Dielectric Properties Of BaTiO3-based Ceramics Research Articles

Colossal permittivity with ultra-wide temperature stability in Bi + Ca co-doped BaTiO3

The poor temperature stability of the BaTiO3 ceramic has always been the main problem limiting their application. This situation has been improved but sacrifices the intrinsic polarization, which significantly reduces the dielectric constant. In this work, the mechanism of multiple polarization was creatively introduced, and the temperature stability and dielectric properties of BaTiO3-based ceramics are simultaneously enhanced. In particular, the Ba0.9925Bi0.005Ti0.995Ca0.005O2.995 (BBTC0.5) ceramic sample achieved excellent temperature stability (−14.8%–8.85%) over an ultra-wide temperature range (−47–400 oC) and exhibited colossal permittivity (27,125, 25 oC, 1 kHz) and low dielectric loss (0.07, 25 oC, 1 kHz). The dielectric properties, complex impedance spectra combined with XPS results indicate that the defective dipole clusters (, and ) along with surface effects lead to colossal permittivity effect. More importantly, SEM images show the presence of the second phase at grain boundaries, which prevent the carriers within the grains from accumulating at the grain boundaries. As a result, the dielectric loss was reduced and the temperature stability was further extended. This strategy breaks the traditional limitation of single/noncomprehensive enhancement by single-polarization mechanism, and is of great theoretical and practical significance to promote the research and application of high-performance BaTiO3-based ceramic materials.

Significantly enhanced dielectric properties of BaTiO3-based ceramics via synergetic grain size and defect engineering

As a dielectric material, BaTiO3-based ceramics are desirable for high performance ultra-thin multilayer ceramic capacitors (MLCCs) application. In this work, BaTiO3-based dielectric ceramics with superior dielectric properties were synthesized using a reducing atmosphere sintering process. It is found that the contribution of “wet" grain-boundary diffusion become significant as the oxygen partial pressure increases, resulting to a larger grain size and higher permittivity. Especially, for the specimen sintered in higher oxygen partial pressure, the stable temperature coefficient of capacitance (TCC) is dominated by irreversal domain due to the increase of super-lattice phase. Samples with higher oxygen partial pressure exhibit a higher permittivity of 2700 and better permittivity-temperature stability. Furthermore, ultra-thin MLCCs with thickness of 1 μm and capacitance of 10 μF and the TCC of X7R were successfully fabricated. This work provides a comprehensive explanation demonstrating upon the significant roles of grain size and defect engineering in the dielectric performance in BaTiO3-based ceramics, and points out an avenue to obtain excellent permittivity-temperature stability in ultra-thin MLCCs.

Dielectric properties of BaTiO3-based ceramics are tuned by defect dipoles and oxygen vacancies under a reducing atmosphere

BaTiO3-2 mol% MnYbO3-2 mol% CaZrO3-x mol Nb2O5 (x = 0, 0.3%, 0.5%, 0.7%) ceramics were successfully prepared via the conventional solid‐state method, followed by sintering in a reducing atmosphere. The effect of Nb2O5 doping on the crystal structure, micromorphology and dielectric properties of sintered samples was studied, and the correlation mechanisms between the microstructure and dielectric properties were further determined. For x = 0.5 mol%, optimal dielectric properties with high permittivity (ԑr ∼ 3570), low dielectric loss (tanδ ∼ 0.013) and large insulation resistivity (ρv ∼ 4.95 × 1011 Ω cm) are obtained. On this basis, the temperature coefficient of the capacitance (ΔC/C25°C) ranges between ±15% over the temperature range from −55 °C to 125 °C, satisfying the EIA X7R standard. Analysis shows that the increased permittivity of the doped ceramics at room temperature is due to enhanced short-range hoping polarization triggered by the formation of defect dipoles ([MnTi″−2NbTi·]× and [YbTi′−NbTi·]×) and the release of oxygen vacancies. The high insulation resistivity is related to the grain size and electron migration in the ceramics. In addition, the improvement in the temperature stability of the ceramics is ascribed to a decrease in the Curie temperature. The polarization mechanism presented in this work can be extended to BaTiO3 materials, and the results have important application value for BME-MLCC devices.

