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The Y2.97Re0.03Al5O12 ceramics have been prepared with Y3+ ions substituted by rare-earth ions (Re = La, Sm, Gd, Er, Yb). We have analyzed the phase composition, crystal structure, surface micromorphology, and microwave dielectric properties of the Y2.97Re0.03Al5O12 ceramics. The results of x-ray diffraction and Rietveld refinement show that with a doping amount of x = 0.03, a stable Y3Al5O12 phase can be formed, while the crystal structure is slightly changed. Samples of each component illustrate different characteristics of grain boundaries that influence the microwave dielectric properties. Based on the Phillips–Van Vechten–Levine (P-V-L) theory, the ionicity, lattice energy, and bond energy of Y2.97Re0.03Al5O12 ceramics have been calculated to characterize the relative dielectric constant, quality factor, and temperature coefficient, respectively. Among all the samples, La3+ ions substitution significantly improves the quality factor of the YAG ceramics. Optimal microwave dielectric properties (εr = 10.73, Q × f = 178102 GHz, τf = − 35.18 ppm/°C) of Y2.97La0.03Al5O12 ceramics were prepared at 1700 °C for 9 h. [ABSTRACT FROM AUTHOR]

Systemic sclerosis (SSc) is an intractable autoimmune disease with unmet medical needs. Conventional immunosuppressive therapies have modest efficacy and obvious side effects. Targeted therapies with small molecules and antibodies remain under investigation in small pilot studies. The major breakthrough was the development of autologous haematopoietic stem cell transplantation (AHSCT) to treat refractory SSc with rapidly progressive internal organ involvement. However, AHSCT is contraindicated in patients with advanced visceral involvement. Mesenchymal stem cells (MSCs) which are characterized by immunosuppressive, antifibrotic and proangiogenic capabilities may be a promising alternative option for the treatment of SSc. Multiple preclinical and clinical studies on the use of MSCs to treat SSc are underway. However, there are several unresolved limitations and safety concerns of MSC transplantation, such as immune rejections and risks of tumour formation, respectively. Since the major therapeutic potential of MSCs has been ascribed to their paracrine signalling, the use of MSC-derived extracellular vesicles (EVs)/secretomes/exosomes as a "cell-free" therapy might be an alternative option to circumvent the limitations of MSC-based therapies. In the present review, we overview the current knowledge regarding the therapeutic efficacy of MSCs in SSc, focusing on progresses reported in preclinical and clinical studies using MSCs, as well as challenges and future directions of MSC transplantation as a treatment option for patients with SSc. [ABSTRACT FROM AUTHOR]

Temporal control of delivery and release of drugs in tumors are important in improving therapeutic outcomes to patients. Here, we report a sequential stimuli-triggered in situ self-assembly and disassembly strategy to direct delivery and release of theranostic drugs in vivo. Using cisplatin as a model anticancer drug, we design a stimuli-responsive small-molecule cisplatin prodrug (P-CyPt), which undergoes extracellular alkaline phosphatase-triggered in situ self-assembly and succeeding intracellular glutathione-triggered disassembly process, allowing to enhance accumulation and elicit burst release of cisplatin in tumor cells. Compared with cisplatin, P-CyPt greatly improves antitumor efficacy while mitigates off-target toxicity in mice with subcutaneous HeLa tumors and orthotopic HepG2 liver tumors after systemic administration. Moreover, P-CyPt also produces activated near-infrared fluorescence (at 710 nm) and dual photoacoustic imaging signals (at 700 and 750 nm), permitting high sensitivity and spatial-resolution delineation of tumor foci and real-time monitoring of drug delivery and release in vivo. This strategy leverages the advantages offered by in situ self-assembly with those of intracellular disassembly, which may act as a general platform for the design of prodrugs capable of improving drug delivery for cancer theranostics. Manipulating molecular self-assembly and disassembly in vivo may permit temporal control of drug delivery and release. Here, the authors report a fluorogenic cisplatin prodrug for cancer theranostics by leveraging stimuli-triggered in situ self-assembly and intracellular disassembly processes. [ABSTRACT FROM AUTHOR]

Respiratory syncytial virus (RSV) infection in children is the most common viral respiratory infection and can cause severe lung damage or death. There is no licensed vaccine for preventing RSV infection. Previously we demonstrated that an RSV vaccine, BARS13, consisting of recombinant G protein from E. coli plus cyclosporine A (CsA) as an immune-modulator, can protect animals from RSV challenge without inducing vaccine-enhanced disease (VED). To maximize the efficacy of such a vaccine, we introduced RSV pre-fusion F protein (pre-F) to form a new vaccine comprised of the pre-F and G proteins with the CsA. Two intramuscular immunizations with the vaccine induced a higher level of neutralizing antibodies against RSV and protected mice from RSV challenge without incurring VED. Interestingly, the addition of the pre-F to the vaccine facilitated anti-G antibody production and protection from RSV infection mainly via induction of antibodies against the central conserved domain (CCD) of the G protein which correlated with blocking the CX3C-CX3CR1 interaction. A 15 amino acid sequence (FP4) within the F2 region of pre-F served as a CD4+ Th epitope to facilitate the anti-G antibody response. Collectively, such a combination of the FP4 peptide with the G protein and CsA provides a novel strategy for developing a safe and maximally effective recombinant G protein-containing RSV vaccine. [ABSTRACT FROM AUTHOR]

Oncogenic KRAS reprograms pancreatic ductal adenocarcinoma (PDAC) cells to a state that is awfully resistant to apoptosis. An alternative coping strategy is to trigger a nonapoptotic cell death. Herein, a multi specific platinum complex SEP was constructed by conjugating a quinone derivative seratrodast to a prodrug of cisplatin. Interestingly, SEP-treated KRAS-mutant PDAC cells showed the characteristics of pyroptosis, apoptosis and necroptosis, similar to PANoptosis (a newfound inflammatory cell death). Mechanistically, SEP could enter cancer cells effectively, then damage nuclear DNA, boost mitochondrial superoxide anion radicals and affect various signaling pathways related to redox homeostasis and tumor metabolism. To our best knowledge, SEP is the first metal complex, even small molecule, to elicit PANoptosis (pyroptosis, apoptosis and necroptosis) in cancer cells, providing a new strategy to overcome apoptotic resistance of KRAS-mutant PDAC. [ABSTRACT FROM AUTHOR]

