In this study, low-temperature fired CaMg
1−
x
Li
2
x
Si
2
O
6
microwave dielectric ceramics were prepared via the traditional solid-state reaction method. In this process, 0.4 wt% Li
2
CO
3
-B
2
O
3
...-SiO
2
-CaCO
3
-Al
2
O
3
(LBSCA) glass was added as a sintering aid. The results showed that ceramics consisted of CaMgSi
2
O
6
as the main phase. The second phases were CaSiO
3
always existing and Li
2
SiO
3
occurring at substitution content
x
> 0.05. Li
+
substitution effectively lowered sintering temperature due to 0.4 wt% LBSCA and contributed to grain densification, and the most homogeneous morphology could be observed at
x
= 0.05. The effects of relative density, the second phase, and ionic polarizability on dielectric constant (ε
r
) were investigated. The quality factor (
Q
×
f
) varied with packing fraction that concerned the second phase. Moreover, the temperature coefficient of the resonant frequency (τ
f
) was influenced by MgO
6
octahedral distortion and bond valence. Excellent dielectric properties of the CaMg
1−
x
Li
2
x
Si
2
O
6
ceramic was exhibited at
x
= 0.05 with ε
r
= 7.44,
Q
×
f
= 41,017 GHz (
f
= 15.1638 GHz), and τ
f
= −59.3 ppm/°C when sintered at 900 °C. It had a good application prospect in the field of low-temperature co-fired ceramic (LTCC) substrate and devices.
Abstract Background Danshen dripping pill (DSP) is a popular Chinese medicinal product and often compared with isosorbide dinitrate (ISDN) in treating coronary heart disease angina pectoris. Over 100 ...randomized controlled trials (RCT) have been published in Chinese language but have not been evaluated according to the PRISMA systematic review standard. This study aims to provide a comprehensive and PRISMA-compliant systematic review with sensitivity and subgroup analyses. Methods RCTs published between 1994 and 2009 on DSP versus ISDN in treating angina pectoris for 4 or more weeks were retrieved from major databases, including PubMed, Chinese National Knowledge Infrastructure, and WanFang Data. Meta-analysis was performed on the overall effects on symptomatic and electrocardiography (ECG) improvements. Sensitivity analysis was conducted on the study quality of RCTs based on a refined Jadad scale and different efficacy definitions. Results Sixty RCTs with 6931 participants were included. Summary odds ratios for comparing DSP and ISDN were 2.49 (95% CI 2.03–3.05) by symptoms ( n = 60) and 2.14 (95% CI 1.82–2.52) by ECG ( n = 53) according to the basic efficacy definitions and were 1.67 (95% CI 1.45–1.91) by symptoms ( n = 56) and 1.75 (95% CI 1.51–2.04) by ECG ( n = 45) according to the stringent efficacy criteria. Conclusion The 60 eligible RCTs indicate that DSP is apparently more effective than ISDN in treating angina pectoris. However, further RCTs of larger scale, multi-centre/country, longer follow-up periods, and higher quality are still required to verify the efficacy of DSP over all anti-anginal therapies.
The crystal structure, Raman vibration, chemical bond characteristics, and microwave dielectric properties of Zn1-xCuxWO4 (x = 0–0.15) ceramics prepared by a solid-state reaction were investigated by ...XRD refinement, Raman spectroscopy, P-V-L theory and XPS. According to the P-V-L theory, the properties of the W-O bond are stronger than those of the Zn-O bond, which makes a major contribution to the dielectric properties. The relative permittivity is mainly affected by the average bond ionicity, and the variations in the dielectric loss and τf are mainly attributed to the lattice energy and bond energy. XPS shows that the presence of Cu+ could produce oxygen vacancy defects, increasing the dielectric loss. Additionally, Raman spectra show that the increasing molecular polarizability causes the Raman shift to move to a low wavenumber, and the changes in Raman intensity and FWHM lead to a decrease in the degree of short-range ordering. Particularly, Zn0.97Cu0.03WO4 ceramics sintered at 925 °C showed satisfactory properties (εr = 14.20, tanδ = 1.473 × 10−4 at 9.087 GHz, and τf = −40 ppm/°C), which can potentially be applied to LTCC technology and indicate that Cu substitution can not only reduce the sintering temperature, but also optimize the dielectric properties.