Effects of Zn2+/Mg2+ ratio on dielectric properties of BaTiO3-based ceramics with excellent temperature stability: Experiments and the first-principle calculations

To satisfy the development of MLCC devices, the dielectric properties and temperature stability of ceramic materials urgently needs to be improved. In our work, the 0.9BaTiO3-0.1Bi(ZnxMg0.5-xY0.5)O2.75 ceramics with x=0.0–0.5 are successfully prepared based on a traditional solid-state method. Meanwhile, the ceramic sample (core-shell structure) with x = 0.1 exhibits excellent dielectric properties and temperature stability (εr: 1207, tanδ: 0.009 and εr/ε25 ≤±15% within −80 to 200 °C), which satisfies the Electronic Industries Association (EIA) X9R (-55–150 °C, Δεr/ε25 ≤±15%) specification. In addition, the physical mechanism behind dielectric properties and temperature stability is systematic investigated based on experimental characterization and the first-principle calculations. The interface polarization is regarded as the primary cause affecting the dielectric properties, and has a close relationship with shell structure of ceramic samples. The lattice deformation of shell structure is caused by the introduction of heterovalent ions and non-equivalent substitution. Dielectric constant may be advance as content of Zn2+ ions increases due to the electronic enrichment around the zinc site in distorted lattice matrix. However, the weaken force between atom and electron results in the poor temperature stability.

Effects of NiO addition on structure and dielectric properties of BaTiO3-based ceramics

The phase structure, microstructure, ferroelectric and dielectric properties of NiO-modified BaTiO3-4.0 mol%Nb2O5 ceramics (BT-Nb-Ni) were systematically investigated. All the specimens revealed cubic perovskite structure along with Ba3Nb3.2Ti5O21 second phase by XRD analysis. Small amount of NiO addition (x ≤ 0.5) had the effect of inhibiting grain growth, while a further increase of NiO content (x ≥ 1.0) led to relatively large grains with an average grain size of ~ 0.40 μm. From P-E hysteresis loops and modified Curie–Weiss fitting, NiO addition first reduced and then enhanced the relaxor behaviour of the system. The er-T curves of BT-Nb-Ni ceramics were significantly flattened, leading to greatly optimized dielectric temperature stability. The optimum property was achieved in the composition BT-Nb-2.0%Ni with er = 1380 and △C/C25 °C ≤ ± 15% in the temperature range of − 65–170 °C.

Effect of Bi2O3 additive on dielectric properties of BaTiO3-based ceramics for improving energy density

ABSTRACTIn this paper, the effect of Bi2O3 additive on dielectric properties of BaTiO3-based ceramics was investigated for improving energy density. When x = 0.05, the created defect dipoles in BT–BN system achieved a balance in the system with the minimum value of Pr. Because of the created dipole, the long-range dipolar interaction was interrupted and the weak couplings of the defect dipoles were formed. Energy storage density achieved the maximum values of 0.68 J cm−3 with energy efficiency 91.5% in 0.95BaTiO3–Bi0.05Nb0.05O4. The nonlinearity was suppressed obviously with low Pr, which was good for in lead-free relaxor materials for the energy storage applications.

Effect of Mg on the dielectric and electrical properties of BaTiO3-based ceramics

BaTiO3-based dielectric ceramics with grain sizes of 100–120 nm were prepared by the chemical coating approach and are promising for the application of ultrathin multilayer ceramic capacitors. The doping effects of Mg on the microstructures and dielectric properties of the BaTiO3-based ceramics were investigated. The addition of Mg was beneficial for inhibiting the grain growth and improving sintering characteristics and improving the dielectric properties and reliability of the nano-BaTiO3-based ceramics. The highly accelerated lifetime test and thermally stimulated depolarization current were employed to study the resistance degradation and conduction mechanism of the Mg-doped BaTiO3 ceramics. It was determined that the reliability characteristics greatly depended on the Mg content. The addition of 2 mol% Mg was suitable for improving the reliability of the nano-BaTiO3-based ceramics, which is an important parameter for the application of multilayer ceramic capacitors. However, further increasing the addition amount of Mg decreased the performance of the BaTiO3-based ceramics.

