Internal Barrier Layer Capacitance Effect Research Articles

Huge low-frequency dielectric response of (Nb,In)-doped TiO2 ceramics

The (Nb,In)-doped TiO2 ceramics have drawn considerable attention as a type of promising giant-permittivity dielectric materials in recent years. However, a significant controversy concerning the giant dielectric mechanism currently exists, and clarifying it is vitally important from both scientific and technological viewpoints. This letter reports the results of a systematical comparison study, where two kinds of (Nb,In)-doped TiO2 ceramics with a substantial difference in dielectric loss are used. Dielectric properties and complex impedance are investigated over a broad frequency band of 3 mHz–110 MHz. A huge low-frequency dielectric response in addition to the giant dielectric relaxation appearing above 1 MHz is observed for both kinds of (Nb,In)-doped TiO2 ceramics in dielectric dispersion. The huge dielectric response observed in the low frequency range can be ascribed to a non-ohmic electrode-contact, and the dielectric relaxation appearing above 1 MHz can be attributed to an internal barrier layer capacitance effect. An electrical equivalent circuit model suggested can well describe the observed dielectric properties and electrical behaviors.

High dielectric-permittivity properties of NaCu3Ti3Sb0.5Nb0.5O12 ceramics

A series of NaCu3Ti3Sb0.5Nb0.5O12 ceramics were prepared by the conventional solid-state reaction technique under different sintering temperatures. Their crystalline structures, microstructures, dielectric properties and complex impedance were investigated systematically. All the ceramics show the main phases of perovskite-related crystallographic structure, and their dielectric properties change significantly with sintering temperature. Those ceramics sintered above 1293K perform high dielectric-permittivity properties with ε′ over 5000. Impedance spectroscopy analysis reveals that NaCu3Ti3Sb0.5Nb0.5O12 ceramics are electrically heterogeneous and composed of semiconducting grains and insulating grain boundaries. Moreover, a small amount of CuO secondary phase and Cu2+/Cu1+, Ti4+/Ti3+, Sb5+/Sb3+ and Nb5+/Nb4+ aliovalences is found to exist in NaCu3Ti3Sb0.5Nb0.5O12 ceramics through XRD and XPS analysis. Internal barrier layer capacitance effect is suggested to be the origin of the high dielectric-permittivity properties in NaCu3Ti3Sb0.5Nb0.5O12 ceramics.

Giant dielectric properties of fine-grained Na1/2Y1/2Cu3Ti4O12 ceramics prepared by mechanosynthesis and spark plasma sintering

Fine-grained ceramics of Na1/2Y1/2Cu3Ti4O12 (NYCTO) were prepared by spark plasma sintering (SPS) of mechanosynthesized nano-powder. Effect of SPS temperature from 900 up to 1000 °C on the microstructure, phase structure and the dielectric and transport properties of NYCTO ceramics has been studied. The structural studies by X-ray powder diffraction indicated the formation of pure cubic phase of the NYCTO ceramics up to SPS temperature of 975 °C. Decomposition of the NYCTO material was observed with increasing the SPS temperature to 1000 °C. The mictrostructural studies by FE-SEM showed that the grain size increases from 245 to 520 nm when increasing the SPS temperature from 900 to 1000 °C. The dielectric and transport properties of the investigated materials have been studied by impedance spectroscopy in the 120–470 K temperature range. All of the SPS NYCTO ceramics exhibit giant dielectric constant with the highest value of 3 × 103 observed for the sample sintered at 975 °C. The observed giant dielectric response is assigned to the internal barrier layer capacitance effect, which originates from the electrical heterogeneous structure of the materials. This picture is supported by the impedance and modulus spectra of the investigated materials where semiconducting grains separated by insulating grain boundaries are observed.

