Composite Dielectric Ceramics Research Articles

Microwave dielectric properties of (Na0.5Bi0.5)MoO4–BaMoO4 composite ceramics with ultralow sintering temperature

AbstractThe rapidly ever‐growing wireless communication demands development of low loss, ultralow sintering temperature dielectric ceramics with excellent microwave properties. In this work, fabrication and properties of novel microwave dielectric composite ceramics (1 − x)(Na0.5Bi0.5)MoO4–xBaMoO4 (x = 0.3–0.6), in short as ((1 − x)NBM–xBM), synthesized via solid‐state reaction method with an ultralow sintering temperature is reported. X‐ray diffraction analysis confirms the coexistence of both (Na0.5Bi0.5)MoO4 and BaMoO4 scheelite phases. Scanning electron microscopy analysis demonstrated dense microstructures of ceramics sintered at 650°C and 700°C. The dielectric properties of (1 − x)NBM–xBM (x = 0.3–0.6) ceramic are significantly tailored by incorporation of BaMoO4. With the increase in x from 0.3 to 0.6, the (1 − x)(Na0.5Bi0.5)MoO4–xBaMoO4 displays noticeable change in microwave permittivity (varying from 25.4 to 16.6), quality factor values, and temperature coefficient of frequency (range tunable from +37.6 ppm/°C to −14.2 ppm/°C). The microwave dielectric ceramic, 0.5(Na0.5Bi0.5)MoO4–0.5BaMoO4, has optimum dielectric properties (, = 15 164 GHz, τf = −0.2 ppm/°C) at sintering temperature of 650°C. The dielectric resonator antenna designed using (1 − x)(Na0.5Bi0.5)MoO4–xBaMoO4 ceramics demonstrated excellent radiation performance at resonance frequency of 5.905 GHz, gain of ∼5.8 dBi and 140 MHz bandwidth, which validates its microwave applications utilization within the field of ultralow temperature cofired ceramics technology.

Microstructure and dielectric properties of novel MgTiO3-x wt% MgAl2O4 microwave dielectric composite ceramics

Microstructure and dielectric properties of novel MgTiO3-x wt% MgAl2O4 microwave dielectric composite ceramics

Phase compositions and microwave dielectric characteristics of xMg2B2O5-(1-x)Ba3V2O8 (0.5 ≤x ≤ 0.7) ceramics

Herein, xMg2B2O5-(1-x)Ba3V2O8 (0.5 ≤x ≤ 0.7) microwave dielectric composite ceramics were prepared via the solid-state reaction method at a relatively low sintering temperature (around 940–1020 °C). The phase compositions, microstructure, and elemental compositions of the ceramics were characterized by X-ray diffraction (XRD), and scanning electron microscopy (SEM) combined with energy-dispersive spectroscopy (EDS), respectively. According to the results, both Mg2B2O5 and Ba3V2O8 phases coexisted after sintering in the temperature range of 940–1020 °C. The growth of Ba3V2O8 grains was inhibited by the increase in amount of Mg2B2O5 inclusions. Moreover, mixing these two phases in a proper ratio did not only reduce the sintering temperature, but also improved the temperature coefficient of resonant frequency (τf) and Q×f value (Q is quality factor=1/ dielectric loss, f=resonant frequency) of the xMg2B2O5-(1-x)Ba3V2O8 microwave dielectric ceramics. In particular, the optimal microwave dielectric properties (εr = 10.1, Q×f = 48,050 GHz, τf = −3 ppm/°C) were reached after 2 h of sintering at 960 °C for the ceramic with x = 0.7.

An alternative way to design excellent energy-storage properties in Na0.5Bi0.5TiO3-based lead-free system by constructing relaxor dielectric composites

With growing concerns over environmental protection, lead-free dielectric ceramic capacitors are attracting much attention. In this work, a series of novel (1-x) Na0.5Bi0.5TiO3-x Ba5LaTi3Ta7O30 ((1-x)NBT-xBLTT) dielectric composite ceramics were fabricated by a traditional solid‐state method. All the samples possess a compact microstructure with refined grain morphology with increasing BLTT content, and tend to exhibit a diphase dielectric composite as x reaches up to 0.05. Furthermore, the addition of BLTT enhances the dielectric relaxor behavior of NBT-based ceramics, such that the x = 0.15 composite ceramic exhibits a typical feature of relaxor ferroelectrics. As a result, a high recoverable energy-storage density of Wrec~3.67 J/cm3, an ultrahigh energy-storage efficiency of η~97.3%, and a high power density of PD~333 MW/cm3 can be simultaneously obtained in the x = 0.15 relaxor composite ceramic. This study provides an alternative way to design excellent energy-storage performances in NBT-based compositions through constructing dielectric relaxor composites via introducing non-polar tungsten bronze oxides.

