Synthesis and characterization of Zn-B-Si-O nano-composites and their doped BaTiO3 ceramics

We synthesized Zn-B-Si-O (ZBSO) nano-composites via sol-gel process, and then used them to dope BaTiO₃ ceramics. The ZBSO nano-composites and their ceramics were characterized by means of thermogravimetric, Fourier-transform infrared, and X-ray diffraction methods, and using scanning and transmission electron microscopy. We also characterized the dielectric properties of the ceramics. The results indicated that the ZBSO nano-composites were nanometer-scale powders with an amorphous structure. The particle size of the powders increased with increasing pH value, but initially decreased and then increased with increasing calcining temperature. At pH about 2 and with calcining at 400 °C, the nano-composites attained minimum particle size (about 30 nm). The sintering temperature of the BaTiO₃ ceramics could be reduced to 1100 °C by adding 5 wt% of the ZBSO nano-composites. Uniform, fine-grained BaTiO₃ ceramics with a high permittivity (?_r = 2946 and ?_max = 5072) were obtained by adding nano-composites; these properties were superior to the ZBSO glass doped BaTiO₃ ceramics.     

Study of glass-nanocomposite and glass–ceramic containing ferroelectric phase

Transparent glass nanocomposite in the pseudo binary system (100 − x) Li₂B₄O₇–xBaTiO₃ with x = 0 and 60 (in mol%) were prepared. Amorphous and glassy characteristics of the as-prepared samples were established via X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC) respectively. The precipitated BaTiO₃ nanocrystal phase embedded in the glass sample at x = 60 mol% was identified by transmission electron microscopic (TEM). The optical transmission bands at 598 and 660 nm were assigned to Ti³⁺ ions in tetragonal distorted octahedral sites. The precipitated Li₂B₄O₇, BaTi(BO₃)₂ and BaTiO₃ nanocrystallites phases with heat-treatment at 923 K for 6 h (HT923) in glass–ceramic were identified by XRD, TEM and infrared absorption spectroscopy. The as-prepared at x = 60 mol% and the HT923 samples exhibit broad dielectric anomalies in the vicinity of the ferroelectric-to-paraelectric transition temperature. The results demonstrate that the method presented may be an effective way to fabricate ferroelectric host and development of multifunctional ferroelectrics.     

Study on the microstructure and dielectric properties of X9R ceramics based on BaTiO3

This paper investigated the microstructure and dielectric properties of BaTiO₃-Pb(Sn, Ti)O₃ system ceramics. The Curie point of BaTiO₃ is 130 °C. When the temperature is higher than 130 °C, the dielectric constant of BaTiO₃ drops severely according to Curie-Weiss law. Pb(Ti, Sn)O₃(PTS) was selected to compensate the dielectric constant doping of BaTiO₃ since it has high Curie temperature (Tc) point that is about 296 °C. The Curie temperature (Tc) point of BaTiO₃ was broadened and shifted to higher temperature because of the doping of PTS, so the temperature coefficient of capacitance (TCC) curves of the ceramics based on BaTiO₃ was flattened. When 2 wt% Pb(Ti_0.55Sn_0.45)O₃ was added, the sample showed super dielectric properties that the dielectric constant was >1750 at 25 °C, dielectric loss was lower than 2.0% and TCC was <±10% from −55 °C to 200 °C. Therefore the materials satisfied EIA X9R specifications.     

Processing, dielectric properties and impedance characteristics of Na0.5Bi0.5Cu3Ti4O12 ceramics

Na_0.5Bi_0.5Cu₃Ti₄O₁₂ (NBCTO) ceramics were prepared by conventional solid-state reaction method. The phase structure, microstructure and dielectric properties of NBCTO ceramics sintered at various temperatures with different soaking time were investigated. Pure NBCTO phase could be obtained with increasing the temperature and prolonging the soaking time. High dielectric permittivity (13,495) and low dielectric loss (0.031) could be obtained when the ceramics were sintered at 1000 °C for 7.5 h. The ceramics sintered at 1000 °C for 7.5 h also showed good temperature stability (−4.00 to −0.69%) over a large temperature range from −50 to 150 °C. Complex impedances results revealed that the grain was semiconducting and the grain boundaries was insulating. The grain resistance (R_g) was 12.10 Ω cm and the grain boundary resistance (R_gb) was 2.009 × 10⁵ Ω cm when the ceramics were sintered at 1000 °C for 7.5 h.     

