Giant Dielectric Properties Research Articles

Significantly improved non-ohmic and giant dielectric response in CaCu3Ti4O12 ceramics by incorporating Portland cement

The giant dielectric and nonlinear current–voltage properties of CaCu3Ti4O12 (CCTO) incorporating Portland cement (PC) were investigated. Analysis revealed that the microstructure of the CCTO/PC ceramics was highly dense. Using the microstructure analysis and theoretical calculation, the elements in PC (i.e., Al, Si, Fe, K, Cr, and Mg) can substitute into the CCTO structure, giving rise to enhanced electrical properties of the grains and grain boundaries. As a result, the giant dielectric and nonlinear current–voltage properties of CCTO/PC were significantly improved. The low–frequency loss tangent of CCTO/PC was greatly reduced, by a factor of 10, while the dielectric permittivity of the ceramics was still large (∼104) over a frequency range of 102–106 Hz. Interestingly, the nonlinear coefficient (α) and electric field breakdown (Eb) of the CCTO/PC ceramics were greatly enhanced by factors of 2 and 30, respectively. Impedance spectroscopy analysis revealed large increases in α and Eb, as well as a decrease in the loss tangent due to a significant increase in the grain boundary resistance of CCTO/PC ceramics. Changes in giant dielectric and nonlinear electrical properties can be well described by the internal barrier layer capacitor model based on space charge polarization at the internal interfaces.

Investigation of the dielectric properties and nonlinear electrical response of CaCu3Ti4O12 ceramics prepared by a chemical combustion method

CaCu3Ti4O12 (CCTO) ceramic powders were successfully prepared by a wet-chemical combustion method. The phase formation, microstructure, giant dielectric response, and nonlinear electrical properties of the sintered ceramics were systematically investigated. The main phase in the CCTO powder is clearly indicated in the XRD pattern. A dense and fine-grained microstructure was obtained by sintering the compacted CCTO powders. Dielectric permittivity values are in the range of ~ 103–104 with a very low tan δ of ~ 0.03–0.11 at 1 kHz. Interestingly, a high breakdown electric field (9741.6 V/cm) and nonlinear coefficient (9.9) are observed in the CCTO ceramic sintered at 1030 °C for 1 h. Impedance spectroscopy analysis revealed that the electrical conductivity in the grains and grain boundaries is completely different. The electrically heterogeneous microstructure clearly indicates that the giant dielectric response and nonlinear electrical properties are correlated with the electrical response of the insulating grain boundaries. The origin of the n-type semiconducting grains is evident by considering the oxidation states of the Ti and Cu ions, which are quantitatively and qualitatively analyzed using X-ray absorption spectroscopy.

Giant dielectric permittivity of CaCu3Ti4O12 via a green solution-egg white method

CaCu3Ti4O12 ceramics were prepared using a green solution-egg white method. A main phase of CaCu3Ti4O12 is observed in the obtained powder and all sintered ceramics. The microstructure of all ceramics is studied. Their grain sizes are found to be in the range of 4–7 µm. Giant dielectric properties with low dielectric loss (tanδ ∼ 0.07) and large dielectric permittivity (e′ ∼ 7000) are achieved in the sintered CaCu3Ti4O12 ceramic. An impedance spectroscopy analysis confirms a heterogeneous microstructure in sintered CaCu3Ti4O12 ceramics, consisting of highly resistive grain boundaries and semiconducting grains. Mixed Cu3+/Cu2+/Cu+ and Ti4+/Ti3+ phases are detected using X-ray photoelectron spectroscopy, confirming the presence of semiconducting grains.