Low dielectric loss ceramics in the Mg4Nb2O9-ZnAl2O4-TiO2 ternary system

This study used a traditional solid-state reaction method to prepare a series of composite ceramics in the 0.7Mg4Nb2O9-(0.3-x)ZnAl2O4-xTiO2 ternary system. Crystalline phases and microstructure of Mg4Nb2O9-ZnAl2O4-TiO2 dielectric ceramic composites were investigated and correlated with the relevant dielectric properties. It was observed that the addition of Ti4+ substituted Nb5+ in the Mg4Nb2O9 structure, which promoted the decomposition of Mg4Nb2O9 to form the second phase, Mg5Nb4O15, during sintering. The synergistic effect of ZnAl2O4-TiO2 co-doping promoted the Mg4Nb2O9 ceramic densification. The sample (0.7Mg4Nb2O9-(0.3-x)ZnAl2O4-xTiO2) with x = 0.15−0.2 exhibited dielectric constants of 13–14, larger than those of ZnAl2O4, Mg4Nb2O9 and Mg5Nb4O15, due to the NbO6 octahedra distortion resulting from the substitution of Al3+/Ti4+ for Nb5+ in Mg4Nb2O9 and Mg5Nb4O15. The long-range order of the NbO6 octahedra was enhanced by co-doping ZnAl2O4 and TiO2, thereby enhancing the Qxf value. A dielectric constant of 13.1, Qxf value of 366,000 GHz and a τf of −60.8 ppm/°C were obtained from 1300 °C sintered 0.7Mg4Nb2O9-0.15ZnAl2O4-0.15TiO2. These results show that 0.7Mg4Nb2O9-0.15 ZnAl2O4-0.15TiO2 ceramic is a good candidate for microwave electronic device applications.

High-performance microwave dielectric composite ceramics sintered at low temperature without sintering-aids

(1-x)Li2(Mg0.96Ni0.04)SiO4+xLiZn0.93Co0.07PO4 composite ceramics were synthesised through solid-state reaction, and their sintering kinetics, microstructure and microwave dielectric properties were investigated. The perfect disconnection model was applied to explain the variation in grain growth with different x values and sintering temperatures. X-ray diffraction, scanning electron microscopy, thermo-mechanical analysis and network analysis were used to determine the macro and micro properties of the composite ceramics. Results showed that LiZn0.93Co0.07PO4 ceramic could promote grain growth and grain boundary modification, due to the different levels of shear stress and free energy density of the Si-rich and P-rich phases. The shrinkage onset point of the composite ceramics was adjusted to achieve full densification at 900 °C. The peak microwave dielectric properties are εr = 5.78, Q × f = 48,168 GHz at 16 GHz and τf = −44.7 ppm/°C when x = 0.5, sintering temperature is 900 °C and relative density is 96.1%. Therefore, mixing LiZn0.93Co0.07PO4 (pre-sintered) and Li2(Mg0.96Ni0.04)SiO4 (pre-sintered) ceramics is a feasible synthesis method for microwave dielectric materials with excellent sintering and dielectric properties.

Dielectric ceramic composites with controllable thermal expansion: SrTiO3/Zr2P2WO12

SrTiO3/Zr2P2WO12 dielectric ceramic composites with controllable coefficient of thermal expansion (CTE) were prepared by using the solid-state method, and X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS) spectrum were used to analyze its composition and microstructure. The coefficients of thermal expansion and dielectric properties were measured with a dilatometer and precision impedance analyzer, respectively. Results showed that the solid-state method was effective in obtaining composites with controllable thermal expansion coefficients (9.23–2.37) × 10−6/K and dielectric constants (17.15–39.56, 1 MHz) by combining the negative thermal expansion materials Zr2P2WO12 and SrTiO3.

