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The aim of this study is to investigate the impact of the Kovar glass content on the mechanical and electrical properties of Si3N4–Kovar composites sintering at air atmosphere. To achieve this, Si3N4–Kovar composites were prepared using molding technology with the Kovar glass powder ranging from 20 to 70 wt%. The phase composition, morphology, bulk density, apparent porosity, flexural strength at room temperature, dielectric constant, and dielectric loss of the composites were all examined in relation to changing the Kovar glass content. During the sintering process, the α‐quartz on the surface of Si3N4 particles acted as the crystal nucleus, inducing the crystallization of the glass at the wetting position that the Kovar glass and the surface of the Si3N4 particles. A small amount of the β‐quartz phase was crystallized at 750–850°C, followed by a large amount of the β‐quartz phase crystallizing above 900°C. Additionally, some β‐quartz phase transformed into the metastable β‐cristobalite phase that could exist below 1470°C. During the cooling process, the β‐cristobalite phase transformed into a low‐temperature α‐cristobalite phase, while the β‐quartz phase transformed into a low‐temperature α‐quartz phase. The results indicate that the Si3N4–Kovar glass composite with 60 wt% the Kovar glass content sintered at 900°C exhibits higher density (1.88 g/cm3), lower porosity (25.4%), higher flexural strength (55.34 MPa), lower dielectric constant (3.46), and lower dielectric loss (4.26 × 10−3). [ABSTRACT FROM AUTHOR]

A novel category of polyphenylene oxide/high-impact polystyrene (PPO/HIPS) alloy was used as the polymer matrix (abbreviated as mPPO) and loaded with different volume fractions (0, 10, 20, 30, 40, 50 vol.%) of MgTiO3–Ca 0. 7 La 0. 2 TiO3 (abbreviated as MTCLT) ceramics to prepare composites by injection molding. Its micromorphology, density, dielectric, thermal and mechanical properties were analyzed in detail. The experimental results show that the composites possess a compact microstructure because HIPS increases the fluidity of PPO. Due to the excellent dielectric properties of both mPPO and MTCLT, the composites have an extremely low dielectric loss. The realization of the high ceramic filler fraction greatly limits the thermal expansion of the polymer chain by introducing the interphase, so that the coefficient of thermal expansion of the composite material could be as low as 21.8 ppm/ ∘ C. At the same time, the presence of ceramic particles could reinforce the mechanical property of the composites. When the ceramic filler fraction is higher than 20 vol.%, the bending strength of the composite material is around 110 MPa. When the ceramic filler fraction is 40 vol.%, the composite possesses the best comprehensive performance. The dielectric constant is 6.81, the dielectric loss is 0.00104, the thermal expansion coefficient is as low as 25.3 ppm/ ∘ C, and the bending strength is 110.4 MPa. Due to its excellent properties, this material can be a good candidate in the field of microwave communication. [ABSTRACT FROM AUTHOR]

Polyphenylene oxide (PPO)-based microwave composite substrates filled with different volume fractions (10, 20, 30, 40, 50 vol%) of MgTiO3-Ca0.7La0.2TiO3 (MTCLT) ceramics were prepared by injection-molding process. The microstructure, thermal, mechanical, and dielectric properties of the PPO/MTCLT substrates were fully studied. The results showed that PPO/MTCLT substrates with dense microstructure and uniform filler distribution were obtained when the filler fraction didn't exceed 30vol%. Further increase of the filler fraction brought about agglomeration of ceramics and weakened interfacial bonding, producing more pores in the substrates. With increasing volume fraction of ceramics, the coefficient of thermal expansion (CTE) of the substrates decreased significantly, while the bending strength increased first and then decreased, reaching a maximum at 30 vol%. Moreover, the dielectric constant of the substrates increased remarkably, while the dissipation factor decreased first and then increased. Increasing the testing frequency had little effect on the dielectric constant but increased the dissipation factor gradually. PPO/MTCLT composite substrate with filler fraction near 30 vol% exhibited the best performance and was used to fabricate a microstrip antenna. The antenna showed good performance with antenna gain over 3.54 dB and low axial ratio below 1.24 dB. The PPO/MTCLT microwave composite substrates prepared by injection-molding process exhibited good comprehensive properties, being important candidates for microwave and millimeter-wave applications. [ABSTRACT FROM AUTHOR]

MgNb2O6 ceramics doping with different amounts of LiF (0–0.4 wt%) were prepared via a solid-state reaction method. The sintering behavior, phase evolution, microstructure, and microwave dielectric properties of the LiF-doped MgNb2O6 ceramics were fully investigated. The results showed that with the increase of LiF from 0 to 0.4 wt%, the sintering temperature of MgNb2O6 ceramic decreased significantly from 1300 to 1100 °C, as the sintering activation energy of the MgNb2O6 ceramic was reduced. A second-phase LiNbO3 was identified when the amount of LiF reached 0.2 wt%, leading to an obvious deterioration to the Qf value of MgNb2O6 ceramic. MgNb2O6 ceramic doped with 0.1 wt% LiF exhibited excellent microwave dielectric properties with εr = 20.7, Qf = 90,300 GHz, and τf = − 71.3 ppm/°C, after sintering at 1175 °C for 4 h. [ABSTRACT FROM AUTHOR]

The combination of low dielectric constant (εr) and a high-quality factor (Q × f) in MgO ceramics makes them attractive for 5G applications. However, the large negative temperature coefficient of resonance frequency (τf) impedes these applications. In this paper, the composite ceramics of MgO–xMTiO3 (M = Ca, Sr; x = 0, 2.5, 5, 7.5, 10 wt%) with the addition of 4 mol% LiF as a sintering aid were fabricated by the traditional solid-state reaction method. The coexistence both MgO and MT phases can be observed in XRD and SEM in the 4 mol% LiF–MgO–wt%MTiO3 systems under the high-temperature sintering process. With the addition of MT, the grain size of MgO decreased, the εr value improved with τf value gradually increasing from negative to positive value. Optimized microwave dielectric properties were achieved for 4 mol%LiF–MgO–10wt%SrTiO3 ceramics sintered at 1300 °C for 6 h, yielding εr = 11.2, Q × f = 46, 815 GHz, and τf = + 3.51 ppm/°C. Based on it, a prototype of microstrip patch antenna was designed and fabricated with a center frequency at 5.64 GHz for 5G–Sub6GHz communication applications. [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]

