Dielectric Properties Of CaCu3Ti4O12 Research Articles

Enhanced dielectric properties of CCTO ceramics doped by different halogen elements

In this work, effects of different halogen elements (F, Br, and I) on the microstructure, morphology, and dielectric properties of CaCu3Ti4O12 (CCTO) ceramics prepared through sol–gel method were systematically studied. It was found that the dielectric loss of the CCTO ceramics doped with F reduced to 0.022 and the breakdown field strength increased to 9.4 kV/cm, simultaneously. Moreover, the Br-doped samples exhibited the lowest dielectric loss of 0.019 and the highest dielectric constant of about 82,047, while the breakdown field strength declined obviously compared to pure CCTO samples. However, in contrast to F or Br element, the I element did not significantly improve the dielectric properties of CCTO ceramics. In addition, the decreased dielectric loss for the doped CCTO ceramics could be owed to the increasing resistance of the grain boundaries, and the improved breakdown field strength could be attributed to the enhanced potential barrier height. All the results suggest that introducing anions, like halogen elements, is an efficient approach to improve the dielectric properties of CCTO ceramics.

Dielectric properties of Al2O3 modified CaCu3Ti4O12 ceramics

In this work, CaCu3Ti4O12 modified by Al2O3 (w = 0, 0.05, 0.1, 1%) powders were prepared via a sol–gel process, and then the ceramics were prepared by conventional process using the obtained powders. The dependence of structure and properties of CaCu3Ti4O12 ceramics on the addition fractions of Al2O3 were studied. The results showed that the grain size and density of the samples greatly increase after modifying Al2O3. Moreover, all the samples exhibit giant dielectric properties (~ 104) and relatively low dielectric loss over a wide temperature and frequency range (20–200 °C, 102–106 Hz). The giant dielectric properties of these samples could be explained by the internal barrier layer capacitance (IBLC) model, which consists of semiconducting grains and insulating grain boundaries. Specifically, the optimal Al2O3 modified CaCu3Ti4O12 (w = 0.05%) ceramic shows colossal permittivity (~ 4.29 × 104) and low dielectric loss (~ 0.06) at room temperature and 1 kHz. The results indicated that the microstructures and dielectric properties of CaCu3Ti4O12 were significantly improved after modifying Al2O3.

The dielectric properties of CCTO ceramics prepared via different quick quenching methods

In this work, the microstructure and dielectric properties of CaCu3Ti4O12 (CCTO) ceramics based on sol-gel method prepared via different cooling methods (furnace cooling, air quenching, and water quenching) were systematically studied. The results showed that the dielectric constant of quick quenching samples (air quenching and water quenching) did not drop a lot contrasting to that of the furnace cooling CCTO ceramics. Furthermore, it was also found that the dielectric loss of air quenching CCTO ceramics decreased to 0.030, which was about 40% of the furnace cooling CCTO ceramics (0.074), and the dielectric loss of water quenching samples was as low as 0.044. In addition, the breakdown electric field could also be improved by air quenching. These enhancements could be attributed to the improved properties of the grain boundaries. The results above indicate that a proper quenching method can promote the dielectric properties of CCTO ceramics efficiently.

Fine representation of dielectric properties by impedance spectroscopy

Dielectric spectroscopy is used as a quick, precise and nondestructive examination tool of macroscopical dielectric properties for dielectrics. However, if the information of the microstructure and the location of a certain dielectric relaxation can be learned also by dielectric spectroscopy, it will help to reveal point defect structure and macroscopic and microscopic mechanisms of conduction and dielectric relaxation. Fine representation of dielectric properties by impedance spectroscopy (IS) is analyzed carefully in this paper. It is found that IS is not a good tool to describe a uniform system because a pseudo relaxation peaks exists at low frequency limit corresponding to direct current (DC) conductivity, and two relaxation peaks appears simultaneously corresponding to only one relaxation process for a high loss system with tanδ>1. However it is very convenient to describe a multiple phase system with IS for that only one Cole-Cole arc with some distortion appears for every phase with several relaxations, therefore it is very easy to distinguish different phases from each other. Especially, the location of a true relaxation process can be deduced by IS without any uncertainly according to pseudo relaxation theory which is built in this paper. Furthermore, when dielectric properties are shown with specific impedance spectroscopy (SIS), the information of the microstructure can be obtained conveniently. Based on these theoretical results above, dielectric properties of CaCu3Ti4O12 (CCTO) ceramics with giant dielectric constant (GDC) are investigated. It is found that GDC comes from pseudo relaxation of grain.