Enhanced extrinsic dielectric response of TiO2 modified CaCu3Ti4O12 ceramics

TiO2 modified CaCu3Ti4O12 (CCTO) has been synthesized via a facile sol–gel precipitation process followed by solid state sintering. The influence of the precipitated TiO2 crystallites on the microstructure, phase composition, and dielectric properties of CCTO has been investigated. The morphology and chemistry of grain boundaries in CCTO ceramics can be significantly tailored by the initial TiO2 crystallites, which results in enhanced barrier layer capacitor structures. The formation mechanism of barrier layers based on the instability of Cu ions has been discussed. A new bimodal brick layer mechanism has been proposed to explain the effect of TiO2 modification. The optimized TiO2 modified CCTO sample exhibits stable dielectric permittivity which is twice as high as the unmodified one, and shows relatively low dielectric loss over the frequency range from 102 to 105Hz. Such enhancement is deemed to arise from the modified and bimodal internal barrier layer capacitor effect.

Colossal permittivity and dielectric relaxations in BaTi0.99(Nb0.5Ga0.5)0.02O3 ceramics

Dielectric properties of pure phase BaTi0.99(Nb0.5Ga0.5)0.02O3 ceramics, prepared via a conventional solid-state method, have been studied in the frequency range 0.01Hz–10MHz, at temperatures −130°C to 200°C. Colossal dielectric constant, εr~2×105, and low dielectric loss, tanδ~0.05 at 1kHz have been obtained. The permittivity showed weak frequency dependency in a broad range of frequency from 1Hz to 30kHz and less than ±20% capacitance deviation over the temperature range from 243 to 358K. The AC impedance spectroscopy analysis indicated three relaxation mechanisms, the electrode interfacial polarization, internal barrier layer capacitor effect and hopping polaron polarization contributed to the colossal dielectric constant.

Giant dielectric permittivity and electronic structure in (Al + Sb)co-doped TiO2 ceramics

Dielectric properties of (Al+Sb) co-doped TiO2 (ASTO) ceramics prepared by a solid state reaction method were investigated. It was found that sintering temperature had a remarkable influence on the microstructure of ASTO ceramics. The mean grain size largely increased with increasing sintering temperature from 1300 to 1500°C. Interestingly, the dielectric permittivity of ASTO ceramics was significantly reduced from 6572 to 454 at 102Hz as the mean grain size increased. Therefore, the primary contribution to the observed high dielectric response in ASTO ceramics is not related to the internal barrier layer capacitor effect. The charge analysis revealed that the existence of both Al and O vacancy caused creation of defect-dipole moments in the TiO2 structure. Similarly, the Sb atoms could also generate the charge trapping in this structure. Consequently, high dielectric response in the ASTO ceramics is significantly enhanced in comparison to the un-doped TiO2 ceramic.

Intrinsic and extrinsic dielectric responses in BiCu3Ti3FeO12 ceramics

BiCu3Ti3FeO12 ceramics with cubic perovskite-related crystal structure were prepared by a solid-state reaction method. Both the intrinsic and extrinsic dielectric responses of the ceramics are investigated. When being calcined at 800°C and sintered at 980°C for 20h, BiCu3Ti3FeO12 ceramics are relatively dense, which exhibit a high intrinsic dielectric constant (~500 at 30°C). Interestingly, a giant permittivity (>5000) of the ceramics is observed at high temperature, which is attributed to an extrinsic effect. Based on the results of electric impedance and modulus, it can be concluded that the giant permittivity results from the internal barrier layer capacitance effect.

Preparation process, microstructure and dielectric properties of Na0.5La0.5Cu3Ti4O12 ceramics by a sol–gel method

Effect of concentration, water content (molar ratio of the water and titanium) and pH value of the sol, and sintering temperatures and holding time on microstructure and dielectric properties of Na0.5La0.5Cu3Ti4O12 (NLCTO) ceramics by a sol–gel method were investigated in detail, respectively. It is found that the optimum concentration, the molar ratio of the water and titanium, and pH value of the sol were 1.00 mol/L, 11.0, and 0.3, respectively. The NLCTO ceramics sintered at 1,080 °C for 10 h exhibited more homogeneous microstructure, higher dielectric constant (about 1.1–1.8 × 104) and lower dielectric loss (about 0.051–0.064 at 1–10 kHz). The higher dielectric constant of the NLCTO ceramics might be due to the internal barrier layer capacitor effect. The NLCTO ceramics prepared by the sol–gel method showed two kinds of dielectric relaxation at higher temperature by electric modulus analysis, and two relaxation activation energy values were obtained.

