Giant permittivity up to 100 MHz in La and Nb co-doped rutile TiO2 ceramics

Dielectric spectroscopy was carried out for reduced and stoichiometric La_0.0025Nb_0.0025Ti_0.995O₂ ceramics synthesized by sintering in different atmospheres. A giant permittivity (~1 × 10⁴) was obtained at a frequency of 100 MHz and temperature range from 170 to 350 K. Three dielectric relaxation mechanisms were observed within the temperature range of 10-300 K via dielectric spectroscopy. A low temperature dipole relaxation peak (in the temperature range of 10-30 K) in the spectra was identified to be associated with the giant permittivity specifically measured at 100 MHz. The origin of such giant permittivity was attributed to dipole orientation polarization. Hopping polaron and interfacial effect contributed to giant permittivity. After annealing treatment, all the relaxation contributions were weakened. Low dielectric loss was attributed to high resistance of grain and grain boundaries. Annealing in ambient conditions led to decreased relaxation times which gives the signature of decreased concentration of oxygen vacancies and Ti³⁺. Dipoles which were related to oxygen vacancies and Ti³⁺, resulted in giant permittivity up to 100 MHz.     

Optimize the dielectric properties of CaCu3Ti4O12 ceramics by adjusting the conductivities of grains and grain boundaries

Reduction of dielectric loss for CCTO ceramics is a prerequisite for their applications. Considering internal barrier layer capacitance effect, improving the capacitance and grain boundary resistance is an effective way to reduce dielectric loss. Therefore, more conductive Ti³⁺ and Cu⁺ ions were introduced to grains by adding carbon to ceramic bodies, improving the permittivity of CCTO ceramics. Annealing was performed to increase the grain boundary resistance. The dielectric loss of the CCTO ceramics thus prepared, which maintain a giant permittivity, is significantly reduced. Specifically, the CCTO ceramic with carbon addition, which was sintered at 1080 °C for 8 h and air annealed at 950 °C for 2 h, exhibits a giant permittivity of about 2.50(5)×10⁴ and a low dielectric loss of less than 0.050(2) from below 20 Hz to 50 kHz at room temperature. Meanwhile, its dielectric loss at 1–10 kHz is less than 0.050(2) from below room temperature to about 100 °C.     

Giant permittivity and low dielectric loss of SrTiO3 ceramics sintered in nitrogen atmosphere

The dielectric properties of SrTiO₃ ceramics sintered in nitrogen (N₂) exhibit a weak temperature- and frequency-dependent giant permittivity (>10⁴) as well as a very low dielectric loss (mostly < 0.02) over a broad temperature range from −100 to 200 °C. Based on the results of ac conductivity and structural analysis, the giant permittivity and low dielectric loss were due to the fully ionized oxygen vacancies and giant defect-dipoles. When further sintering these ceramics in air, the materials exhibit a large temperature- and frequency-dependent high dielectric loss, which were due to the ionization and motion of oxygen vacancies.     

Good dielectric performance and broadband dielectric polarization in Ag,Nb co-doped TiO2

Due to the demand of miniaturization and integration for ceramic capacitors in electronic components market, TiO₂-based ceramics with colossal permittivity has become a research hotspot in recent years. In this work, we report that Ag⁺/Nb⁵⁺ co-doped (Ag_1/4Nb_3/4)_xTi_1−xO₂ (ANTOx) ceramics with colossal permittivity over a wide frequency and temperature range were successfully prepared by a traditional solid–state method. Notably, compositions of ANTO0.005 and ANTO0.01 respectively exhibit both low dielectric loss (0.040 and 0.050 at 1 kHz), high dielectric permittivity (9.2 × 10³ and 1.6 × 10⁴ at 1 kHz), and good thermal stability, which satisfy the requirements for the temperature range of application of X9R and X8R ceramic capacitors, respectively. The origin of the dielectric behavior was attributed to five dielectric relaxation phenomena, i.e., localized carriers' hopping, electron–pinned defect–dipoles, interfacial polarization, and oxygen vacancies ionization and diffusion, as suggested by dielectric temperature spectra and valence state analysis via XPS; wherein, electron-pinned defect–dipoles and internal barrier layer capacitance are believed to be the main causes for the giant dielectric permittivity in ANTOx ceramics.     