Effect of Gd amphoteric substitution on structure and dielectric properties of BaTiO3-based ceramics

BaTiO3-based ceramics (doped with a small amount of Ni2+, Mn2+, Nb5+, Ca2+ and Zr4+) with various Gd2O3 concentrations were prepared by the conventional solid-state reaction method. Effects of Gd2O3 doping concentrations on the structure and dielectric properties were investigated. It was deduced from XRD patterns that different substitution sites of Gd3+ ions could be affected by Gd2O3 doping amount. Gd3+ tended to occupy Ba-site when Gd2O3 concentration was less than 0.25 mol%. With increasing Gd2O3 doping amount to 0.3 mol%, Gd3+ substituted into both Ba- and Ti-site which contributed to an obvious improvement on dielectric constant of BaTiO3-based ceramics. Influences of the Gd3+ amphoteric substitution on the improvement of the dielectric constant were discussed based on the self-compensation mechanism.

Effect of synthesized BaTiO3 doping on the dielectric properties of ultra temperature-stable ceramics

The high performance X9R ceramics could be sintered at as low as 1,120 °C by doping 3 mol% synthesized BaTiO3 (SB) additives into the BaTiO3-based ceramics, with a dielectric constant greater than 2,200 at 25 °C and dielectric loss lower than 1.7 %. The effects of SB additives on the microstructure and dielectric properties of BaTiO3-based ceramics were investigated. The dielectric constant of BaTiO3-based ceramics doped with 3 mol% SB was increased due to the promotion of the densification of ceramics. With SB content up to 4.5 mol%, Ti4+’s polarization was depressed, which resulted in the decrease of augmented dielectric constant at 25 °C. The partial solid solution was formed between Pb(Ti, Sn)O3 and BaTiO3, and the substitutions of Pb at A-sites and Sn at B-sites were existed. The strengthen of Ti–O bonds and higher Curie point of Pb(Ti0.55Sn0.45)O3 was helpful to increased the Curie point of the ceramics effectively. Doped with SB additives, the volume of ferroelectric core was increased, and the sharp peak intensity at Curie point was increased accordingly. Capacitance temperature characteristics was improved attributed to the mutual effects of SB and Pb(Ti0.55Sn0.45)O3. The formation of core–shell structure was sensitive to the sintering temperature, so the dielectric properties of ceramics were highly depended on the sintering temperature.

The Effect of Nb<sub>2</sub>O<sub>5</sub> Addition on the Dielectric Properties of BaTiO<sub>3</sub>-Based Ceramics

In this paper, the effect of Nb2O5 on the microstructure and dielectric properties of BaTiO3-based ceramics has been investigated. In the study，Nb2O5 is added to the BaTiO3-based ferroelectric material by conventional solid state synthesis. The structure is identified by X-ray diffraction method and SEM is also employed to observe the surface morphologies of the sample. The specimens of the ferroelectric doped with 2wt% Nb2O5 sintered at 1260°C for 1h exhibit attractive properties, its dielectric temperature coefficient is lower than 15% over a wide temperature range from －55 to +180°C.

Microstructure and Dielectric Properties of BaTiO<sub>3</sub>-Based Ferroelectric Materials

The microstructure and dielectric properties of BaTiO3-based ceramics and films were investigated. In BaZr0.2Ti0.8O3 ceramics domains with herribone, lamellar and “water-mark” characters are observed and 90◦-domain has not been observed in large grain size sample. It is shown that the average grain size and the remanent polarization of doped BZT ceramics decrease with the increasing of Al content. The dielectric constant and tunability of the BaZr0.2Ti0.8O3 films using inorganic zirconate are 113 and 10.2%, respectively. It is found that nanowires of BaTiO3 annealed for 2.5 min are very clear-cut, orderly and almost uninterrupted.