IBLC effect leading to colossal dielectric constant in layered structured Eu2CuO4 ceramic

Dielectric (εr′) studies of phase pure T′-type Eu2CuO4 ceramics of two markedly different grain sizes (D), prepared by (i) conventional powder mixing and (ii) citrate complexation-Pechini process, have been carried out in the frequency range 0.1Hz to 1MHz, and at temperatures −100°C to 150°C. εr′ is found to be highly grain size dependent. For the sample with coarse bar-like grains (D2~17×6μm2) εr′ is >103, and for the finer grain size sample with bimodal distribution (D1~1μm, D2~3μm) εr′ is ~105; for both the samples, high εr′ value is nearly frequency independent over 500Hz≤f<100kHz and T≥30°C. The impedance spectroscopy (IS) study has clearly shown that both, the coarse- and the fine-grained samples consist of semiconducting grains and insulating grain boundaries that primarily lead to an internal barrier layer capacitance (IBLC) effect. And thus, manifest colossal dielectric constant (εr′>103) in Eu2CuO4 ceramics. The smaller grain size (Pechini) sample, with over an order higher number of grains and grain boundary network, showing over an order higher εr′ (~105) compared to the coarse grained one, further endorses the IBLC effect.

Dielectric properties of giant permittivity NaCu3Ti3NbO12 ceramics

Abstract A series of NaCu 3 Ti 3 NbO 12 ceramics was fabricated by the conventional solid-state reaction method, and their microstructures, phase structures, electric and dielectric properties were systematically investigated. Single phase of NaCu 3 Ti 3 NbO 12 with body-centered cubic perovskite-related structure was confirmed by X-ray diffraction. Normal grain growth was observed, and the average size of grains was limited to less than 6 µm. Impedance spectroscopy analysis reveals that NaCu 3 Ti 3 NbO 12 ceramics are electrically heterogeneous, consisting of semiconducting grains and insulating grain boundaries. The activation energy for the dc conduction process is comparable to that for conduction at the grain boundaries, indicating that the dc conduction process is associated with the electric response of grain boundaries in NaCu 3 Ti 3 NbO 12 ceramics. The dielectric properties can be well described by the internal barrier layer capacitor effect based on Maxwell–Wagner polarization at grain boundaries.

Origin of colossal permittivity in BaTiO3 via broadband dielectric spectroscopy

Barium titanate (BT) ceramics with Ba/Ti ratios of 0.95 and 1.00 were synthesized using spark plasma sintering (SPS) technique. Dielectric spectroscopy (frequency range from 40 Hz to 1 MHz and temperature range from 300 K to 30 K) was performed on those ceramics (SPS BT). SPS BT showed extremely high permittivity up to ∼105, which can be referred to as colossal permittivity, with relatively low dielectric loss of ∼0.05. Data analyses following Debye relaxation and universal dielectric response models indicate that the origin of colossal permittivity in BT ceramics is the result of a hopping polaron within semiconducting grains in combination with interfacial polarization at the insulating grain boundary. Furthermore, the contributions of each polarization mechanism to the colossal permittivity in SPS BT, such as a hopping polarization, internal barrier layer capacitance effect, and electrode effect, were estimated.

AC electrical properties of TiO2 and Magnéli phases, TinO2n − 1

This paper presents a comprehensive impedance spectroscopy comparison of the AC properties of dense stoichiometric TiO2 and conductive TinO2n−1 Magnéli phases over a broad temperature range (up to 1000°C for TiO2 and 375°C for TinO2n−1). The frequency dependent conductivity and permittivity of both materials is explained in terms of “universal” power law behaviour. A deviation from the law, with a giant relative permittivity which is largely independent of frequency from 0.1Hz to 100–200kHz is observed in the case of TinO2n−1, due to the presence of residual TiO2 generating an Internal Barrier Layer Capacitor (IBLC) effect. The real–imaginary impedance plots are interpreted using an RC model and allow separation of the contribution of the grain bulk and the grain boundaries to the total resistivity of the material. In the case of the TinO2n−1 based materials this confirms that the IBLC effect is generated by insulating grain boundaries. The conduction mechanism in both TiO2 and TinO2n−1 appears to be dominated by electronic conductivities, activated mainly through shallow donor levels up to 200°C and over the entire band gap, which is narrower for TinO2n−1, above 200°C. A deeper understanding of the AC properties of Magnéli phases of Ti at different temperatures aids in the optimisation of electrical properties for a variety of sensor and electrical applications.