Influence of Bi2O3 and CuO addition on low-temperature sintering and dielectric properties of Ba0.6Sr0.4TiO3 ceramics

In this study, we tried to lower the sintering temperature of Ba_0.6Sr_0.4TiO₃ (BST) ceramics by several kinds of adding methods of Bi₂O₃, CuO and CuBi₂O₄ additives. The effects of different adding methods on the microstructures and the dielectric properties of BST ceramics have been studied. In the all additive systems, the single addition of CuBi₂O₄ was the most effective way for lowering the sintering temperature of BST. When CuBi₂O₄ of 0.6 mol% was mixed with starting BST powders and sintered at 1100 °C, the derived ceramics demonstrated dense microstructure with a low dielectric constant (? = 4240), low dielectric loss (tan δ = 0.0058), high tunability (Tun = 38.3%) and high Q value (Q = 251). It was noteworthy that the sintering temperature was significantly lowered by 350 °C compared with no-additive system, and the derived ceramics maintained the excellent microwave dielectric properties corresponding to pure BST.     

Synthesis, characterization, and dielectric properties of Ba(Ti1−xSnx)O3 nanopowders and ceramics

We prepared Ba(Ti_1−xSn_x)O₃ powders and ceramics by means of the sol-gel process, with dibutyltin dilaurate as the Sn precursor. The samples were characterized by means of Fourier-transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and scanning electron microscopy, and also determined the dielectric properties of the ceramics. The powders synthesized by means of the sol-gel process had a grain size on the nanometer scale, with the grains mainly composed of a cubic BaTiO₃ phase. Sn can disperse into BaTiO₃ more uniformly in the sol-gel technique using dibutyltin dilaurate as the Sn precursor. With increasing Sn concentration, the grain size of the Ba(Ti_1-xSn_x)O₃ ceramics increased and the maximum dielectric constant (?_max) first increased and then decreased. At a Sn concentration of 5 mol%, ?_max reached its maximum value (19,235).     

Effect of Pb(Ti,Sn)O<Subscript>3</Subscript> on the dielectric properties of high dielectric constant X8R BaTiO<Subscript>3</Subscript>-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.     

Modified tunable dielectric properties by addition of MgO on BaZr0.25Ti0.75O3 ceramics

Phase composition, microstructure and tunable dielectric properties of (1 − x)BaZr_0.25Ti_0.75O₃-xMgO (BZTM) composite ceramics fabricated by solid-state reaction were investigated. It was found Mg not only existed in the matrix as MgO, there was also trace amount of Mg²⁺ ions dissolved in the BZT grains, which led to Curie temperature of the BZTM composites ceramics shifting to below −100 °C. Dielectric permittivity of the BZTM composite ceramics was reduced from thousands to hundreds by manipulating the content of MgO. Johnson's phenomenological equation based on Devonshire's theory was used to describe the nonlinear dielectric permittivity of the ceramics with increasing applied DC field. With increasing content of MgO, anharmonic constant α_(T) increased monotonously. Dielectric permittivity was 672, while dielectric tunability was as high as 30.0% at 30 kV/cm and dielectric loss was around 0.0016 for the 0.6BaZr_0.25Ti_0.75O₃-0.4MgO sample at 10 kHz and room temperature.     

Locating the normal to relaxor phase boundary in Ba(Ti1−xHfx)O3 ceramics

In this article, we report our studies on the relaxor behavior of Ba(Ti_1−xHf_x)O₃ ceramics, made with close compositions between 0.20 ≤ x ≤ 0.30, to locate the hafnium concentration boundary for the normal to relaxor crossover. X-ray diffraction followed by Rietveld refinement shows the occurrence of single-phase cubic structure for the synthesized Ba(Ti_1−xHf_x)O₃ ceramics. Temperature and frequency dependence of the real (?′) and imaginary (?″) parts of the dielectric permittivity has been studied in the temperature range of 90-350 K at frequencies of 0.1, 1, 10, and 100 kHz. A diffuse phase transition accompanying frequency dispersion is observed in the permittivity versus temperature plots revealing the occurrence of relaxor ferroelectric behavior. The T_m verses Hf concentration plot shows a discontinuous jump and change in the slope at x = 0.23. Quantitative characterization based on phenomenological models has also been presented. The plausible mechanism of the relaxor behavior has been discussed. Substitution of Hf⁴⁺ for Ti⁴⁺ in BaTiO₃ reduces the long-range polar ordering yielding a diffuse ferroelectric phase transition.     