Study of the dielectric responses of Eu-doped CaCu3Ti4O12

We reported the effect of europium (Eu) on the dielectric properties of CaCu3Ti4O12 (CCTO). The experimental results show that the doping of Eu on a calcium (Ca) site improves the dielectric loss and decreases the dielectric constant of CCTO. To understand the underlying reasons for the depressed dielectric response of Eu-doped CCTO, scanning electron microscopy, high-temperature dielectric measurement, and complex impedance measurement were carried out. The DC bias was also used in the measurements. The results show that the depressed dielectric responses of Eu-doped CCTO may be related to the lack of the oxygen vacancies in the samples. Furthermore, the absence of the electrode contact response may be another factor responsible for the decreased dielectric constant.

Local analysis of the grain and grain boundary contributions to the bulk dielectric properties of Ca(Cu3−yMgy)Ti4O12 ceramics: Importance of the potential barrier at the grain boundary

The present work focuses on two aspects related to the synthesis and the dielectric properties of CaCu3Ti4O12 (CCTO) ceramics. Effective strategies able to synthesize high quality CCTO, with reduced dielectric losses and high relative permittivity, are achieved by the substitution of Cu ion by Mg one in the crystal. Ca(Cu3−yMgy)Ti4O12 ceramics have been synthesized by conventional mixed oxide method involving CCTO and MgO. This approach is found to drastically reduce the synthesis time by lowering the eutectic point of CCTO as a result of the small fraction (1–3wt%) of MgO added to the mixture. Experimental data have been used to successfully confirm this substitution and the only presence of CuO at grain-boundaries. The role of grain and grain boundary contributions on the dielectric properties of ceramics are investigated. It is found that samples containing 1% MgO lead to excellent relative permittivity values of the order of 3.5×104. In these substituted ceramics, extracted relative permittivity values are found to be extremely stable, with low loss tangent (<0.06), up to 100kHz at room temperature. From the various samples investigated, the optimized ceramics are found to contain large grains (≥15μm). Local intra-grain and inter-grain electrical transport measurements show that the grains and their respective grain boundaries exhibit metallic and semiconducting behaviors, respectively. This approach confirms the crucial role of the potential barrier at the grain boundary in determining the dielectric properties of such Ca(Cu3−yMgy)Ti4O12 ceramics.

Improved dielectric properties of CaCu3Ti4O12 films with a CaTiO3 interlayer on Pt/TiO2/SiO2/Si substrates prepared by pulsed laser deposition

We report the greatly improved dielectric properties of CaCu3Ti4O12 (CCTO) films with a 60 nm-thick CaTiO3 (CTO) interlayer on Pt/TiO2/SiO2/Si substrates. Both CCTO films and CTO interlayers were prepared by pulsed laser deposition (PLD). With increasing the thickness of CCTO from 200 nm to 1.3 μm, the dielectric constants (e r ) at 10 kHz in both CCTO single-layered and CCTO/CTO double-layered films increased from ∼260 to ∼6000 and from ∼630 to ∼3700, respectively. Compared with CCTO single-layered films, CCTO/CTO double-layered films irrespective of CCTO film thickness exhibited a remarkable decrease in their dielectric losses (tanδ) (<0.1 at the frequency region of 1 - 100 kHz) and highly reduced leakage current density at room temperature. The reduced leakage currents in CCTO/CTO double-layered films are attributable to relatively higher trap ionization energies in the Poole-Frenkel conduction model.

Influence of lithium disilicate addition on the dielectric properties of chemically synthesized CaCu3Ti4O12

The effects of the method of synthesis along with the introduction of a sintering aid on the electric and dielectric properties of CaCu3Ti4O12 were investigated in detail. The mixed oxide with perovskite structure was synthesized by the coprecipitation method. Polycrystalline specimens were prepared by adding 0.5 mol% Li2Si2O5 to the mixed oxide followed by sintering in the 1000–1100 °C range for 12 h. A high density value was obtained for sintering at a temperature as low as 1000 °C. Average grain sizes of sintered specimens are of the same order of magnitude as those of specimens prepared by the same method without the additive. The activation energy values for electric conduction were found to be 0.1 eV (grain) and varying from 0.4 to 0.6 eV (grain boundary). The dielectric properties are similar to those of specimens without the additive. The overall results evidence the possibility of reduction of the sintering temperature by about 100 °C with the introduction of a small amount of lithium disilicate while keeping the dielectric properties of pure CaCu3Ti4O12.

