Internal Barrier Layer Capacitor Model Research Articles

(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.

Effects of Co–Doping on Dielectric and Electrical Responses of CaCu3Ti4-x(Nb1/2In1/2)xO12 Ceramics

In this work, CaCu3Ti4-x(Nb1/2In1/2)xO12 ceramics, x = 0, 0.025, 0.05, 0.10, and 0.20, were prepared using a conventional solid state reaction method. Their crystal structure, microstructure, dielectric, and electrical properties were systematically investigated. A primary phase of CaCu3Ti4O12 ceramic was clearly observed in all samples. The average grain size of CaCu3Ti4O12 was decreased by (Nb5+, In3+) doping. The dielectric permittivity of CaCu3Ti4-x(Nb1/2In1/2)xO12 ceramics was slightly dependent on frequency as the co-dopant concentration increased, which was due to a decrease in its grain size. Their dielectric behavior can be well described by the internal barrier layer capacitor (IBLC) model based on interfacial polarization at grain boundaries. The grain boundary resistance and potential barrier height at the grain boundary of CaCu3Ti4O12 were reduced by co–doping with (Nb5+, In3+) ions, resulting in an enhancement of DC conductivity and the related dielectric loss tangent.

Nonlinear electrical properties and giant dielectric response in Na1/3Ca1/3Y1/3Cu3Ti4O12 ceramic

A new isostructural CaCu3Ti4O12–type perovskite, Na1/3Ca1/3Y1/3Cu3Ti4O12, was successfully synthesized using a solid state reaction method. In this material, Ca–sites in the CaCu3Ti4O12 structure were occupied by Na+, Ca2+, and Y3+ ions, each at a level of ∼33.3 at.%. The dielectric and non –Ohmic properties were investigated. The mean grain sizes of the Na1/3Ca1/3Y1/3Cu3Ti4O12 ceramics sintered at 1100–1110°C for 10–15h were of about ≈15μm. All of the sintered ceramics exhibited high dielectric permittivities (ε′) and low loss tangents (tanδ). By optimizing sintering conditions, a high ε′≈1.2×104 and low tanδ≈0.04 were achieved. Na1/3Ca1/3Y1/3Cu3Ti4O12 ceramics can exhibit nonlinear current-voltage behavior. The existence of Cu+, Cu3+, and Ti3+ ions was confirmed using an X–ray Absorption Near Edge Structure (XANES) and X–ray photoelectron spectroscopic analyses. The n–type semiconductivity inside the grains was primarily caused by the presence of Ti3+ ions, while the existence of Cu+ and Cu3+ may also have an effect on conduction inside the grains. Using impedance and admittance spectroscopy analyses under different conditions (i.e., varying frequency, temperature and DC bias), the giant dielectric response and nonlinear electrical properties could be well explained based on the internal barrier layer capacitor model.

Surface barrier layer effect in (In + Nb) co‐doped TiO2 ceramics: An alternative route to design low dielectric loss

AbstractGiant dielectric permittivity (ε′) with low loss tangent (tanδ) was reported in (In + Nb) co‐doped TiO2 ceramics. Either of electron‐pinned defect‐dipole or internal barrier layer capacitor model was proposed to be the origin of this high dielectric performance. Here, we proposed an effectively alternative route for designing low‐tanδ in co‐doped TiO2 ceramics by creating a resistive outer surface layer. A pure rutile‐TiO2 phase with a dense microstructure and homogeneous dispersion of dopants was achieved in (In + Nb) co‐doped TiO2 ceramics prepared by a simple sol‐gel method. Two giant dielectric responses were observed in low‐ and high‐frequency ranges, corresponding to extremely high ε′≈106‐107 and large ε′≈104‐105, respectively. After annealing in air, a low‐frequency dielectric response disappeared and could be restored by removing the outer surface of the annealed sample, indicating the dominant electrode effect in the initial sample. Annealing can cause improved dielectric properties with a temperature‐ and frequency‐independent ε′ value of ≈1.9 × 104 and cause a decrease in tanδ from 0.1 to 0.035. High dielectric performance in (In0.5Nb0.5)xTi1−xO2 ceramics can be achieved by eliminating the electrode effect and forming a resistive outer surface layer.

