Effects of SrO–B2O3–SiO2 glass additive on densification and energy storage properties of Ba0.4Sr0.6TiO3 ceramics

SrO–B₂O₃–SiO₂ glass powders were prepared and employed as sintering aids to reduce the sintering temperature of Ba_0.4Sr_0.6TiO₃ ceramics. The effects of glass content and sintering temperature on the densification, dielectric properties and energy storage properties of Ba_0.4Sr_0.6TiO₃ ceramics have been investigated. The relative density characterization results indicate that densification of Ba_0.4Sr_0.6TiO₃ ceramics with glass content becomes apparently from sintering temperature of 1,060 °C. XRD results show all Ba_0.4Sr_0.6TiO₃ ceramics exhibit a perovskite structure without the formation of a secondary phase. The dielectric constant and dielectric loss decreased gradually with increasing glass content. The relationship between dielectric constant and breakdown strength was discussed using the thermochemical model. A discharged energy density of 0.44 J/cm³ with an energy efficiency of 67.4% was achieved for Ba_0.4Sr_0.6TiO₃ ceramic with 2.0 wt% glass addition sintered at 1,180 °C.     

Dielectric properties of La/Zr codoped Ba0.67Sr0.33TiO3 ceramics prepared from citrate–nitrate combustion derived powders

La/Zr codoped Ba_0.67Sr_0.33TiO₃ (BST) ceramics were fabricated via citrate–nitrate combustion derived powders, and the microstructure and dielectric properties of BST ceramics were investigated. All ceramic samples show a pure perovskite structure. The dielectric constant and loss decrease with increasing Zr content. The additions effectively suppress the grain growth of BST ceramics. It is found that the temperature-permittivity characteristics for codoped BST ceramics could be controlled using various doping content.     

Low temperature sintering and properties of Ca–Al–B–Si–O glass/ceramic composites with various ceramic fillers

Low-temperature sintering and properties of low temperature co-fired ceramics materials based on a typical Ca–Al–B–Si–O glass and various ceramic fillers such as (Zr_0.8Sn_0.2)TiO₄, (Ca_0.5Mg_0.5)TiO₃, BaSm₂Ti₄O₁₂ and CaTiO₃ were investigated. Densification, crystallization and dielectric properties are found to strongly depend on the type of filler. The densification process of glass/ceramic composites with different ceramic fillers is mainly from 600 to 925 °C, and the initial compacting temperature of samples is 600 °C. The initial rapid densification of samples starts after glass softening temperature of samples. The XRD patterns of (Ca_0.5Mg_0.5)TiO₃ and CaTiO₃ samples demonstrate crystalline phases, CaTiO(SiO₄) and CaTiSiO₅, respectively, as a result of firing at 875 °C for 15 min. The high dielectric constant fillers produce high ε_r values of the dielectric samples. The maximum dielectric constant of samples for (Zr_0.8Sn_0.2)TiO₄, (Ca_0.5Mg_0.5)TiO₃, BaSm₂Ti₄O₁₂ and CaTiO₃ filler is 14.02, 16.21, 18.64 and 23.78, respectively. Comparing with other samples, the specimens for (Ca_0.5Mg_0.5)TiO₃ and CaTiO₃ ceramic filler have lower dielectric loss. Especially, the sample for (Ca_0.5Mg_0.5)TiO₃ filler exhibits the lowest dielectric loss of 0.00011.     

Effects of Kaolinite additions on sintering behavior and dielectric properties of CaCu3Ti4O12 ceramics

Commercial Kaolinite was employed as sintering aid to reduce the sintering temperature of CaCu₃Ti₄O₁₂ (CCTO) ceramics. The effects of Kaolinite content and sintering temperature on the densification, microstructure and dielectric properties of CCTO ceramics have been investigated. The density characterization results show that the addition of Kaolinite significantly enhanced the relative density of CCTO ceramics to about 92 %. X-ray diffraction results show CCTO ceramics with a low amount of Kaolinite exhibited perovskite-like structure, but 1.0 wt% Kaolinite additions resulted in the formation of a secondary phase, CaO–TiO₂–Al₂O₃–SiO₂ glass phase was formed and improved the dielectric constant of ceramics, which was supported by scanning electron microscopy–energy dispersive X-ray results. CCTO ceramic with 1.0 wt% Kaolinite addition possessed well temperature and frequency stability of dielectric constant. It was found that Kaolinite lowered the dielectric loss of the samples.     