Significantly improved giant dielectric response in giant dielectric response in CaCu2.95Ni0.05Ti4-xGexO12 (x = 0.05, 0.10) ceramics

The dielectric properties and electrical responses of an undoped CaCu3Ti4O12 ceramic and isovalent codoped CaCu2.95Ni0.05Ti4-xGexO12 (x = 0.05 and 0.10) ceramics were investigated. Significant increases in the grain size can be observed in all the CaCu2.95Ni0.05Ti4-xGexO12 ceramics. The CaCu2.95Ni0.05Ti4-xGexO12 ceramics were shown to exhibit giant dielectric properties, high dielectric permittivities ∼4.83–4.96 × 104, and very low tanδ values ∼0.029–0.030. Additionally, the ceramics all demonstrated nonlinear current density-electric field (J-E) characteristics. The significantly improved dielectric properties of the (Ni2+, Ge4+)-codoped CaCu3Ti4O12 ceramics are closely associated with the enhanced grain boundary response. Clearly, the giant dielectric properties of the CaCu3Ti4O12 and CaCu2.95Ni0.05Ti4-xGexO12 ceramics could be well described by an internal barrier layer capacitor (IBLC) mechanism, which was confirmed by the results of the impedance spectroscopy and applied DC bias analysis. The important roles of the Ni2+ and Ge4+ isovalent dopants are discussed.

Improved electrical performance of MgO-modified CaCu3Ti4O12 ceramics

Colossal permittivity material CaCu3Ti4O12 (CCTO) ceramics modified by MgO with the mass fraction of 0%, 0.5%, 1%, and 2% were synthesized using a sol-gel method followed by a conventional ceramic preparation process. The scanning electron microscope exhibits that all CCTO ceramics possess the high densities and large grain size. The results of dielectric measurement show that all the samples possess giant dielectric properties. The colossal dielectric constant of CCTO ceramics increases firstly and then decreases with the increase of mass fraction from 0% to 2% at room temperature, while the value of dielectric loss is opposite. Specifically, the sample with the mass fraction of 1% shows the highest density, largest grains and most obvious grain boundaries. 1% sample also shows better electrical properties with giant dielectric constant (~6.59 × 104 at 1 kHz) and low dielectric loss (~0.06 at 1 kHz) at room temperature. In addition, the optimal sample with the mass fraction of 1% shows a more stable dielectric constant from 20 °C to 200 °C. The electrical properties of the CCTO ceramics have achieved good performance by the addition of MgO.

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.

Optimizing giant dielectric properties via interface composition: A study of rutile-based ceramics

Abstract In this study, the interface compositions, polarization behaviors, and dielectric properties of Ti1-x(Cu0.333Ta0.667)xO2 (x = 5%, 20%, and 45%) ceramics prepared at various sintering conditions are systematically investigated. An analysis of the crystal structure, cation valence state, and element distribution indicates that increasing the sintering temperature and prolonging the sintering time hardly change the lattice symmetry of the bulk phase of the ceramics, but it does alter their interface chemical composition to produce phase separations of Cu and Ta ions and mixed valence states of Ti and Cu cations. Measurement of their dielectric properties further demonstrates that the altered interface composition changes the polarization mechanism of the ceramic samples. For Ti1-x(Cu0.333Ta0.667)xO2 ceramics, increasing the doping level (x) produces larger lattice parameters and more oxygen vacancies and Cu+ ions. Meanwhile, Cu-rich or Ta-rich phases appear at the grain boundary of the highly doped samples. The Ti0.8(Cu0.333Ta0.667)0.2O2 ceramic has giant permittivity (e’ = 65314) due to the competitive coexistence of the internal barrier layer capacitor and surface barrier layer capacitor effects. This study can provide new possibilities for the design of ceramics with desired performance characteristics by purposefully changing the interface features with different preparation conditions.

Colossal permittivity and ultralow dielectric loss in (Nd0.5Ta0.5)xTi1-xO2 ceramics