Grain boundary engineering that induces ultrahigh permittivity and decreased dielectric loss in CdCu3Ti4O12 ceramics

Dielectric materials with ultrahigh permittivity are attracting attention due to the increasing demand for these types of materials for microelectronics and energy storage applications. In this work, we successfully synthesized Zn-doped CdCu₃Ti₄O₁₂ (CdCTO) ceramics with low dielectric loss and large permittivity via an ordinary mixed-oxide technique. Remarkably, at a Zn doping level of 0.10, a CdCu_2.9Zn_0.1Ti₄O₁₂ ceramic exhibited both decreased dielectric loss tangent of ~0.058 and large dielectric permittivity > 4.0 × 10⁴, as well as a good frequency stability over a wide frequency range from 40 Hz to 10⁶ Hz. The high dielectric performance was attributed to the enhanced grain boundary resistance and internal barrier layer capacitor (IBLC) effect due to the fine and uniform grains that formed upon Zn doping. The findings reported in this work provide valuable insights into how to simultaneously realize a low dielectric loss and high permittivity in CdCTO and other related dielectric ceramics.     

An effective optimization strategy and analysis for BaTiO3–Na0.5Bi0.5TiO3 system with colossal permittivity

Colossal permittivity (CP, ε＞10⁴) behavior in BaTiO₃–Na_0.5Bi_0.5TiO₃ (BT-NBT) ceramics has been studied, which showed extremely high permittivity up to ~10⁵. Dielectric properties of samples showed Debye-like relaxations in the frequency range 20 Hz–30 MHz. Two different polarizations located in grain boundaries and grains respectively are responsible for the CP behavior and the models of defect charge compensation achieved by niobium doping are proposed to explain the phenomenon of abnormal variation of dielectric constant.By using defect engineering, a Nb-doped BaTiO₃ ceramics with stable colossal permittivity (ε_r =1.3×10⁴ at 1 kHz and room temperature),high bulk resistivity (>10¹⁰ Ω·cm) as well as relative low dielectric loss (tanδ~0.06) has been obtained over a wide temperature range of −55–150 °C, satisfying IEA X8R specification, which has a potential application prospect in high capacity solid supercapacitor.     

Controllable low-temperature flash sintering and giant dielectric performance of (Zn,Ta) co-doped TiO2 ceramics

In this study, the challenge of high-temperature and long-time sintering of (Zn, Ta) co-doped TiO₂ ceramics is solved successfully using flash sintering technology. Joule heating and a high heating rate make the sample compact rapidly at low temperatures (1050 °C in 24 min). When the electric field was equal to 200 V/cm, high permittivity (ε' ～ 1.32 × 10⁴), low dielectric loss tangent (tan δ ～ 0.27), and nonlinear coefficient ($\alpha$ ～ 5.8) values were obtained. Flash sintered samples have more free electrons, resulting in a high dielectric constant. Further, the higher the electric field, the smaller the grain resistance of the sample; this condition is conducive to reducing dielectric loss. giant dielectric performance is explained by the combined action of the electron-pinned defect dipole theory and the internal barrier layer capacitance effect. Therefore, this study provides a promising prospect for the green preparation of co-doped TiO₂ giant dielectric ceramics.     

