Synthesis and microwave dielectric properties of Ba4Ti3P2O15 ceramics

Present work introduces a new kind of microwave dielectric ceramic, Ba₄Ti₃P₂O₁₅. Ba₄Ti₃P₂O₁₅ ceramic can be prepared by solid state reaction method and be well densified after being sintered at above 1175 °C for 4 h in air. All the XRD patterns can be fully indexed as single-phase structure. The best microwave dielectric properties can be obtained in ceramic sintered at 1200 °C for 4 h with permittivity about 20.7, Q × f about 42,210 GHz and TCF about 37 ppm °C^?1. Measurements of the microwave dielectric properties of Ba₄Ti₃P₂O₁₅ ceramic revealed the existence of a maximum in the temperature dependence of the dielectric loss because of the defect dipoles relaxation.     

Preparation, characterization and dielectric properties of Ba3Ln3Ti5Nb5O30 (Ln=La, Nd) ceramics

Ba₃Ln₃Ti₅Nb₅O₃₀ (Ln=La, Nd) ceramics were prepared by the conventional solid-state ceramic route. The sintered samples were characterized by X-ray diffraction and scanning electron microscopy (SEM) methods. They have high dielectric constants, 141 and 203 at 13 MHz for La-based and Nd-based ceramics, respectively. The loss factor of the ceramics increases with frequency.     

Microwave dielectric properties of Ba3La2Ti2Nb2−xTaxO15 ceramics

High dielectric constant and low loss ceramics in the system Ba₃La₂Ti₂Nb_2−xTa_xO₁₅ (x = 0–2) have been prepared by conventional solid-state ceramic route. Ba₃La₂Ti₂Nb_2−xTa_xO₁₅ solid solutions adopted A₅B₄O₁₅ cation-deficient hexagonal perovskite structure for all compositions. The materials were characterized at microwave frequencies. They show a linear variation of dielectric properties with the value of x. Their dielectric constant varies from 49.8 to 45.1, quality factor Q_u × f from 22,000 to 31,040 GHz and temperature variation of resonant frequency from + 6.9 to − 13.4 ppm/°C as the value of x increases. These low loss ceramics might be used for dielectric resonator (DR) applications.     

Ba4Nd2Ti4Ta6O30 dielectric ceramics modified by Bi substitution for Nd

Modification of dielectric properties for Ba₄Nd₂Ti₄Ta₆O₃₀ ceramic was investigated through Bi partial substitution for Nd. The dielectric constant increased and the dielectric loss decreased with increasing concentration of Bi, and the dielectric constant reached 142, combined with a low dielectric loss of 10^–4 (at 1 MHz) for the composition Ba₄(Nd_0.975Bi_0.025)₂Ti₄Ta₆O₃₀. The temperature coefficient () can be slightly improved.     

Low temperature sintering and dielectric properties of Ba2Ti3Nb4O18 ceramics for silver co-sintering application

Low temperature sintering and dielectric properties of Ba₂Ti₃Nb₄O₁₈ ceramics with ZnO–B₂O₃–SiO₂ (ZBS) frit and lithium salts addition were investigated for silver co-sintering application. The sintering temperature of dense Ba₂Ti₃Nb₄O₁₈ ceramics with ZBS frit or LiNO₃ addition was effectively lowered to 950 or 1,000 °C, respectively. LiNO₃ is found to be more efficient than LiF or Li₂CO₃ to lower the sintering temperature of Ba₂Ti₃Nb₄O₁₈ ceramics. The sintering temperature of 900 °C was obtained for the Ba₂Ti₃Nb₄O₁₈ ceramics with a combination of ZBS frit and LiNO₃ addition. The dielectric properties of Ba₂Ti₃Nb₄O₁₈ ceramics with 1 wt.% ZBS and 0.5 wt.% LiNO₃ sintered at 900 °C are as follows: ε_r ~ 37.8, tan δ ~ 0.0003, τ_ε ~ 4.6 ppm/°C.     

Modification of Ba4Sm2Ti4Ta6O30 dielectric ceramics

Modification of promising tungsten bronze-type dielectric ceramic Ba₄Sm₂Ti₄Ta₆O₃₀ has been investigated by adjusting the composition in Ba_4-3xSm_2+2xTi₄Ta₆O₃₀. The temperature coefficient of dielectric constant has been significantly improved by such modification together with the suppressed dielectric loss, but the dielectric constant decreased significantly. © 2000 Kluwer Academic Publishers     

PbTiO3+Bi2Ti2O7掺杂的Ba4.5Nd9Ti18O54微波介质陶瓷

研究了PbTiO3 Bi2Ti2O7掺杂的Ba4.5Nd9Ti18O54微波介质陶瓷材料的结构和介电性能.结果表明,随着掺杂量的增加,陶瓷材料的密度呈现出轻微下降的趋势,介电常数则保持较高的数值,Q值及τf随掺杂量的增加而下降.当PbTiO3 Bi2Ti2O7掺杂量为20%时,材料的εr≈93,Q.f≈5800 GHz,τf≈3×10-5/℃.XRD分析表明,当PbTiO3 Bi2Ti2O7掺杂量小于24%时,Ba4.5Nd9Ti18O54材料仍呈现出单相结构.利用电介质极化理论初步解释了材料介电性能变化的原因.     