Effect of Bi 2O 3 Additive on the Microstructure and Dielectric Properties of BaTiO 3-Based Ceramics Sintered at Lower Temperature

High performance X8R dielectric ceramics were prepared by doping Bi2O3 to BaTiO3-based ceramics. The effect of small amounts ≤1.2 mol%) of Bi2O3 additive on the microstructure and dielectric properties of BaTiO3-based ceramics have been investigated. The Bi2O3, acting as a sintering additive, can effectively lower the sintering temperature of BaTiO3-based ceramics from 1300 to 1130°C The bulk density of BaTiO3-based ceramics increased and reached the maximum value with increasing Bi2O3 content. The dielectric constant increased with increasing Bi2O3 until it reached the maximum value with 0.8 mol% Bi2O3 additive, and the dielectric loss decreased with increasing Bi2O3 content. Optimal dielectric properties of ɛ=2470, tanδ=0.011 and Δɛ/ɛ25≤±9% (−55–150°C) were obtained for the BaTiO3-based ceramics doped with 0.8 mol% Bi2O3 sintered at 1130°C for 6 h.

Effect of BaTiO3 heat treatment on the microstructure and dielectric properties of BaTiO3-based ceramics

We have studied the effect of heat treatment of the starting BaTiO3 powder on the dielectric properties and microstructure of X7R-type BaTiO3-based ceramics. The results demonstrate that annealing of BaTiO3 stabilizes the degree of tetragonality in the crystal lattice of the ceramics. Microstructural analysis shows that the annealing temperature has no effect on the average grain size of the ceramics. Increasing the BaTiO3 annealing temperature increases the dielectric permittivity of the core phase and reduces the temperature coefficient of capacitance (TCC). We obtained an X7R-type BaTiO3-based ceramic material (BaTiO3 annealing temperature, 1150°C; firing temperature, 1160°C) with the following properties: ɛ25°C = 2230, TCC = ±12% (−55 to 125°C), and tanδ25°C = 0.013.

Effect of Pb(Ti, Sn)O3 on the dielectric properties of high dielectric constant X8R BaTiO3-based ceramics

The high dielectric constant X8R dielectric materials could be sintered at 1,240 °C by doping 2.5 mol% Pb(Ti,Sn)O3 additives into the BaTiO3 ceramics, with a dielectric constant greater than 3,400 at 25 °C, dielectric loss lower than 2.0% and temperature coefficient of capacitance (TCC) less than ±15% from −55 to 150 °C, which satisfied X8R specification. The effects of Pb(Ti,Sn)O3 on the microstructure and dielectric properties of BaTiO3-based ceramics were investigated. Doped with Pb(Ti,Sn)O3 additives, the partial solid solution was formed between Pb(Ti,Sn)O3 and BaTiO3. Due to the high Curie point of Pb(Ti,Sn)O3, the Curie point of the ceramics was markedly shifted to higher temperature about 150 °C, and the temperature coefficient of capacitance curves was flattened. The increase of the tetragonality (c/a ratio) and the fine microstructure were resulted in the increase of dielectric constant. With Pb(Ti, Sn)O3 content up to 3 mol%, the depression of Ti4+’s polarization and the decrease of the tetragonality (c/a ratio) were resulted in the decrease of dielectric constant.