MgO ceramics have good microwave dielectric properties, but the high sintering temperatures limit its application. The effects of TiO 2 additive on the phase composition and microwave dielectric properties of MgO ceramics with 4mol%LiF were investigated by solid state reaction method. TiO 2 and MgO form Mg 2 TiO 4 in a magnesium-rich environment with 4mol%LiF at about 900 °C, which as a solid solution or second phase had a huge impact on MgO ceramic with 4mol % LiF. When the content of TiO 2 less than 2mol %, Mg 2 TiO 4 as a solid solution in MgO ceramics, which made the grain of MgO larger. When the content of TiO 2 more than 2mol %, Mg 2 TiO 4 as a second phase in MgO ceramics, which made the microwave dielectric properties of MgO ceramics bad. Typically, the MgO-4mol%LiF-0.5mol%TiO 2 ceramic sintered at 1075 °C for 6 h acquired the best dielectric properties: ε r = 9.7, Qf = 617,000 GHz and τ f = −59.49 ppm/°C. [ABSTRACT FROM AUTHOR]

Gehlenite‐type Ca2Al2SiO7 ceramics were prepared by the conventional solid‐state reaction. Two anomalies were found in the plot of dielectric constant vs temperature, which were associated with space charge polarization. Pure phase crystal structure and no phase transition were observed in the temperature‐dependent X‐ray diffraction (XRD) patterns and Raman spectra from room temperature (RT) to 900°C. There was relevant relation between Q × f and τƒ with the stretching vibrations of Ca‐O bond and O‐Ca‐O bending in CaO8 polyhedron. Excellent microwave dielectric properties (εr = 8.86, Q × f = 22 457 GHz, and τf = −51.06 ppm/°C) were obtained for Ca2Al2SiO7 sintered at 1440°C in air, which had the potential application to use in microwave and millimeter‐wave devices such as capacitors and substrates. [ABSTRACT FROM AUTHOR]

MgTa 2 O 6 is a very promising microwave dielectric material, but the residual Ta 2 O 5 which produced during the reaction process of MgO and Ta 2 O 5 with stoichiometric ratio limits its further development. In this study, B 2 O 3 and MgO sintering additives were applied to reduce Ta 2 O 5 phase and enhance the microstructure and microwave dielectric properties. Results show that B 2 O 3 has an advantages over MgO in improving the material properties, the best microwave dielectric properties (ε r = 27.8, Qf = 184000 GHz, τ f = 53 ppm/oC) were acquired at x(B 2 O 3) = 0.5 wt%. The mechanisms of both B 2 O 3 and MgO additives were analyzed in detail. [ABSTRACT FROM AUTHOR]

0.8MgTiO3 − 0.2(Ca0.7La0.2)TiO3 (MTCLT) ceramic fillers with excellent microwave dielectric properties have been incorporated in a novel polysilylaryl-enyne (PSAE) resin with low dielectric loss to prepare PSAE/MTCLT composite. A unique process free of organic solvent has been employed to fabricate the composite. The results showed that highly dense and homogeneous microstructure was observed in all the composites with different filler volume fractions. With the increase in MTCLT volume fraction, the dielectric constant of the composite increased significantly from 2.8 to 10.0, while the dielectric loss decreased from 0.0056 to 0.0030 at 10 GHz. The coefficient of thermal expansion (CTE) of the composite could be reduced to less than 20 ppm/°C when 40 V% MTCLT ceramic was loaded which achieved a good match with copper foil. TGA and DMA results showed that the composite possessed excellent temperature resistance with the temperature at 5% mass loss (Td5)> 850 °C and glass transition temperature (Tg) > 400 °C at N2 atmosphere. The novel thermosetting PSAE/MTCLT composite reported in this work has good application prospects in high-power integrated circuits and some high-temperature-resistant environments. [ABSTRACT FROM AUTHOR]

Dense Sm 2- x Ce x O 3+ x /2 (x = 0.10−0.25) ceramics were obtained by the solid-state method. Main-phase Sm 2 O 3 with monoclinic structure and a small amount of fluorite-structured CeO 2 were achieved. As the x value increased, the τ f significantly reduced from 18.8 ± 2.0 ppm/°C to −20.3 ± 2.0 ppm/°C and the Q × f enhanced from 21,382 ± 300–32,927 ± 300 GHz. The τ f variating from positive to negative was related to the increasing temperature coefficient of ion polarizability (τ αm) from 20.6 ppm/°C to 27.9 ppm/°C. The rise in Q × f was attributed to the reduced AC conductivity resulting from the decreasing oxygen vacancy concentration. The addition of Ce could effectively inhibit the decomposition of Sm 2 O 3 ceramics in atmospheric condition. Notably, the Sm 1.80 Ce 0.20 O 3.10 ceramic sintered at 1475 °C demonstrated optimal microwave dielectric properties of ε r = 19.2 ± 0.2, Q × f = 28,033 ± 300 GHz, and τ f = 1.8 ± 2.0 ppm/°C. [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 novel low temperature co-fired ceramic (LTCC) material was fabricated by zinc titanate (ZnTiO3) ceramics doped with B2O3-BaO-SiO2-ZnO-Li2O (BBSZL) glass. The influences of BBSZL glass on wetting behavior, sintering activation energy, phase composition, microstructure and microwave dielectric properties were investigated. The experimental results show that the sintering temperature of ZnTiO3 ceramics can be reduced from 1 100 to 925 °C, meanwhile the sintering activation energy is decreased from 465.32 to 390.54 kJ·mol-1 by BBSZL glass aid, respectively. Moreover, BBSZL glass can inhibit the high Q×f ZnTiO3 phase decompose into the low Q×f value Zn2TiO4 phase, which is propitious to obtain high Q×f value LTCC material. The ZnTiO3-BBSZL composite sintered at 925 °C displays the excellent microwave dielectric properties with εr of 21.8, Q×f value of 42000 GHz, and τf of -75 ppm·°C-1. [ABSTRACT FROM AUTHOR]