Giant permittivity in Nb-doped SrTiO3 single crystal: Compositional gradient and local structure

Nb-doped SrTiO₃ single crystal exhibited a giant permittivity (>6.5 × 10⁵) with an acceptably low dielectric loss (<10^?1) in a wide temperature range from ?120 to 200 °C, making this material a good candidate for energy storage devices and modern microelectronics components. The mechanisms responsible for the giant permittivity of Nb-doped SrTiO₃ single crystals were studied by means of microstructure characterizations, dielectric measurements, and density-functional theory calculations. A chemical compositional gradient extending from the surfaces was found, forming the internal barrier layer capacitance (IBLC) effect. Polar nanoregions (PNRs) were observed because of local fluctuations in distributions of Nb and oxygen vacancies. While both compositional gradients and local chemistry fluctuations increased polarization of the Nb-doped SrTiO₃ single crystals, the local fluctuations dominated enhanced polarizability. This work suggests that optimizing local structures and chemistries in dielectrics is an effective way to tailor the desired dielectric performance.     

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

Giant 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 (In_0.5Nb_0.5)_xTi_1?xO₂ ceramics can be achieved by eliminating the electrode effect and forming a resistive outer surface layer.     

Frequency and temperature independent (Nb0.5Ga0.5)x(Ti0.9Zr0.1)1-xO2 ceramics with giant dielectric permittivity and low loss

Nb⁵⁺ and Ga³⁺ co-doped Ti_0.9Zr_0.1O₂ ceramics were synthesized using the conventional solid-state reaction method. Single rutile-liked phase of octahedron structure were identified for all compositions in (Nb_0.5Ga_0.5)_x(Ti_0.9Zr_0.1)_1-xO₂ (NGT) with x = 0.01 to 0.10 by X-ray diffraction patterns coupled with Rietveld refinement. Microstructural scanning image, together with energy dispersive x-ray spectroscopy (EDX), revealed good chemical homogeneity in NGT samples. A giant dielectric permittivity of 5 × 10⁴ and a low loss of 0.02 was obtained in NGT with x = 0.01 due to the contribution of electron-pinned and defect-dipole effect. Furthermore, a temperature (-20–120 °C), frequency (0.1–10⁴ Hz) and bias electric field (100–200 V/mm) independent dielectric permittivity and loss was found in this composition, which is critical for potential applications of supercapacitors.     

Effect of Sn4+–Isovalent doping concentration on giant dielectric properties of SnxTa0.025Ti0.975-xO2 ceramics

The Sn_xTa_0.025Ti_0.975-xO₂ (x%Sn(TTO)) ceramics with x = 2.5–10% were prepared using a standard mixed-oxide method and sintered at 1450 °C for 3 h to achieve a dense microstructure. The effects of the isovalent–Sn⁴⁺ doping concentration on the crystal structure, microstructure, giant dielectric behavior, and electrical properties were systematically investigated. Continuously enlarged lattice parameters and bond lengths with a single rutile–TiO₂ phase were observed as x% increased. The mean grain size was slightly reduced (～17.3–14.6 μm) due to an increased oxygen vacancy and the solute drag effect. The dielectric permittivity (ε′) decreased with increasing x%, whereas the loss tangent (tanδ) was remarkably reduced. The semiconducting grain resistance of the x%Sn(TTO) ceramics remained unchanged owing to the same Ta⁵⁺ donor concentration. The insulating grain boundary (GB) resistance was extremely increased by more than two orders of magnitude when x% increased from 2.5 to 5.0%, leading to the significantly improved giant dielectric properties. The optimized low tanδ～0.02 and high ε′～10⁴ with temperature coefficient less than ±15% in the range of -60–210 °C were reasonably described by the internal barrier layer capacitor model. Improved dielectric properties can be obtained by engineering GB by varying the Sn⁴⁺–isovalent doping concentration. This study provides an important approach for improving the dielectric properties of co–doped TiO₂ without the creation of complex defect clusters inside the grains.     

