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.     

Preparation of BaTiO<Subscript>3</Subscript>-based ceramics by nanocomposite doping process

BaTiO₃-based ultrafine nonreducible dielectrics for multilayer ceramic capacitors were prepared by a newly developed nanocomposite doping process. According to TG-DTA, XRD and TEM analysis, the nanocomposite dopants via sol–gel method were uniform and well dispersive. The micromechanism was investigated based on comparing conventional process with nano-doping process. It indicated that due to the special nano-effect, doping effect of additives became more effective and the microstructure and dielectric properties of ceramics were improved. The results showed that high performance dielectrics satisfying X8R specification were achieved, with high dielectric constant of 2,900, low dielectric loss of 0.6% and large insulation resistivity of 10¹² Ω cm.     

Preparation of BaTiO3-Based Nonreducible X7R Dielectric Materials Via Nanometer Powders Doping

Nonreducible X7R dielectric materials, which can be cofired with Ni electrode, were obtained by doping nanometer additives to BaTiO₃ powders synthesized by employing a sol-gel method. The crystallization process, structure and constituent of nanometer additives, as well as morphologies were studied via differential thermal and thermogravimetric analyses (DTA/TG), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effects of the calcining temperature of dopants on the dielectric properties were also discussed. The experiment results proved that higher-performance X7R dielectric materials could be obtained via nanometer doping compared with conventional doping. At room temperature, dielectric constant is more than 3000; dielectric loss lower than 1.0% and insulation resistance more than 10¹¹Ω ⋅cm.     

Microstructure and dielectric properties of BaTiO3-based X7R ceramics

The relationship between the microstructures and dielectric properties of BaTiO₃-based X7R ceramics has been investigated at different calcination temperatures. The XRD and SEM results show that calcinations of BaTiO₃ raw powders increase the grain size and stabilize the tetragonality (c/a ratio) of the ceramics. The grain growth caused by the calcination prevents the doped ions from diffusing into the interior of the grains, and then increases the volume fraction of the tetragonal phased core. This process greatly increases the dielectric constant by improving the ferroelectricity. As a result, the relaxation mechanism of the domain reorientation generates high loss tangent. The BaTiO₃ ceramics with X7R specifications were prepared at the calcination temperature of 1200 °C and the sintering temperature of 1240 °C, whose dielectric properties were ɛ _r ≥ 4500, Δɛ _r/ɛ _r25 ≤ ± 10%(−55∼125 °C), tanδ ≤ 0.012(25 °C), respectively.     

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

The microstructure and dielectric properties of ternary system BaTiO₃ (BT)–Bi_0.5Na_0.5TiO₃ (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.     

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.     

Preparation and characterization of Ag-doped BaTiO3 based X7R ceramics

Ag-doped BaTiO₃ based X7R (temperature coefficient of capacitance within the range of ±15% between −55 and +125 °C) ceramics with different amounts of silver (0.0-20.0 mol%) were prepared in this paper. The X-ray diffraction analysis indicated that no phases other than BaTiO₃ and silver were observed in the ceramics. The energy dispersive X-ray spectroscopy analysis showed that the silver particles presented homogeneous distribution in the BaTiO₃ ceramics. The dielectric properties of Ag-doped ceramics were investigated. A small amount of silver (<0.5 mol%) and a large amount of silver (>2.0 mol%) could both improve the sintered density and permittivity, but more content of silver (0.5-2.0 mol%) would decrease the relative density and permittivity. Specially, the temperature coefficient of capacitors of the ceramics doped with 20 mol% silver still met the X7R characteristics, and the room temperature permittivity of the ceramics was 6823, which was the highest dielectric constant in the BaTiO₃ based X7R ceramics.     

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.     

Influence of 3d-elements on dielectric properties of BaTiO<Subscript>3</Subscript> ceramics

The microstructure and dielectric properties of Yb-Mn- and Yb-Ni-substituted BaTiO₃ ceramics are investigated in this paper. Both Yb-Mn- and Yb-Ni-substituted BaTiO₃ ceramics satisfy the X8R specification (−55 ^∘C to 150 ^∘C, Δ C = ±15% or less) for automotive application when CaZrO₃ is incorporated in the formulations. It is found that both Mn and Ni ions can suppress the diffusion of Yb and CaZrO₃ into BaTiO₃ grains, resulting in formation of core-shell structures in the grains. It is found that Mn is more favorable to stabilize the core-shell structure in BaTiO₃ ceramics as compared with Ni.     

