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BaTi4O9–Ba2Ti9O20 composite phase ceramics with high Q × f as well as near-zero τf were obtained using a conventional solid-phase reaction method. The effect of WO3/CeO2 co-doping on the microwave dielectric properties of the samples was analyzed. The effect of CeO2 doping on the microwave dielectric properties of composite ceramics was investigated. The relationship between WO3 doping and phase evolution, grain morphology distribution and microwave dielectric properties were investigated. The εr, Q × f and τf values were closely correlated to phase composition, such as BaTi4O9, Ba2Ti9O20, BaWO4. When sintered at 1325 °C, the ceramics co-doped 0.07WO3/0.5wt%CeO2 have excellent dielectric properties: εr = 37.81, Q × f = 51,531 GHz, τf = + 3.33 ppm/°C. It may be a candidate material for 5G ceramic filter applications. [ABSTRACT FROM AUTHOR]

BaTi1-x(Sb0.5Nb0.5)xO3 ceramics (0.01 ≤ x ≤ 0.3) were prepared by solid-state reaction method. The effect of co-substituting Ti4+ with Sb3+ and Nb5+ on its crystal structure, microstructure, and dielectric properties was studied. When 0.01 ≤ x ≤ 0.1, a single-phase barium titanate solid solution can be obtained; when 0.15 ≤ x ≤ 0.25, a small amount of unknown second phase was appeared; and when the composition (x) increases to 0.3, a large amount of unknown second phases are precipitated. The main crystal phase of BaTi1-x(Sb0.5Nb0.5)xO3 ceramics has a change of tetragonal to cubic with the increase of x. As x increases from 0.1 to 0.25, the dielectric constant decreases from 1264 to 214, the dielectric loss decreases from 0.253% to 0.046% (1 MHz, 25 °C), the capacitance temperature coefficient changes from − 7897 to − 1657 ppm/ °C, and the insulation resistivity is greater than 1012 Ω cm. This means that BaTi1-x(Sb0.5Nb0.5)xO3 (x = 0.1 ~ 0.25) ceramics can be suitable for temperature-compensated ceramic capacitors. [ABSTRACT FROM AUTHOR]

In this work, Al2O3–CeMgAl11O19 composites were sintered at 1530 °C for 3 h with the wet nitrogen–hydrogen atmosphere in the tunnel kiln for HTCC application. The effects of the CeMgAl11O19 content on the mechanical and dielectric properties were investigated. The results indicated that the CeMgAl11O19 platelets significantly enhanced the mechanical property and slightly reduced the grain size of Al2O3. The optimum bending strength was 450 MPa with 8 wt% CeMgAl11O19 addition. But further additions would promote the abnormal growth of grains and increase porosity. CeMgAl11O19 exhibited insignificant effects on the dielectric properties of composite ceramics, with all samples having dielectric constants in the range of 9–10 and acceptable dielectric losses. For the composite ceramics with 8 wt% CeMgAl11O19, a strong metal–ceramic combination was obtained with metallization adhesion strength greater than 44.5 N/mm2. [ABSTRACT FROM AUTHOR]

0.8Mg2SiO4–0.2Ca0.9Sm0.2/3Al4x/3Ti1−xO3 (x = 0, 0.05, 0.1, 0.15, 0.2, and 0.25) ceramics with zero τf and high Q × f value were prepared by a traditional solid-state reaction method. The influences of Al content on phase evolution, sintering behavior, microstructure and microwave dielectric properties of ceramics have been systematically investigated. With the increase of x, the exchange of Ti4+ and Al3+ at B site leads to the decrease of dielectric constant and the increase of quality factor Q × f. The τf increases first and then decreases to close to 0 with a rise of x from 0.05 to 0.025. The results show that 0.8Mg2SiO4–0.2Ca0.9Sm0.2/3Al0.8/3Ti0.8O3 samples sintered at 1410 °C for 3 h exhibited excellent microwave dielectric properties: εr = 10.69, Q × f = 70,769 GHz, τf = − 0.66 ppm/°C. Therefore 0.8Mg2SiO4–0.2Ca0.9Sm0.2/3Al4x/3Ti1−xO3 ceramics are considered as potential candidates for microwave dielectric applications. [ABSTRACT FROM AUTHOR]

In this work, (1−x)Mg2SiO4–xCa1−ySm2y/3TiO3 ceramics were fabricated using the conventional solid-state reaction method. When y = 0.2, the effects of Ca1−ySm2y/3TiO3 contents on microstructure, phase evolution, and microwave dielectric properties of the samples were studied. The X-ray diffraction showed that Mg2SiO4 and Ca0.8Sm0.4/3TiO3 co-existed in composite ceramics. The dielectric constant (εr) and temperature coefficient of resonant frequency (τf) increased with the increasing content of Ca0.8Sm0.4/3TiO3, while the quality factor (Q × f) decreased. At x = 0.22, the (1−x) Mg2SiO4–xCa0.8Sm0.4/3TiO3 ceramics sintered at 1325 °C for 3 h possessed optimal microwave dielectric properties: εr ~ 11.89, Q × f value ~ 32,703 GHz and τf ~ + 0.49 ppm/°C. As a result, the εr of (1−x) Mg2SiO4 + xCa1−ySm2y/3TiO3 ceramics could be adjusted in the range of 10.83 to 13.88 while the τf is near-zero. [ABSTRACT FROM AUTHOR]

