. The elusive nano-sized domain structure inside the grains of 40% BST co-doped BLFO was observed by a scanning electron microscopy technique. The domains and domain boundaries are generally formed inside the grain due to strained/unstrained lattice defects and/or mismatch with the substitution of ions of different sizes at the A and B sites. An equivalent circuit model (internal barrier layer capacitor), based on domain, domain boundary, and grain boundary relaxations, has been established to justify the enhancement of the dielectric response with BST concentrations.

An approach for correlating electrically heterogeneous structure to enhanced dielectric properties of Sr and Zn co-substituted CaCu3Ti4O12 ceramics

In the present work, the most pristine as well as strontium (Sr) and zinc (Zn) modified Calcium copper titanate ceramics having formula Ca0.95Sr0.05Cu3Ti4-xZnxO12 (x = 0.01, 0.025, 0.05 & 0.10) were synthesized by the solid state reaction method. X-ray diffraction pattern and Raman analysis confirmed the single phase formation of the samples. Detailed structural information was carried out by Rietveld refinement, analysis of X-ray data. Microstructure investigation revealed that the grain development of the doped ceramics was controlled by dopant (Zn) ions due to solute drag effect. Impedance spectroscopy was used to investigate the contribution of grains, grain boundaries and electrode interface effect to the dielectric response. Dielectric parameters observed to be improved for higher Zn/Sr ratio in studied compositions. The Ca0.95Sr0.05Cu3Ti3.90Zn0.10O12 ceramic composition shows a colossal dielectric permittivity of ∼37,788 and loss ∼0.049, which are stable within a broad frequency region. Reduced tanδ over a broad range of frequency was well ascribed to the highly insulating grain boundaries. The giant dielectric properties of the system were found to be in accordance with Internal Barrier Layer Capacitance (IBLC) model and correlated to their electrically heterogeneous structure.

Effect of Zr doping on dielectric properties and grain boundary response of CdCu3Ti4O12 ceramics

An effective strategy to improve the dielectric properties of CdCu3Ti4O12 ceramics was proposed via doping with Zr4+ substituting in Ti4+ sites using the sol-gel method. SEM images of samples with high densification show a fine-grained and uniform-sized microstructure, and the average grain sizes of the ceramics decrease with increasing content of Zr doping. A proper amount of Zr substitution in the CdCu3ZrxTi4-xO12 ceramics was of great benefit to depress the dielectric loss tangent. A CdCTO-Zr05 ceramic exhibited a relatively low dielectric loss tangent value of 0.048 at 1 kHz. Meanwhile, the improved grain boundary response and dielectric properties were closely linked to the enhanced grain-boundary resistance. Data obtained based on complex impedance spectroscopy assessments demonstrated that the giant dielectric permittivity of the samples should be ascribed to the internal barrier layer capacitor (IBLC) effect. Overlapped spectroscopy of scaling behaviours indicated that the electric conduction and dielectric relaxation mechanisms shown in CdCu3ZrxTi4-xO12 ceramics are the same in this work.

Novel multifunctional capacitor-varistor ceramics based on SnO2

Up to now, multifunctional varistor-capacitor materials were based on TiO2, even though these materials failed to have practical applications. For the first time, in this research, multifunctional varistor-capacitor properties are observed in the CuO-doped SnO2-CoO-Sb2O3 system. The XRD analysis showed that this system has a single phase microstructure. SEM images indicated that the CuO addition resulted in a better densification and larger grain size. The very low electric breakdown field of the CuO-doped SnO2-CoO-Sb2O3 system (12 V/mm, similar to TiO2), is a consequence of coarse-grained microstructure. This varistor had a suitable surge withstand capability as well. The colossal dielectric constant of about 4.5 * 104 was observed in CuO doped-SnO2 system. This immense constant dielectric can be explained by the internal barrier layer capacitor model. These results attest that the novel multifunctional varistor-capacitor materials based on SnO2 can be used in practical applications.