Modulus spectroscopy of grain–grain boundary binary system

Understanding various polarization mechanisms in complex dielectric systems and specifying their physical origins are key issues in dielectric physics. In this paper, four different methods for representing dielectric properties were analyzed and compared. Depending on the details of the system under study, i.e., uniform or non-uniform, it was suggested that different representing approaches should be used to obtain more valuable information. Especially, for the grain–grain boundary binary non-uniform system, its dielectric response was analyzed in detail in terms of modulus spectroscopy (MS). Furthermore, it was found that through MS, the dielectric responses between uniform and non-uniform systems, grain and grain boundary, Maxwell–Wagner polarization and intrinsic polarization can be distinguished. Finally, with the proposed model, the dielectric properties of CaCu3Ti4O12 (CCTO) ceramics were studied. The colossal dielectric constant of CCTO at low frequency was attributed to the pseudo relaxation process of grain.

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 thermobaric treatment on the structure and properties of CaCu3Ti4O12

CaCu3Ti4O12 is prepared by means of solid-state sintering. The effect of thermobaric treatment (P = 8.0 GPa and T = 1100°C) and partial replacement of titanium by vanadium on the microstructure and dielectric properties of CaCu3Ti4O12 are investigated.

Effect of Platinum Substitution on the Microstructures and Dielectric Relaxation of CaCu&lt;sub&gt;3&lt;/sub&gt;Ti&lt;sub&gt;4&lt;/sub&gt;O&lt;sub&gt;12&lt;/sub&gt; Ceramics

The CaCu3Ti4O12(CCTO) has the advantage for the various applications especially for capacitive elements in microelectronic devices over the ferroelectric materials including BaTiO3. CCTO is a ceramic compound with a high dielectric constant but it has a high loss tangent at room temperature. In this work, the Influences of PtO2doping on the dielectric properties of CaCu3Ti4O12(CCTO) ceramics were investigate. The ceramics CCTO and PtO2doping CCTO were studied by X- ray diffraction, scanning electron microscopy. The dielectric properties have been measured as a function of temperature and frequency range 0.1 - 500 kHz. The XRD shows the CCTO structure does not changes after doping with platinum. The results show that PtO2doped can reduce the mean grain sizes of CCTO, but the dielectric constant still remained a height. The samples of 2.0 mol% Pt-doped have exhibited high dielectric constant of about 22,000 and the loss tangent about 0.7 at room temperature and frequency at 10 kHz. The reduced of the loss tangent could be interpreted with the internal barrier layer capacitor model (IBLC)

Polaron relaxation and non-ohmic behavior in CaCu3Ti4O12 ceramics with different cooling methods

Structure, defects, non-ohmic behavior and dielectric properties of CaCu3Ti4O12 (CCTO) ceramics with furnace-cooled and water-quenched methods have been systemically investigated. Cooling methods make an influence on reoxidation process and cause changes of electric properties in grains and at grain boundaries. SEM–EDS provides detailed imaging information about Cu-rich phase on the fracture of CCTO ceramics which is explained by the reoxidation reaction during cooling. Morphologies of the water-quenched sample show very small grains floating in bigger grains; whereas they reveal that many grains are surrounded by an exfoliated sheet of Cu-rich phases in the furnace-cooled sample. The polaron relaxation associated with Ti3+ ions and oxygen vacancies occurs at low temperatures, and more Ti3+ ions are remained in the water-quenched sample. The Schottky barrier height (I–V, non-ohmic behavior) associated with the reoxidation of grain boundaries can be modified by cooling method.

Dielectric anomalies in CaCu3Ti4O12 at high temperatures

We reported the dielectric properties of CaCu3Ti4O12 in the temperature range from room temperature to 800°C and the frequency range from 20 Hz to 10 MHz. Apart from the widely reported dielectric anomaly occurring around 200°C, three additional dielectric anomalies were found. The new anomalies are very sensitive to electrode sintering conditions and annealing atmospheres, indicating that they are dependent not only on the electrode-sample contact but also on oxygen vacancies.