The alumina/glass fibers cloth/polytetrafluoroethylene composites were prepared by blending impregnation followed by hot compression method, and the dielectric, thermal, and mechanical properties of the composites with various Al2O3 contents (15–40 wt%) were investigated. The results show that the thermal conductivity and dielectric constant of the composites increase gradually, while the coefficient of thermal expansion decreases, with the Al2O3 content increasing. Composite substrates with 40 wt% Al2O3 exhibited ideal performance, which have reliable dielectric constant (εr = 3.49), admissible dielectric loss (tanδ = 0.0027), low water absorption (0.04 %), low CTE of 8.73, 10.14 and 110.39 ppm/°C (X-, Y-, Z-direction, respectively), relatively high thermal conductivity (0.61 W m−1 K−1), and satisfactory flexural strength (66.1 MPa). Such compositions may be a promising material in high-frequency microwave substrates. [ABSTRACT FROM AUTHOR]

The effects of injecting TiO2 to a Li2O–MgO–ZnO–B2O3–SiO2 (LMZBS) microwave dielectric composite on sinterability, microstructure, crystalline phase, dielectric characteristics, mechanical characteristics, and coefficient of thermal expansion (CTE) were investigated. With the increase of TiO2 content, the main crystal orientation of the samples gradually changed from Li2MgSiO4 phase, Mg3B2O6 phase, and Mg2SiO4 phase to Li5.48Mg0.74Ti7.26O18, ZnTiO3 phase, and Mg2B2O5 and the densification temperature decreased, whisker-like crystal grains gradually increased, and the porous microstructure appeared at 15% TiO2. With the increase of TiO2 content, the densification temperature of LMZBS ceramics increases, and the dielectric constant increases with the increase of densification temperature. The CTE value decreases with the increase of titanium dioxide content, and the bending strength increases first and then decreases with the increase of titanium dioxide content. The composite with 10 wt% TiO2 content sintered at 900 °C exhibits superior performance: ε r of 7.97, Q value of 1305 (10 GHz), flexural strength of 259 MPa, CTE value of 10.2 ppm/°C, and τ f value of − 13 ppm/°C. The LMZBS/TiO2 composites are suitable for LTCC application with match-well Ag electrodes. [ABSTRACT FROM AUTHOR]

The alumina/hexagonal boron nitride/glass fibers cloth/Polytetrafluoroethylene (Al2O3–hBN/GFs/PTFE) composites were prepared by blending-impregnation followed by hot compression method, and the dielectric, thermal properties of the composites with various hBN fillers content (0–20 wt.%) were investigated. The results show that the thermal conductivity of the composites increase significantly, while the coefficient of thermal expansion (CTE) decrease gradually, with the hBN content increasing. Composite substrates with 20 wt.% hBN exhibited high thermal conductivity as 1.05 W m−1 K−1, which is 5.3 times that of pure PTFE. Such compositions may be a promising material in high thermal conductivity copper clad laminate. [ABSTRACT FROM AUTHOR]

In order to improve the thermal properties of polytetrafluoroethylene (PTFE) as a high-frequency microwave dielectric substrate, PTFE/glass fiber (GF) composites filled with Si3N4 were prepared by the method of combining cold pressing and normal pressure sintering. The effects of content of Si3N4 on microstructure, thermal and dielectric properties of the PTFE/GF composites were studied by scanning electron microscope, laser thermal conductivity analyzer, thermal dilatometer and impedance analyzer, respectively. The results showed that silane coupling agent (KH550) could improve the dispersibility of the Si3N4 particles in PTFE to some extent and Si3N4 fillers could significantly improve the thermal properties of PTFE. Compared with pure PTFE, the coefficient of thermal expansion of PTFE/GF composite filled with 45wt% Si3N4 decreased from 109 to 27 ppm/°C and the thermal conductivity increased nearly twice. The dielectric constant of PTFE/GF composites grew with the content of Si3N4 and had good frequency stability. Although the dielectric loss of the composites deteriorated with the addition of Si3N4, it was significantly decreased with increasing frequency, indicating that there is a potential application of Si3N4 filled PTFE/GF composites in the field of high-frequency dielectric substrate. [ABSTRACT FROM AUTHOR]