In this study, single-phase MgZr1−x(Mg1/3Ta2/3)xNb2O8 (0 ≤ x ≤ 0.08) ceramics with monoclinic wolframite structure were synthesized by the traditional solid-state method. The influences of (Mg1/3Ta2/3)4+ substitution for Zr4+ on phase composition, microstructure, packing fractions, bond valences, and the microwave dielectric properties of the ceramics were systematically investigated. According to the Rietveld refinement results, with the doping of (Mg1/3Ta2/3)4+, the decline of unit cell volume led to the shift of the main peak in XRD pattern to a higher angle. Furthermore, the trend of the experimental dielectric constant kept in line with the theoretical dielectric constant calculated by the Shannon complex polarizability theory. With the introduction of (Mg1/3Ta2/3)4+ ion, the Q × f values were greatly improved due to the increase of the packing fractions, but the porosity caused by excessive substitution deteriorates the quality factor. The increase of B-site bond valence explained the decline of τf. In particular, the MgZr1−x(Mg1/3Ta2/3)xNb2O8 (x = 0.04) ceramics sintered at 1340 °C for 4 h exhibited optimal microwave dielectric properties of εr = 25.42, Q × f = 65,950 GHz, and τf = − 61.04 ppm/°C. [ABSTRACT FROM AUTHOR]

In this work, a novel material candidate, containing Li2SiO3 (LS) ceramic and CaO–B2O3–SiO2 (CBS) glass for low-temperature co-fired ceramics (LTCC) application was developed via the traditional solid-state reaction process. It is shown that the addition of CBS glass significantly improves the sintering characteristics of LS + CBS glass–ceramic systems at low temperatures by lowering the sintering activation energy. Phase coexistence of the main crystalline phase of Li2SiO3 and minor trace of Li2Si2O5 phase was confirmed. The LS + 6 wt% CBS system presents excellent properties, sintered at 875 °C for 2 h: a εr value of 6.28, a Q × f value about 3527 GHz, a flexural strength 272 MPa, a CTE value of 7.35 × 10–6/°C, and a thermal conductivity λ > 10 W/m/K, denoting its promising future for LTCC substrate application. [ABSTRACT FROM AUTHOR]

For the first time, B2O3–SiO2 (BS) glass-doped Ba5Nb4O15 (BN) ceramics for low-temperature co-fired ceramic (LTCC) applications were facilely synthesized by the conventional solid-phase synthesis strategy. The influences of glass additive content on phase evolution, microstructure, and sintering activation energy were systematically deciphered associated with the microwave dielectric properties of the ceramics. While remaining original phase of Ba5Nb4O15, trace BS additive doping will effectively lessen the sintering temperature from 1350 to 925 °C excluding sacrificing microwave dielectric properties significantly. Optimized dielectric property is achieved via further time modulation: with 0.6 wt.% doping BS glass, Ba5Nb4O15 ceramics sintered at 925 °C for 4 h exhibits best characteristics of εr = 41.2, Q × f = 22,238 GHz, τf = 53.1 ppm/°C. Therefore, Ba5Nb4O15 ceramics doped with BS glass are potential candidates for LTCC. [ABSTRACT FROM AUTHOR]

Li3Mg2NbO6 + x wt% Li2O–MgO–ZnO–B2O3–SiO2 (LMZBS, x = 2, 4, 6, 8, 10) microwave dielectric ceramics with the rock-salt structure were primarily investigated by the traditional solid-state method. The microstructures, microwave dielectric properties, and sintering characteristics were studied systematically according to the doping concentration and sintering temperature. It could be seen that the LMZBS glass effectively lower the sintering temperature of Li3Mg2NbO6 ceramics from 1250 to 925 °C with microwave dielectric properties changing as a function of the amounts of the LMZBS glass. The experimental results showed that 4 wt% LMZBS glass enabled Li3Mg2NbO6 ceramics sintered at 925 °C for 4 h to have excellent microwave dielectric properties: εr = 16.02, Q × f = 56,455 GHz, τf = − 18.81 ppm/°C. Therefore, Li3Mg2NbO6 ceramics doped with LMZBS glass meet the requirements of low-temperature co-fired ceramics. [ABSTRACT FROM AUTHOR]

The influences of Zr4+ substituted for Ti4+ on the microwave dielectric properties of LiNb0.6Ti(0.5−x)ZrxO3 (0.00 ≤ x ≤ 0.14) ceramics prepared via conventional solid-state method have been studied and are discussed. X-ray diffraction analysis indicated that the Li1.075Nb0.625Ti0.45O3 phase was formed, while a small trace of ZrO2 was observed when x reaches 0.08. With the increase of Zr4+ substitution, variation of the dielectric constant (εr) was dominated by phase constitutions and densification. The quality factor (Q × f) showed a continuously decrease tendency, which was attributed to the increasing number of grain boundaries and the content of the secondary phase. The temperature coefficient of the resonant frequency (τf) value shifted from 30.60 ppm/°C to − 14.50 ppm/°C. Temperature-stable microwave dielectric ceramics was obtained with εr = 63.14, Q × f = 4626 GHz and τf =1.38 ppm/°C, at x = 0.10. [ABSTRACT FROM AUTHOR]

In this paper, the (1−x)BaTiO3-xBi(Zn1/2Zr1/2)O3 (x = 0.04-0.20) solid solutions were prepared using conventional solid-state reaction method. The X-ray diffraction results showed that all samples were crystalized as the perovskite structure, and there was no secondary phase in whole compositional range. For x = 0.04, the ceramics were in tetragonal phase, and transformed to a pesudocubic phase for x ≥ 0.08 at ambient temperature. Temperature-dependent dielectric measurements indicated a crossover from ferroelectric behavior to relaxor-like characteristics. As the BZZ content increased, the polarization-electric field (P-E) hysteresis loops became slimmer, and the discharge energy density increased firstly, but dropped. For x = 0.12, the maximum discharge energy density was 0.758 J/cm3 at 100 kV/cm, and the corresponding energy efficiency was 98%, indicating that (1−x)BaTiO3-xBi(Zn1/2Zr1/2)O3 ceramics were promising candidates for energy storage applications. [ABSTRACT FROM AUTHOR]