PTFE matrix loaded with different volume fractions of MgTiO3 ceramic powder with particle sizes of around 5 μm and 15 μm (abbreviated as MT-5 and MT-15, respectively) was prepared. The microstructure, microwave dielectric properties and thermal properties of the composites were studied by scanning electron microscope, vector network analyzer and thermal dilatometer. The results show that PTFE/MT-15 composite exhibits higher relative density and better dielectric properties than the PTFE/MT-5 composite, since the former with coarse particles possesses lower surface energy to weaken the particle agglomeration effect. Even at 40% filler volume fraction, the ultra-low dielectric loss of PTFE/MT-15 composite can be maintained in the order of 10− 4 at 10 GHz. Different models are used to predict the dielectric constant of the composites. Among which, the effective medium theory shows the least deviation from the experimental results. PTFE matrix filled with 40V% MT-15 ceramic powder shows excellent microwave dielectric properties: εr = 5.5, tanδ = 2.7 × 10− 4 (at 10 GHz), which may be a promising material in electronic packaging field. [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]

A low temperature co-fired ceramic (LTCC) was fabricated at 910 °C /2 h from the powder mixture of Li2Zn3Ti4O12, TiO2 and a B2O3-La2O3-MgO-TiO2 glass (BLMT), and the influence of TiO2 on microstructure and dielectric properties of the composite was investigated in the composition range (wt%) of 20BLMT-(80 − x)Li2Zn3Ti4O12-xTiO2 (x = 0, 2.5, 5, 7.5, 9 and 10). The results showed that all samples consisted of Li2Zn3Ti4O12, TiO2, LaBO3 and LaMgB5O10 phase. And LaBO3, LaMgB5O10 and a small amounts of TiO2 were crystallized from BLMT glass during sintering process. As x increases, dielectric constant and temperature coefficient of resonance frequency of the composites demonstrated gradually increase, whereas the quality factor of the sample of x = 0 wt% was about 41,500 GHz and the ones maintained stable at a high level of 49,000-51,000 GHz for other samples. The composite with x = 9 wt% had an optimal microwave dielectric properties with the dielectric constant of 20.2, quality factor of 50,000 GHz and temperature coefficient of resonant frequency of − 0.33 ppm/°C. [ABSTRACT FROM AUTHOR]

Novel microwave dielectric ceramic YZnAlSiO were synthesized by solid-state route. The crystal structure of synthesized samples was characterized by X-ray diffraction and refined with Rietveld method. Microstructure and microwave dielectric properties of YZnAlSiO ceramics were investigated using Scanning Electron Microscopy and Hakki-Coleman method. X-ray data display that major phase of YZnAlSiO is isostructural to YAlO with a cubic garnet structure and space group of Ia-3d, which is composed of (Al/Si)O tetrahedron, (Zn/Al)O octahedron and YO dodecahedron, besides minor YSiO secondary phase. The distribution of grain sizes is closer to Gauss distribution. Bulk density of samples has a similar variation curve with Q* f of samples. YZnAlSiO ceramics exhibit excellent microwave dielectric properties: ε = 10.2, Q* f = 37938.2 (@9.47 GHz), τ = −31.7 ppm/°C at sintering temperature of 1500 °C. Our results indicate YZnAlSiO could be a potential material for millimeter wave communication systems as microwave substrates. [ABSTRACT FROM AUTHOR]

Microstructure and microwave dielectric properties of (1-x)LiMgTiO-xCaSrTiO (x = 0.03, 0.06, 0.08, 0.09, 0.12) ceramics prepared by the conventional solid state route have been investigated. XRD and SEM-EDS analysis confirmed that ceramics contain LiMgTiO and CaSrTiO phases. The microwave properties exhibited a significant dependence on the sintering temperature and CaSrTiO content. With increasing addition of CaSrTiO, the dielectric constant $$({\varepsilon _r})$$ increased from 14.3 to 17.4 when samples sintered at 1410 °C for 4 h; the quality factor (Q × f) decreased from 133,905 to 101,000 GHz, and the temperature coefficient of resonant frequency ( $${\tau _f}$$ ) significantly increased from −39 to 6.35 ppm/°C when samples sintered at 1370 °C for 4 h. Sample with 0.91LiMgTiO-0.09CaSrTiO sintered at 1370 °C for 4 h possess excellent microwave properties with $${\varepsilon _r}$$ of 16.4, a Q × f of 113,000 GHz and $${\tau _f}$$ of −3.65 ppm/°C. It is proposed as low-loss and low-cost dielectric materials for microwave and millimeter wave application. [ABSTRACT FROM AUTHOR]