Low-firing, temperature stable and improved microwave dielectric properties of ZnO[sbnd]TiO2[sbnd]Nb2O5 composite ceramics

This article presents low-firing, low-loss and temperature stable ZnOTiO2Nb2O5 microwave dielectric composite ceramics with the assistance of lithium borosilicate (LBS) and zinc borosilicate (ZBS) glass frits. There is a liquid phase (eutectic mixture) generated by LBS (ZBS) glass, and solid particles could be wetted and dissolved. Therefore, the migrations and rearrangements of particles could be performed. Besides, compared with ceramics undoped with glass frits, lower activation energies (Ea) of ceramics doped with LBS and ZBS glass suggest that the low-temperature sintering behavior is easier to carry out. The results indicated that LBS and ZBS glass both are effective sintering aids to accelerate the sintering process and improve the microwave dielectric properties of composite ceramics by controlling the phase compositions under low temperature. Combination great properties of ZnOTiO2Nb2O5 ceramics were obtained when sintered at 900 °C for 4 h: εr = 36.7, Q × f = 20,000 GHz, τf = 7 ppm/oC.

Effects of Al2O3 on sinterability and properties of MgTiO3/CaO–B2O3–SiO2 dielectric ceramic composites

Al2O3 amended the new-type MgTiO3/CaO–B2O3–SiO2 (CBS) ceramic composites for low temperature co-fired ceramic (LTCC) applications were prepared via solid-state reaction, and the sinterability, crystalline composition, microstructure and performance of the synthesized samples were determined. The Al2O3 additive significantly promoted the dielectric performance of the ceramic composites, but also effectively promoted the bulk density and mechanical performance of the composites. Compared with other experimental samples and commercial products, the composite sample doped 4 wt% Al2O3 sintered at 850 °C for 60 min showed superior performance, which comprised a relatively-high bulk density, dielectric constant (er) of 11.47, dielectric loss (tanδ) of 2.4 × 10−4 and volume resistivity (ρv) of 12.80 × 1011 Ω cm at 1 MHz, and flexural strength (σf) of 269.23 MPa.

Sintering behavior and properties of MgTiO3/CaO-B2O3-SiO2 ceramic composites for LTCC applications

In this study, a new-type dielectric substrate composed of MgTiO3/CaO-B2O3-SiO2 (CBS) dielectric ceramic composites was prepared via solid-state reaction. The sinterability, crystalline composition, microstructure, dielectric performance and mechanical property of the synthesized ceramic composites were determined. As high performance dielectrics, MgTiO3 ceramics significantly promoted the dielectric performance of the ceramic composites, but also effectively promoted the bulk density and mechanical performance of the composites. The composite sample containing 40 wt% MgTiO3 sintered at 830 °C for 60 min showed superior performance, which comprised a relatively-high bulk density, dielectric constant (εr) of 10.85, dielectric loss (tanδ) of 3.3 × 10−4 and volume resistivity (ρv) of 8.03 × 1011 Ω cm at 1 MHz, and flexural strength (σf) of 214.85 MPa.

Influence of Mg2SiO4 addition on crystal structure and microwave properties of Mg2Al4Si5O18 ceramic system

In this work, (1 − x)Mg2Al4Si5O18–xMg2SiO4 (x = 0–80 wt%) composite dielectric ceramics were prepared via traditional solid-state reaction. The results indicate the sinterability of Mg2Al4Si5O18 ceramics is greatly enhanced with the increasing content of Mg2SiO4 by reducing densified temperature from 1460 to 1340 °C. Rietveld refinement analysis shows a great chemical compatibility between two phases. With the increase of Mg2SiO4 content, the densifications of ceramics can be improved. However, excessive amount of Mg2SiO4 induces abnormal grain growth, which deteriorates the microwave dielectric properties. At x = 50 wt%, low-er dielectric ceramics with high Q × f value was obtained when sintered at 1340 °C: er = 5.73, Q × f = 76,374 GHz and τf = − 24 ppm/ °C. Relative cheap raw materials and adjustable permittivity values, which makes it promising for low-permittivity microwave applications.