A study on polytetrafluoroethylene (PTFE) composites with Na1/2Nd1/2TiO3 (NNT) ceramic and E glass shorten fiber (E-GF) was described. The E-GF content was fixed at 5 wt.%, and the NNT content varied from 12.1 vol.% to 42.8 vol.%. This paper systematically introduced the preparation process of composites and the effects of NNT filling content on the properties of composites. The surface modification of ceramic powders was observed by Fourier Transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), which proved that NNT surfaces have been modified by Perfluorooctyltriethoxysilane (F8261) successfully. When the NNT filling content was 42.8 vol.%, substrate material with a low water absorption of 0.12%, high dielectric constant of 9.45, low dielectric loss of 0.0024, and τε of -222 ppm/°C were achieved, which is of great reference significance for the miniaturization and integration of microwave devices. [ABSTRACT FROM AUTHOR]

In recent reports, the microwave dielectric properties of Li2ZnTi3O8 ceramic deviate largely from the optimal value. In this paper by the Rietveld refinement method, the co-existence of the secondary phases is confirmed which is due to the zinc volatilization. Thus, the excessive ZnO addition is introduced to obtain a high purity Li2ZnTi3O8 phase. Microwave dielectric properties are theoretically calculated to prove the above statement, based on the property indices of these phases. The calculated result is consistent to the measured data, with relative deviation around 5%. The optimized properties make the ceramic a promising ceramic candidate for the microwave applications. [ABSTRACT FROM AUTHOR]

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-εr dielectric ceramics with high Q × f value was obtained when sintered at 1340 °C: εr = 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. [ABSTRACT FROM AUTHOR]

A study on fabrication and characterization of different filler ratios AlN/ PTFE composite substrates was described. Phenyltrimethoxysilane (Z6124) was used to modify AlN ceramic powder. The contents of Z6124 were 0.8, 1.0, 1.2, 1.4, 1.6 wt%, respectively. The infrared spectroscopy, microstructure, contact angle and the pH changes in water of AlN ceramic powder were investigated in detail. The results revealed that 1.0 wt% Z6124 modified AlN ceramic powder exhibited the largest contact angle (θ = 148.4°), obvious coupling agent characteristic peak, and excellent water resistance. Next, 1.0 wt% Z6124 modified AlN powders were used to manufacture AlN/PTFE composites, and the contents of AlN ceramic filler were 25, 30, 35, 40, 45, 50 and 55 wt%, respectively. The effects of AlN ceramic content on the microwave dielectric properties, water absorption and thermal conductivity of AlN/PTFE composite substrates were systematically investigated. When the content of filler was 45 wt%, composite substrates exhibited reliable dielectric constant (εr = 3.38), acceptable dielectric loss (tan δ = 0.006) and excellent temperature coefficient of dielectric constant (− 32.6 ppm/°C), lower water absorption (0.056%) and high thermal conductivity (0.957 W/m K). [ABSTRACT FROM AUTHOR]

(1 − x)Zn0.9Mg0.1TiO3-xZn0.15Nb0.3Ti0.55O2 ((1 − x)ZMT-xZNT) (x = 0.100, 0.125, 0.150, 0.175, 0.200) ceramics were prepared at 900 °C by conventional mixed-oxide method. The phase content, microstructure and microwave dielectric properties had been investigated in detail. Rietveld refinement shows the coexistence of Zn0.9Mg0.1TiO3, Zn0.15Nb0.3Ti0.55O2, Zn(BO2)2 and Zn2TiO4 phases. With ZnO-B2O3-SiO2 (ZBS) glass added, the ceramics can be sintered well at 900 °C with a smaller grain size of 0.12 µm and a higher relative density (> 95%). The microwave dielectric properties are largely influenced by the phase composition according to mixture rule. A typical sample of 0.825ZMT-0.175ZNT ceramic with optimal dielectric properties (εr = 26.14, Q × ƒ = 27184 GHz, τƒ = − 3.46 ppm °C−1) was sintered at 900 °C for 4 h. [ABSTRACT FROM AUTHOR]

MgTiO3-based microwave dielectric ceramics were prepared successfully by reaction sintering method. The X-ray diffraction patterns of the sintered samples revealed a major phase of MgTiO3-based and CaTiO3 phases, accompanied with Mg2TiO4 or MgTi2O5 determined by the sintering temperature and time. The microwave dielectric properties had a strong dependence of sintering condition due to the different phase compositions and the microstructure characteristics. The ceramics sintered at 1360 °C for 4 h exhibited good microwave dielectric properties: a dielectric constant of 20.3, a high quality factor of 48,723 GHz (at 9GHz), and a temperature coefficient of resonant frequency of −1.8 ppm/oC. The obtained results demonstrated that the reaction-sintering process is a simple and effective method to prepare the MgTiO3-based ceramics for microwave applications. [ABSTRACT FROM AUTHOR]

The glass-ceramic in the Li2O-Al2O3-SiO2 system has been prepared by melt quenching route. The crystallization kinetics was studied by differential scanning calorimetry. The effects of sintering temperature on the phase transformation, sintering behavior, bulk density, microstructure, thermal expansion, bending strength and dielectric properties were also investigated by X-ray diffractometry and scanning electron microscopy. (Li, Mg, Zn)1.7Al2O4Si6O12 is the first crystalline phase forming in the glass-ceramic and transforms to LiAlSi3O8 phase at 800 °C. The other two crystalline phases of ZrO2 and CaMgSi2O6 precipitate at 700 and 750 °C, respectively. The densification of this LAS glass-ceramic starts at around 730 °C and stops at about 805 °C. The coefficient of thermal expansion increases with the increasing sintering temperature. The sample sintered at 800 °C for 30 min exhibited excellent properties. The nonisothermal activation energy of crystallization is 149 kJ/mol and the values of Avrami constant (n) are in the range of 3.2 to 3.9. The LAS glass-ceramic sintered at 800 °C for 30 min showed excellent properties. This makes that this material suitable for a number of LTCC applications. [ABSTRACT FROM AUTHOR]