The (1− x)Mg2Al4Si5O18- xTiO2 |(1− x) MAS- xT| (0 ≤ x ≤ 0.35) cordierite ceramics are fabricated by solid-state reaction method for obtaining near-zero temperature coefficient of resonant frequency (τf). The XRD and SEM results show that (1− x) MAS- xT (0 ≤ x ≤ 0.10) ceramics exhibit single cordierite solid solution, whereas as 0.15 ≤ x ≤ 0.35, present composite phases of Mg2Al4Si5O18 solution and TiO2. Rietveld refinements of XRD data suggest that the [(Si4Al2)O18] hexagonal shape in cordierite structure happens to alternate change from nonsymmetrical hexagonal rings to almost centrosymmetrical equilateral rings as x increases to 0.10 comparing to that of x = 0. As Ti4+ ions squeeze into the [(Si4Al2)O18] rings structure, the orientation and shapes of the rings begin to rotate and expand from initial state of [1-20] ( x = 0) to near [210] direction ( x = 0.10), and then continue to expand toward close to [110] direction ( x = 0.25). Due to centrosymmetry adjustment of [(Si4Al2)O18] hexagonal rings and of other microstructure factors improvement, the (1− x) MAS- xT ( x = 0.10) cordierite solution achieves optimum quality factor Qf: εr = 6.3, Qf = 55 400 GHz (17.6 GHz), τf = −21 ppm/°C. The (1− x) MAS- xT ( x = 0.25) composites obtain a near-zero temperature coefficient of resonance frequency: εr = 6.8, Qf = 37 800 GHz (18.4 GHz), τf = −0.2 ppm/°C. [ABSTRACT FROM AUTHOR]

The temperature coefficient of dielectric constant (τ ε) is a crucial parameter for assessing the performance stability of microwave devices operating under varying temperature conditions. In this study, polyphenylene oxide (PPO) resin was utilized as the matrix and six types of ceramics with distinct temperature coefficients of dielectric constant were employed as fillers. Six PPO-based composites were fabricated through twin-screw extrusion combined with hot pressing route. The dielectric properties of the ceramics and their influence on the dielectric properties of the composites, particularly the τ ε , were systematically investigated. The results revealed that all six types of composites exhibited dense structures and uniform filler distribution, with a relative density exceeding 98.0 % and a water absorption below 0.1 %. The dielectric constant and its temperature coefficient of the fillers had a more pronounced effect on the dielectric properties of the composites, compared to dielectric loss. The dielectric constants of the six types of composites aligned well with the theoretical values predicted by the effective medium theory. Reaching up to 9.7 (at 10 GHz). The dielectric loss ranged from 1.0 × 10−3 to 3.0 × 10−3. Notably, the PPO/Mg 0.95 Ca 0.05 TiO 3 composite substrate with a filler ratio of 40 vol% exhibited exceptional dielectric properties: ε r = 6.8, tg δ = 1.4 × 10−3, τ ε = −8.6 ppm/°C, highlighting its significant advantages for communication applications under varying temperature conditions. [ABSTRACT FROM AUTHOR]

Mg1/3A11/3A21/3Ta2O6 ceramics (where A1 and A2 represent Co, Ni, or Zn) were prepared using the solid‐phase reaction route. The results of X‐ray diffraction and Raman tests showed that (Co1/2Ni1/2)2+, (Co1/ 2Zn1/2)2+, and (Ni1/2Zn1/2)2+ ions replaced Mg2+ ions in the lattice of MgTa2O6, resulting in the formation of a pure tri‐rutile structure. All three complex ions could significantly reduce the sintering temperature of the ceramics (by 150°C–200°C) and could broaden the sintering window. The large deviation (48.8%–69.2%) between the porosity corrected relative permittivity εr‐corr. and the theoretical relative permittivity εr‐theo. might be due to the overestimation of the ionic polarizability of Ta5+ by Shannon. (Co1/2Ni1/2)2+ has the most significant effect of increasing the bond energy of ceramic A–O bonds, reducing the τf value from 51 to 36 ppm/°C. In addition, the mechanisms affecting their dielectric properties are discussed based on bond ionicity (fi), full width at half maximum (FWHM) of Raman peak, and bond energy (E). Mg1/3Co1/3Ni1/3Ta2O6 ceramic sintered at 1350°C have the most excellent microwave dielectric properties: εr = 26.8, Q × f = 86,000 GHz, and τf = 36 ppm/°C. [ABSTRACT FROM AUTHOR]

In this work, a novel anti-reduction mechanism was put up by substituting (Mg 1/3 Ta 2/3)4+ complex ion for Ti4+ ion in Ba 4.2 Sm 9.2 Ti 18-x (Mg 1/3 Ta 2/3) x O 54 (0 ≤ x ≤ 0.1) ceramics. The influence of (Mg 1/3 Ta 2/3)4+ complex ion on the sintering behavior, crystal structure, anti-reduction mechanism and microwave dielectric properties of Ba 4.2 Sm 9.2 Ti 18-x (Mg 1/3 Ta 2/3) x O 54 ceramics was investigated. The results indicated that Ba 4.2 Sm 9.2 Ti 18-x (Mg 1/3 Ta 2/3) x O 54 ceramics maintained a typical single-phase tungsten bronze structure. After doping, the ceramic exhibited dense structure and typical columnar grains. Raman spectroscopy and XPS analysis confirmed the reduction of oxygen vacancies and obtained a 7.86 % decrease of Ti3+ ions. Due to the anti-reduction of Ti4+ ions, Ba 4.2 Sm 9.2 Ti 18-x (Mg 1/3 Ta 2/3) x O 54 ceramics possessed an improvement in microwave dielectric properties. In Ba 4.2 Sm 9.2 Ti 18-x (Mg 1/3 Ta 2/3) x O 54 (0 ≤ x ≤ 0.1) ceramics, the Ba 4.2 Sm 9.2 Ti 17·95 (Mg 1/3 Ta 2/3) 0.05 O 54 (x = 0.05) ceramic sintered at 1350 °C for 4 h showed the best integrated microwave dielectric properties with ε r = 79.62, Q f = 10,450 GHz and τ f = −10.66 ppm/°C. [ABSTRACT FROM AUTHOR]

In this study, Ba(Mg 1/3 Ta 2/3)O 3 (BMT) ceramics added with different amounts of CaO–B 2 O 3 –ZnO (CBZ) glass were prepared through the solid-state sintering route. The sintering behavior, microstructure, phase composition and dielectric properties of the BMT ceramics added with CBZ glass were investigated. The addition of CBZ glass decreased the sintering temperature of BMT ceramics by over 300 °C, resulting in a highly dense microstructure without interacting with the main BMT phase. The lower sintering temperature led to small ceramic grains and caused a decrease in the Q × f value. Prolonging the sintering time improved the ordering degree of cations on the B-site in BMT ceramic, leading to an enhancement in the Q × f value. The BMT ceramic added with 0.4 wt% CBZ glass exhibited excellent microwave dielectric properties: ε r = 24.19, Q × f = 115,100 GHz, τ f = 9.84 ppm/°C, after sintering at 1400 °C for 12 h. [ABSTRACT FROM AUTHOR]