Colossal dielectric permittivity and relevant mechanism of Bi2/3Cu3Ti4O12 ceramics

Bi_2/3Cu₃Ti₄O₁₂ (BCTO) ceramics with pure perovskite phase were successfully prepared by traditional solid-state reaction technique. Uniformly distributed and dense grains with the grain size of 2–3 μm were observed by SEM. A giant low-frequency dielectric permittivity of ~3.3×10⁵ was obtained. The analysis of complex impedance revealed that Bi_2/3Cu₃Ti₄O₁₂ ceramics are electrically heterogeneous. There are three kinds of dielectric response detected in Bi_2/3Cu₃Ti₄O₁₂ ceramics, which existed in the low-frequency range, middle-frequency range, and high-frequency range, respectively. Through the study of dielectric spectrum at different temperatures, the relatively low activation energy of 0.30 eV for middle-frequency dielectric response was calculated, which suggested that this Middle-frequency dielectric response can be ascribed to grain boundaries response. In view of the analysis of dielectric spectrum at low temperatures, the activation energy of 0.07 eV for high frequency dielectric response was found. This value illustrated that dielectric response at high frequencies was associated with grains polarization effect. The comparison of dielectric spectra of Bi_2/3Cu₃Ti₄O₁₂ ceramics with different types of electrodes revealed that giant low-frequency dielectric constant was attributed to the electrode polarization effect.     

Dielectric Relaxation in Zr‐Doped SrTiO3 Ceramics Sintered in N2 with Giant Permittivity and Low Dielectric Loss

SrTiZr_xO₃ (x = 0, 0.002, 0.006, 0.01, and 0.014) ceramics with a weak temperature‐dependent giant permittivity (>10⁴) and a very low dielectric loss (<0.01) were fabricated using the conventional solid‐state reaction method by sintering them in N₂ at 1500°C. With increasing Zr content, the permittivity decreased from approximately 48 000 to 18 000 and the dielectric loss decreased from approximately 0.005 to 0.003. According to the XRD, XPS, and ac conductivity analysis, the dielectric properties of pure SrTiO₃ ceramics sintered in N₂ were due to the existence of the giant defect dipoles generated by the fully ionized oxygen vacancies and Ti³⁺ ions, while the dielectric properties of SrTiZr_xO₃ (x > 0) ceramics were also influenced by the defect dipoles (). The giant permittivity and low dielectric loss phenomenon could be explained by giant defect dipoles related to oxygen vacancies.     

A Novel Magnetodielectric Solid Solution Ceramic 0.4LiFe5O8–0.6Li2MgTi3O8 with Excellent Microwave Dielectric Properties

In this study, a novel spinel solid solution ceramic of 0.4LiFe₅O₈–0.6Li₂MgTi₃O₈ (0.4LFO–0.6LMT) has been developed and investigated. It is found that the 40 mol% LiFe₅O₈ and 60 mol% Li₂MgTi₃O₈ are fully soluble in each other and a disordered spinel phase is formed. The ceramic sample sintered at 1050°C/2 h exhibits both good magnetic and dielectric properties in the frequency range 1–10 MHz, with a permeability between 29.9~14.1 and magnetic loss tangent between 0.12~0.67, permittivity between 16.92~16.94 and dielectric loss tangent between 5.9 × 10^?3–2.3 × 10^?2. The sample also has good microwave dielectric properties with a relative permittivity of 16.1, a high quality factor (Q × f) ~28 500 GHz (at 7.8 GHz). Furthermore, 3 wt% H₃BO₃–CuO (BCu) addition can effectively lower the sintering temperature to 925°C and does not degrade the magnetodielectric properties. The chemical compatibility with silver electrode indicates that this kind of ceramics is a good candidate for the low‐temperature cofired ceramic (LTCC) application.     