A novel CaO–2CuO–Nb2O5 (CCN) ceramic composite was prepared by the solid-state reaction method in the temperature range of 810–890 °C. Typically, the CCN sintered at 870 °C exhibited the excellent microwave properties of εr = 15.7, Q × f = 28,700 GHz, τf = − 38.4 ppm/°C. The τf of CCN was turned to be near zero by adding TiO2, while the εr increased slightly and the Q × f decreased. The 0.91CCN–0.09TiO2 ceramic sintered at 920 °C showed modified properties of εr = 16.9, Q × f = 21,500 GHz, τf = − 1.6 ppm/°C, which shows potential in LTCC applications. [ABSTRACT FROM AUTHOR]

The effects of Li2ZnTi3O8 addition on the sintering behavior, phase formation, microstructure and microwave dielectric properties of 0.94MgTiO3–0.06CaTiO3 ceramics have been investigated. These results suggested that Li2ZnTi3O8 addition not only contributes in decreasing the sintering temperature, but also enhances grain growth. A new microwave dielectric ceramic, 0.94MgTiO3–0.06CaTiO3–0.015Li2ZnTi3O8 sintered at 1220 °C had optimal dielectric properties (εr = 20.97, Q × f = 70,832 GHz, τf = 3.45 ppm/°C), which satisfies microwave applications in resonators, filters and antenna substrates. [ABSTRACT FROM AUTHOR]

Composite substrates for microwave circuit applications have been fabricated by filling polytetrafluoroethylene (PTFE) polymer matrix with ceramic powder consisting of rutile TiO ( D ≈ 5 μm) partially substituted with fused amorphous SiO ( D ≈ 8 μm) with composition x vol.% SiO + (50 − x) vol.% TiO ( x = 0, 3, 6, 9, 12), and the effects of SiO addition on characteristics such as the density, moisture absorption, microwave dielectric properties, and thermal properties systematically investigated. The results show that the filler was well distributed throughout the matrix. High dielectric constant ( ε > 7.19) and extremely low moisture absorption (<0.02%) were obtained, resulting from the relatively high density of the composites. The ceramic particles served as barriers and improved the thermal stability of the PTFE polymer, retarding its decomposition. The temperature coefficient of dielectric constant ( τ ) of the composites shifted toward the positive direction (from − 309 ppm/°C to − 179 ppm/°C) as the SiO content was increased, while the coefficient of thermal expansion remained almost unchanged (∼ 35 ppm/°C). [ABSTRACT FROM AUTHOR]

The BaNdTiCrO (0 ≤ z ≤ 3.0) ceramics were prepared using the solid-state reaction route. The influence of substitution of Cr for Ti on microstructure and microwave dielectric properties of BaNdTiCrO (BNTC z) ceramics was investigated in this study. The X-ray diffraction patterns (XRD) of the specimens showed that pure BaNdTiO phase with tungsten bronze structure existed for z ≤ 1, but the secondary phase BaTiO was observed for 1.5 ≤ z ≤ 3. The substitution of Cr for Ti was confirmed by the results of scanning electron microscopy and energy dispersive spectrometer. The dielectric constant ( ε ) was deteriorated with the increment of substitution which was in accord with the tendency of apparent density. The quality factor value ( Q× f) was improved by a small amount of substitution for z ≤ 0.5, but deteriorated seriously when excessive Cr content was added ( z > 0.5). The temperature coefficient of the resonant frequency ( τ ) was effectively reduced from + 63 ppm/°C to − 7.1 ppm/°C with the increase of substitution content. At last, the excellent dielectric properties with ε = 81.53, Q× f = 11,294 GHz and τ = + 39.2 ppm/°C were obtained as z = 0.5 sintered at 1420 °C for 2 h. [ABSTRACT FROM AUTHOR]

In this article, LiMgTiO + x wt% (x = 5-9) CaTiO microwave dielectric ceramics with high temperature stability were prepared by solid-state reaction. The crystal structure, microstructure, microwave dielectric properties were discussed systematically as function of x value and sintering temperature. The results show that LiMgTiO and CaTiO phases coexist and the content of CaTiO phase increases, the dielectric constant increases, quality factor and temperature coefficient of resonant frequency decreases because of the increase of CaTiO content. The LiMgTiO + 6 wt% CaTiO ceramics sintered at 1210 °C for 4 h show great properties: ε = 18.03, Q × f = 69,022 (at 7.886 GHz), τ = − 3.03 ppm/°C. [ABSTRACT FROM AUTHOR]

The lithium silicate glass-ceramic was synthesized by conventional solid-state methods at low sintering temperatures. The effects of different sintering temperature on the crystal composition, microstructure, flexural strength, bulk density, thermal expansion coefficient (TEC) and microwave dielectric properties of lithium silicate glass ceramic have been investigated in detail. The research shows that the lithium silicate ceramic was synthesized successfully at a lower temperature (1010 °C). Excellent properties obtained at 1010 °C for 30 min: the flexural strength σ = 189.782 Mpa, the coefficient of thermal conductivity λ= 7.807 w/(m k), ε = 6.11, Q × f = 3686 GHz, the bulk density was 2.429 g/cm and α = 10.6992 × 10/°C, indicating its potential value for LTCC application. [ABSTRACT FROM AUTHOR]

The LaO-BO-ZnO (LBZ) and VO-CuO (VC) glasses were co-doped to the CaLaTiO (CLT) ceramics as the sintering aids. The effects of LBZ and VC glasses on the low temperature sintering characteristics, phase composition, microstructure, activation energy and dielectric properties of CLT ceramics were investigated systematically. The results show that the synergistic effect of the LBZ and VC co-doped glasses can greatly reduce the sintering temperature of CLT from 1350 to 900 °C with excellent microwave dielectric properties, attributing to the reduction of the activation energy ( Ea) of the CLT with co-doped glasses. Typically, CLT ceramics with 3 wt% LBZ and 1 wt% VC sintered at 900 °C/4 h exhibited good microwave dielectric properties of ε = 98.94, Q × f = 4885 GHz (f = 3.25 GHz) and τ = 305.17 ppm/°C. [ABSTRACT FROM AUTHOR]