Co-substitution of Ce3+ at the A-site and Nb5+ at the B-site by smaller Ca2+ and W6+ in (Ce 1- x Ca x)(Nb 1- x W x)O 4 ceramics drives the structure from monoclinic fergusonite (x = 0.1 - 0.3) to tetragonal scheelite (x = 0.4). Adjusting the A-O and B-O bond characteristics could drastically tune the microwave dielectric properties. The ε r decreased from 20.7 to 16.2, and the negative deviations between ε r and ε r (C-M) resulted from the rattling effect of Nb5+/W6+ cations in the octahedron along the b -axis direction. The τ f varied from negative (−11 ppm/°C at x = 0.1) to positive (+87.8 ppm/°C at x = 0.4), mainly attributed to the rattling effect of Nb5+/W6+. Q×f increased from 21,006 to 45,025 GHz (x = 0.3) and then decreased to 36,563 GHZ (x = 0.4), accompanied by increasing packing fraction and decreasing Raman FWHM. The ceramic at x = 0.15 exhibited the optimum microwave dielectric properties of ε r = 19.7, Q×f = 35,450 GHz, and τ f = 0.8 ppm/°C. [ABSTRACT FROM AUTHOR]

In order to explore the effects of BN addition on the mechanical and electrical properties of oxidative sintered Si 3 N 4 -BN composites, Si 3 N 4 -BN composites with BN powder dosage of 0-40 wt% are prepared by molding technology, and the effects of different BN contents on the phase, morphology, bulk density, porosity, flexural strength at room temperature, dielectric constant and dielectr loss of the composite system are studied. With the increase of BN content, at different temperatures, the oxidation product B 2 O 3 of BN and the oxidation product SiO 2 of Si 3 N 4 firstly react on the surface to form B 2 O 3 –SiO 2 glass phase, which densify the surface and affects the oxidation degree of internal grains. At the same time, a small amount of B 2 O 3 escaping from the surface, so that the open pores of the composites decrease firstly and then increase slightly, and the dielectric constant increases firstly and then decreases. The results show that when the amount of BN micronized powder is 10 wt%, the oxidation sintered Si 3 N 4 -BN composite material at 1500 °C have pores that retain the sheet structure of boron nitride, and the amorphous material flows to fill the pores, so it have high volume density (1.85 g/cm3), low porosity (apparent porosity 6.37%), and high mechanical properties (flexural strength 127.86Mpa), higher dielectric constant (3.94) and lower dielectr loss (4.0 × 10−4). [ABSTRACT FROM AUTHOR]

In this work, a novel low permittivity and high expansion coefficient rare-earth rich BaO–SiO 2 –La 2 O 3 (BSL) glass-ceramic for millimeter-wave technology was systematically investigated by the network structure, crystallization the phase transformation, microstructure and microwave dielectric properties. With the decrease of the SiO 2 /BaO mol ratio from 3.75 to 0.9, the crystallization activation energy (E c) of BSL glass calculated by the Kissiger equation continued to fall from 400.65 to 316.85 kJ/mol, and the crystal growth mode of all samples judging by Avrami parameter (n) was 1-D volume crystallization, implying that the crystallization ability of the BSL glass was enhanced. The main crystal phase of BSL glass-ceramic transformed from BaSi 2 O 5 to BaSiO 3 phase, coincided with a second phase Ba 4 La 6 O(SiO 4) 6. And then, the relative permittivity ε r of BSL glass-ceramic had increased from 7.8 to 11, while quality factor (Q × f), temperature coefficient of frequency τ f , and coefficient of thermal expansion (CTE) had decreased with the decrease of SiO 2 /BaO ratio. By adjusting the mol ratio of SiO 2 /BaO, the best comprehensive properties of 20BaO–75SiO 2 –5La 2 O 3 glass-ceramic could be obtained with ε r = 7.8, Q × f = 21000 GHz, CTE = 12.39 × 10−6/°C (30–800 °C), which was favorable properties for microwave dielectric applications. [ABSTRACT FROM AUTHOR]

MgNb 2 O 6 ceramics doped with different amounts of flake Al 2 O 3 (0–5 wt%) were prepared using a solid-state reaction method. The phase evolution, microstructure, microwave dielectric properties, and mechanical behavior of flake Al 2 O 3 doped MgNb 2 O 6 ceramics were investigated. The results show that flake Al 2 O 3 has good chemical stability and acts as a second phase to improve the mechanical properties of the MgNb 2 O 6 ceramics. The synergistic effects of pinning and fine grain strengthening from flake Al 2 O 3 effectively improved the flexural strength of MgNb 2 O 6 ceramics. The MgNb 2 O 6 ceramics doped with 1.0 wt% flake Al 2 O 3 exhibited excellent microwave dielectric and mechanical properties: ε r = 20.1, Qf = 109 100 GHz, τ f = −69 ppm/°C, and σ b = 153 MPa, after sintering at 1300 °C for 4 h. [ABSTRACT FROM AUTHOR]

In this paper, a systematic experimental design is used to study the influence of different content ratios of MgO/La2O3 co-doping on the microstructure, real inline transmittance (RIT) and microwave dielectric properties of translucent polycrystalline alumina (PCA). Compared with those doped only with MgO, translucent PCA co-doped with different ratios of MgO/La2O3 demonstrates a higher and more stable Q×f value. The increased solubility of La in alumina and the elimination of the second phase are possible reasons for the decrease in dielectric loss. An optimized Q×f value of~300,000GHz could be attained for samples co-doped with 1500ppm MgO/300ppm La2O3. Besides, a high RIT of~30% at a wavelength of 600nm could be achieved when 500ppm MgO/500ppm La2O3 was co-doped, the reasons for these phenomena are also discussed in the paper. [ABSTRACT FROM AUTHOR]