Wide range dielectric and infrared spectroscopy of (Nb+In) co-doped rutile ceramics

The dielectric response of ceramics of co-doped rutile $\mathrm{T}{\mathrm{i}}_{1\text{\ensuremath{-}}x}{(\mathrm{N}{\mathrm{b}}_{0.5}\mathrm{I}{\mathrm{n}}_{0.5})}_{x}{\mathrm{O}}_{2}$ has been measured via a combination of impedance, high-frequency coaxial, terahertz transmission, and infrared reflectivity spectroscopies spanning 15 decades of frequency between 0.1 Hz and 240 THz. It is argued that the colossal dielectric permittivity reported by Hu et al. [Hu et al., Nat. Mater. 12, 821 (2013)] has the same explanation as in the original colossal permittivity material $\mathrm{CaC}{\mathrm{u}}_{3}\mathrm{Ti}{\mathrm{O}}_{4}{\mathrm{O}}_{12}$ (CCTO), namely, a combination of the internal barrier layer capacitor (IBLC) and the surface barrier layer capacitor (SBLC) effects. The IBLC effect is caused by a microstructure consisting of insulating grain boundaries (thickness \ensuremath{\sim}1 nm and conductivity of $\ensuremath{\sim}{10}^{\ensuremath{-}6}\phantom{\rule{0.16em}{0ex}}\mathrm{S}/\mathrm{cm})$ surrounding interior regions of bulk conductivity approximately equal to ${10}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}\mathrm{S}/\mathrm{cm}$. The SBLC effect is the result of a depletion layer adjacent to the contacts approximately 100 nm thick with conductivity of $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}\phantom{\rule{0.16em}{0ex}}\mathrm{S}/\mathrm{cm}$. The SBLC and IBLC effects give rise to dielectric relaxations in low-frequency and radiofrequency regions, respectively. The temperature dependence of both relaxation rates measured down to 20 K is thermally activated. No separate absorption process has been observed that could be linked to giant defect dipoles. Infrared spectroscopy has revealed four weak defect-related modes at frequencies close to the Raman mode frequencies of rutile, activated in the infrared through a symmetry-breaking process. Co-doping produces a significant loss in the partial spectral weight between 75 and $350\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$ associated with the lowest transverse optical mode, which softens on cooling. The loss in its spectral weight corresponds to the gain in near-infrared spectral weight, previously assigned to small polaron absorption.

Origin of the colossal permittivity of (Nb + In) co-doped rutile ceramics by wide-range dielectric spectroscopy

ABSTRACT Searching for giant dipolar defects, suggested as the explanation of the colossal permittivity (CP) in (Nb + In) co-doped rutile, we have recently published (J. Appl. Phys. 119, 154105 (2016) and Phys. Rev. Mat., in press) temperature-dependent dielectric spectra from sub-Hz to THz range (including 4-point DC conductivity) of several (Nb + In) co-doped rutile ceramics. Using the model of two leaky capacitor in series below ∼1 MHz, we estimated the depletion layer thickness and conductivity. The spectra below ∼10 GHz were fitted with two Cole–Cole relaxations obeying the Arrhenius law, assigned to the effect of depletion layers and grain boundaries. In this paper, using effective medium models, we have for the first time modelled the spectra as a composite of semiconducting grains and substantially less-conducting grain boundaries and near-electrode depletion layers. The CP effect has been fully explained by the combination of surface and internal barrier-layer capacitor effects, without any measurable contribution from the dipolar defects.

Influence of MgTiO3-Doping on Microstructure and Dielectric Properties of CaCu3Ti4O12 Ceramics

The application of CaCu3Ti4O12 (CCTO) is limited due to its high low-frequency dielectric loss. An internal barrier layer capacitance effect seems to be the most widely accepted explanation for the giant-e′ phenomenon of CCTO ceramics. According to the effect, wrapping the semiconducting grains of CCTO ceramics in insulating materials is an effective way to reduce the low-frequency dielectric loss. CCTO/MgTiO3 composite ceramics were prepared, and their crystalline structures, microstructures, dielectrical properties and complex impedance were systematically investigated. The results show that MgTiO3 has been wrapped around the CCTO grains in our CCTO-based ceramics. Compared with pure CCTO ceramics, the low-frequency dielectric loss was not reduced by MgTiO3-doping, because the resistance of MgTiO3 phase boundaries in the CCTO/MgTiO3 composite ceramics as prepared is lower than the grain boundaries resistance of pure CCTO ceramics. After annealing in oxygen, the low-frequency permittivity and dielectric loss of CCTO/MgTiO3 composite ceramics significantly decreased, which should be attributed to the increase of the resistance of insulating MgTiO3 phase boundaries and CCTO grains.