Electrical hetero-structure of Nd0.1Sr0.9TiO3 ceramic for energy storage applications

Both high dielectric constant and high bulk resistance was required to meet high energy storage density in high-voltage ceramic capacitors. In this paper, Nd_0.1Sr_0.9TiO₃ (NSTO) ceramic with pure tetragonal perovskite structure was prepared by solid state reaction route. Dielectric response of NSTO ceramic was investigated in the temperature range of ?60 to 550 °C over the frequency 20 Hz–1 MHz. Complex impedance spectroscopy (IS) analysis was employed to study the electrical conductive behavior of NSTO ceramic. IS results revealed that the NSTO ceramic showing electrical hetero-structure, which includes semiconducting grains, inter-grains and insulating grain boundaries. The space charge polarization at heterointerfaces by conductive charge carries was contributed to high dielectric constant, while insulating grain boundaries to high bulk resistance for NSTO ceramic. The mechanism of such electrical hetero-structure formation associated with charge compensation induced by trivalent Nd ions substitution for divalent Sr, as well as the first and second ionization of oxygen vacancies was discussed tentatively.     

Successive relaxor ferroelectric behavior in La modified (Ba,Sr)TiO3 borosilicate glass ceramics

In the present investigation, we are reporting the successive ferroelectric relaxor behavior of (Ba,Sr)TiO₃ borosilicate glass ceramics. The ferroelectric relaxor nature of the present glass ceramics is attributed to structural phase transition from the rhombohedral to orthorhombic to tetragonal to cubic. A very high value of dielectric constant was found to be 89,684 at 100 Hz in glass ceramic sample 64[(Ba_0.7Sr_0.3)TiO₃]–30[2SiO₂–B₂O₃]–5[K₂O]–1[La₂O₃], BST5K1L0.3S831 and such large value may be due to space charge polarization in glassy matrix. The various contribution in polarization processes are confirmed by impedance spectroscopic analysis.     

Dielectric and microstructural behaviour of strontium titanate borosilicate glass ceramic system

65(SrO·TiO₂)−35(2SiO₂·B₂O₃) wt% glass was synthesized. Differential thermal analysis study shows one exothermic peak which shifts towards higher temperature with increasing heating rate. Glass ceramics prepared by controlled crystallization of strontium titanate borosilicate glass produce uniform distribution of crystallites in a glassy matrix. Attempt was made to crystallize strontium titanate phase in this glass ceramic. Different phases precipitated out during ceramization have been identified by X-ray diffraction. It appears that due to high reactivity of SrO with B₂O₃, strontium borate crystallizes as principal phase followed by TiO₂ (rutile) and Sr₃Ti₂O₇ phases. Dielectric constant of these glass ceramics was observed to be more or less temperature independent over wide range of temperatures with low values of dielectric constant and dissipation factor.     

Preparation of Barium Strontium Titanate Ceramic by Sol-Gel Method and Microwave Sintering

The (Ba,Sr)TiO₃ amorphous gel was prepared by sol-gel process and calcined in the 2.45-GHz multimode microwave furnace to synthesize (Ba,Sr)TiO₃ nanopowder. The calcination temperature of the (Ba,Sr)TiO₃ ceramic powders that convert the material into prevoskite phase can be reduced from 1100°C to 900°C, the nanopowder displays the highest sinterability. Using a new kind of insulator materials made of MgAl₂O₄–LaCrO₃, the crack-free and dense (Ba_0.80Sr_0.20)TiO₃ ceramics with fine grain size (<1 µm) were prepared by microwave sintering at 1310°C for 15 min. The fine (Ba,Sr)TiO₃ ceramics sintered by microwave sintering technique display lower dielectric loss than that of conventional samples, indicating a reduction of the influence of defects with the microwave process.     

The effect of glass addition on the dielectric properties of barium strontium titanate

Ba_0.7Sr_0.3TiO₃ (BST) ceramics were prepared by the conventional solid state ceramic route. Different weight percentages of twelve different glasses were added to the calcined BST ceramics and sintered. The structure and microstructure of the sintered materials were investigated by X-ray diffraction and Scanning Electron Microscopic techniques. The low frequency dielectric properties of the glass-ceramic composites were measured using LCR meter. Some of the glasses improved the dielectric properties and considerably lowered the sintering temperature. The glasses were prepared and characterized under identical conditions. Among the different glasses, 1.5 wt% addition of 71ZnO–29B₂O₃ lowered the sintering temperature of BST to 975 °C with a dielectric loss of 9 × 10⁻³ and dielectric constant of 875 at 1 MHz. The curie temperature of BST ceramics was found to shift towards lower temperature with glass addition.     