Sintering behavior,structure and dielectric properties of CuO-ZnO-MgO-B2O3 glass-ceramics for ULTCC applications

High performance ultra-low temperature co-fired ceramic (ULTCC) materials were prepared from CuO- MgO- ZnO- Al₂O₃- B₂O₃- Li₂O glass-ceramics. The sintering behaviors, crystalline phase evolution, microstructure and dielectric properties, as well as their compatibility with Ag and Al electrodes, were investigated. With the suitable substitution of MgO for ZnO, the dielectric properties of glass-ceramics were improved. It is mainly associated with the fine microstructure, highly crystallinity, and decrease in tetrahedral distortion in the crystal lattice. All the glasses completed the densification at 575–600 °C, and ZnB₄O₇ is the only crystalline phase precipitated from the glasses. Moreover, the glass-ceramic with 1 wt% MgO sintered at 575 °C for 5 h, exhibited low relative permittivity ~ 7.1 and low dielectric loss ~ 6.40 × 10^?4. And the glass-ceramic with 4 wt% MgO sintered at 600 °C for 5 h, also displayed low relative permittivity ~ 7.1 and low dielectric loss ~ 5.77 × 10^?4. Both two glasses have good sintering compatibility with silver and aluminum electrodes, which provided high potential for ULTCC application.     

Good thermal stability,giant permittivity,and low dielectric loss for X9R-type (Ag1/4Nb3/4)0.005Ti0.995O2 ceramics

With the intense demand of the developing microelectronics market, the study of giant permittivity dielectric materials is being promoted. However, it is difficult to obtain suitable dielectric materials for such applications, especially due to high dielectric loss at low frequencies. In this work, Ag+Nb codoped TiO₂ ceramics were designed and fabricated in a conventional solid reaction by sintering at 1290-1340°C for 5-10 hours. The issue of how the microstructure and dielectric properties of (Ag_1/4Nb_3/4)_0.005Ti_0.995O₂ ceramics are affected by the sintering conditions was discussed. By optimizing sintering conditions, a dense microstructure, a high dielectric constant (ε_r ≈ 9410), and a low dielectric loss (tanδ ≈ 0.037) at 1 kHz were achieved. Most importantly, the temperature coefficient value of ε_r at different frequencies remained stable between −14.3% and 13.7% within the temperature range from −190 to 200°C, which has potential applications in X9R capacitor.     

Ge4+ doped CaCu2.95Zn0.05Ti4O12 ceramics: Two-step reduction of loss tangent

CaCu₃Ti₄O₁₂ ceramics have been extensively studied for their potential applications as capacitors in recent years; however, these materials exhibit very large dielectric losses. A novel approach to reducing the dielectric loss tangent in two steps, while increasing the dielectric permittivity, is presented herein. Doping CaCu₃Ti₄O₁₂ with a Zn dopant reduces the loss tangent of the ceramic material from 0.227 to 0.074, which is due to the increase in grain boundary (GB) resistance by an order of magnitude (from 6.3× 10³ to 3.93 × 10⁴ Ω cm). Zn-doping slightly changes the microstructure and dielectric permittivity of the CaCu₃Ti₄O₁₂ ceramic, which reveals that the primary role of the Zn dopant is to tune the intrinsic properties of the GBs. Surprisingly, the addition of the Ge⁴⁺ dopant into the Zn²⁺-doped CaCu₃Ti₄O₁₂ ceramic sample led to a further decrease in the loss tangent from 0.074 to 0.014, due to enhanced GB resistance (3.1 × 10⁵ Ω cm). The grain size increased remarkably from 2–3 μm to 85–90 μm, corresponding to a significant increase in the dielectric permittivity (~1–4 × 10⁴). The large increase in GB resistance is due to the intrinsic potential barrier height at the GBs and the segregation of the Cu-rich phase in the GB region. First-principles calculations revealed that Zn and Ge are preferentially located at the Cu sites in the CaCu₃Ti₄O₁₂ structure. The substitution of the Ge dopant does not hinder the role of the Zn dopant in terms of improving the electrical properties at the GBs. These phenomena are effectively explained by the internal barrier layer capacitor model. This study provides a way of improving the dielectric properties of ceramics for their practical use as capacitors.     