Fused amorphous SiO filled polytetrafluoroethylene (PTFE) microwave substrate composites were manufactured. The composition of all the samples was 57 wt% SiO and 43 wt% PTFE. The effects of compound silane coupling agents on the properties of the SiO filled PTFE composites were investigated, including density, water absorption, dielectric properties and temperature coefficient of dielectric constant. Compound coupling agents x wt% KH550+ (1.5−x) wt% F8261 (x: mass ratio to SiO ceramic, x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) were used to pre-treat SiO fillers and the performance of composites were improved with appropriate amounts of coupling agents. The SEM results show that SiO particles modified with compound coupling agents are well dispersed in PTFE polymer and exhibit a strong connection with PTFE. The dielectric constant of all the composites shows excellent frequency stability within the frequency from 1 to 18 GHz. The SiO ceramic filler modified with 1.1 wt% F8261 and 0.4 wt% KH550 simultaneously has the highest contact angle and the lowest surface energy, besides, the composite achieves a most compact structure with a maximum density of 2.059 g/cm. At the same time, this composite obtains optimal properties, including good dielectric properties ( ε ~ 2.89, tanδ ~ 0.0007), acceptable water absorption of 0.2%, temperature coefficient of dielectric constant ( τ ) of 32.32 ppm/°C. Moreover, the ratio of experimental and theoretical dielectric constant can achieve 98.86%, which is far greater than that in previous reports. [ABSTRACT FROM AUTHOR]

Polytetrafluoroethylene (PTFE)/glass fiber (GF) composites modified by Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) was investigated. This study included the manufacturing process of PTFE/GF/FEP composites and the effects of the content of FEP on the properties of composites, such as porosity, dielectric properties ( $${{D}_{k}}$$ , $${{D}_{f}}$$ ), water absorption, temperature coefficient of dielectric constant ( $${{\tau }_{\varepsilon }}$$ ) and coefficient of thermal expansion (CTE). Furthermore, the miscibility of PTFE and FEP was also investigated. The compositions of the resin mixture are x wt% FEP + (100 − x) wt% PTFE (x = 0, 10, 20, 30, 40). The results show that as the content of FEP is 30 wt%, the composite has a minimum porosity, at the same time achieves optimum properties, including dielectric constant ( $${{D}_{k}}$$ ) of 2.2343, dielectric loss ( $${{D}_{f}}$$ ) of 1.4 × 10, water absorption of 0.019%, CTE of 29, 36 and 231 ppm/°C (X, Y, Z direction, respectively) and temperature coefficient of dielectric constant ( $${{\tau }_{\varepsilon }}$$ ) of −71 ppm/°C. It has been found that FEP addition results in improved performance of the composites than that of previous reported work. [ABSTRACT FROM AUTHOR]

In this study, effects of Bi substitution upon microwave dielectric properties of the (CrNb) replaced BaNdTiO (0 ≤ x ≤ 0.2) ceramic have been reported. The x-ray diffraction (XRD) result shows a single phase for all compositions with peak position fluctuation. Within the whole x range, while the quality factor ( Q) is degraded, the dielectric constant ( ε ) can be improved by as high as 32% and the temperature coefficient of resonant frequency ( τ ) is tailored from around +40 ppm/°C to the vicinity of zero. Considering practical requirements, we can obtain a series of temperature-insensitive ceramics ( τ ∼ 0 ppm/°C) with relative permittivity about 95 and Qf (defined as Q times the resonant frequency f) higher than 6000 GHz. They have the potential of being utilized in wireless microwave communication applications. [ABSTRACT FROM AUTHOR]

The microwave dielectric properties and microstructures of 0.95MgTiO-0.05CaTiO ceramics with different amount of NdAlO additions, prepared by the solid-state route, were investigated. It is found that doping of NdAlO can significantly improve the density and dielectric properties of 0.95MgTiO-0.05CaTiO ceramic and the sintering temperature of 0.95MgTiO-0.05CaTiO ceramic can be lowed to 1275 °C. Microwave dielectric properties were correlated with the singtering temperature and the amount of NdAlO additions. A maximum Q × f of 78000 GHz associated with an ε of 20.94 and a τ of −10.31 × 10/°C was achieved for the 5 wt% NdAlO-doped 0.95MgTiO-0.05CaTiO ceramic sintered at 1275 °C/4 h. [ABSTRACT FROM AUTHOR]

CaO-AlO-SiO glass-ceramic were prepared by melt quenching technique. The crystallization behavior and properties were studied by means of a non-isothermal, thermal analysis technique, X-ray diffraction and scanning electron microscopy. The influence of sintering temperature on phase formation, microstructure, bending strength, dielectric and thermal properties were determined. The activation energy of crystallization and the Avrami parameter were also discussed. The X-ray diffraction results show that SiO phase could be found in all samples and CaSiO and anorthite phases could only be observed in the samples sintered at above 875°C. The densification of glass-ceramic starts at 730°C after the liquid glass is formed and stops at 803°C. Complete densification was achieved at 875°C and the highest mechanical strength was obtained at 850°C, but density significantly decreased at higher temperatures. The coefficient of thermal expansion and the dielectric constant increase with the increasing sintering temperature. The value of the Avrami parameter (n) is ~1.6 and the apparent activation energy (E) is 298 kJ/mol. [ABSTRACT FROM AUTHOR]

Effects of different glass/ceramic weight ratio on the physics and dielectric properties of AlO-BO-SiO (ABS) glass/AlO ceramic composites were investigated. The results show that when glass/ceramic = 50:50 (mass fraction), the composite had the excellent comprehensive properties. Then the lower softening temperature CaO-BO-SiO (CBS) glass was added to the ABS glass as sintering flux on this composite. When the CBS glass content was 2 wt%, the composites showed good properties: ε = 4.98, tanδ = 3.59 × 10 (which was 10 % lower than sample without CBS glass), and the flexural strength was 154.77 MPa (which was 16.2 % higher than the sample without CBS glass). [ABSTRACT FROM AUTHOR]