Mg 1–3 x (CoNiZn) x Ta 2 O 6 ceramics (x = 0.00, 0.05, 0.10, 0.20, and 0.25) were synthesized by the solid-phase reaction method. The XRD and Rietveld refinement results suggest that the Mg 1–3 x (CoNiZn) x Ta 2 O 6 ceramics have a pure tri-rutile structure. (Co 1/3 Ni 1/3 Zn 1/3)2+ can significantly broaden the sintering temperature range of ceramics. The chemical bonding theory reveals that the A-O bond (A = Mg, Co, Ni, or Zn) ionicity and Ta-O bond ionicity are closely related to the porosity corrected relative permittivity (ε r -corr.). The increase in A-O bond energy contributes to the greater stability of the AO 6 octahedron, resulting in a decrease in | τ f |. Additionally, the Raman spectroscopy reveals that there is a negative relationship between the Qf value and the full width at half maximum (FWHM) of the strongest peak of the A 1g mode. Correspondingly, Mg 0.4 (CoNiZn) 0.2 Ta 2 O 6 ceramic has excellent microwave dielectric properties after sintering at 1450°C for 4 h: ε r = 28.9, Qf = 91,900 GHz (at 7.4 GHz), and τ f = 44 ppm/°C. Furthermore, Mg 0.4 (CoNiZn) 0.2 Ta 2 O 6 ceramic can maintain a stable Qf value (∼ 91,000 GHz) across a broad range of sintering temperatures (150°C), which is a result of the combination of densification and FWHM. This characteristic facilitates adaptation to changes in furnace temperature in large-scale production. The strategy of multiple-element substitution to extend the sintering temperature range is expected to be applied to other ceramic systems. • (Co 1/3 Ni 1/3 Zn 1/3)2+ could broaden the sintering temperature range of MgTa 2 O 6 ceramic. • The reduction in | τ f | of MCNZ- x ceramics was caused by an increase in bond energy. • MCNZ-0.20 ceramic had stable Qf values in the sintering temperature range of 150℃. [ABSTRACT FROM AUTHOR]

In this work, the effects of divalent ions on the phase structure, microstructure, and microwave dielectric properties of Mg 1.8 R 0.2 Al 4 Si 5 O 18 (R = Mg, Ca, Sr, Ba, Mn, Co, Ni, Cu, Zn) cordierite ceramics were investigated. Complex chemical bond theory, Raman spectrum and infrared reflectance spectrum were employed to understand the relationship among structural characteristics, vibration modes and microwave dielectric properties for alkaline earth and transitional metal divalent elements doped cordierite ceramics. The optimal microwave dielectric properties were obtained for Mg 1.8 Ni 0.2 Al 4 Si 5 O 18 with ε r of 4.53, Q× f of 61,880 GHz and τ f of -32 ppm/℃. Finally, a 5G-Sub 6GHz patch antennas with a central frequency of 4.91 GHz was successfully designed and fabricated using a Mg 1.8 Ni 0.2 Al 4 Si 5 O 18 substrate. The antenna exhibited excellent performance with a gain of 5.83 dBi and an efficiency of 76 %, showing promise to be employed in 5 G/6G millimeter-wave communication technology. [ABSTRACT FROM AUTHOR]

Si 3 N 4 –BaTiO 3 composite ceramics were prepared by hot pressing sintering. The effects of the amount of BaTiO 3 and annealing process on the microstructure, phase composition, dielectric properties and thermal conductivity of Si 3 N 4 composite ceramics were studied. With the increase of BaTiO 3 content, the density and the dielectric performance of the Si 3 N 4 -based composite ceramics are improved, while the thermal conductivity is reduced. The annealing treatment can not only inhibit the growth of β-Si 3 N 4 , refine the grain, reduce the content of intercrystalline glass phase and porosity, but also promote the precipitation of hexagonal barium titanate, all of which are beneficial to increase the dielectric constant and decrease the dielectric loss, but will slightly reduce the thermal conductivity of Si 3 N 4 –BaTiO 3 composite ceramic. The sample A2BT15 with 15% BaTiO 3 sintered at 1750 °C for 2 h and annealed at 1300 °C exhibited the maximum dielectric constant (ε = 10.57), the minimum dielectric loss (tanδ = 9×10-4), a high relative density (98.8%) and an acceptable thermal conductivity (14.5 W·m-1·K-1). Therefore, the selection of appropriate BaTiO 3 content and annealing process can regulate the dielectric property, thermal performance and mechanical property of Si 3 N 4 –BaTiO 3 composite ceramics in a certain range. [ABSTRACT FROM AUTHOR]

In this paper, thermal stable Y 3 MgAl 3 SibO 12 -TiO 2 microwave composite ceramics were firstly fabricated by the high temperature solid phase reaction method. The influence of the sintering temperature, microstructure on microwave dielectric properties of Y 3 MgAl 3 SiO 12 by doping TiO 2 were investigated in detailed. TiO 2 addition reduced the ceramic sintering temperature and improved the distribution of grain size. The negative temperature coefficient of resonant frequency (τ f = −32 ppm/°C) of Y 3 MgAl 3 SiO 12 was adjusted to near zero value. 0.8Y 3 MgAl 3 SiO 12 -0.2TiO 2 ceramic sintered at 1475 °C for 6 h achieved the optimized microwave dielectric properties: ε r = 12.2, Q × f = 21,050 GHz, τ f = +5.2 ppm/°C, which indicated that 0.8Y 3 MgAl 3 SiO 12 -0.2TiO 2 is a potential candidate for dielectric patch antenna and substrate. [ABSTRACT FROM AUTHOR]