Effect of Bi2O3 doping on the dielectric properties of medium-temperature sintering BaTiO3-based X8R ceramics

Medium-temperature sintering X8R ceramics were fabricated based on BaTiO₃-based ceramics with Bi₂O₃ additives. The effects of sintering aids Bi₂O₃ on crystalline structure and electrical properties of BaTiO₃-based ceramics were investigated. The sinterability of BaTiO₃ ceramics was significantly improved by adding Bi₂O₃, whose densification sintering temperature reduced from 1,260 to 1,130 °C. However, the dielectric constant (ε) of BaTiO₃-based ceramics doped with Bi₂O₃ was decreased dramatically. Both low ε phase Bi₄Ti₃O₁₂ and the decrease of the tetragonality (c/a ratio), which are demonstrated by XRD pattern, are resulted in the decrease of ε. The ε of samples doped with 5.5 wt% Bi₂O₃ was higher than the other doped samples. The substitution of Bi³⁺ for the Ba²⁺ in BaTiO₃ resulted in the increase of electrovalence (from +2 to +3) of A-site ion, so the attractive force between A and B (Ti⁴⁺) sites becomes stronger. Thus Ti⁴⁺’s polarization enhances, then ε was increased to some extent. The X8R BaTiO₃-based ceramics could be sintered at as low as 1,130 °C by doping 5.5 wt% Bi₂O₃ additives into the BaTiO₃-based ceramics, with a ε greater than 2,430 at 25 °C, dielectric loss lower than 1.3 % and temperature coefficient of capacitance <±15 % (?55–150 °C).     

Effect of simultaneous double doping in Ba and Ti sites on dielectric and ferroelectric properties of sol–gel synthesized nano-BaTiO<Subscript>3</Subscript>

Lead free (Ba_(1−3x)Nd_(2x))(Ti_(1−y)Zr_y)O₃ (x = 0, 0.025, y = 0, 0.025, 0.05) ceramics were prepared successfully using sol–gel method. The effect of Nd, Zr content on dielectric and polarisation properties of BaTiO₃ were studied using dielectric and hysteresis measurements. SEM analysis proved that the particle size of compounds as prepared were in the order of 30–60 nm. The ferroelectric phase transition from tetragonal to cubic phase was observed around 130 °C for pure BaTiO₃. With the addition of Nd (2.5 mol%) and increasing content of Zr (2.5 and 5 mol%), it was observed that transition temperature (T_c) shifts to lower temperatures (70–50 °C), but didn’t show any relaxor behaviour. Dielectric measurements showed an increase in the values at room temperature in all the doped samples. The synthesized ceramics exhibited typical P–E hysteresis loops at room temperature accompanied by saturation polarisation (P_s) and remanent polarisation (P_r). Behaviour of polarisation phenomena in these compounds showed interesting results with increasing temperature.     

Synthesis and characterization of BaTiO<Subscript>3</Subscript>-based X9R ceramics

The effects of (Na_0.5Bi_0.5)TiO₃ (NBT) and MgO addition on the dielectric properties and microstructures of BaTiO₃ (BT) ceramics were investigated. NBT was first added to Nb₂O₅-doped BT system. As NBT content increases from 0 to 0.2 mol, the Curie temperature of the systems shifts to high temperatures and dielectric constant peak at T _c is suppressed evidently. The variation of capacity (ΔC/C _20 °C (%)) of the system at 200 °C decreases with increasing NBT content from 0.1 to 0.2 mol, but that of −55 and 125 °C increases monotonously. The stable temperature characteristics of the dielectric properties improved by NBT doping would be connected with the distortion and deformation of the structure induced by substitution of Na⁺ and Bi³⁺ into Ba sites. MgO was employed to further flatten the ΔC/C _20 °C–T curve. It is very helpful for this ceramic system to satisfy the requirement of EIA-X9R specification on ΔC/C _20 °C and still keep a satisfied dielectric constant. The addition of MgO improved effectively the temperature stability of the dielectric properties. Changes of the crystalline structure and microstructure induced by MgO doping might contribute to these improvements.     

Compositionally graded multilayer Ba<Subscript>x</Subscript>Sr<Subscript>0.95−x</Subscript>Ca<Subscript>0.05</Subscript>TiO<Subscript>3</Subscript> ceramics prepared by tape casting for use as dielectric materials

Compositionally graded multilayer Ba_xSr_0.95−xCa_0.05TiO₃ (BSCT) ceramics were prepared via tape casting method using nanometer powders from co-precipitation. Microstructures and dielectric properties of the BSCT system were investigated. The powders were characterized by using transmission electron microscope and BET surface area measurement. Surface morphologies of the sintered samples and multilayer structure were examined by scanning electron microscopy. BSCT particles were of spherical shape with diameters in the range of 73–93 nm. Their specific surface areas were in the range of 11.7–14.6 m²/g. The graded BSCT ceramics with nine layers laminated in vertical way exhibited a higher sintered density, with an average grain size of 0.4 μm, after sintered at 1,200 °C. Dielectric constant, dielectric loss and tunability of the graded ceramics were 2223.94, 1.5 × 10⁻³ at 2 MHz and 42.9% at 3.0 kV/mm, with good dielectric temperature and frequency stability, which made it a promising candidate used for tunable ceramic capacitors and phase shifters.     