The present study investigated the effect of sintering temperature on the crystallization behavior of polytetrafluoroethylene (PTFE) polymer in SiO filled PTFE (PTFE/SiO) composites, as well as the dependences of dielectric properties, thermal conductivity, water absorption and density on the sintering temperature of composites. The composites were sintered by hot pressing at temperatures of 350-390 °C. The melting peaks of the sintered composites were recorded by the differential scanning calorimetry (DSC), and heats of melting were calculated from the peak areas in DSC curves, then the crystallinity of PTFE in composites was deduced. The intensities of the crystal diffraction peak for PTFE were observed by X-ray diffraction analysis. Moisture absorption of the composites was measured conforming to IPC-TM-650 2.6.2. Archimedes' principle was used to find out the density of the composites. The dielectric constant and loss tangent of the composites were evaluated at microwave frequency region using strip line resonator method according to IPC-TM-650 2.5.5.5 specification. Thermal conductivity was measured by laser thermal conductivity meter. Morphology of PTFE crystals and dispersion of fillers in the PTFE matrix were studied using scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Single-phase Sr(NdLa)AlO ( x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1) solid solutions with tetragonal KNiF-type structure were obtained by a standard solid-state reaction approach in the entire composition range. Their microwave dielectric characteristics were investigated together with microstructures, and were significantly modified by La-substitution. The X-ray diffraction results presented that the samples were SrNdAlO and SrLaAlO. And the dielectric constant ( ε ) changed slightly, the temperature coefficient of resonant frequency ( τ ) varied from −9 to −34 ppm/°C. The significantly improved Q × f value was achieved in the present ceramics with x = 0.9 and reached the maximum of 65,900 GHz. The ionic radius difference of A-site affects the distortion in the rock-salt layer and the tolerance t affects the interlayer mismatch, both of them will predominantly affect the Q × f value. The best combination of microwave characteristics was achieved at x = 0.9: ε = 18.49, Q × f = 65,900 GHz, τ = −27 ppm/°C. [ABSTRACT FROM AUTHOR]

In this paper, the compound NaNdSmTiZrO (NNSTZ x, x = 0.00, 0.01, 0.02, 0.05, 0.09, 0.14, 0.20, 0.30) ceramics were prepared by the conventional solid-state route. The main phase of all NNSTZ x samples were indexed as an orthorhombic perovskite structure. The permittivity ( ε ) and quality factor ( Q × f) were improved because of improvement of relative density and homogeneous microstructure with minor Zr substitution ( x ≤ 0.02). When x ≤ 0.14, the temperature coefficient of the resonant frequency ( τ ) could be effectively tuned to a relatively low value of 110.3 ppm/°C due to a continuous decrease of tolerance factors. A remarkable decrease of τ from 110.3 ppm/°C to −2.38 ppm/°C was obtained since a certain amount of NdTiO phase was observed with x ≥ 0.20. Typically, the NNSTZ x ( x = 0.20) ceramic sintered in air at 1450°C for 2 h exhibited good microwave dielectric properties of ε = 75.4, Q × f=6813 GHz, and τ = 67.8 ppm/°C. [ABSTRACT FROM AUTHOR]

Microwave dielectric properties of Ba(NdSm)TiAlO (0 ≤ x ≤ 0.4, 0 ≤ z ≤ 0.9) ceramic have been determined in this study. All samples showed a single tungsten-bronze like structure. Albeit dielectric constant was degraded by aluminum doping, the quality factor improved by 20 % and the temperature coefficient of resonant frequency decreased by 60 %. Based on this result, samarium replacement was implemented and improved microwave properties, including relative permittivity higher than 80, quality factor around 10,000 GHz and temperature coefficient of resonant frequency at the vicinity of zero, can be obtained. At last, with appropriate site-substitution content control ( x = 0.2, z = 0.6), we gained a ceramic, with dielectric constant of 81, quality factor of 8650 GHz and temperature coefficient of resonant frequency of +3.8 ppm/°C, that possesses the potentials for radio frequency identification applications. [ABSTRACT FROM AUTHOR]

The effects of SrTiO on the sintering behaviors, phase structures, microstructures and the microwave dielectric properties of CaO-BO-SiO (CBS) glasses/AlO ceramics were investigated in this study. The results show that the SrTiO additions can be well sintered with CBS glasses/AlO ceramics at low temperature, and increase the density and the dielectric constant of the CBS glasses/AlO ceramics. Especially, the temperature coefficient of the resonant frequency τ could be adjusted to zero with SrTiO added. And the sample with 15 wt% SrTiO sintered at 850 °C exhibited promising properties of: ε = 10.13, tanδ = 0.00323, τ = −5.35, and σ ≥ 200 MPa. [ABSTRACT FROM AUTHOR]

Glass-ceramics based on the LiO-AlO-SiO system were synthesized by the conventional melt-quenching technology. The glass-ceramics were designed based on silicon oxide replacement with simultaneous increasing calcium oxide. The effects of CaO on the microstructure, densification, thermal, dielectric and mechanical properties of the glass-ceramics were investigated. This glass-ceramic has a low softening point and could be sintered at a low temperature of 800 °C. The addition of CaO promotes the formation of the CaMgSiO phase and could improve the microstructure, densification and mechanical property. The coefficient of thermal expansion of the glass-ceramic increases with the content of CaO and could match that of silicon chips. The sample LAS2 (2.1 wt% CaO) sintered at 800 °C for 0.5 h exhibits excellent properties: high density of 2.48 g/cm, low dielectric constant of 6.8 and loss of 3.7 × 10, high three point bending strength of 154 MPa, and low CTE value of 1.9 × 10/°C. [ABSTRACT FROM AUTHOR]

KO-BO-SiO (KBS) synthesized via a solid-state reaction process was chosen as a novel sintering aid for Ba(Sm, Nd)TiO + 2TiO (x = 2/3 and y = 0.5; BSNTT) ceramics. Effects of KBS doping on sintering behavior, microstructure and microwave dielectric properties of BSNTT ceramic were investigated. The appropriate KBS addition significantly lowered the sintering temperature of BSNTT ceramic with slightly damaging its microwave dielectric properties. The X-ray diffraction results showed that all the well sintered samples exhibited the main phase Ba(Sm,Nd)TiO and a certain amount of BaTiO and TiO secondary phases. Besides, the other secondary phase SmTiO formed when 9 wt% KBS added. Then the scanning electron microscopy micrographs of the optimally well-sintered (1075 °C for 3 h) ceramics showed a dense microstructure. With the increasing content of KBS addition, both the dielectric constant ( ε) and quality factor ( Q × f) value decreased. At last, the good microwave dielectric properties of ε = 68.8, Q × f = 6766 GHz, τ = 28.76 ppm/°C were obtained for BSNTT + 5 wt% KBS ceramic sintered in air at 1075 °C for 3 h. [ABSTRACT FROM AUTHOR]