Microstructure and permittivity of sintered BaTiO3: influence of particle surface chemistry in an aqueous medium

The influence of changes in the surface chemistry and surface composition of colloidal BaTiO₃, due to its dissolution and adsorption/precipitation of Ba²⁺ in an aqueous medium, on the microstructure and permittivity of sintered powder compacts was investigated. For BaTiO₃ powder with Ba-deficient (Ti-excess) surface prepared at pH 3, grain growth was enhanced at 1350 °C (above the eutectic) and permittivity was reduced (relative to stoichiometric BaTiO₃ prepared at pH 9) with increasing sintering temperature due to the liquid phase formed at grain boundaries. This same sample showed minimal grain growth and moderate enhancement of sinterability at 1300 °C (below the eutectic) attributed to sliding of the Ti-excess surface phase. BaTiO₃ powder treated at pH 3 and subsequently adjusted to pH 10 results in a core-shell structure with a varying near-surface stoichiometry, and produced abnormal grain growth for the compact sintered at 1350 °C. Permittivity of this sample was significantly reduced at 1350 °C due to the formation of the liquid phase, while exhibiting a similar permittivity to that of the stoichiometric sample when sintered at 1300 °C, despite significant microstructural coarsening. We conclude that changes in the surface-phase Ba/Ti ratio of particulate precursors, due to dissolution, adsorption and precipitation reactions in aqueous media, are as significant in determining the mechanical and electronic properties of the sintered material as are variations in the bulk stoichiometry of BaTiO₃.     

Electrical conduction, dielectric behavior and magnetoelectric effect in (x)BaTiO3 + (1 − x)Ni0.94Co0.01Mn0.05Fe2O4 ME composites

Electrical and magnetoelectric properties of magnetoelectric (ME) composites containing barium titanate as electrical component and a mixed Ni-Co-Mn ferrite as the magnetic component are reported. The ME composites with a general formula (x)BaTiO₃ + (1 − x)Ni_0.94Co_0.01Mn_0.05Fe₂O₄ where x varies as 0, 0.55, 0.70, 0.85 and 1 were prepared by standard double sintering ceramic method. The presence of both the phases was confirmed by X-ray diffraction technique. The dc resistivity was measured as a function of temperature. The variation of dielectric constant (?) and loss tangent (tan δ) with frequency (100 Hz-1 MHz) and with temperature was studied. The conduction is explained on the basis of small polaron model based on ac conductivity measurements. The static value of ME conversion factor i.e. dc (ME)_H was studied as function of intensity of magnetic field. The changes were observed in dielectric properties as well as ME effect as the molar ratio of the components was varied. A maximum value of ME conversion factor of 610 μV/cm Oe was observed in the case of a composite containing 15 mol% ferrite phase.     

Sol-gel derived CaCu3Ti4O12 ceramics: Synthesis, characterization and electrical properties

The giant dielectric constant material CaCu₃Ti₄O₁₂ (CCTO) has been synthesized by sol-gel method, for the first time, using nitrate and alkoxide precursor. The electrical properties of CCTO ceramics, showing an enormously large dielectric constant ? ∼ 60,000 (100 Hz at RT), were investigated in the temperature range from 298 to 358 K at 0, 5, 10, 20, and 40 V dc. The phases, microstructures, and impedance properties of final samples were characterized by X-ray diffraction, scanning electron microscopy, and precision impedance analyzer. The dielectric permittivity of CCTO synthesized by sol-gel method is at least three times of magnitude larger than that synthesized by other low-temperature method and solid-state reaction method. Furthermore, the results support the internal barrier layer capacitor (IBLC) model of Schottky barriers at grain boundaries between semiconducting grains.     

Effect of BaTiO<Subscript>3</Subscript> heat treatment on the microstructure and dielectric properties of BaTiO<Subscript>3</Subscript>-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: ɛ_25°C = 2230, TCC = ±12% (−55 to 125°C), and tanδ_25°C = 0.013.     

Effect of temperature on nonlinear electrical behavior and dielectric properties of (Ca, Ta)-doped TiO2 ceramics

TiO₂ ceramics doped with 0.75 mol% Ca and 2.5 mol% Ta were sintered at different temperatures ranging from 1300 to 1450°C. The effects of sintering temperature on the microstructure, nonlinear electrical behavior, and dielectric properties of the ceramics were studied. The sample sintered at 1300°C exhibits the highest nonlinear coefficient (5.5) and a comparatively lower relative dielectric constant.     