Brilliant effect of Ni substitution in the appearance of high dielectric constant in CaCu2.9Ni0.1Ti3.9Ni0.1O12 ceramics

CaCu2.9Ni0.1Ti3.9Ni0.1O12 (CCNTNO) polycrystalline powder of giant dielectric constant material was successfully obtained by solid-state reaction. The sample, characterized by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM) and Raman spectroscopy, confirmed to be a pure phase CCTO associated with large grains surrounded by small ones of nearly cubic shape. The effect of Ni doping on optical properties of CaCu2.9Ni0.1Ti3.9Ni0.1O12 has been determined. Furthermore, the dielectric constants of these co-doped ceramics (CCNTNO) were higher than that of CCTO pure prepared under the same conditions of synthesis. The grain size and the dielectric constant depended absolutely on doped and sintering time. Results confirm that co-doping CCTO by Ni in both copper and titanium sintered enhanced the grain growth as the sintered time is higher than 6 h. Especially ceramic sintered at 1100 °C for 12 h shows excellent abnormal growth grain with approximately 50–100 μm sized crystallites which displayed extraordinarily high dielectric constants up to 105 at 25 °C (most exceptional behavior). Based on these results, internal barrier layer capacitance (IBLC) model was invoked to correlate the observed dielectric constant with the grain size in these samples. Loss factor and resistivity of these ceramics were equally interpreted. It must be noted also that the resistivity decreased largely if the sintering time is around 12 h as evidenced in the impedance plots.

Direct and hybrid microwave solid state synthesis of CaCu3Ti4O12 ceramic: Microstructures and dielectric properties

CaCu3Ti4O12 (CCTO) electroceramic possesses unusual giant dielectric permittivity up to ε = 104 at low frequency range and room temperature. CCTO dielectric properties strongly depend on its microstructure therefore it is essential to pay attention to the processing techniques which impact grain size and microstructure. In this work, direct and hybrid microwave solid state synthesis was specifically designed and used for the synthesis of CCTO. The microwave process was also compared to the conventional process which involves usual infrared heating. The structural (XRD) and microstructural (SEM) characterizations indicate that microwave synthesis is particularly efficient to get rapidly pure CCTO powder. The fully automated 915 MHz single-mode microwave cavity used for hybrid synthesis allows a perfect control of the temperature distribution and heating rate. Therefore hybrid microwave synthesis leads to a fine, mono-disperse and practically pure CCTO powder in the range of 300 – 500 nm. The advantages of the hybrid microwave heating method are discussed and compared to the conventional and direct microwave heating processes. From the powders synthesized by the different routes, dense compacts were sintered in air at 1050 °C in a conventional furnace. Microstructural characterizations reveal abnormal grain growth during sintering which levels dielectric properties. All exhibit a giant dielectric constant ε > 103 at room temperature which decreases drastically to ε = 90 at 10 K. Those properties are discussed according to the well-established Internal Barrier Layer Capacitor (IBLC) model.

Dielectric properties and nonlinear I–V electrical behavior of (Li1+, Al3+) co-doped CaCu3Ti4O12 ceramics

(Li1+, Al3+) co-doped CaCu3Ti4O12 ceramics (CaCu3−2xLixAlxTi4O12, x = 0.05, 0.1, 0.15) were prepared by a sol–gel method and were sintered at 1020–1080 °C for 8 h to improve the geometric microstructure, dielectric and nonlinear I–V electrical properties. Notably, very high dielectric constant of 1 × 105 with good dielectric-frequency as well as dielectric-temperature stability can be achieved in CaCu2.8Li0.1Al0.1Ti4O12 ceramic sintered at 1060 °C. The average grain sizes, resistivity and the non-Ohmic properties are also improved compared to pure CaCu3Ti4O12. These results indicate that (Li1+, Al3+) co-doping at the Cu2+ site can improve the dielectric properties of CaCu3Ti4O12, supporting the internal barrier layer capacitance effect of Schottky barriers at grain boundaries.