Abstract Giant permittivity ceramic is one of the most significant classes of material to realize the miniaturization and integration of a high-performance capacitor. In this paper, to realize good giant dielectric properties, the (Nd0.5Ta0.5)xTi1-xO2 ceramics (NTTO x = 0.005, 0.01, 0.03, 0.05) were synthesized by a standard conventional solid-state reaction. Comparing with the previous co-doped TiO2 ceramics giant permittivity material system, NTTO ceramics perform extremely colossal permittivity and ultralow dielectric loss (1%NTTO: e = 82052, tanδ = 0.008 at 1 kHz; 5%NTTO: e = 170131, tanδ = 0.090 at 1 kHz). The broad distinction of the dielectric behavior between the (Nd0.5Ta0.5)xTi1-xO2 ceramics can be explained by the impedance analysis and the calculated polarization activation energies. The main electron-pinned defect-dipole (denoted as EPDD) polarization corresponds to the ultralow loss, embodying in the maximum value of Egb (the activation energy of the grain boundary), Ea2 (the EPDD polarization activation energies) and the minimum value of Ea1 (the total polarization activation energies). Though the interfacial polarization can cause the permittivity increase, it can also give rise to poor frequency stability and higher loss.

Nonlinear current-voltage and giant dielectric properties of Al3+ and Ta5+ co-doped TiO2 ceramics

The nonlinear current-voltage and dielectric properties of (Al3++Ta5+) co-doped TiO2 (ATTO) ceramics are represented. Microstructural analysis reveals that sintered ceramics are highly dense and nonporous. ATTO ceramics exhibit low loss tangent (tanδ<0.1) and large dielectric permittivity (ε′˜103-104). Furthermore, ATTO ceramics exhibited nonlinear current-voltage characteristics. The best dielectric properties are achieved in the (Al1/2Ta1/2)0.05Ti0.95O2 ceramic with a very low tanδ (˜0.012) and high ε′ (˜104) with excellent dielectric-temperature stability with a temperature coefficient at 150 °C as low as 2.69%. The resistivity of insulating phases decreases with increasing Al3+ and Ta5+ concentrations, which is correlated to decreased breakdown voltage. The nonlinear electrical properties and dielectric response are explained based on the electrical response of internal interfaces.

Giant anomalous dielectric behaviour of BaSnO3 at high temperature

BaSnO3 ceramic was synthesized by conventional solid state route at high sintering temperature 1450 °C which leading to oxygen loss in air. X-ray diffraction (XRD) analysis has confirmed the phase purity of BaSnO3 with cubic structure and space group Pm-3m. The unexpected giant anomalous dielectric properties of pure BaSnO3 ceramic was revealed by impedance spectroscopy analysis when the dielectric constant (er) value rapidly increased by temperature and gives the highest er peak at 220 °C with 87,290 and 6027 measured at 10 Hz and 1 kHz respectively. Then, it decreases gradually by increasing the temperature above 220 °C. This anomalous giant er was observed during heating impedance measurement and disappear upon cooling. The anomalous behaviour is expected due to oxygen deficiency.

Giant dielectric response, electrical properties and nonlinear current-voltage characteristic of Al2O3-CaCu3Ti4O12 nanocomposites

In this work, xAl2O3-(1 − x)CaCu3Ti4O12, where x = 0, 2, and 10 vol%, nanocomposites were prepared by a conventional mixed oxide method using Al2O3 nanopowders with particle sizes of ≈20–40 nm. The giant dielectric properties, electrical responses and nonlinear characteristics of Al2O3-CaCu3Ti4O12 nanocomposites were investigated. Interestingly, the (2 vol%)Al2O3-CaCu3Ti4O12 ceramic exhibited significantly improved dielectric properties with large dielectric constant and low loss tangent values of about of 2.0 × 104 and 0.038, respectively. The nonlinear current-voltage properties of CaCu3Ti4O12 ceramics were also enhanced by the addition of Al2O3. X-ray photoelectron spectroscopy technique was used to confirm the existence of Cu+, Cu3+ and Ti3+ ions in the composite ceramics, indicating the primary cause of the conduction mechanism inside the grains. The first principle calculation was performed to predict the most possibility of site preference of Al ion in CCTO lattice structure. The improved dielectric and nonlinear electrical properties can be well explained based on the internal barrier layer capacitor effect, resulting from the improved electrical properties of internal interfaces.