The effects of ZnO content and sintering temperature on the microstructure, bending strength, coefficient of thermal expansion and dielectric properties of LiO-AlO-SiO glass-ceramic are presented. The prepared LiO-AlO-SiO glass-ceramic could be used for the application of LTCC substrate. Glass powders were produced by conventional melt-quenching technique. The sintering and crystallization behavior of glass powders was explored using scanning electron microscopy, differential thermal and X-ray diffraction analyses. The crystalline phase formation in the calcination of LiO-AlO-SiO samples has shown a major phase of LiOAlO7.5SiO and two minor phases ZrO and CaMgSiO. Increasing ZnO content at the expense of SiO was shown to not only promote the densification and lower the linear shrinkage, but also enhance the bending strength and the coefficient of thermal expansion of the glass-ceramic. The linear shrinkage and density of samples will decrease with the increasing sintering temperature. [ABSTRACT FROM AUTHOR]

During past over 30 years, low temperature co-fired ceramic (LTCC) technology has been developed to meet with the requirements of small, light weight and multifunctional electronic components through enabling fabrication of three-dimensional ceramic modules with low dielectric loss and embedded silver electrode. A recent technology is to develop new dielectrics with ultra-low sintering temperature (usually <650 °C) to save energy, reduce processing time, and to enable further integrations with semiconductors, metals or even plastics. In this review, we summarized the materials with ultra-low sintering temperature developed in past over 10 years, which will be helpful for those researchers to not only develop new materials but also improve all technologies in ultra-LTCC fields. [ABSTRACT FROM AUTHOR]

In this work, frequency-stable NaNdSmTiSnO ( x = 0.00, 0.01, 0.02, 0.05, 0.09, 0.14, 0.20, 0.30, 0.40, 0.50) ceramics with low dielectric loss were prepared by the conventional solid-state route. The effects of the Sn ratio on the structure, sintering behavior, and microwave dielectric properties of NaNdSmTiSnO (NNST) were systematically investigated. All samples were indexed as having orthorhombic perovskite structure; replacement of Ti by Sn at the B-site occurred and increased the lattice parameters for x ≤ 0.4. ε decreased monotonically with increasing Sn concentration. The quality factor could be significantly enhanced because of the improved densification, reaching a maximum value at x = 0.3. It was remarkable that the τ value could be effectively tuned from a large value of 206 ppm/°C to near zero due to a continuously dramatic change of lattice structure. The results showed that the Sn content significantly influenced the microstructure and sintering behavior because of the appearance of liquid phase. NNST ceramic with x = 0.3 sintered at 1350°C for 2 h showed good microwave dielectric properties of ε = 56, Q × f = 10,734 GHz, and τ = 22 ppm/°C. [ABSTRACT FROM AUTHOR]

The impact of bismuth substitution at neodymium (Nd) site in aluminum-replaced BaNdTiO ceramics on dielectric constant ( ε), quality factor ( Qf), and temperature coefficient of resonant frequency ( τ) has been determined (0.05 ≤ x ≤ 0.2). With appropriate quality factor values ( Qf > 5000 GHz), the dielectric constant increased from 74.42 to a maximum of 90.8 and the temperature coefficient of resonant frequency was tailored from approximately +20 ppm/°C to the vicinity of 0 ppm/°C. The X-ray diffraction patterns showed a single phase for all compositions, while the scanning electron microscopy and energy-dispersive spectrometer data confirmed XRD results. Factors, such as bulk density, average polarizability, microstructure, and tolerance factor which were caused by the substitution, were taken into consideration to discuss the microwave dielectric properties' variation. Within substituting limit, a series of controllable microwave dielectric properties ( ε = 75.8, Qf = 8994 GHz, τ = 7.2 ppm/°C; ε = 79.1, Qf = 7282 GHz, τ = 2.3 ppm/°C; ε = 87.07, Qf = 5548 GHz, τ = −8.6 ppm/°C) could be obtained when sintered at 1350 °C for 2 h for x = 0.05, 0.1, and 0.15, respectively. [ABSTRACT FROM AUTHOR]

The effects of YO substitution on the microstructure and microwave dielectric properties of Ba(CoYZn)NbO (x = 0-0.06) ceramics prepared by the conventional solid-state route technique were investigated. The X-ray diffraction results presented that all the well sintered samples exhibited the main phase BaZnNbO-BaCoNbO and a certain amount of BaCoNbO second phase. The 1:2 B-site cation ordering degree was found to influenced by the replacement of Y, especially for x = 0.02. Then the scanning electron microscopy pictures of the optimally well-sintered (1375 °C for 20 h) ceramics has shown a dense microstructure. Although the ε almost kept unchanged, appropriate doping content would greatly improve the Q × f value. Meanwhile, the τ value increased slightly with increasing x. At last, the excellent microwave dielectric properties of ε = 35.21, Q × f = 72,046 GHz, τ = 3.65 ppm/°C were obtained for x = 0.02 sintered in air at 1375 °C for 20 h. [ABSTRACT FROM AUTHOR]

The influences of different doping contents of composite additive LaO-BO-ZnO-CaO (LBZC) on the sintering behavior, microstructure and microwave properties of BaSr(NdBi)TiO (BSNBT) microwave ceramics were investigated. With an increasing doping content of LBZC, the sintering temperature gradually decreased. The sintering temperature of BSNBT ceramics was significantly lowered to 880 °C by the addition of 20 wt% LBZC. The scanning electron microscopy photographs showed that the fraction of liquid phase increased as increasing the content of LBZC, resulting in deteriorated microwave properties. According to the X-ray diffraction patterns, the dominant crystal phase of samples transformed from BaNdTiOto the minor phase of BaTiO with 10 wt% LBZC dopant, which was further confirmed by energy dispersive spectrometer. The sample with 15 wt% LBZC sintered at 900 °C exhibited the optimum microwave dielectric properties: ε = 54.9, Q × f = 2949 GHz, and τ = 17.2 ppm/°C. [ABSTRACT FROM AUTHOR]