Dielectric Properties of Sol–Gel‐Derived Bi12SiO20 Thin Films

In this paper the dielectric properties of crack‐free, Bi₁₂SiO₂₀ thin films were investigated. The films were prepared on Pt/TiO₂/SiO₂/Si and corundum substrates using the sol–gel method. The formation of a pure Bi₁₂SiO₂₀ phase was observed at a temperature of 700°C. The Bi₁₂SiO₂₀ thin films, heat treated at 700°C for 1 h, had a dense microstructure with an average roughness (R_a) of 50 nm. The dielectric properties of the film were characterized by using both low‐ and microwave‐frequency measurement techniques. The low‐frequency measurements were conducted with a parallel capacitor configuration. The dielectric constant and dielectric losses were 44 and 7.5 × 10^?3, respectively. The thin‐film dielectric properties at the microwave frequency were measured using the split‐post, dielectric resonator method (15 GHz) and the planar capacitor configuration (1–5 GHz). The dielectric constant and the dielectric losses measured at 15 GHz were 40 and 17 × 10^?3, respectively, while the dielectric constant and the dielectric losses measured with the planar capacitor configuration were 39 and 65 × 10^?3, respectively.     

Enhanced dielectric performance of (Ag1/4Nb3/4)0.01Ti0.99O2 ceramic prepared by a wet-chemistry method

The (Ag_1/4Nb_3/4)_0.01Ti_0.99O₂ ceramic, with ultra-high permittivity and relatively low dielectric loss, was synthetized by a sol-seed method. Significant influences of Ti concentration on the phase structure, microstructure, and dielectric performances were observed. By optimizing the Ti concentration, high active powders and effectively controlled grain uniformity were obtained, which is great benefit for depressing the calcining temperature. The sample shows an ultra-high permittivity (ε_r ~43271 at 1 kHz) and relatively low dielectric loss (tanδ ~ 0.048 at 1 kHz) at room temperature, meanwhile, the temperature coefficient of ε_r keeps in ±15% within the temperature range from −78 to 130°C, fortunately for X7R capacitor. Based on the XPS results, the defect cluster structure was revealed and giant permittivity is closely associated with the electron pinned defect dipole.     

Suppressing resistance degradation in SrTiO3-based colossal permittivity capacitor material

At present, research on colossal permittivity materials is extensive but challenging to achieve simultaneous properties of colossal permittivity, low loss, and high resistivity. Resistance degradation also restricts industrial application of colossal permittivity materials. In this work, a new method has been proposed to improve resistivity of colossal permittivity ceramics by making metal ions diffuse on ceramic grain boundaries, thus inhibiting the diffusion of oxygen vacancies at grain boundaries. Sr_0.99La_0.01TiO₃(SLT10) ceramics were synthesized by traditional solid-state method, and then Bi₂O₃ (35%)-Al₂O₃ (10%)-MgO (20%)-CuO (25%)-SiO₂ (10%) mixed oxidant was selected to percolate into ceramics. The resistivity of SLT10 ceramics improved remarkably (from 2.1×10⁸ Ω cm to 1.23×10¹¹ Ω cm under DC 100 V) with a colossal permittivity (16695 @1 kHz) and a low dielectric loss (0.016 @1 kHz), as well as excellent frequency stability (20 Hz–2 MHz) and temperature stability (-170 °C to 375 °C). The source of high insulation resistivity of the SLT10 ceramic sample was discussed. Subsequent examination uncovered that grain in the SLT10 ceramics percolated with metal ions displayed semiconducting characteristics, wherein insulation grain boundaries significantly influenced the ceramic's resistivity and served as formidable potential barriers constraining long-range movement of charge carriers. Experimental analysis demonstrated that the resistance degradation behavior of the SLT10 ceramics was suppressed, the breakdown voltage was increased, and the service life was extended.