Preparation and characterization of K-substituted NaCa4Nb5O17 microwave dielectric ceramics

The effect of K substitution for Na on the phase, microstructure and microwave dielectric properties of the Na_1?x K _x Ca₄Nb₅O₁₇ (x = 0–1) composition series was investigated. The compositions with x = 0, 0.5 and 1 formed single-phase Na_1?x K _x Ca₄Nb₅O₁₇ ceramics within the detection limit of the in-house XRD facility when sintered at 1,200–1,300 °C. At x = 0.25 and 0.75, the major Na_1?x K _x Ca₄Nb₅O₁₇ phase formed but along with a secondary CaNb₂O₆ phase. Relative permittivity (ε _r ) and temperature coefficient of resonant frequency (τ_f) increased from 45 to 51 and ?120 to +473 ppm/ °C respectively while the quality factor (Q × f _o ) decreased from 13,838 to 2,374 GHz with an increase in x from 0 to 1. Optimum microwave dielectric properties (i.e. ε _r  = 47, Q × f _o  = 5,047 GHz and τ_f = ? 23 ppm/ °C) were achieved for the x = 0.5 (i.e. Na_0.5K_0.5Ca₄Nb₅O₁₇) composition. Further investigations are required to improve the density and hence microwave dielectric properties of Na_1?x K _x Ca₄Nb₅O₁₇ ceramics.     

Microwave dielectric properties and compatibility with silver of low-fired Ba2Ti3Nb4O18 ceramics with BaCu(B2O5) addition

The effects of BaCu(B₂O₅) (BCB) additions on the sintering temperature and microwave dielectric properties of Ba₂Ti₃Nb₄O₁₈ ceramic have been investigated. The addition of BCB can lower the sintering temperature of Ba₂Ti₃Nb₄O₁₈ ceramic from 1,250 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 5 wt% BCB added Ba₂Ti₃Nb₄O₁₈ ceramic sintered at 900 °C for 2 h exhibited good microwave dielectric properties of Q × f = 17,600 GHz, ε _r = 38.2 and τ _f  = 7 ppm/°C. The dielectric ceramic demonstrated stability against the reaction with the Ag electrode, which suggests that the ceramics could be applied in multilayer microwave devices requiring low sintering temperatures.     

Preparation and microwave dielectric properties of Bi2Ti4O11 ceramics

Single phase of Bi₂Ti₄O₁₁ ceramics, which belong to meta-stable phase compounds, were synthesized by controlling the reaction time through conventional solid-state method. The effects of annealing time on phase composition of Bi₂Ti₄O₁₁ ceramic powders and sintered ceramics were studied by XRD analysis. Second phase Bi₂Ti₂O₇ appeared when the annealing time shorter than 4 h. However, pure phase of Bi₂Ti₄O₁₁ powders can be formed by prolonging the annealing time to 6 h at 1,000 °C. The sintering temperatures on microstructure and microwave dielectric properties of Bi₂Ti₄O₁₁ ceramics were investigated. The results show that ceramics sintered at 1,075–1,175 °C are single phase of Bi₂Ti₄O₁₁ and present two different sizes of prismatic shape grains. Smaller size crystals grow into larger ones with increasing sintering temperature. The ceramics sintered at 1,125 °C reach a maximum density and have a microwave dielectric properties of ε_r = 51.2, Q × f = 3,050 GHz and τ_f = ?297 ppm/°C.     

Low-temperature sintering and microwave dielectric properties of Ba3Ti4Nb4O21 with MnCO3–CuO

Effects of MnCO₃–CuO (for short MC) additives on densification and dielectric properties of Ba₃Ti₄Nb₄O₂₁ ceramics have been investigated. The densification temperature of Ba₃Ti₄Nb₄O₂₁ is greatly reduced from 1280 °C for pure Ba₃Ti₄Nb₄O₂₁ to 950 °C with the presence of MC. This is caused by the liquid phase sintering taking place between MC and Ba₃Ti₄Nb₄O₂₁ during sintering. The dielectric constant and the quality factor decrease with increasing MC additives. At a given amount of sintering additive, the dielectric constant and the quality factor decrease with increasing Mn content in the MC mixture. The Ba₃Ti₄Nb₄O₂₁ ceramics with 1 wt% 0.2MnCO₃–0.8CuO sintered at 950 °C for 2 h shows dielectric properties: ε _r  = 66, Q  ×  f = 13,400 GHz and τ _f  = 60 ppm/°C. Also, the material is compatible with Ag electrodes and, therefore, is suitable for LTCC application.     