The glass-ceramic composites were prepared from low-softening glass CaO-BO-SiO, micrometer and nanometer alumina. The influences of nano-AlO on the sinterability, microstructure, dielectric property, mechanical strength, and thermal expansion of glass-alumina composites were investigated. The densification mechanism of nano-AlO modified glass-alumina composites was revealed further. The results show that nano-AlO effectively lowers the densification temperature of glass-alumina ≤900°C. The density gradually increases with increasing nano-AlO to 15 wt %, and then decreases. Dielectric constant, dielectric loss, and flexural strength respectively versus nano-AlO exhibit a similar change trend to the density. The sample with 15 wt % nano-AlO sintered at 900°C could form the dense microstructure (~2.95 g/cm) and achieve the high performance: low dielectric constant (6.13), low dielectric loss (5.2 × 10), low thermal expansion (4.21 × 10/°C), and high mechanical strength (178 MPa). [ABSTRACT FROM AUTHOR]

The effects of x wt% HBO+ 1.0 wt% CuO (x = 1.0-10.0) co-doping on microstructure and microwave dielectric properties of 0.85BaTiO-0.15BaZnTiO (BZT) have been investigated according to the conventional solid-state reaction in this study. The X-Ray Diffraction results showed that the main crystal phase in the sintered ceramics was BaTiO. The addition of HBO-CuO resulted in the liquid phase sintering mechanism, which effectively improved their relative densities and lowered the sintering temperature. As HBO doping amount increased from 1.0 to 10.0 wt%, the relative density and ε displayed a sharp increase at first and then a decline when x = 6.0 wt%. The Q × f value experienced a continuously decrease with the addition of HBO when sintered at sintering temperature. The development in τ was different, increasing persistently with the increase of doping amount at different sintering temperature. The HBO-CuO co-doped 0.85BaTiO9-0.15BaZnTiO ceramics had a low sintering temperature of 1000 °C and a high ε value. Good microwave dielectric properties with values of ε = 35.0, Q × f = 20,700 GHz and τ = 12.0 ppm/°C were obtained in the BZT ceramics with 6.0 wt% HBO and 1.0 wt% CuO sintered at 1000 °C for 2 h. [ABSTRACT FROM AUTHOR]

The microstructure and microwave dielectric characteristics of (BaSr)NdTi(ZnNb)O ceramics solid solutions (0 ≤ x ≤ 2.5) were investigated in this study. X-ray diffraction indicated that only BaNdTiO existed in the sintered samples when x value was lower than 2.0, but subsequently a new phase generated with increasing of x value. The dielectric constant (ε) of the samples increased slightly from 83.4 to 85.2 before falling down and quality factor value (Q × f) declined radically from 10,873 to 1321 GHz at optimum sintering temperature of 1450 °C, as x value increased from 0.0 to 2.5. And the temperature coefficient of resonant frequency (τ) could be adjusted to a minimum value and then rebounded because of the second phase NdNbTiO which also sharply deteriorated the quality factor of the samples. At last, the excellent microwave dielectric properties of the samples with values of ε = 85.2, Q × f = 5989 GHz, τ = +14.9 ppm/°C were obtained as x was 1.0 sintered at 1450 °C for 3 h in air. [ABSTRACT FROM AUTHOR]

The effects of magnesium and niobium substitution for titanium on the microwave dielectric properties of BaNdTi(MgNb)O (0 ≤ z ≤ 3) ceramics were studied. The temperature coefficient of resonant frequency (τ) decreased from about +60 ppm/°C to +17 ppm/°C when z ≤ 1. Excellent quality factor ( Qf = 7300 GHz) as well as high dielectric constant ( ε = 80.96) were obtained. For z ≥ 1.5, Nd(Ti,Mg,Nb)O secondary phase appeared which would obviously influence the microwave dielectric properties. As z varied from 0 to 3, matrix grain size degraded which would obviously deteriorate the microwave dielectric properties by conducting more pores, especially the Qf value. The τ value was found to be related to b-site bond valence ( V) and unit cell volume ( V). Average ionic polarizability ( α) and relative density evidently influenced the dielectric constant. [ABSTRACT FROM AUTHOR]

The AlO filler was added to a LiO-AlO-SiO glass-ceramic in order to increasing the bending strength and coefficient of thermal expansion of these composites for low temperature co-fired ceramic applications. The influence of the AlO filler on the sintering, microstructure and characteristics was investigated. When the content of AlO increases from 0 to 20 wt%, the bending strength increases from 104 to 155 MPa and the coefficient of thermal expansion increases from 1.26 to 2.65 ppm/°C. The AlO filler also plays an important role for obtaining desired sintering, microstructure and dielectric properties. But the linear shrinkage, microstructure, mechanical and dielectric properties would deteriorate because of the excessive AlO and the decrease of glass content. The composite with 20 wt% AlO filler exhibits excellent properties: a low sintering temperature of 800 °C, a good density of 2.78 g/cm, a dense microstructure, an high bending strength of 155 MPa, good dielectric properties (ε: 8.0 and tan δ: 2.4 × 10) and a low CTE of 2.65 ppm/°C. [ABSTRACT FROM AUTHOR]

A low temperature co-fired ceramic based on the CaO-AlO-SiO system was prepared by traditional solid-state process. The effects of increasing replacement of SiO by ZnO on the sintering, mechanical, thermal and dielectric properties were investigated. X-ray diffraction results showed that anorthite was the major crystalline phase. The results revealed that the addition of ZnO could augment the degree of crystallinity but excess ZnO content would worsen the porosity of the ceramics. The specimen sintered at 900 °C for 2 h, with 2.5 wt% ZnO addition, attained optimal properties: a good density of 2.495 g/cm, high bending strength of 125 MPa, excellent dielectric properties (dielectric constant: 5.8, dielectric loss: 3.4 × 10), high resistivity (ρ > 10 Ω cm) and a low CTE of 5.97 ppm/°C, matching that of GaAs. It was shown that the prepared ceramic could meet the property requirements for low temperature co-fired ceramic applications. [ABSTRACT FROM AUTHOR]