Effects of DC bias on dielectric and electrical responses in (Y + Zn) co-doped CaCu3Ti4O12 perovskite oxides

The dielectric and electrical properties of Zn-doped Ca0.925Y0.05Cu3Ti4O12 ceramics were investigated under an applied DC bias. Crystalline structure, ceramic microstructure, electrical responses and dielectric properties were systematically investigated. The lattice parameter of Zn-doped Ca0.925Y0.05Cu3Ti4O12 ceramics increased with increasing Zn2+ dopant concentration. The microstructure had grain sizes of 2–4 μm and was slightly changed with Zn2+ concentration. High dielectric permittivities (e′ ~ 4400–5000) and very-low loss tangents (tanδ ~ 0.03–0.06) were successfully achieved. At 1 kHz, e′ slightly increased with increasing Zn2+ concentration, while tanδ was significantly reduced. Variations in a low-frequency tanδ values in a low-frequency range were consistent with changes in the grain boundary resistance. Using impedance spectroscopy, it was found that the grain boundary resistance was significantly reduced by applying a DC bias, while the grain resistance remained unchanged. The conduction activation energy at the grain boundaries tended to decrease with increasing DC bias voltage (0–36 V), which was due to the reduction in the potential barrier height at the grain boundaries. The dielectric and electrical properties were described by the internal barrier layer capacitor model of Schottky barriers at the grain boundaries.

Synthesis and dielectric properties of Cu3Ti2Ta2O12 ceramics

A novel perovskite ceramic based on crystalline structure of ACu3Ti4O12 compound, is presented. Ti-sites were occupied by ∼50 at.% of Ta5+, and A-sites remained vacant, leading a formation of Cu3Ti2Ta2O12. This ceramic exhibited a high ε′ value in a low frequency range at room temperature. The high-frequency dielectric relaxation behavior showed activation energies of 0.146 eV. Valence states of Cu and Ti cations (i.e., Cu+, Cu3+ and Ti3+) in Cu3Ti2Ta2O12 ceramic were investigated using X-ray photoelectron spectroscopy. Impedance spectroscopy analysis revealed that Cu3Ti2Ta2O12 was electrically heterogeneous and comprised of semiconducting grains and insulating grain boundaries. Maxwell-Wagner polarization related to internal barrier layer capacitor model was suggested to be the origin of this high dielectric response.

Central role of TiO2 anatase grain boundaries on resistivity of CaCu3Ti4O12-based materials probed by Raman spectroscopy

This study focuses on characterization and control of grain boundaries to enhance the properties of CaCu3Ti4O12 (CCTO) ceramics capacitors for industrial applications. A novel factor deals with TiO2 anatase revealed by Raman scattering in grain boundaries, found as a dominant parameter of largest sample resistivity, consistent with higher grain boundary resistivity and higher breakdown voltage. Four selected samples of CCTO-based compositions showing very different properties in terms of permittivity ranging from 1000 to 684 000 measured at 1 kHz, capacitance of grain boundaries ranging from 8 10−10 to 4.5 10−7 F cm−1, grain boundary resistivity ranging from 193 to 30,000,000 Ω cm and sample resistivity extending from 450 to 1011 Ω cm. The relationship between permittivity weighted by grain size and capacitance of grain boundaries confirms the internal barrier layer capacitance model over 5 orders of magnitude.

ZnO microvaristors doped polymer composites with electrical field dependent nonlinear conductive and dielectric characteristics

ZnO microvaristor/rubber composites with nonlinear conductive and dielectric properties were fabricated and investigated for the first time. The composites exhibit nonlinear conductive behaviors only when the filler concentration is above percolation threshold (39vol%), but show nonlinear dielectric properties with various filler concentration (viz. 30–60vol%). Both the nonlinear conductive and dielectric properties can be tuned by adjusting the filler concentration. Percolation threshold theory was utilized to explain the nonlinear electrical properties, and an internal barrier layer capacitor (IBLC) model was proposed to successfully explain the novel nonlinear dielectric properties, which demonstrates that the hole injection might be the key to the dramatic increase of the permittivity.