In present work, the microwave dielectric properties of CaTiO3-added Li2Zn3Ti4O12 ceramics prepared by the conventional solid-state method have been investigated. The phase composition, microstructure and microwave dielectric properties of (1 − x) Li2Zn3Ti4O12–x CaTiO3 (x = 3, 4, 5, 6 and 7 wt%) ceramics were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), EDS and network analyzer. The XRD and EDS results indicated that the ceramics involved Li2Zn3Ti4O12 and CaTiO3 phases. The SEM micrographs shown that as the CaTiO3 contents increased, the average grain size of the composition ceramics decreased. The microwave dielectric properties of the composition ceramics can be effectively controlled by varying the CaTiO3 contents. The values of dielectric constant (εr) and τf of the composition ceramics were increased, and the quality factor (Q × f) was decreased with increasing the CaTiO3 contents. Typically, a new temperature stable microwave dielectric material of 0.94 Li2Zn3Ti4O12–0.06 CaTiO3 with excellent microwave dielectric properties of εr = 21.7, Q × f = 61,490 GHz, and τf = + 2.68 ppm/°C was attained when sintered at 1175 °C for 4 h. [ABSTRACT FROM AUTHOR]

A novel glass-free MoO3-based dielectric ceramic of Li2Ni2(MoO4)3 was prepared by the conventional solid-state route. The phase compositions, microstructures and microwave dielectric properties were investigated. The XRD data analysis shown that Li2Ni2(MoO4)3 belongs to an orthorhmbic lyonsite-type structure with Pmcn (62) space group during the sintering temperature range from 650 to 725 °C. The Li2Ni2(MoO4)3 ceramic could be well densification at 700 °C for 2 h with 96.8% relative density and exhibited excellent microwave dielectric properties: εr = 9.2, Q × f = 41,064 GHz, τf = − 68.86 ppm/°C. Moreover, the Li2Ni2(MoO4)3 ceramic shown excellent compatible with Ag electrode, which makes it a promising candidate for advanced substrate materials in low temperature co-fired ceramic applications. [ABSTRACT FROM AUTHOR]

A low temperature co-fired ceramic (LTCC) material of Li2ZnTi3O8-TiO2 (L2ZT3-TiO2) doped with BaO-B2O3-ZnO (BBZ) glass were prepared by conventional solid-state method. The effects of BBZ glass on the phase composition, microstructure, and microwave dielectric properties were investigated. The results indicated that BBZ glass as a sintering aid could effectively reduce the sintering temperature of L2ZT3-TiO2 ceramic below 950 °C. The XRD patterns indicated that L2ZT3-TiO2 ceramic consisted of Li2ZnTi3O8 and TiO2 phases. BBZ glass addition did not change the phase composition. In addition, the SEM demonstrated that BBZ glass could significantly improve the grain growth and densification. The sintering mechanism was analyzed through the wetting behavior and the activation energy (Ea). When added 2.5 wt% BBZ glass, the average activation energy reduced from 492.38 ± 139.03 to 370.69 ± 20.98 kJ/mol, which indicated that the BBZ glass not only effective lowered the sintering temperature but also promoted the sintering process. The L2ZT3-TiO2 ceramic with 2.5 wt% BBZ sintered at 925 °C for 4 h had excellent microwave dielectric properties of εr = 26.3, Q × f = 36,554 GHz and τf = − 4.16 ppm/°C. In addition, the good chemical compatibility of this material with Ag electrode could make it as a potential candidate for LTCC technology. [ABSTRACT FROM AUTHOR]

The (1 − x)Li2TiO3-xLi2Mg3TiO6 (x = 0.1, 0.15, 0.2, 0.3, 0.4, 0.5) ceramics system was fabricated by solid-state synthesis. Test results of X-ray diffraction and electron diffraction spectrum show that all ceramic samples only contain Li2TO3 and Li2Mg3TiO6 phase. Scanning electron microscope shows that pores were found in crystal grain due to Li volatilization in high temperature (> 1000 °C). With the rise proportion of Li2Mg3TiO6 in ceramics, dielectric constant (ɛr) decreases from 19.55 to 14.53, quality factor (Q×f) increases from 102,800 to 126,000 GHz and temperature coefficient (τf) decreases from + 15.9 to − 30.08 ppm/°C. High performance microwave dielectric properties of ɛr = 18.5, Q×f = 108,000 GHz, τf = 4.2 ppm/°C were obtained at 1390 °C for 0.85Li2TiO3-0.15Li2Mg3TiO6 ceramics. To suppress Li volatilization, LiF, a low temperature melting addition, was added to 0.85Li2TiO3-0.15Li2Mg3TiO6 ceramics. LiF effective lowers sintering temperature from 1390 to 1175 °C due to LiF liquid-phase sintering and restricts Li evaporation, and a well-developed grain morphology and excellent dielectric properties (ɛr = 18.5, Q×f = 87,000 GHz, τf = − 18 ppm/°C) was obtained which hold promise in 4G tele-communication applications. [ABSTRACT FROM AUTHOR]