Dielectric Properties of Sr-Doped Na0.5Bi0.5TiO3–Ba(1–x)Sr x Ti0.995Zr0.005O3 Ceramics Synthesized by Wet Solid-State Method

New dielectric composite ceramics Na0.5Bi0.5TiO3–Ba(1–x)Sr x Ti0.995Zr0.005O3 (NBT–BSTZ) ( x= 0.05, 0.1, 0.2, 0.3) have been fabricated by the wet solid-state route. The effect of Sr content on phase structure and electrical properties has been studied in detail. The X-ray diffraction analysis illustrates that the composites consist of tetragonal perovskite. With increasing Sr content, the ceramic capacitors display larger dielectric constant, better temperature stability, and lower dielectric loss in dielectric behavior. The ceramics with composition x = 0.3 possess a large dielectric constant (er) of 2522. The temperature coefficient of capacitance of NBT–BSTZ varies from –39% to 36% in the temperature range between 0 and 200°C. The dielectric loss of capacitance is below 0.07 while the Sr content is 0.3 in the whole range of measured temperatures. The results indicate that Sr-doping is an effective method to modulate the temperature stability and dielectric loss of the NBT– BSTZ dielectric ceramics.

A novel temperature-stable and low-loss microwave dielectric composite ceramics Li2Mg3SnO6-SrTiO3

Phase structure, microstructure and microwave dielectric properties of temperature-stable (1 − x)Li2Mg3SnO6-xSrTiO3 (x = 0.08, 0.12, 0.16, 0.20, 0.24, 0.28) composite ceramics were investigated. The results showed that ceramics contain Li2Mg3SnO6 and SrTiO3 phases and well-densified microstructure were obtained at 1375 °C. The microwave dielectric properties strongly depended on SrTiO3 content x. With increasing x, the dielectric constant (εr) increased from 11.0 to 17.0, the quality factor (Q × f) decreased from 105,100 GHz to 30,770 GHz, and the temperature coefficient of resonant frequency (τf) significantly increased from −35.4 ppm/°C to 37.3 ppm/°C. 0.8Li2Mg3SnO6-0.2SrTiO3 composite ceramics displayed a higher relative density of 97.2% and well microwave dielectric properties of εr = 14.2, Q × f = 67,260 GHz, τf = −4.8 ppm/°C.

The abnormal increase of tunability in ferroelectric-dielectric composite ceramics and its origin

The ternary ferroelectric–dielectric composite ceramics Ba0.45Sr0.55TiO3–MgO–Mg2TiO4 were prepared by solid-stated method and the dielectric tunable properties of composite ceramics were investigated. The abnormal increased tunability in the ternary ferroelectric-dielectric composite ceramics was observed, which shows further that the abnormal increase of tunability exists universally in ferroelectric-dielectric composite. A simple 3D Finite Element Method model was constructed to simulate the dielectric response and explore the origin of abnormal increase of tunability in ferroelectric-dielectric composite. The simulation results of tunability show the same trend as the experimental data. Further analysis of the electric field distribution in ferroelectric-dielectric composites indicated that the abnormal increase of tunability originates from the enhancement of the electric field on a fraction of the ferroelectrics around dielectrics.

Fabrication and enhanced characterization of copper powder filled copper calcium titanate/poly(vinylidene difluoride) composite

The dielectric composite ceramics copper calcium titanate/poly vinylidene fluoride (CaCu3Ti4O12/PVDF) with Cu powder as a modified agent are successfully prepared by solution mixing processing and hot pressing method. The relative dielectric constants of these composites are significantly enhanced with increase in the volume fraction of copper powder. These composites also possess stable frequency and thermal stability properties in the frequency range of 100–1 MHz. The dielectric permittivity of the 60 vol%PVDF/20 vol%CCTO/20 vol%Cu composite ceramics is higher two times than those with undoped Cu powder and reaches the maximum value of 135 (1 kHz) at Cu powder concentration of 20 vol%. The results indicate that using Cu powder as a modification agent can greatly enhance the dielectric permittivity of the ceramic–polymer composite and achieve high-stability for super capacitor applications.

Effects of Mg2.05SiO4.05 addition on phase structure and microwave properties of MgTiO3–CaTiO3 ceramic system

The (1−x) MgTiO3−xMg2.05SiO4.05–0.06CaTiO3 ceramic system composite dielectric ceramics with different amounts of Mg2.05SiO4.05 addition were prepared by solid state reaction method. The results indicated that exceeding Mg in Mg2.05SiO4.05 not only hold back the formation of MgSiO3 but also inhibits the formation of second phase MgTi2O5. A new microwave dielectric material, 0.8MgTiO3–0.2Mg2.05SiO4.05–0.06CaTiO3 ceramics sintered at 1380°C for 4h had optimal dielectric properties (εr=15.4, Q×f=72,705GHz and τf=−1.45ppm/°C) which satisfied microwave applications in resonators, filters and antenna substrates.