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•Cu2+ substitution effectively lowered sintering temperature and contributed to the optimization of value and reduced the dielectric loss.•Proper Cu2+ substitution reduced the dielectric loss associated with the lattice energy.•XPS shows that the presence of Cu+ could produce oxygen vacancy defects, increasing the dielectric loss.•The relative permittivity is mainly affected by the average bond ionicity.•Excellent dielectric properties were exhibited at x=0.03 with εr = 14.20, tanδ = 1.473×10-4 at 9.087 GHz, and τf = -40 ppm/°C.
Ceramics with low dielectric constant are widely used in high frequency substrates. The low temperature sintered CaMg0.9-xNa2xLi0.2Si2O6(x = 0–0.05 and 0.1) ceramics with low dielectric constant and ...dielectric loss were prepared by the traditional solid-state reaction method, with 0.5wt%LBSCA additive. The XRD patterns of the samples were obtained by X-ray diffraction and it was found that there were three ceramic components, CaMgSi2O6, CaSiO3 and Na2MgSiO4, which indicated that the experimental sample was a multiphase ceramic system. Through the trend of bulk density as functions of the content of substitution and the change of SEM morphology, it could be found that appropriate amount of Na+ substitution can promote the grain growing and the densification of ceramics. Results demonstrated that both the Q × f and εr were relevant to bulk density and the second phase. The τf was also affected by the second phase to some extent. In particular, the ceramics sintered at 925 °C for 3h possessed the desirable microwave dielectric properties for LTCC application: εr = 7.03, Q × f = 17,956 GHz, and τf= −79 ppm/°C.
The sintering behaviour and microwave dielectric properties of LiCaPO4 ceramic synthesized by the solid-state reaction method have been investigated, and the vibration property has been discussed ...with the help of the first principle calculation. Characterisation methods include X-ray diffraction, scanning electron microscopy, network analysis, differentia-thermal and thermo-mechanical analysis, and Raman spectrometry. The increasing sintering temperature results in the formation of the second phase. The composite ceramic with two phases (LiCaPO4 and Ca3(PO4)2) has formed when sintered at 950°C, 2.99g/cm3 for density, 20.09 for ɛr and tanδ=0.008 at 8GHz.
In this work, two low-temperature co-fired silicate ceramics (CaMg0.9-xLi0.2CoxSi2O6, x = 0.15–0.75, CMLCS; CaMg0.9-yLi0.2SrySi2O6, y = 0, 0.05, 0.1–0.5, CMLSS) were synthesized via solid-state ...reaction method with 0.5 wt%LBSCA glass addition. CMLCS and CMLSS were densely sintered at 925 °C, and had good chemical compatibility with silver. Optimal microwave dielectric properties (εr = 6.71, Q×f = 30124 GHz, and τf = −79.06 ppm/°C) and (εr = 6.78, Q×f = 32530 GHz, and τf = −52.99 ppm/°C) were obtained for CMLC0.15S and CMLS0.05S respectively. With increase in Co and Sr substitution, XRD and Raman spectra showed that second phases were produced, and densification process of CaMgSi2O6-based ceramics was promoted. Dielectric constant was influenced by relative density, Raman shift and second phase. The parameter Q×f was affected by the FWHM of Raman peaks as well as extrinsic factors that affected the temperature coefficient of resonant frequency. Therefore, the results suggested the potential of these two ceramics as candidates for LTCC application.
•The Ni2+ ions were incorporated into BaZnP2O7 ceramics that were synthesized via solid-state reaction method to improve their performance.•The most optimal microwave dielectric properties were ...observed for BaZn0.94Ni0.06P2O7 sintered at 900 °C for 3h: εr = 7.43, q×f = 102,538 GHz, and τf = −64 ppm/ °C, and the quality factor was improved to at least 200% of the unsubstituted BaZnP2O7 ceramics.•The lattice energy and band gap were calculated based on the P-V-L theory and DFT, respectively. The results showed that the optimized q×f value (102,538 GHz) of the BaZn0.94Ni0.06P2O7 ceramics sintered at 900 °C stems from the increased bond energy of P1-O and Zn-O bonds and the larger band gap.
