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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]

Glasses with the composition 50SiO2 · 20TiO2 · 15BaO · 7.5SrO · 7.5CaO doped with the varied content of CeO2 were prepared by conventional melt quenching technique. The effect of CeO2 on the structure of glasses was investigated by X-ray photoelectron spectroscopy and Raman spectroscopy. The density, thermal stability, dielectric properties and acid resistance of glasses were studied by Archimedes method, differential thermal scanning analysis and X-ray diffraction, dielectric measuring as well as the powder method. The results showed that the coordination of Ti, which existed in glasses as [TiO4], did not change. An increase in the content of non-bridging oxygen atoms and a corresponding decrease in the content of bridging oxygens correlated. The depolymerization of the glass network was attributed to an increase in the number of Si–O–Ti bonds and the change of the Qn distribution. With an increase in the CeO2 content, the thermal stability and acid resistance of glass first increased and then decreased, and the dielectric constant and dielectric loss of glass decreased first and then increased. [ABSTRACT FROM AUTHOR]

A temperature stable high-Q Li2Zn0.95Sr0.05Ti3O8 microwave dielectric ceramic is fabricated by conventional solid-state reaction route and the phase composition, microstructures and microwave dielectric properties are investigated in this paper. The bulk density and FESEM results indicate that this ceramic can be well-sintered at 1075 °C for 4 h. Since the difficulty in Sr2+ ions diffused into the Li2ZnTi3O8 crystal lattice to form solid solutions owing to the large radii difference between Sr2+ (1.44Å) and Zn2+ (0.74Å), there are three phases including the main phase Li2ZnTi3O8 and the second phase SrTiO3 and unknown phase according to the XRD and element-distribution mapping results. The formation of second phase is advantageous to improve the relative permittivity (εr) and temperature coefficient of resonant frequency (τf), but degrades the quality factor (Q × f) slightly. The Li2Zn0.95Sr0.05Ti3O8 ceramic sintered at 1075 °C/4 h displays a temperature stable high-Q properties: εr = 26.6, Q × f= 62300 GHz, and τf = 0.27 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 temperature stable low temperature co-fired ceramic (LTCC) was fabricated by the powder mixture of Li2ZnTi3O8 ceramic, TiO2 τf-tailoring dopant and B2O3-La2O3-MgO-TiO2 (BLMT) glass sintering aid, and the sintering behavior, activation energy, phase composition, microstructure and microwave dielectric properties of the composite were investigated in the composition range (wt%) of 5 BLMT-(95-x) Li2ZnTi3O8−X TiO2 (x = 0, 1, 2, 3, 4 and 5). The sintering behavior results showed that all composites could be well sintered at 910 °C for 2 h through liquid-phase sintering. The activation energy of Li2ZnTi3O8 ceramic was calculated to be 520.9 ± 40.46 kJ/mol, while 5BLMT-93Li2ZnTi3O8-2TiO2 (in wt%) composite was reduced to 330.98 ± 47.34 kJ/mol. The XRD results showed that Li2ZnTi3O8 and TiO2 phase stably existed in all sample and a new phase LaBO3 was crystallized from BLMT glass during sintering process. As x increases, the rutile TiO2 phase increased in composite, which could adjust the temperature coefficient of resonant frequency (τf) to near-zero owing to the opposite τf value to other phases. And simultaneously dielectric constant (εr) demonstrated gradually increase, whereas the quality factor (Q × f) decreased gradually. The composite with x = 2 had an optimal microwave dielectric properties with εr = 25.3, Q × f = 32,800 GHz, and τf = − 0.54 ppm/°C. The corresponding fitting equations of εr, Q × f and τf on the x value were obtained by the Origin software, indicating that the dielectric properties of the composite could be precisely controlled by varying the content of TiO2. In addition, the good chemical compatibility of this material with Ag electrode made it as a potential candidate for LTCC technology. [ABSTRACT FROM AUTHOR]

Abstract: Four MgO‐Ta2O5 ceramics with the MgO/Ta2O5 mole ratio x = 1, 2, 3, and 4 were prepared by traditional solid‐state reaction method, and the influence of x on the phase composition, microstructure, and dielectric properties (the dielectric constant εr, the temperature coefficient of resonant frequency τf and the quality factor Qf) of the materials was investigated using XRD, SEM, etc. The results indicated that the ceramics were composed of two crystalline phases MgTa2O6 and Mg4Ta2O9 in the composition range studied, and that the dielectric properties ln ε, 1/Qf, and τf changed proportionally to the fraction of main crystal phases, which meet perfectly with the mixing model proposed in this study. It is obvious that the proportion of the two crystal phases could be precisely controlled by x, and thereby, the dielectric properties can be conveniently and precisely tailored. Our research provided a new microwave dielectric ceramic with the composition of 2MgO‐Ta2O5, which has an ultrahigh Qf value (211 000 GHz), low dielectric constant εr (19.9), and near zero temperature coefficient of resonant frequency τf (8 ppm/°C). [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]

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]

The effects of BO additive on the phase composition and microwave dielectric properties of MgTaO ceramic were investigated by solid state reaction method. The results showed that the BO additive can lower sintering temperatures of MgTaO ceramics from 1425 °C to below 1325 °C. The XRD patterns exhibited that chemical reactions happened between MgTaO and BO forming two new phases MgTaO and MgTaO (BO) during sintering in the materials. As BO additive increased from 0 to 5 wt%, MgTaO and MgTaO (BO) phases also gradually increased. At the same time, the relative permittivity (ε) increased from 11.67 to 12.57, whereas the quality factor (Qf) decreased from 280,000 GHz to 170,000 GHz, and the temperature coefficient of resonant frequency (τ) remained unchanged. The changes of the dielectric properties with the BO additive content were correlated with the phase evolutions of the material during sintering. Typically, the MgTaO-1 wt% BO ceramic sintered at 1325 °C for 4 h acquired the best dielectric properties: ε = 12.15,Qf = 260000 GHz,and τ = − 64 ppm/°C. [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]