Sm/YTi (Ta/Nb) O6: Optical and Microwave Ceramic Composites

The xSmTiTaO6 (1-x)YTiNbO6 dielectric ceramic composites were prepared through the solid state ceramic route. The samples were calcined at 1150 oC and sintered in the range 1380-1450 oC. The structural analysis of the materials was done using X-ray diffraction technique. The surface morphology was studied using scanning electron microscopy and the elemental composition of the composite was confirmed using energy dispersive spectrum. The dielectric properties of the samples were measured in the microwave frequency range using cavity resonator method. The dielectric constant at the radio frequency region is also measured. The UV–Visible spectrum was recorded and band gap was calculated. The photoluminescence spectrum of the representative composite was recorded and transitions causing emissions were studied. Most of the samples possess high dielectric constant, high quality factor and low temperature coefficient of resonant frequency, hence suitable for the fabrication of devices in microwave communication. These materials were useful in optoelectronics also since they have strong emission lines in the visible region.

Microwave dielectric properties of low-temperature sinterable Ba3(VO4)2–LiMgPO4 composite ceramics

New (1−x)Ba3(VO4)2–xLiMgPO4 (x=0.40–0.60) microwave dielectric composite ceramics were prepared by sintering mixtures of Ba3(VO4)2 and LiMgPO4. The composite ceramics can be sintered in the temperature range of 850–875°C. Ba3(VO4)2 and LiMgPO4 coexist and no secondary phase is detected in the sintered bodies. Near-zero temperature coefficients of resonant frequency (τf) can be achieved by changing the relative content of the two phases, due to their opposite τf values. The composite ceramic with x=0.45 sintered at 850°C shows desirable microwave dielectric properties of εr=9.67, Q×f=50,700GHz, and τf=+1.1ppm/°C.

Effects of Mg2SiO4 Addition on the Microstructure and Dielectric Properties of MgTiO3-CaTiO3 Ceramics

The Mg2SiO4-MgTiO3-CaTiO3 composite dielectric ceramics with different Mg2SiO4 addition amounts were prepared by solid state reaction method. The effects of Mg2SiO4 addition amounts on the microstructure and dielectric properties as well as sintering temperature of xMg2SiO4-(0.95-x)MgTiO3-0.05CaTiO3 (abbreviated as xMSTC, 0.25≦x≦0.75) composite ceramics were investigated. The results indicated that the sintering temperature of MgTiO3-CaTiO3 based ceramics with Mg2SiO4 addition could be lowered effectively to 1320~1340°C, and the dielectric constant decreased and dielectric loss increased gradually with the increase of Mg2SiO4 content. The 0.45MSTC ceramics containing 45 wt% Mg2SiO4 and sintered at 1340°C showed desirable dielectric properties with dielectric constant εr=13.3，dielectric loss tanδ=4.5×10-4 and temperature coefficient of relative permittivity τε =10 ppm/°C.

11Li2O-3Nb2O5-12TiO2复合微波介质陶瓷的研究*

本文采用传统固相法制备了11Li2O-3Nb2O5-12TiO2(LNT)复合微波介质陶瓷，通过XRD、SEM分析手段，结合介电性能测试结果，探讨了烧结温度对材料相结构、介电性能的影响。结果表明，原料粉末经850℃预合成后，主要生成Li2TiO3ss以及M-phase固溶体。致密陶瓷片主要由Li2TiO3ss与M-phase固溶体两相复合组成，并没有其他相结构存在。陶瓷片中两相的组分与预合成粉末中两相的组分并不同。烧结温度达1100℃时，陶瓷片烧结致密，密度达3.76 g/cm3，相对介电常数达49，Q × f值为9482 GHz，且具有相当小的温度系数，tf = ~22 ppm/℃。 The 11Li2O-3Nb2O5-12TiO2(LNT) microwave dielectric ceramic composites have been prepared by the solid-state reaction method. The effects of the sintering temperature on phase structure and properties were investigated by XRD, SEM and the measured dielectric properties. The calcined powders at 850˚C and the dense ceramics were mainly composed of Li2TiO3ss and M-phase solid solution. No other phase structure could be found in the dense LNT ceramics. And the compositions of two phases in the dense ceramics are different from those in the calcined powders. The LNT ceramics could be sintered densely at 1100˚C with density of about3.76g/cm3 and good microwave dielectric properties of er = 49, Q × f = 9842 GHz and tf = −22 ppm/˚C.