Polymer/ceramic composites used as microwave dielectric combine the excellent dielectric properties of ceramic with the toughness of polymer. The properties of composites are not only determined by the properties of components but also influenced by the polymer-ceramic interface. In this work, we conducted experiments and simulations on the dielectric properties and thermal conductivity of modified poly(phenylene oxide)/(CaSr)TiO 3 (mPPO/CST) composites. A comparison of composites filled with different sizes (2.5, 11, and 20 µm) of CST fillers demonstrates that smaller particle (more filler-matrix interface) is beneficial to mechanical properties but detrimental to dielectric properties and heat transfer. The finite element simulation results are in good agreement with the experimental values, which is of significance for guiding future experiments. The composite filled with 80 wt. % CST 20 has a high relative density of 97%, an ultrahigh ε r of ∼20, and a low tan δ of 0.0019 at 10 GHz. Meanwhile, the mPPO/CST composites are eco-friendly and suitable for mass production and are promising candidates for automotive and aerospace applications. • The mPPO/CST composites possess both ultrahigh ε r and low tan δ by optimizing components and interfaces. • The high thermal conductivity of composites is beneficial for thermal management. • Eco-friendly and suitable for mass production. • The finite element simulation results are in good agreement with the experimental values. [ABSTRACT FROM AUTHOR]

In this paper, the crystal structure, phase evolution, microstructure and microwave dielectric properties were investigated in Li 2 Zn (1-x) Ti 3 O 8 -xSrTiO 3 (x = 0–0.075) ceramic system well-sintered at 1075 °C for 4 h through one-step solid state reaction route. The XRD results showed that except for the main Li 2 ZnTi 3 O 8 phase, the unknown phase started appearing at x = 0.01, and as x value was further increased to 0.025, the SrTiO 3 phase appeared in sample and the relative content gradually increased. However, the slight deficiency of Zn2+ (x ≤ 0.025) could be used the decrease of molecular volume for Li 2 ZnTi 3 O 8 crystal structure. Consequently, the relative permittivity (ε r) and temperature coefficient of resonant frequency (τ f) demonstrated a trend of fall first then rise as the cutoff point in x = 0.01, whereas the quality factor (Q × f) increased initially and then decreased. Typically, the Li 2 Zn 0.95 Ti 3 O 8 -0.05SrTiO 3 ceramic showed a temperature stable high-Q material with ε r = 26.6, Q × f = 62300 GHz, and τ f = 0.27 ppm/°C. It could be found that the variation of Li 2 ZnTi 3 O 8 crystal structure had an essential effect on dielectric properties of composite with ≤0.01, whereas that of composite with x ≥ 0.025 was determined by the relative content of Li 2 ZnTi 3 O 8 and SrTiO 3 phase. In addition, the unknown phase seemed to have no effect on dielectric properties. • The Li 2 Zn (1-x) Ti 3 O 8 –xSrTiO 3 system is sintered and investigated at 1075 °C/4 h. • The slight deficiency of Zn2+ causes the volume of Li 2 ZnTi 3 O 8 structure to reduce. • As x is raised, ε r and τ f fall and then rise, yet Q × f increases and then decreases. • Li 2 Zn 0.95 Ti 3 O 8 –0.05SrTiO 3 has good properties:ε r = 26.6,Q × f = 62300 GHz,τ f = 0.27 ppm/°C. [ABSTRACT FROM AUTHOR]

Glasses with the composition 50SiO 2 -20TiO 2 -15BaO-7.5SrO-7.5CaO doped varied content of La 2 O 3 have been prepared by the conventional melt quench technique. The effect of La 2 O 3 on structure of the glasses was investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectra and Raman spectra. The density, thermal stability and dielectric properties of glass were measured and compared by the Archimedes method, differential thermal scanning analysis (DSC) and impedance spectroscopy, respectively. The results showed that the coordination of the titanium remained invariable with the addition of La 2 O 3 , while the number of Si-O-Ti bonds increased and the distribution of Q n changed. And the depolymerization of the glass network was observed. The thermal stability and resistance to crystallization increased significantly for glass containing 4 mol% of La 2 O 3 resulting from the strong strength of La O bond and the La 3+ clustering. However, the resistance to crystallization for glasses was decreased with further increasing La 2 O 3 . The dielectric constant of glass decreased first and then increased with the increase of La 2 O 3 content, while the dielectric loss was almost constant. [ABSTRACT FROM AUTHOR]

The novel low-temperature sinterable ceramic composites were fabricated by mixing B 2 O 3 -La 2 O 3 -MgO-TiO 2 (BLMT) glass with Li 2 ZnTi 3 O 8 ceramic. All composites could be well sintered at 900 °C for 2 h through liquid-phase sintering and viscous sintering process. With BLMT glass increasing, the main phase of composites changed from Li 2 ZnTi 3 O 8 to LaBO 3 phase crystallized from glass. Nevertheless, the rutile phase was observed in composites with ≥10 wt% glass, which could adjust the temperature coefficient of resonant frequency (τ f ) to near-zero owing to the opposite τ f value to other phases. Simultaneously relative permittivity (ε r ) and quality factor (Q × f) could be controlled by varying the content of Li 2 ZnTi 3 O 8 ceramic and BLMT glass. The composite with 20 wt% glass exhibited excellent dielectric properties: ε r  = 22.7, Q × f = 19,900 GHz, and τ f  = 0.28 ppm/°C. In addition, the good chemical compatibility between the composite with 5 wt% glass and Ag electrode made it as a potential candidate for LTCC technology. [ABSTRACT FROM AUTHOR]