Structural investigation and giant dielectric response of CaCu3Ti4O12 ceramic by Nd/Zr co-doping for energy storage applications

High performance dielectric materials are highly required for practical application for energy storage technologies. In this work, high-k pristine and modified calcium copper titanate having nominal formula Ca0.95Nd0.05Cu3Ti4−xZrxO12 (x = 0.01, 0.03 & 0.10) were synthesized and characterized for structural and dielectric properties. Single phase formation of the synthesized compositions was confirmed by X-ray diffraction patterns and further analysed using Rietveld refinement technique. Phase purity of the synthesized ceramics was further confirmed by Energy-dispersive X-ray Spectroscopy (EDX) analysis. SEM images demonstrated that grain size of the modified CCTO ceramics was controlled by Zr4+ ions due to solute drag effect. Impedance spectroscopy was employed to understand the grain, grain boundaries and electrode contribution to the dielectric response. Nyquist plots were fitted with a 2R-CPE model which confirms the non-ideality of the system. Substitution of specific concentration of Nd and Zr improved the dielectric properties of high dielectric permittivity (e′ ~ 16,902) and minimal tanδ (≤ 0.10) over a wide frequency range. The giant e′ of the investigated system was attributed to internal barrier layer capacitance (IBLC) effect and reduced tanδ accredited to enhanced grain boundaries resistance due to substitution of Zr4+ ions at Ti4+ site.

Correction to Multiple Interfacial Fe3O4@BaTiO3/P(VDF-HFP) Core-Shell-Matrix Films with Internal Barrier Layer Capacitor (IBLC) Effects and High Energy Storage Density.

Correction to Multiple Interfacial Fe3O4@BaTiO3/P(VDF-HFP) Core-Shell-Matrix Films with Internal Barrier Layer Capacitor (IBLC) Effects and High Energy Storage Density.

Colossal dielectric properties in (Ta0.5Al0.5)xTi1−xO2 ceramics

In this study, (Ta0.5Al0.5)xTi1−xO2 (x = 0–0.125) and Ta-doped ceramics were fabricated by conventional solid-state method. The phases and microstructures indicate that all ceramics show pure tetragonal rutile TiO2 with different grain size. Notably, by co-doping TiO2 with 0.08 (Ta+Al) ions, a colossal permittivity (εr, ∼6.24 × 104) and low dielectric loss (tan δ, ∼0.05) at room temperature were achieved. While the ceramic doped with same amount of Ta displays the giant εr but higher tan δ value, and the pure TiO2 exhibits a low permittivity value. The co-doped ceramics exhibit more excellent dielectric properties than that of pure TiO2 and Ta-doped TiO2 ceramics when they are subjected to temperature (20–200 °C) and frequency (102–106 Hz) variations. Moreover, the detailed dielectric and impedance spectra analyses for all samples indicate that the colossal permittivity could be explained by the internal barrier layer capacitance (IBLC) model. According to the model, the microstructures of ceramics are consisting of semiconducting grains and insulating grain boundaries, leading to formation of numerous micro-capacitors.

Frequency and temperature dependent dielectric properties of TiO2-V2O5 nanocomposites

In this manuscript, we have reported the crystal structure, dielectric response, and transport phenomenon of TiO2-V2O5 nanocomposites. The nanocomposites were synthesized using a sol-gel technique having different molar ratios of Ti:V (10:10, 10:15, and 10:20). The phase composition and the morphology have been studied using X-ray diffraction and field emission scanning electron microscope, respectively. The impedance spectroscopy studies of the three samples over a wide range of temperature (50 K–300 K) have been extensively described using the internal barrier layer capacitor model. It is based on the contribution of domain and domain boundary, relaxations of the materials, which are the main crucial factors for the enhancement of the dielectric response. The frequency dependent ac conductivity of the ceramics strongly obeys the well-known Jonscher's power law, and it has been clearly explained using the theory of jump relaxation model. The temperature dependent bulk conductivity is fairly recognized to the variable-range hopping of localized polarons. The co-existence of mixed valence state of Ti ions (Ti3+ and Ti4+) in the sample significantly contributes to the change of dielectric property. The overall study of dielectric response explains that the dielectric constant and the dielectric loss are strongly dependent on temperature and frequency and decrease with an increase of frequency as well as temperature.