Influence of Sr/Ba ratio on the energy storage properties and dielectric relaxation behaviors of strontium barium titanate ceramics

Sr _x Ba_1?x TiO₃ (x = 0.50–0.70) ceramics were prepared by conventional solid-state method. The effects of Sr/Ba ratio on the microstructures, energy storage properties and dielectric relaxation behaviors of ceramics were systematically investigated. Scanning electron microscopy observations revealed that the grain size was inhibited with increasing Sr molar fraction. The Sr_0.6Ba_0.4TiO₃ ceramics obtained the highest energy density of 0.3629 J/cm³ attributed to the increase of average breakdown strength resulting from the decrease of grain size and the optimizing of microstructure. In order to investigate the influence of Sr/Ba ratio on the dielectric relaxation behaviors, the activation energy has been calculated from the relaxation of dielectric loss and the complex impedance spectra by the Arrhenius relationship, respectively. The same results indicated that the decrease of grain size resulting in more grain boundaries, it was difficult for transferring charge and making an orientation under external electric field. Meanwhile, more defects existed at grain boundary and accelerated the thermally activated motions of defects, leading to the increase of activation energy.     

Synthesis and dielectric properties of a new class of MX6Ti6O19 (M=Ba,Sr and Ca; X=Mg and Zn) ceramics

MX₆Ti₆O₁₉ (M=Ba, Sr and Ca; X=Mg and Zn) ceramics have been synthesized by the conventional solid state ceramic route. The dielectric properties such as dielectric constant (ε_r), loss tangent (tanδ) and temperature coefficient of dielectric constant (τ_εr) of the sintered ceramic compacts are studied using an impedance analyzer up to the 13-MHz region. The zinc compositions have relatively high dielectric constant and low loss tangent compared to the Mg analogue. Out of the samples studied, BaZn₆Ti₆O₁₉ ceramics show excellent dielectric properties. The structure and microstructure of these ceramic samples are also studied using powder X-ray diffraction, FTIR and SEM methods, and the results are presented.     

Energy storage properties of (1 − x)(Bi0.5Na0.5)TiO3–xKNbO3 lead-free ceramics

In this study, a simple compound (1 ? x)(Bi_0.5Na_0.5)TiO₃–xKNbO₃ (x = 0 – 0.12) lead-free bulk ceramic was developed for high electric power pulse energy storage applications. The dielectric and ferroelectric properties of the ceramics were measured. The results illustrate that the energy storage density of the ceramics is enhanced by the addition of KNbO₃. The influence of applied electric field, temperature, and fatigue on the energy storage properties of the ceramics was evaluated for the composition-optimized (Bi_0.5Na_0.5)TiO₃–0.1KNbO₃ ceramic. The results demonstrate that (Bi_0.5Na_0.5)TiO₃–0.1KNbO₃ ceramic is a promising lead-free material for high power pulse capacitor applications. The excellent energy storage properties of the (Bi_0.5Na_0.5)TiO₃–0.1KNbO₃ ceramics are ascribed to the reversible relaxor–ferroelectric phase transition induced by the electric field.     

Lead-strontium titanate glass ceramics: II-dielectric behaviour

Dielectric properties of glass ceramic samples prepared in the system [(Pb_1-xSr_x)O.TiO₂)]- [2SiO₂.B₂O₃]-[K₂O]-[BaO] have been studied. Dielectric constant vs temperature plots of lead rich glass ceramics samples show a peak similar to Curie peak in case of ceramic lead strontium titanate. The Curie temperature of tetragonal crystalline phase of various glass ceramics has been found to decrease with Pb/Sr ratio in the initial glass. This complements X-ray diffraction (XRD) studies carried out previously to establish that the crystallites in various glass ceramic samples are (Pb_1−xSr_x)TiO₃ solid solutions.     

Crystal structure and properties of BaTiO<Subscript>3</Subscript>–(Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)TiO<Subscript>3</Subscript> ceramic system

(1 − x)BaTiO₃–x(Bi_0.5Na_0.5)TiO₃ (x ranged from 0.01 to 0.96) ceramics were fabricated by the conventional ceramic technique. The crystal structure, as well as dielectric and piezoelectric properties of the ceramics were studied. All the ceramics formed single-phase solid solutions with perovskite structure after sintering in air at 1150–1250 °C for 2–4 h. The crystal structure and microstructure varied gradually with the increase of (Bi_0.5Na_0.5)TiO₃ (BNT) content. The Curie temperature, T _c, shifted monotonously to high temperature as BNT increased. The ceramics with 20–90 mol% BNT had relatively low and stable dielectric loss characteristics. The piezoelectric constant, d ₃₃, enhanced with the increase of BNT content through a maximum value in a composition of 93 mol% BNT and then tended to decrease. The maximum value, 148 pC/N, of piezoelectric constant d ₃₃ together with the electromechanical coupling factors, k _t, 19.8% and k _p, 15.8%, were obtained when BNT was 93 mol%.     