Origin of significantly enhanced dielectric response and nonlinear electrical behavior in Ni2+-doped CaCu3Ti4O12: Influence of DC bias on electrical properties of grain boundary and associated giant dielectric properties

CaCu3-xNixTi4O12 (x = 0, 0.05, and 0.10) powders were synthesized using a solid state reaction method. Phase structure and microstructure analyses revealed that all sintered CaCu3-xNixTi4O12 ceramics were of a pure phase. The CaCu3Ti4O12 ceramics had a dense microstructure and grain sizes were enlarged by doping with Ni2+. Interestingly, the dielectric permittivity was significantly enhanced, whereas the loss tangent was greatly suppressed to ∼0.046–0.034 at 1 kHz. All sintered ceramics exhibited non-Ohmic characteristics. Clarification of the influences of DC bias showed that the dielectric permittivity and loss tangent values were increased by DC bias. The resistance of grain boundaries and the associated conduction activation energy of CaCu3-xNixTi4O12 ceramics were reduced as the DC bias voltage increased. Therefore, the observed non-Ohmic behavior and significantly enhanced dielectric properties should be closely related to variation in the Schottky barriers at the grain boundaries.

Effect of barium doping on the microstructure, dielectric and magnetic properties of GdMnO3 multiferroic ceramics

Undoped GdMnO3 (GMO) and Gd0.95Ba0.05MnO3 (GBMO) multiferroic ceramics were prepared by solid state reaction method, and the effects of Ba doping on the structure, morphology, dielectric and magnetic properties of GMO system were investigated. The XRD results show that the two samples yield single phase, and Ba doping induce structure distortion. The SEM images show that Ba doping can inhibit the grain growth. The XPS analysis indicates that more Mn4+ and oxygen vacancies are involved in the Ba doped GMO ceramics. Raman measurements show that Ba substitutes Gd into the lattice of GMO and induces lattice disorder. The dielectric measurements reveal that the Ba doped GMO exhibits the giant dielectric properties, but the dielectric loss of Ba doped samples is higher than that of the undoped samples. Temperature and magnetic field dependent magnetization measurements reveal that the low temperature magnetic behaviors of GMO system can be altered by Ba doping. The paramagnetic–antiferromagnetic transition temperature and magnetization of GMO system are decreased after Ba doping. In addition, Ba doping can also influence the long-range order of Gd moments at about 8 K. The possible reasons for the above results are discussed.

Giant dielectric permittivity and dielectric relaxation behaviour in (Fe1/2Nb1/2)xTi1-xO2 ceramics

In this work, the giant dielectric properties and dielectric relaxation behaviour in (Fe1/2Nb1/2)xTi1-xO2 (x = 0–0.1) ceramics prepared by a conventional solid state reaction method were investigated. Pure phase of rutile-TiO2 was obtained in all ceramic compositions. Dense ceramic microstructure without porosity was achieved in the sintered ceramics. High dielectric permittivity of > 103 was obtained. The existence of Ti4+ and Ti3+ was confirmed by X-ray photoelectron spectroscopy. The thermally activated dielectric relaxation behaviour in (Fe1/2Nb1/2)xTi1-xO2 ceramics was observed and attributed to the electron hopping mechanism.

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.

Improved giant dielectric properties in microwave flash combustion derived and microwave sintered CaCu3Ti4O12 ceramics

The nanocrystals of CaCu3Ti4O12 ceramic were prepared by microwave flash combustion technique. The microwave sintering of powders was optimized to 1025 − 1075 °C for 20 min with heating and cooling rate of 50 °C/min. Microstructural evaluation of sintered sample was carried out using SEM. The dielectric properties were measured in the frequency range 10–2 × 106 Hz and the temperature range 30–100 °C. The CCTO sample sintered at 1075 °C had giant dielectric constant 53,300 at 100 Hz. It was observed that dielectric constant was greatly increased on a slight increase in sintering temperature. Modulus and impedance analysis were performed to explore the observed unusual dielectric response. Grain and grain boundary resistance were observed as 8 Ω and 350,000 Ω, respectively. The grain boundary activation energy for electro-conduction was calculated as 0.65 eV by using the characteristic frequencies in cole-cole plots. It was noticed that the thermally activated charge carriers had long-range mobility.