Giant dielectric and electrical properties of sodium yttrium copper titanate: Na1/2Y1/2Cu3Ti4O12

The electrical properties and dielectric response in Na1/2Y1/2Cu3Ti4O12 ceramic prepared by conventional solid-state reaction method and sintered at 1,090 °C for 5 h were investigated as functions of frequency and temperature. Main phase of Na1/2Y1/2Cu3Ti4O12 with CaCu3Ti4O12-like crystallographic structure and CuO secondary phase were observed in the X-ray diffraction pattern. Abnormal grain growth was observed just as observed in CaCu3Ti4O12 ceramics. The Na1/2Y1/2Cu3Ti4O12 ceramic exhibits a high e′ of ~2.04 × 104 at 20 °C and 1 kHz and low tan δ (with the minimum 0.080 at 5 kHz). Impedance spectroscopy analysis reveals that Na1/2Y1/2Cu3Ti4O12 ceramic is electrically heterogeneous, consisting of semiconducting grains and insulating grain boundaries. Giant e′ response in Na1/2Y1/2Cu3Ti4O12 ceramic is therefore attributed to an internal barrier layer capacitor effect.

Nanoscale electrical probing of heterogeneous ceramics: the case of giant permittivity calcium copper titanate (CaCu3Ti4O12)

Scanning Probe Microscopy with conductive tips has been used to image and study the dielectric properties of giant permittivity CaCu3Ti4O12 ceramics at the nanoscale. Since measurements are generally carried out on sections of a sample, particular attention has been devoted to possible artefacts due to surface imperfections, such as substantial surface roughness and/or contamination that can result in controversial interpretation, particularly at nanometric spatial dimensions. A reliable surface investigation has been carried out after the definition of both the physical and geometrical unbiased criteria to avoid any artefacts due to surface roughness and/or anomalous tip-sample contact variations. The presence of insulating grain boundaries and the measurement of a depletion layer at the grain-grain boundary interfaces unambiguously demonstrate the relevance of the Internal Barrier Layer Capacitor effect, among all the proposed physical mechanisms, to explain the giant dielectric behaviour. Such imaging provided a clear correlation between the macroscopic dielectric properties and the nanometric structure at the interfaces. Moreover, the "general criteria" for reliable nanoelectrical characterization as well as the related measurement resolution have been defined.

Giant Dielectric Permittivity Properties and Relevant Mechanism of NaCu3Ti3SbO12 Ceramics

A series of NaCu3Ti3SbO12 ceramics were prepared by the conventional solid-state reaction technique under different sintering temperature conditions. Their crystalline structure, microstructure, dielectric properties, and complex impedance were systematically investigated. It has been found that they are in general quite similar to CaCu3Ti4O12 ceramics reported in the literature, showing giant dielectric permittivity properties with ɛ′ as high as 104. Within the measuring frequency range of 40–100 MHz, a single dielectric relaxation with the characteristic frequency around 1 MHz is seen at room temperature or below, whereas an additional one in the low-frequency region is also observed at high temperatures. Dielectric properties and microstructures change largely with sintering temperature, and a small amount of CuO secondary phase and Cu2+/Cu+, Ti4+/Ti3+ and Sb5+/Sb3+ aliovalences exist in these NaCu3Ti3SbO12 ceramics. On the basis of an electrode comparison experiment, the two dielectric relaxations are ascribed to an internal barrier layer capacitance effect and an electrode polarization effect, respectively.