Relaxor ferroelectric like giant permittivity in PrCrO3 semiconductor ceramics

The electrical behavior of PrCrO₃ ceramics prepared by citric acid route and sintered at 1200 °C has been characterized by a combination of permittivity measurements, and impedance spectroscopy (IS). The effective permittivity obtained in frequency range 100 Hz to 1 MHz and temperature range 80–300 K, exhibits giant permittivity value of 3 × 10⁴ near room temperature. The response is similar to that observed for relaxor ferroelectrics. IS data analysis revealed the ceramics to be electrically heterogeneous semiconductor with room temperature resistivity <10² Ω m consisting of semiconducting grains with permittivity ?′ ∼ 100 and more resistive grain boundaries with effective permittivity ?′ ∼ 10⁴. We conclude, therefore that grain boundary effect is the primary source for the high effective permittivity in PrCrO₃ ceramics.     

Preparation, structure and dielectric properties of Ba4LaMNb3O15 (M = Ti, Sn ) ceramics

Two new cation-deficient hexagonal perovskites Ba₄LaMNb₃O₁₅ (M = Ti, Sn) ceramics were prepared by high temperature solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction, scanning electron microscopy (SEM). The microwave dielectric properties of the ceramics were studied using a network analyzer. The Ba₄LaTiNb₃O₁₅ has high dielectric constant of 52, high quality factors (Q) 3500 (at 4.472 GHz), and temperature variation of resonant frequency (τ_f) +93 ppm °C⁻¹ at room temperature; Ba₄LaSnNb₃O₁₅ has dielectric constant of 39 with high Q value of 2510 (at 5.924 GHz), and τ_f −29 ppm °C⁻¹.     

Dielectric properties and substitution mechanism of samarium-doped Ba0.68Sr0.32TiO3 ceramics

Ba_0.68Sr_0.32TiO₃ ceramics of perovskite structure are prepared by solid state reaction method with addition of x mol% Sm₂O₃, and their dielectric properties are investigated. It is found that, integrating with the lattice parameters and tolerance factor t, there is an alternation of substitution preference of Sm³⁺ for the host cations in perovskite lattice. Owing to the replacement of Sm³⁺ ions for Ba²⁺ ions in the A site, T_c rises with the increase of Sm₂O₃ doping when the doping content is below 0.1 mol%; meanwhile, when the content is more than 0.1 mol%, Sm³⁺ ions tend to occupy the B-site, causing a drop of T_c. Owing to the modifications of Sm³⁺ doping, dielectric constant, dissipation factor and temperature stability of dissipation factor are influenced remarkably, making it a superior candidate for environment-friendly applications. Moreover, the creation of oxygen vacancies controls the dielectric constant when the addition is above 0.1 mol%, so the dielectric constant decreases with increasing of samarium.     

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(Ti_0.55Sn_0.45)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(Ti_0.55Sn_0.45)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.     

Improvement of dielectric thermal stability of BST ferroelectric material for tunable applications

100(1 − y)wt%(Ba_0.6Sr_0.4)(Ti_0.8Zr_0.2)O₃-100y wt%MgO (BSTZ20-MgO, y = 0.4, 0.5, 0.6, 0.7) composite ceramics were synthesized via a solid-state reaction route, aiming at improving the dielectric thermal stability of BST for tunable applications. Excellent dielectric thermal stability (low temperature coefficient of permittivity value) was gained in this system. According to our experiment, diffuse phase transition (DPT) induced by Zr ion substitution, ferroelectric-dilution effect of MgO phase and grain size refinement were considered as contributions to this good dielectric thermal stability.     

Preparation and dielectric properties of BaCu(B2O5)-doped SrTiO3-based ceramics for energy storage

BaCu(B₂O₅) (BCB) was used as sintering aids to lower the sintering temperature of multi-ions doped SrTiO₃ ceramics effectively from 1300 °C to 1075 °C by conventional solid state method. The effect of BCB content on crystalline structures, microstructures and properties of the ceramics was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and dielectric measurements, respectively. The addition of BCB enhanced the breakdown strength (BDS) while did not sacrifice the dielectric constant. The enhancement of BDS should be due to the modification of microstructures, i.e., smaller and more homogeneous grain sizes after BCB addition. The dielectric constant of BCB-doped ceramics maintained a stable value with 1.0 mol% BCB, which was dominated by the combination of two opposite effects caused by the presence of second phases and the incorporation of Cu²⁺ and Ba²⁺, while further increase was owing to the increase of dissolved Ba²⁺ ions when the content of BCB is more than 2.0 mol%. The multi-ions doped SrTiO₃ ceramics with 1.0 mol% BCB addition showed optimal dielectric properties as follows: dielectric constant of 311.37, average breakdown strength of 28.78 kV/mm, discharged energy density of 1.05 J/cm³ and energy efficiency of 98.83%.