Copper cadmium titanate prepared by different methods: Phase formation, dielectric properties and relaxor behaviors

Giant permittivity was performed in CdCu3Ti4O12 ceramics separately fabricated via the sol-gel technique (SG) and the standard solid-state technique (SS). XRD patterns and Raman spectrums revealed that CdCu3Ti4O12 ceramics with single perovskite-related crystal phase were obtained irrespective of the preparation processing. TG-DSC, XRD, and FT-IR were carried out to explore the formation temperature of crystal phases as well as reaction mechanisms. The results indicated that the phase formation temperature of CdCTO-SG powders is at least 100 °C lower than that of CdCTO-SS powders and the dielectric properties of the CdCTO-SG ceramics are superior to those of the CdCTO-SS ceramics. In addition, three abnormal dielectric peaks were observed in dielectric temperature spectrum regardless of the two methods. Besides, data acquired from impedance and modulus assessments indicated that Maxwell-Wagner polarization contributed to the dielectric responses of samples. Therefore, giant dielectric properties of CdCu3Ti4O12 ceramics conformed to internal barrier layer capacitor (IBLC) effect. Semiconducting grains are closely associated with the presence of mixed valence states of Cu+/Cu2+ and Ti3+/Ti4+ in samples.

Effects of Secondary Phases on the High-Performance Colossal Permittivity in Titanium Dioxide Ceramics.

The intensive demands of microelectronics and energy-storage applications are driving the increasing investigations on the colossal permittivity (CP) materials. In this study, we designed a new system of Dy and Nb co-doped TiO2 ceramics [(Dy0.5Nb0.5)xTi1-xO2] with the formation of secondary phases, and then the enhancement of overall dielectric properties (εr ∼ 5.0-6.5 × 104 and tan δ < 8%) was realized in the broad composition range of 0.5 ≤ x ≤ 5%. More importantly, effects of secondary phases on microstructure, dielectric properties, and stability were explored from the views of defect-dipoles and internal barrier layer capacitance (IBLC) effect. According to the defect-dipoles theory, the CP should mainly originate from Nb5+, and the Dy3+ largely contributes to the decreased dielectric loss. Both CP and low dielectric loss were obtained for co-doping with Dy3+ and Nb5+. Besides, the Dy enrichment induced the formation of secondary phases, which were regarded as the low loss unit dispersed into the ceramic matrix, and largely facilitate the decreased dielectric loss. In particular, the analysis of temperature-dependent complex impedance spectra indicated that a stronger IBLC effect caused by the increased grain boundary resistance can also contribute to the optimized CP and low dielectric loss under appropriate contents of secondary phases.

Excellent dielectric performance and nonlinear electrical behaviors of Zr-doped CaCu3Ti4O12 thin films

The dielectric and nonlinear current–voltage properties of CaCu3Ti4−xZr x O12 (x = 0, 0.05, 0.1, 0.15 and 0.2) thin films prepared by the modified sol–gel method and annealed at 750 °C for 1 h were systematically studied. Zr doping resulted in a significant reduction in the mean grain size from 177.4 to 42.9 nm. The dielectric properties of the thin films increased significantly with the increase of Zr content from x = 0 to 0.2, indicating the importance of microstructure in controlling the dielectric properties of CaCu3Ti4−xZr x O12 thin films. A highly frequency-independent giant dielectric permittivity from 102 to 106 Hz was successfully achieved in CaCu3Ti3.8Zr0.2O12 thin film, which possessed a very high dielectric permittivity value of 7591 and a very low tanδ value of 0.023 at 1 kHz. The results indicated that reduction in the mean grain size affected the number of polarized ions per unit volume n0 (to improve e′) and the number of grain boundaries (to reduce tanδ). CaCu3Ti3.75Zr0.15O12 thin film showed the highest nonlinear coefficient (5.8) and lowest leakage current (131 μA). In addition, the relaxation mechanism based on the internal barrier layer capacitance model and the back-to-back dual Schottky barrier model were used to explain the dielectric properties and the nonlinear electrical behaviors of the samples.

Microstructure and dielectrical properties of CaCu3Ti4O12/TiO2 composite ceramics with core-shell structure

The large low-frequency dielectric loss of CaCu3Ti4O12 (CCTO) ceramics limit their applications. According to the internal barrier layer capacitance effect, which is the most widely accepted explanation for the giant-ε′ phenomenon of CCTO ceramics, increasing the resistance of grain boundary is an effective way to reduce their low-frequency dielectric loss. In this work, CCTO/TiO2 composite ceramics with core-shell structure were prepared by sol-gel-like method, and their crystalline structures, microstructures, dielectrical properties and complex impedance were investigated systematically. The results show that the room temperature low-frequency dielectric loss of our CCTO-based ceramics decreased significantly by TiO2-doping and annealing in oxygen, which should be attributed to the increasing resistance of the insulating grain boundary.