Electrical properties of R<Subscript>2</Subscript>O–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> glass–ceramics for anodic bonding

Temperature and frequency dependence on electrical properties (dielectric constant, dielectric loss and conductivity) of Li₂O–Na₂O–K₂O–Al₂O₃–SiO₂(R₂O–Al₂O₃–SiO₂) system glass–ceramics used as anodic bonding materials were discussed. The results showed that the main crystal phase of glass–ceramics was lithium metasilicate (Li₂SiO₃). Compared with the parent glass, both the dielectric constant and dielectric loss of glass–ceramics decreased, the dielectric constant and dielectric loss increased gradually with the increasing of the test temperature from room temperature to 400 °C, Testing frequency (30–300 MHz) had very little influence on the dielectric properties of samples. The electrical conductivity of glass–ceramics showed a trend of first decrease and then increase with the increasing of temperature. The glass–ceramics which has a lower dielectric constant, dielectric loss and better stability under high frequency was obtained after an appropriate heat treatment; it could be used as anodic bonding materials under very high frequency.     

Effects of Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> doping on the microstructure and the dielectric temperature characteristics of barium titanate ceramics

In this work, the effects of Nb₂O₅ addition on the dielectric properties and phase formation of BaTiO₃ were investigated. A core–shell structure was formed for Nb-doped BaTiO₃ resulted from a low diffusivity of Nb⁵⁺ ions into BaTiO₃ when grain growth was inhibited. In the case of 0.3–4.8 mol% Nb₂O₅ additions, two dielectric constant peaks were observed. The Curie dielectric peak was determined by the ferroelectric-paraelectric transition of grain core, whereas the secondary broad peak at lower temperature was due to strong chemical inhomogeneity in Nb-doped BaTiO₃ ceramics. The dielectric constant peak at Curie temperature was markedly depressed with the addition of Nb₂O₅. On the other hand, the secondary dielectric constant peak was enhanced when sintered above 1280 °C for higher Nb₂O₅ concentrations (≥1.2 mol%). The Curie temperature was shifted to higher temperatures, whereas the transition temperature corresponding to the secondary peak moved to lower temperatures as increasing the amount of Nb₂O₅ more than 1.2 mol%. The decrease of this lower transition temperature was assumed to be closely related with the secondary phase formation when Nb concentration greater than 1.2 mol%. From XRD analyses, a large amount of secondary phases was observed when Nb₂O₅ amount exceeded 1.2 mol%. The coefficients of thermal expansion of Nb-doped BaTiO₃ were increased with increasing Nb₂O₅ contents, resulting in large internal stress between cores and shells. Therefore, the shift of Curie temperature to higher temperatures was attributed to internal stress resulting from the formation of a core–shell structure and a large amount of secondary phase grains.     

Preparation and properties of pressureless-sintered porous Si3N4

Wave-transparent materials used at high temperature environment generated by high supersonic and hypersonic speeds must possess excellent mechanical property. In this paper, porous Si₃N₄ ceramics with high strength were fabricated by low molding pressure (10 MPa) and pressureless sintering process, without any other pore forming agents. The sintering behavior and the effect of porosity on the mechanical strength and dielectric properties were investigated. The flexural strength of porous Si₃N₄ ceramics was up to 57–176 MPa with porosity of 45–60%, dielectric constant of 2.35–3.39, and dielectric loss of 1.6–3.5 × 10⁻³ in the frequency range of 8–18 GHz, at room temperature. With the increase of porosity, the flexural strength, dielectric constant, and dielectric loss all decreased.     

The effect of doping process on microstructure and dielectric properties of BaTiO3-based X7R materials

The effect of doping process on the dielectric properties, sintering behavior and microstructure were investigated on the BaTiO₃–Nb₂O₅–Co₃O₄ ternary system ceramic. Temperature stable dielectric ceramics were obtained by different doping processes if only appropriate Nb⁵⁺+Co³⁺ amount and Nb⁵⁺/Co³⁺ ratio were adopted. The dielectric constant was enhanced to the largest extent by nanometer oxide doping and the temperature characteristic satisfied the X7R specification. Two kinds of grains were observed in all the samples: matrix grains (BaTiO₃) and the secondary phase grains (Ba₆Ti₁₇O₄₀) formed by the incorporation of Nb⁵⁺ and Co³⁺ into BaTiO₃ lattice and Ti⁴⁺ segregation. The matrix grains were about 1 m in diameter and showed little grain growth with increasing temperature in all the doped samples, whereas the sizes of the secondary phase grains were strongly dependent on the doping process. The secondary phase formed liquid phase during firing, but the liquid phase contributed little to the densification of ceramics.     

Structure and dielectric properties of potassium niobate nano glass–ceramics

Glasses in the composition of 25K₂O-25Nb₂O₅-50SiO₂ (mol %) have been prepared by melt quenching technique and isothermally heat-treated at 800 °C for different duration (0–200 h). The formed nanocrystalline KNbO₃ phase, crystallite size and morphology are examined by X-ray diffraction, Fourier transform infrared reflection spectroscopy, field emission scanning and transmission electron microscopes. The frequency and temperature dependent dielectric constant and loss tangent are measured in the frequency and temperature ranges 0.1–1000 kHz and 200–500 °C respectively. The dielectric constant and loss tangent are found to decrease with increasing frequency and increase with increasing temperature. The dielectric constant and loss tangent versus temperature curve at different frequency revealed the phase transition of KNbO₃ from paraelectric cubic to ferroelectric tetragonal around 425 and 397 °C (Curie temperature) for nano glass–ceramics obtained after 1 and 200 h heat-treatment respectively.     

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%.