Giant Dielectric‐Permittivity Phenomena of Compositionally and Structurally CaCu3Ti4O12‐Like Oxide Ceramics

SrCu3Ti4O12, La2/3Cu3Ti4O12, and Bi2/3Cu3Ti4O12 ceramics were representatively investigated to obtain a systematical understanding about the dielectric behaviors of the compositionally and structurally CaCu3Ti4O12‐like oxides and the underlying related mechanism. In opposite to the literature results, giant dielectric‐permittivity phenomena with low‐frequency ɛ′ larger than 1.5 × 104 have been observed in all of these ceramics. Furthermore, the existence of CuO secondary phase has been confirmed in them. In general, the results can be explained by the similar mechanism of internal barrier layer capacitance effect formerly proposed for CaCu3Ti4O12 ceramics and indicate that the giant‐ɛ′ phenomena should be quite common in the large family of compositionally and structurally CaCu3Ti4O12‐like oxide ceramics.

Dielectric and optical properties of CaCu 3Ti 4O 12 thin films containing Ag nanoparticles

Simple sol–gel techniques are used to prepare thin films of a high dielectric constant perovskite CaCu 3Ti 4O 12, containing different amounts of metallic silver nanoparticles. The formations of the silver nanoparticles are verified by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and optical absorption studies. The dielectric properties are found to be significantly affected by the presence of the silver nanoparticles. A maximum in the dielectric constant is observed at an intermediate metal particle concentration. This is explained in terms of the polarization at the particle–dielectric interface and the internal barrier layer capacitor effect. The optical absorption spectrum is compared with Mie theory in electrodynamics for the optical absorption of small particles to extract the particle size of the silver particle. Non-uniform distributions of Ag particles through the thickness of the thin films are reported.

Giant dielectric constant response of the composites in ternary system CuO–TiO 2–CaO

The subsolidus phase relations of the ternary system CuO–TiO 2–CaO sintered at 950 °C in air have been determined by powder X-ray diffraction method. Only one ternary compound CaCu 3Ti 4O 12 was found in this system. From room-temperature dielectric property mapping at 10 kHz, a giant dielectric constant ( ε r >10 4) was observed for most of the ceramic composites in the CuO-rich region and in the region along the CaO–CuO binary line. The composites in the CaCu 3Ti 4O 12-rich region were found to give a comparable giant dielectric constant when sintered at 1050 °C. The particular microstructure of larger grains with predominant phase surrounded by smaller grains with the secondary phases was found in such composites with a high dielectric constant. The relations between structures and dielectric properties were investigated. An internal barrier layer capacitance effect is the most probable mechanism to explain this particular dielectric behavior.

Microstructure and dielectric properties of NaxTiyNi1−x−yO (x = 0.05–0.30, y = 0.02)

The microstructure of NaxTiyNi1−x−yO (abbreviated as NaTNO), a high dielectric material, has been investigated by scanning electron microscopy. Dielectric dispersion and complex impedance of NaTNO ceramics (in the frequency range 10–107 Hz) are discussed. The relatively lower value of the dielectric constant (ε′) of NaTNO compared with those of LixTiyNi1−x−yO (LTNO) and KxTiyNi1−x−yO (KTNO) is attributed to the typical distinguishing behaviour of its microstructure. Ac impedance spectroscopic studies indicate that the internal barrier layer capacitance effect, arising from differing electrical properties of grains and grain boundaries, is responsible for high dielectric permittivity of this non-ferroelectric material. The ratios of dielectric dispersion strengths, in the low (<100 kHz) and high (>100 kHz) frequency ranges, increase with an increase in the Na content. Deviation of the measured ε′ value of NaTNO from that predicted by the boundary layer capacitance mechanism is attributed to its typical microstructure.

Internal Barrier Layer Capacitance Effect in Hexagonal Perovskite Ba4YMn3O11.5 Ceramics

Ba4YMn3O11.5, a 12R hexagonal perovskite that consists of face-sharing Mn3O12 trimers isolated by single YO6 octahedral layers, is presented. The presence of locally 5- and 6-coordinated Y3+ and Mn4+ cations is observed in this structure. A high dielectric permittivity (er ≈ 1 × 104), which is almost frequency independent over the ∼1 × 102 to 1 × 105Hz range from room temperature to 120 °C, has been observed in ceramics of this material. AC impedance spectroscopy indicates that the internal barrier layer capacitance effect arising from the differing electrical properties of the grains and grain boundaries is responsible for the high dielectric permittivity of this non-ferroelectric material.