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.

Surface layer characterizations and sintering time effect on electrical and giant dielectric properties of (In0.05Nb0.05)Ti0.9O2 ceramics

In3+ and Nb5+ co-doped TiO2 (INTO) ceramics were sintered at 1400 °C for 5 and 10 h. The room temperature dielectric permittivity of the as-fired INTO ceramics significantly decreased from ε′≈ 7824 to 4669 (at 1 kHz) as sintering time increased, while the microstructure changed slightly. The corresponding loss tangent (tanδ) values were ≈ 0.040–0.047. The resistance of the insulating part and associated conduction activation energy greatly increased with increasing sintering time, corresponding to an increase in the breakdown voltage (Eb). After removing the outer surface layer, Eb was greatly reduced from 104 to 101 V/cm, corresponding to the large increase in tanδ (≈ 0.3–0.4) and ε′ (≈ 105–106). Very high ε′≈ 50,000 with low tanδ≈ 0.06 can be achieved by annealing the polished samples in air, indicating the important role of the surface layer in controlling the dielectric and electrical properties of INTO ceramics. Characterizations revealed that the formation of an insulating surface layer of the as-fired INTO ceramics may not be associated with the chemical compositional gradients of either the Ti3+ or oxygen vacancies. It was suggested that the inner and outer surface regions of INTO ceramics may consist of the same phase but with a slightly different composition.

Effect of sintering atmosphere on the microstructure and dielectric properties of barium strontium titanate glass–ceramics

The sintering of barium strontium titanate glass–ceramics in nitrogen modified their dielectric properties significantly compared to the sintering in air. The experimental results demonstrate that the glass–ceramics sintered at low temperatures contain a major phase Ba2TiSi2O8 (BTS), known as fresnoite. The fresnoite phase disappeared and the barium strontium titanate perovskite phase became the major phase when the sintering temperature was increased. In addition, the microstructure observation showed that both the proportion of crystal phase and the crystal size increase obviously with the increase of sintering temperature. Most importantly, impedance spectroscopy has been employed to study the electrical responses arising from the glass and the crystal phases in the glass–ceramics sintered at low temperatures and high temperatures. The magnitudes of impedance and modulus changed significantly for the glass–ceramics sintered at the two temperature ranges. The activation energy calculated from the complex impedance, complex modulus and dc conductivity suggests that the dielectric relaxation for the glass phase and the glass–crystal interface may be attributed to the motion of the dipole associated with oxygen vacancy. And for the barium strontium titanate perovskite glass–ceramics, the motion of the electrons from the second ionization of oxygen vacancies leads to dc electrical conduction. The mechanism for the giant dielectric properties of the glass–ceramics sintered at high temperatures in nitrogen is discussed.

(Al3+, Nb5+) co–doped CaCu3Ti4O12: An extended approach for acceptor–donor heteroatomic substitutions to achieve high–performance giant–dielectric permittivity

Substitution of (Al3+, Nb5+) co–dopants into TiO6 octahedral sites of CaCu3Ti4O12 ceramics, which were prepared by a solid state reaction method and sintered at 1090°C for 18h, can cause a great reduction in a low–frequency loss tangent (tanδ≈0.045–0.058) compared to those of Al3+ or Nb5+ single–doped CaCu3Ti4O12. Notably, very high dielectric permittivities of 2.9−4.1×104 with good dielectric–temperature stability are achieved. The room–temperature grain boundary resistance (Rgb≈0.37–1.17×109Ω.cm) and related conduction activation energy (Egb≈0.781–0.817eV), as well as the non–Ohmic properties of the co–doped ceramics are greatly enhanced compared to single–doped ceramics (Rgb≈104–106Ωcm and Egb≈0.353–0.619eV). The results show the importance of grain boundary properties for controlling the nonlinear–electrical and giant–dielectric properties of CaCu3Ti4O12 ceramics, supporting the internal barrier layer capacitor model of Schottky barriers at grain boundaries.