Effects of Zr doping on the microstructures and dielectric properties of CaCu3Ti4O12 ceramics

Zr-doped CaCu3Ti3.95Zr0.05O12 (CCTZO) ceramics were prepared by sol–gel method, and pure-phased structures were observed by the X-ray diffraction. The microstructures and dielectric properties of CaCu3Ti4O12 (CCTO) and CCTZO ceramics were investigated. The CCTZO ceramics possessed a fine-grained microstructure with grain sizes of about 3–5μm, and the grain size uniformity of CCTZO ceramics were enhanced via doping Zr in CCTO ceramics. Meanwhile, CCTZO ceramics exhibited a broadband stability of the dielectric constant and a lower dielectric loss at high frequency ranges. The dielectric relaxation mechanisms of CCTO and CCTZO ceramics were analyzed using the mixed-valent structures. The impedance analysis suggested CCTO and CCTZO ceramics consisted of semiconducting grains and insulating grain boundaries.

Phase Evolution, Microstructure and Dielectric Properties of CaCu3Ti4O12 Ceramics Fabricated by Combustion Technique

The effects of calcination temperature (750–1000 °C) and sintering temperature (1000–1125°C) on phase evolution, microstructure and the dielectric properties of CaCu3Ti4O12 (CCTO) ceramics were investigated. CCTO powders were synthesized by the combustion technique. The pure cubic perovskite phase of CCTO powders was detected above a calcination temperature of 950°C and it was also obtained from the ceramics sintered below 1125°C. The lattice parameter a of CCTO powder (7.3829–7.3870 Å) and ceramic (7.3721–7.3857 Å) increased with the higher firing temperatures. The increasing of the average particle size and the average grain size of samples was caused by the increase of firing temperatures. The highest density was ∼96% of the theoretical density, and was obtained from the sample sintered at 1100°C for 2 h. This sample also exhibited a maximum dielectric constant of approximately 29664 and a low dielectric loss of about 0.0925. Most importantly, the combustion fuel (glycine) carried out an important role by reducing the dwell time and improving the density and dielectric properties.

Dielectric properties of CaCu3Ti4O12, Ba(Fe1/2Nb1/2)O3, and Sr(Fe1/2Nb1/2)O3 giant permittivity ceramics at microwave frequencies

The dielectric properties of CaCu3Ti4O12, Ba(Fe1/2Nb1/2)O3, and Sr(Fe1/2Nb1/2)O3 giant permittivity ceramics were evaluated at microwave frequencies using a modified resonant cavity method. In the frequency range between 3.4 and 9.5 GHz, the permittivities of the three ceramics were around 84.6, 43.9, and 40.4 at 20 °C and were nearly independent of frequency. The dielectric losses decreased and the Qf values increased significantly with increasing frequency. The temperature dependence of the dielectric properties was also investigated at about 6.02 GHz. With increasing temperature from −60 °C to 80 °C, the permittivities of CaCu3Ti4O12, Ba(Fe1/2Nb1/2)O3, and Sr(Fe1/2Nb1/2)O3 ceramics varied nearly linearly, and the corresponding temperature coefficients of permittivity were −700, 175, and 164 ppm/ °C, respectively.

Dielectric Constant Enhancement in Calcium Copper Titanate Ceramics

The structural, morphological, and dielectric properties of CaCu3Ti4O12 (CCTO) ceramics without and with 10% HfO2 by weight were investigated in this work. The main effect of adding HfO2 on the microstructure was the segregation of HfO2 subgrains within CCTO grains, which consequently causes the inhomogeneous electric structure of the HfO2-modified sample. The HfO2-modified sample presented the much larger dielectric constant than the pure CCTO one, which resulted from HfO2 subgrains’ effect as another new origin of the dielectric constant.

Effect of the MgO substitution for CuO on the properties of CaCu3Ti4O12 ceramics

In this work, the effect of MgO substitution for CuO on the dielectric properties of CaCu3Ti4O12 (CCTO) was studied. Ceramic samples of CaCu3−xMgxTi4O12 were prepared by a two-step solid-state reaction. The samples were sintered at 600°C for 2h and then heated to the final sintering temperature of 1100°C for 8h. The lattice parameter of CCTO decreases with Mg substitution from X-ray diffraction (XRD) analysis, since the ionic radius of Mg2+ is smaller than that of Cu2+. Mg substitution in CCTO causes apparent change in microstructure with much smaller grains due to the grain growth inhibition. The maximum of the dielectric constant can reach to 7.8×105 at f=100Hz for Mg substitution with x=0.6. The sample with Mg substitution (x>0.2) yields an apparent semicircle in the impedance spectra. The correlation between the microstructure and dielectric properties suggests the presence of a thin barrier layer forming at the grain boundary.

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).