Preparation,characterization and dielectric properties of Ba3−xSrxM4Ti4O21 (M = Nb,Ta and 0 ≤ x ≤ 3) ceramics

Ba_3−xSr_xM₄Ti₄O₂₁ (M = Nb, Ta and 0 ≤ x ≤ 3) ceramics have been prepared through solid state ceramic route. The structure and microstructure of the compositions have been studied using powder X-ray diffraction and Scanning Electron Microscopic studies. In the present study, both Ba₃Nb₄Ti₄O₂₁ and Ba₃Ta₄Ti₄O₂₁ are obtained as single phase compositions whereas strontium rich compositions exhibit multiphase in nature. Energy dispersive X-ray analysis has been performed to identify the nature of additional phases present in the strontium rich compositions. The dielectric constant, dielectric loss and temperature variation of dielectric constant of the well sintered ceramic specimens have been studied in the low frequency region (< 13 MHz) using an impedance analyzer. The present study reveals that high dielectric compositions can be realized by Sr-substitution in the BaO–TiO₂–Nb₂O₅/Ta₂O₅ ternary systems.     

Microstructure and dielectric relaxor behavior of Ba(Zr0.2Ti0.8)O3–(Ba0.7Ca0.3)TiO3–BaBi4Ti4O15 ceramics by tape casting

Plate-like BaBi₄Ti₄O₁₅ powders were used to fabricate 0.952[Ba(Zr_0.2Ti_0.8)O₃–(Ba_0.7Ca_0.3)TiO₃]–0.048BaBi₄Ti₄O₁₅(abbr. BZCT-BBT) ceramics by tape casting. The microstructure and dielectric relaxor behaviors of BZCT-BBT ceramics were investigated. BZCT-BBT ceramics can be sintered well at 1,100?°C and mainly consisted of tetragonal perovskite phase and BaBi₄Ti₄O₁₅ (abbr. BBT) phase. The lattice constants decrease as the sintering temperature increases due to substitution of Bi³⁺ for the A-site atoms of the perovskite structure. There is no obvious difference between the structure in the perpendicular and parallel directions, however, an evident difference of dielectric properties in the two directions is observed. Comparing with Ba(Zr_0.2Ti_0.8)O₃–(Ba_0.7Ca_0.3)TiO₃(abbr. BZCT) ceramics, BZCT-BBT ceramics show obvious relaxor characteristics which are evidenced by the degree of diffuseness γ calculated using the modified Curie–Weiss law. Meanwhile, the addition of BBT decreases T_m, which results from the decrease of grain size. The reduction of ε_m is mainly caused by phase structure deviation from the coexisting rhombohedral and tetragonal structure to single tetragonal.     

Dielectric properties and high-temperature dielectric relaxation of tungsten-bronze structure ceramics Ba2GdFeNbTa3O15

Ba₂GdFeNbTa₃O₁₅ was synthesized by a standard solid-state technique, which adopts a tetragonal filled tungsten bronze structure and exhibits paraelectric nature at room temperature. The dielectric temperature coefficient of Ba₂GdFeNbTa₃O₁₅ at 1 MHz is 147 ppm °C_.⁻¹ AC impedance plots were used as tools to analyze the electrical behavior of the sample as a function of frequency at different temperatures. The conduction is a thermally activated process with activation energy ~1.30 eV. The frequency-dependent maxima in the imaginary part of impedance are found to obey an Arrhenius law with activation energy ~1.34 eV. Such a value of activation energy suggests the existence of a relaxation mechanism (a conductive process), which may be interpreted by an ion hopping between neighboring sites within the crystalline lattice.     

溶胶凝胶法制备钛酸锶钡(Ba1-xSrx)TiO3陶瓷及其介电性能的研究

采用硝酸钡、硝酸锶、钛酸丁酯和柠檬酸为原料的配合物溶胶凝胶方法制备了(Ba1-xSrx)TiO3(BST)陶瓷.实验结果表明,BST粉体合成温度及烧结温度分别为700及1250℃,均低于传统工艺的相应温度. Sr含量x≥0.40,(Ba1-xSrx)TiO3陶瓷的相结构为立方钙钛矿相;Sr含量x＜0.40,(Ba1-xSrx)TiO3陶瓷的相结构为四方钙钛矿型. (Ba1-xSrx)TiO3(0.5≤x≤0.70)陶瓷的电容率随温度变化曲线,说明存在由铁电四方相到顺电立方相的相变.且随锶(Sr)的摩尔量x的增加,(Ba1-xSrx)TiO3陶瓷样品的相变温度向低温方向移动,相变温度Tc的移动关系为Tc=394.1-272.6x(K).     

Studies of structural and dielectric properties of Ba5BiTi3Nb7O30 ceramics

The polycrystalline samples of Ba₅BiTi₃Nb₇O₃₀ (hereafter BBTN) belonging to ferroelectric oxide family of tungsten bronze structure were prepared by high temperature solid-state reaction method. Preliminary X-ray analysis of the samples provided the lattice parametersa=11·9331 Å,b=14·9684 Å, andc=7·0193 Å, and also formation of a single-phase orthorhombic structure at room temperature (303 K). Detailed studies of dielectric constant (ε) and loss (tanδ) as a function of frequency (500 Hz to 10 KHz) at room temperature and also as a function of temperature (liquid nitrogen to 160°C) show the dielectric anomaly and structural phase transition at 16·8°C.