Effects of BiNbO4 on the microstructure and dielectric properties of BaTiO3-based ceramics

The microstructure and dielectric properties of ternary system BaTiO3 (BT)–Bi0.5Na0.5TiO3 (BNT)–BiNbO4 were investigated. In the case of 1 mol% BNT addition, the Curie point (T c) of BaTiO3 was increased from 130 to 140 °C. The dielectric constant peak at T c was markedly depressed with the addition of BiNbO4, whereas an enhancement in the dielectric constant at lower temperature was observed. The addition of BiNbO4 improved the temperature dependence of the dielectric constants of BaTiO3-BNT system ceramics and the temperature coefficient of capacitance curves satisfied the EIA X8R specification with 3–4 mol% BiNbO4. The dielectric constant peak at T c was suppressed evidently due to over high-sintering temperature. As the BiNbO4 content was increased, the Curie point progressively moved to lower temperatures. SEM indicated that fine and homogeneous grains were observed with 1 mol% BiNbO4 addition. However, secondary phase grains appeared with increasing the BiNbO4 content, which were identified as Ba2TiO4, NaBiTi2O6, and BaTiNb4O13 by XRD. Moreover, the proportion of the secondary phase grains increased as the BiNbO4 content increased.

Measurement and Analysis of Microwave Dielectric Properties of BaTiO3-Based Ceramics

A new measurement technique using micro planar electrode and electromagnetic field analysis was developed to measure the microwave dielectric properties of materials with high dielectric constant and high loss factor. Dielectric dispersions of (Ba0.6Sr0.4)TiO3 and Ba(Zr0.25Ti0.75)O3 were measured up to 3 GHz as a function of temperature, and were well explained by the stretched exponential model of the decay function in dielectric relaxation. The phase transition in these ceramics was investigated by dielectric relaxation analysis, X-ray diffraction analysis and specific heat measurement. (Ba0.6Sr0.4)TiO3 showed a diffused phase transition and its relaxation frequency was much high than Ba(Zr0.25Ti0.75)O3, while Ba(Zr0.25Ti0.75)O3 showed typical relaxors behavior.

Dielectric properties of BaTiO3-based ceramics measured up to GHz region

A new measuring method and analyzing procedure were proposed to determine the complex dielectric constant of materials with relatively high dielectric constant by a lumped impedance measurement using impedance analyzer. Samples used for the measurement were (Ba0.6Sr0.4)TiO3 (BST) and Ba(Zr0.25Ti0.75)O3 (BZT) ceramics. Micro planar electrodes were formed on the surface of samples by electron beam lithography followed by lift-off method. Complex admittances of these samples were measured up to 3 GHz at different temperatures. Electromagnetic simulations were performed for determining the relative dielectric constant and dielectric loss. The complex dielectric constant vs frequency curves of Ba(Zr0.25Ti0.75)O3 showed a broad dielectric relaxation, while that of (Ba0.6Sr0.4)TiO3 was almost flat up to 3 GHz on high-temperature side of T m at which dielectric constant shows maximum value. Dielectric dispersion properties were discussed from the viewpoint of diffuse phase transition in ferroelectrics.

Dielectric Properties of BaTiO3-Based Ceramics under High Electric Field

The dielectric properties under a high electric field (ac-field) of BaTiO3-based ceramics with core grains, shell grains and core-shell grains were compared with those of multilayer ceramic capacitors (MLCCs) with these three kinds of grains. The MLCCs with the X7R specification had a core-shell structure, and the relative dielectric permittivity (εr) of the dielectric layers in the MLCCs increased with increasing ac-field. Similar behavior was observed in the MLCCs consisting of only cores, indicating that the core predominantly determined the dielectric properties of MLCCs under high ac-fields. The dielectric properties of MLCCs and ceramic plates consisting of only shell grains showed that the shell was the relaxor ferroelectrics. A slight change in the shell composition yielded a large shift of the peak temperature of εr. The shell improved the temperature stability of εr at low temperatures under low ac-fields. In a ceramic plate with relatively large BaTiO3 grains (approximately 3 µm), the maximum εr was observed at a moderate ac-field, which was explained from the electric displacement vs electric field hysteresis curves of ferroelectric BaTiO3. The MLCCs and ceramics plates with fine BaTiO3 grains (0.4 to 0.5 µm) showed similar dielectric behavior to the MLCC with the core-shell structure. The size effect of BaTiO3 played an important role in determining the temperature stability of εr. For future MLCCs with very thin dielectric layers, a microstructure with fine BaTiO3 grains and grain boundary layers of the shell was proposed.