Microstructure and Dielectric Properties of SnO2-doped CaCu3Ti4O12 Ceramics

Dielectric CaCu3Ti4O12-xSnO2 ceramics (x = 0, 0.003, 0.006, 0.010, 0.015 and 0.020) have been synthesized by solid-state reaction method. The microstructure was studied by X-ray diffraction, Raman spectrum and Scanning electron microscope. It is revealed that SnO2-doping results in the distortion of crystal structure and various grain growths for CaCu3Ti4O12-based ceramics. Dielectric measurement shows that lower-doped samples (x = 0.003 and 0.006) exhibit enhanced dielectric constants which are over 70,776 and 26,406 at the range of 40-104 Hz, respectively. In addition, the dielectric properties are explained in terms of internal barrier layer capacitance model by using the impedance spectroscopy analysis.

Effects of barium substitution on the dielectric properties of Sr(Fe0.5Nb0.5)O3 ceramics

The Ba-substituted Sr1−x Ba x (Fe0.5Nb0.5)O3 (SBFN, x = 0, 0.2, 0.5, 0.8) ceramics were prepared by a conventional solid-state sintering, and their microstructure and dielectric properties were investigated. The single-phase SBFN were obtained up to x = 0.8 Ba substitution and the lattice parameter increased with Ba substitution concentration. The dielectric constant increased with Ba substitution, and the highest value of ~180,000 was observed in the x = 0.8 Ba-substituted specimen at 1 kHz. Besides, the dielectric constant increased rapidly a giant value more than 106 over a broad temperature range for x = 0.8 Ba-substituted specimen. The obtained electric and dielectric properties in Ba-substituted SBFN were discussed in terms of the internal barrier layer capacitor model and electrode response.

Effect of Platinum Substitution on the Microstructures and Dielectric Relaxation of CaCu<sub>3</sub>Ti<sub>4</sub>O<sub>12</sub> 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)

Microstructure Evolution and Dielectric Characteristics of CaCu3Ti4O12Ceramics with Sn-Substitution

The doping effect of Sn on the microstructure evolution and dielectric properties was studied in CaCu₃Ti 4-x Sn x O 12 polycrystals. Samples were produced by a conventional solid-state reaction method. Sintering was carried out at 1115℃ for 2-16 h in air. The dielectric constant and loss were examined at room temperature over a frequency range between 10² and 10 6 Hz. The microstructure was found to evolve into three stages. Addition of SnO₂ led to an increase in density and advanced formation of abnormal grains. The formation of coarse grains with a reduced thickness of the boundary brought about an enhanced dielectric constant and a lower dielectric loss below ~1 kHz. EDS data showed the Cu-rich phase along the grain boundary, which should contribute to the improved dielectric constant according to the internal barrier layer capacitor model. After all, SnO₂ was an effective dopant to elevate the dielectric characteristics of CaCu₃Ti 4-x Sn x O 12 polycrystals as a promoter for abnormal grain growth.

The origin of giant dielectric relaxation and electrical responses of grains and grain boundaries of W-doped CaCu3Ti4O12 ceramics

The origin of giant dielectric relaxation behavior and related electrical properties of grains and grain boundaries (GBs) of W6+-doped CaCu3Ti4O12 ceramics were studied using admittance and impedance spectroscopy analyses based on the brick–work layer model. Substitution of 1.0 at. % W6+ caused a slight decrease in GB capacitance, leading to a small decrease in the low-frequency dielectric constant. Surprisingly, W6+ doping ions have remarkable effects on the macroscopic dielectric relaxation and electrical properties of grains. X-ray photoelectron spectroscopy analysis suggested that the large enhancements of grain resistance and conduction activation energy of grains for the W6+-doped CaCu3Ti4O12 ceramic are caused by reductions in concentrations of Cu3+ and Ti3+ ions. Considering variation of dielectric properties together with changes in electrical properties of the W6+-doped CaCu3Ti4O12 ceramic, correlation between giant dielectric properties and electrical responses of grains and GBs can be described well by the internal barrier layer capacitor model. This model can ascribe mechanisms related to giant dielectric response and relaxation behavior in CaCu3Ti4O12 ceramics.