In this work, we incorporated Ni2+ ions into BaZnP2O7 ceramics with a low dielectric constant to improve their performance. Enhancement of microwave dielectric properties was observed for BaZn0.94Ni0.06P2O7 sintered at 900 °C for 3 h: εr = 7.43(±0.04), Q×f = 102,538(±3012) GHz, and τf = -64(±2.4) ppm/ °C. XRD, SAED, and EDS mapping indicated that a solid solution was formed in all ceramic samples. The Ni2+ doping promoted grain growth and densification of the samples. The density was a major factor affecting dielectric constant εr, and the pore-corrected εrc was explained by the molecular polarizability. The vibrational characteristics were analyzed by Raman and FTIR spectroscopies. The FWHM of Raman peaks had a marked effect on the Q×f and τf values. Furthermore, the higher lattice energy and larger band gap lead to the higher Q×f value of the BaZn0.94Ni0.06P2O7 ceramic with lower density. The excellent performance of the prepared ceramics makes them a good candidate material for low-temperature co-fired ceramic technology.
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The Sr-substituted CaMgSi2O6 ceramics (CaMg1−xSrxSi2O6, x = 0, 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5) were synthesised via solid-state reaction method. The CaMg0.9Sr0.1Si2O6 sample was dense at 1250 °C, ...and outstanding performance was achieved: εr = 7.85, Q×f = 77,916 GHz (13.65 GHz), and τf = −42.89 ppm/°C. The effects of Mg2+ substituted by Sr2+ on the phase composition, microstructure, lattice vibration and microwave dielectric properties of CaMgSi2O6 ceramics were investigated. The doped Sr2+ with solubility between 0.05 and 0.1 mol promoted the densification and grain growth of ceramics and led to the formation of second phase and red shift of X-ray diffraction peaks and Raman active modes. Density and porosity played an important role in εr. The Q×f value was optimised with homogeneous grain size distribution, high relative density and low full width at half maximum. The τf value was closely related to the second phase and changed nonlinearly with the x value.
This work investigates the influence of niobium pentoxide (Nb2O5) as dopant, on the structural, magnetic, and dielectric properties of NiZnCo ferrites. The results showed that Nb2O5 was an effective ...dopant, and the Nb5+ ions entered the B site to replace Fe3+ ions, which altered the electromagnetic properties of the NiZnCo ferrite. In particular, the coercivity (Hc) was 20∼24 Oe, and the magnetic quality factor (Q), was more than 200 at x = 0 and x = 0.1 wt%, which is 4∼5 times higher than that of NiZn and NiCuZn ferrites. Excellent electromagnetic properties were obtained for 0.1 wt% Nb2O5-doped NiZnCo ferrite, i.e., Ms = 88.3 emu/g, Hc =20.4 Oe, ρ = 2.4 × 105 Ω m and Q = 202 @20 MHz. These excellent electromagnetic properties of Nb2O5-doped NiZnCo ferrites could be potentially applied to resonators and capacitors at high frequency.
New low loss and low-sintering temperature co-fired Ba3-xCuxTi4Nb4O21 (BCTN, 0 ≤ x ≤ 0.12) ceramics with 0.60 wt% Li2O-B2O3-SiO2-CaO-Al2O3 (LBSCA) glass were prepared by solid-state reaction ...methodology. This work showed that CuO and LBSCA were effective sintering aid, which improved the densification and decreased sintering temperature. Thus, the excellent microwave dielectric properties of BCTN ceramics (x = 0.08) were obtained after sintering at 925 ℃ with εr ~ 44.18, Q×f ~ 17,860 GHz (@ 5.6 GHz) and τf ~ 94.76 ppm/℃. Q×f value was increased nearly 3-fold compared to pure BTN ceramics (~ 6090 GHz). Based on the P-V-L bond theory, the Ti-O and Nb-O bonds together contributed greatly to εr. The Nb-O bonds was the main factor affecting the internal loss on Q×f. The τf closely related to the oxygen octahedron Ti1/Nb1O6. The BCTN ceramics would not react with Ag electrodes, and had great potential to be used in LTCC microwave devices.
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