0.9(Zn 0.9 Mg 0.1 )TiO 3 -0.1TiO 2 (ZMT-TiO 2 ) ceramics doped with BaO-B 2 O 3 -ZnO(BBZ) glass were prepared by conventional solid-state routes. The effects of BBZ glass on the phase evolution, microstructure, sintering mechanism and microwave dielectric properties have been investigated. The BBZ glass as a sintering agent can effectively reduce the sintering temperature of ZMT-TiO 2 ceramic below 1000 °C. The XRD patterns indicate that the ZMT-TiO 2 ceramic consisted of ZnTiO 3 , Zn 2 TiO 4 and TiO 2 phases. Added BBZ glass inhibit the decomposition of the ZnTiO 3 into Zn 2 TiO 4 and TiO 2 . In addition, SEM results showed that BBZ significantly improved the grain growth and densification, this is due to the fact that the BBZ glass liquid sintering mechanism. The sintering mechanism was analyzed through the wetting behavior and the activation energy(Ea). When added 3 wt% BBZ glass, the activation energy reduced from 614.79 KJ/mol to 417.49 KJ/mol. This result indicate that the BBZ glass can promote the sintering process. Typically, the ZMT-TiO 2 ceramic with 3 wt% BBZ sintered at 950 °C for 4 h has shown excellent microwave dielectric properties of ε r = 24.46, Q × f = 47500 GHz and τ f = -14.68 ppm/°C. [ABSTRACT FROM AUTHOR]

A series of novel low temperature co-fired ceramics were fabricated in x BLMT-(100-x) Li 2 Zn 3 Ti 4 O 12 (2.5 ≤ x ≤ 80 wt%) composites sintered at 900 °C. The sintering mechanism, phase composition, microstructure and dielectric properties of the composites were investigated. The results showed that the sintering mechanism of composites with <20 wt% BLMT glass could be attributed to non-reactive liquid-phase sintering and LaBO 3 phase was crystallized from glass beside Li 2 Zn 3 Ti 4 O 12 phase, while composites with ≥20 wt% glass were controlled by the coexistence of viscous sintering and reactive liquid-phase sintering, BLMT glass crystallized forming LaBO 3 , MgLaB 5 O 10 and a small amount of rutile phase, nevertheless, more rutile phase was formed by reacting between glass and ceramic. As BLMT glass was increased, LaBO 3 , MgLaB 5 O 10 and rutile phase gradually dominated the material and Li 2 Zn 3 Ti 4 O 12 phase decreased. Meanwhile, the dielectric constant (ε r ) and quality factor (Q × f) demonstrated gradually decrease, whereas the temperature coefficient of resonant frequency (τ f ) presented a trend of fall first then rise. Typically, the composite with 60 wt% glass displayed excellent dielectric properties with ε r = 14, Q × f = 23,000 GHz, and τ f = −3.56 ppm/°C. The corresponding fitting equations of ε r , Q × f and τ f on the BLMT glass content were obtained by the Origin software, which indicated that the dielectric properties of BLMT/Li 2 Zn 3 Ti 4 O 12 composites could be precisely adjusted by adding the suitable content of glass. Therefore, the sintering process, phase composition and dielectric properties of BLMT/Li 2 Zn 3 Ti 4 O 12 composites can be controlled by varying the content of Li 2 Zn 3 Ti 4 O 12 ceramic and B 2 O 3 -La 2 O 3 -MgO-TiO 2 glass. [ABSTRACT FROM AUTHOR]

A low temperature co-fired ceramic (LTCC) material was fabricated by mixing BaTi 4 O 9 ceramic with BaO-B 2 O 3 -ZnO (BBZ) glass. The sintering mechanism was further analyzed through the wetting behavior, activation energy, phase evolution, microstructure and microwave dielectric properties of the BaTi 4 O 9 -BBZ composite. The results show that the sintering temperature of the BaTi 4 O 9 ceramics can be significantly lowered from 1300 to 925 °C by the BBZ glass. This is due to the three-stage partially reactive liquid assisted sintering process which consists of glass redistribution and local grains rearrangement, solution-reprecipitaion including glass crystallization and reactions between the glass and ceramic, and global grain rearrangement, closure of pores and viscous flow. XRD patterns exhibit that BaTi 4 O 9 reacts with the crystallization phase of BBZ glass obviously during sintering to form two new phases BaTi(BO 3 ) 2 and Ba 4 Ti 13 O 30 . The activation energy of BaTi 4 O 9 ceramic is calculated to be 520.9 ± 40.46 kJ/mol, while that of BaTi 4 O 9 -BBZ composite is reduced to 330.98 ± 47.34 kJ/mol. With increasing sintering temperature, the dielectric constant (ε r ) and the quality factor (Q×f) value increases firstly and then decreases, and the temperature coefficient of resonant frequency (τ f ) value slightly decreases. Typically, the BaTi 4 O 9 -BBZ composite sintered at 925 °C for 2 h displays excellent microwave dielectric properties of ε r = 26.4, Q×f = 27300 GHz and τ f = + 0.3 ppm/°C. In addition, the good chemical compatibility of this material with Ag electrode makes it as a potential candidate for LTCC technology. [ABSTRACT FROM AUTHOR]

This article reports a novel category of thermosetting composite prepared by compounding a high temperature resistant polysilylaryl-enyne (PSAE) resin with different volume fractions (vol%) of high dielectric constant Ca 0·7 La 0·2 TiO 3 (CLT) ceramics. The microstructure, dielectric properties and thermal properties of the PSAE/CLT composites were fully investigated. The results show that the PSAE/CLT composite with an ultra-high dielectric constant and low dielectric loss (ε r = 23.0 and tanδ = 3.4 × 10−3, at 10 GHz) was obtained when the filler volume fraction reached 60%. Meanwhile, the coefficient of thermal expansion of the composite was reduced to 15.1 ppm/°C which could match copper foils. And a high thermal conductivity of 0.918 W/(m·K) could be obtained at 60 vol% filler loading. The glass transition temperatures of the PSAE/CLT composites were over 450 °C which indicate that all the PSAE/CLT composites have an excellent temperature resistance. The novel PSAE/CLT composite has important application prospect in high-frequency communication under a harsh temperature environment. Image 1 [ABSTRACT FROM AUTHOR]