Effect of (Ba0.6Sr0.4)TiO3 (BST) Doping on Dielectric Properties of CaCu3Ti4O12 (CCTO)

The effect of (Ba 0.6 Sr 0.4 )TiO 3 (BST) addition on dielectric properties of CaCu 3 Ti 4 O 12 (CCTO) ceramic was investigated. Ceramic samples with the chemical formula (1– x )CaCu 3 Ti 4 O 12 + x (Ba 0 . 6 , Sr 0.4 )TiO 3 ( x =0, 0.05, 0.1, and 0.2) were synthesized from high purity oxide powders by the conventional solid-state synthesis method. X-ray diffraction (XRD) analysis showed the existence of BST as a secondary phase alongside CCTO. Scanning electron microscopy (SEM) investigation showed a slight decrease in grain size of doped CCTO samples. Density measurements showed that porosity content increased with increasing BST addition indicating low densification due to high melting point secondary phase addition. Dielectric constant of undoped CCTO ( x =0) showed lack of stability with frequency which dropped drastically between 10 4 and 10 5 Hz and accompanied by high dielectric loss. Addition of BST into CCTO caused the dielectric constant to slightly decrease but improved stability with frequency compared to the undoped sample. The decrease in dielectric constant of doped CCTO samples was suggested to be partly due to the decrease in average grain size and increase in porosity with BST addition. Nevertheless, a high value of dielectric constant was still maintained around ∼10 4 range for all doped samples. The dielectric loss (tanδ) of all BST-doped samples was lower than that of pure CCTO sample at the frequency range of 10 3 to 10 5 Hz probably due to the increase of grains boundary resistivity. The activation energy of grains boundary ( E gb ) showed higher values as compared to the activation energy of grains ( E g ) for all samples and conforms to the internal barrier layer capacitor (IBLC) model.

Microstructures and dielectric relaxation behaviors of pure and tellurium doped CaCu3Ti4O12 ceramics prepared via vibro-milling method

In this work, we have reported microstructures and the dielectric properties of CaCu 3 Ti 4 O 12 (CCTO) ceramics doped with different proportions of TeO 2 dopant (mol%, x =0, 0.5%, 1.0%, 2.0%). The pure and tellurium doping CCTO ceramics were prepared by a conventional solid-state reaction method and the effects of TeO 2 doping on the electrical properties and microstructures of these ceramics were investigated. XRD analysis confirmed the formation of single-phase material in samples. Scanning electron microscopy (SEM) is used in the micro structural studies of the specimens, which showed that TeO 2 doping can reduce the mean grain size and increasing size of an abnormal grain growth. Lattice parameter increases slightly with tellurium doping in CCTO, the dielectric constant reached a value as high as 18,000 (at 1 kHz) at a tellurium-doping concentration of 2.0 mol% and showed temperature stability at high frequency. The loss tangent of Te-doped CCTO ceramics was less than 0.05 at 1 kHz region below 105 °C. The loss tangent properties could be interpreted by the internal barrier layer capacitor model and the impedance measurement data.

Non-Ohmic and dielectric properties of Ba-doped CaCu3Ti4O12 ceramics

The microstructure, dielectric and electrical properties of Ca1−xBaxCu3Ti4O12 (where x = 0, 0.025, and 0.05) ceramics were investigated. Our microstructural analyses revealed that Ba2+ doping ions preferentially form in a secondary phase, and are not introduced into the CaCu3Ti4O12 lattice. Grain growth rate of CaCu3Ti4O12 ceramics was significantly inhibited by the Ba-related secondary phase particles, resulting in a large decrease in their mean grain size. The dielectric permittivity of CaCu3Ti4O12 ceramics decreased with increasing Ba content. Their loss tangent decreased after addition of CaCu3Ti4O12 with 2.5 mol% of Ba2+, and increased with increasing Ba contents to 5.0 mol%. The nonlinear coefficient and breakdown field of the Ca1−xBaxCu3Ti4O12 ceramics were significantly enhanced by adding 2.5 mol% of Ba2+, followed by a slight decrease as Ba2+ concentration was increased to 5.0 mol%. Using impedance spectroscopy analysis, it was revealed that variations in dielectric and non-Ohmic properties are associated with electrical response of grain boundaries. This supports the internal barrier layer capacitor model.