Synthesis and dielectric properties of MXTi<Subscript>7</Subscript>O<Subscript>16</Subscript> (M = Ba and Sr; X = Mg and Zn) hollandite ceramics

MXTi₇O₁₆ (M = Ba and Sr; X = Mg and Zn) ceramics have been synthesized by the conventional solid state ceramic route. The dielectric properties such as dielectric constant (ε_r), loss tangent (tan δ) and temperature variation of dielectric constant (τ_εr) of the sintered ceramic compacts are studied using an impedance analyser up to 13 MHz region. The strontium compounds have relatively high dielectric constant and low loss tangent compared to the barium analogue. The phase purity of these materials has been examined using X-ray diffraction studies and microstructure using SEM method.     

Structure, dielectric, ferroelectric, and energy density properties of (1 − x)BZT–xBCT ceramic capacitors for energy storage applications

We investigate the dielectric, ferroelectric, and energy density properties of Pb-free (1 ? x)BZT–xBCT ceramic capacitors at higher sintering temperature (1600 °C). A significant increase in the dielectric constant, with relatively low loss was observed for the investigated {Ba(Zr_0.2Ti_0.8)O₃}_(1?x ){(Ba_0.7Ca_0.3)TiO₃} _x (x = 0.10, 0.15, 0.20) ceramics; however, electric breakdown was low (~140, 170, 134 kV/cm), and of which room temperature (300 K) charging curve energy density values are largest ~0.88, 0.94, and 0.87 J/cm³ with maximum high dielectric constant values ~7800, 8400, and 5200, respectively. Bulk ceramic BZT–BCT materials have shown interesting energy densities with good energy storage efficiency (~72 %) at high sintering temperature; they might be one of the strong candidates for high energy density capacitor applications in an environmentally protective atmosphere.     

Dielectric characteristics of composite ceramics in the Ba(Mg1/3Ta2/3)O3-BaO · Nd2O3 · 5TiO2 system

Dielectric characteristics of composite ceramics in the system Ba(Mg_1/3Ta_2/3)O₃-BaO · Nd₂O₃ · 5TiO₂ were investigated to search for a new candidate system for microwave dielectric ceramics with modifiable dielectric constant, low dielectric loss and small temperature dependence. The dielectric constant could be adjusted in the range 25–81 by controlling the concentration of BaO · Nd₂O₃ · 5TiO₂, while the dielectric loss remained of the order of 10^–4 for some compositions. Moreover, the dielectric properties in the present system could be significantly improved by post-densification thermal treatment.     

High dielectric tunability of ferroelectric (Ba1−x,Srx)(Zr0.1,Ti0.9)O3 ceramics

(Ba_1?x,Sr_x)(Zr_0.1,Ti_0.9)O₃ (BSZT) ceramics with x = 0, 0.05, 0.15, 0.25, 0.35 and 0.45 were prepared by conventional solid state reaction method. The structural characterization with X-ray diffraction and scanning electron microscopy indicate a monotonical drop in lattice constants and grain size with the increase of Sr concentration. Consequently, the Curie temperature and remnant polarization of the ceramics exhibit a strong compositional dependence. A linear relationship between the Curie temperature and Sr concentration is revealed. At x = 0.45, the BSZT ceramics show substantially high tunability of over 55 % under 20 kV/cm dc electric field with very low dielectric loss value of 0.0025 at room temperature, suggesting the BSZT ceramics could be a promising alternative to traditional (Ba,Sr) TiO₃ ferroelectrics for developing high frequency tunable dielectric devices.     

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.     

Microstructures and Dielectric Properties of Ba1-xSrxTiO3 Ceramics Doped with B2O3-Li2O Glasses for LTCC Technology Applications

Ba1-xSrxTiO3 ceramics, doped with B2O3-Li2O glasses have been fabricated via a traditional ceramic process at a low sintering temperature of 900 ℃ using liquid-phase sintering aids. The microstructures and di- electric properties of B2O3-Li2O glasses doped Ba1-xSrxTiO3 ceramics have been investigated systemat- ically. The temperature dependence dielectric constant and loss reveals that B2O3-Li2O glasses doped Ba1-xSrxTiO3 ceramics have di?usion phase transformation characteristics. For 5 wt% B2O3-Li2O glasses doped Ba0.55Sr0.45TiO3 composites, the tunability is 15.4% under a dc-applied electric field of 30 kV/cm at 10 kHz; the dielectric loss can be controlled about 0.0025; and the Q value is 286. These composite ceramics sintered at low temperature with suitable dielectric constant, low dielectric loss, relatively high tunability and high Q value are promising candidates for multilayer low-temperature co-fired ceramics (LTCC) and potential microwave tunable devices applications.