Enhancement of giant dielectric response in Ga-doped CaCu3Ti4O12 ceramics

The influences of Ga3+ doping ions on the microstructure, dielectric and electrical properties of CaCu3Ti4O12 ceramics were investigated systematically. Addition of Ga3+ ions can cause a great increase in the mean grain size of CaCu3Ti4O12 ceramics. This is ascribed to the ability of Ga3+ doping to enhance grain boundary mobility. Doping CaCu3Ti4O12 with 0.25mol% of Ga3+ caused a large increase in its dielectric constant from 5439 to 31,331. The loss tangent decreased from 0.153 to 0.044. The giant dielectric response and dielectric relaxation behavior can be well described by the internal barrier layer capacitor model based on Maxwell−Wagner polarization at grain boundaries. The nonlinear coefficient, breakdown field, and electrostatic potential barrier at grain boundaries decreased with increasing Ga3+ content. Our results demonstrated the importance of ceramic microstructure and electrical responses of grain and grain boundaries in controlling the giant dielectric response and dielectric relaxation behavior of CaCu3Ti4O12 ceramics.

Modified giant dielectric properties of samarium doped CaCu3Ti4O12 ceramics

Effects of Sm3+ substitution on the microstructure and dielectric properties of CaCu3Ti4O12 ceramics were investigated. The grain size of CaCu3Ti4O12 ceramics was greatly decreased by doping with Sm3+, resulting from the ability of Sm3+ to inhibit the grain growth rate. This result can cause a decrease in the dielectric constant (ɛ′) and loss tangent (tanδ) of CaCu3Ti4O12 ceramics. Interestingly, high dielectric permittivity (ɛ′∼10,863) and low loss tangent (tanδ∼0.043 at 20°C and 1kHz) were observed in the Ca0.925Sm0.05Cu3Ti4O12 ceramic. Nonlinear electrical properties of CaCu3Ti4O12 ceramics were modified by doping with Sm3+. The dielectric relaxation behavior of Sm-doped CaCu3Ti4O12 ceramics can be well ascribed based on the internal barrier layer capacitor model of Schottky barriers at the grain boundaries.

Electrical responses and dielectric relaxations in giant permittivity NaCu3Ti3TaO12 ceramics

Dielectric relaxations and electrical responses in NaCu3Ti3TaO12 ceramics were investigated as a function of temperature. NaCu3Ti3TaO12 ceramics exhibit giant dielectric constants with values of e′∼1.45–2.08×104. Two sets of thermally activated dielectric relaxations were observed in low and high temperature ranges. Sintering conditions have an insignificant influence on the microstructure of NaCu3Ti3TaO12 ceramics, and have a slight impact on their e′ values. Thermally activated electrical responses of grains and grain boundaries have been studied at different temperatures by using complex admittance and impedance spectroscopy analyses, respectively. The low temperature relaxation mechanism is found to correlate closely with electrical response of semiconducting grains; whereas the apparent high e′ values are attributed to electrical response of insulating grain boundaries. These results support the internal barrier layer capacitor model to explain the giant dielectric properties of NaCu3Ti3TaO12 ceramics. Additionally, high temperature relaxation may be attributed to the sample-electrode effect and/or defect ordering.

Effects of Ta5+ doping on microstructure evolution, dielectric properties and electrical response in CaCu3Ti4O12 ceramics

Abstract The effects of Ta 5+ substitution on the microstructure, electrical response of grain boundary, and dielectric properties of CaCu 3 Ti 4 O 12 ceramics were investigated. The mean grain size decreased with increasing Ta 5+ concentration, which was ascribed to the ability of Ta 5+ doping to inhibit grain boundary mobility. This can decrease dielectric constant values. Grain boundary resistance and potential barrier height of CaCu 3 Ti 4 O 12 ceramics were reduced by doping with Ta 5+ . This results in enhancement of dc conductivity and the related loss tangent. Influence of charge compensations on microstructure and intrinsic electrical properties of grain boundaries resulting from the effects of replacing Ti 4+ with Ta 5+ are discussed. The experimental data and variation caused by the substitution of Ta 5+ can be described well by the internal barrier layer capacitor model based on space charge polarization at the grain boundaries.