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Microwave dielectric ceramics with permittivity (εr) â¼ 20 play an important role in massive multiple-input multiple-output (MIMO) technology in 5G. Although fergusonite-structured materials with low dielectric loss are good candidates for 5G application, tuning the temperature coefficient of resonant frequency (TCF) remains a problem. In the present work, smaller V5+ ions (rV = 0.355 Å, with coordination number (CN) = 4) were substituted for Nb5+ (rNb = 0.48 Å with CN = 4) in the Nd(Nb1-xVx)O4 ceramics, which, according to in situ X-ray diffraction data, lowered the fergusonite-to-scheelite phase transition (TF-S) to 400 °C for x = 0.2. The thermal expansion coefficient (αL) of the high-temperature scheelite phase was +11 ppm/°C, whereas for the low-temperature fergusonite phase, it was + 14 < αL < + 15 ppm/°C. The abrupt change in αL, the associated negative temperature coefficient of permittivity (τε), and the minimum value of εr at TF-S resulted in a near-zero TCF â¼ (+7.8 ppm/°C) for Nd(Nb0.8V0.2)O4 (εr â¼ 18.6 and Qf â¼ 70,100 GHz). A method to design near-zero TCF compositions based on modulation of τε and αL at TF-S is thus demonstrated that may also be extended to other fergusonite systems.
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OBJECTIVE: Infection is a major cause of death in patients with SLE. This study aimed to explore the infection rate in patients with SLE receiving a low dose of intravenous cyclophosphamide (IV-CYC). METHODS: Clinical parameters of 1022 patients with SLE from 24 hospitals in China were collected. Patients were divided into the short-interval and lower-dose (SILD, 400 mg every 2 weeks) IV-CYC group and the high-dose (HD, 500 mg/m2 of body surface area every month) IV-CYC group. The clinical data and infection rate between the two groups were compared. RESULTS: Compared with HD IV-CYC, the infection rate of the SILD IV-CYC group was significantly lower (13.04% vs 22.27%, p=0.001). Respiratory tract infection (10.28% vs 15.23%, p=0.046) and skin/soft tissue infection (1.78% vs 4.3%, p=0.040) were significantly decreased in the SILD IV-CYC group. Moreover, infections occurred most likely in patients with SLE with leucopenia (OR 2.266, 95% CI 1.322 to 3.887, p=0.003), pulmonary arterial hypertension (OR 2.756, 95% CI 1.249 to 6.080, p=0.012) and >15 mg/day of glucocorticoid (OR 2.220, 95% CI 1.097 to 4.489, p=0.027). CONCLUSIONS: SILD IV-CYC showed a lower frequency of infection events than high-dose IV-CYC in patients with SLE.
Asunto(s)
Inmunosupresores , Lupus Eritematoso Sistémico , Humanos , Inmunosupresores/efectos adversos , Lupus Eritematoso Sistémico/complicaciones , Lupus Eritematoso Sistémico/tratamiento farmacológico , Ciclofosfamida/efectos adversos , GlucocorticoidesRESUMEN
Aqueous supercapacitors have the superiorities of high safety, environmental friendliness, inexpensive, etc. High energy density supercapacitors are not conducive to manufacturing due to the limitation of water thermodynamic decomposition potential, resulting in a narrow working voltage window. To address such challenges, a great endeavor has started to investigate high voltage aqueous supercapacitors as well as making some progress. This review summarizes key strategies regarding the realization of wide working voltage of aqueous supercapacitors and analyzes the involved mechanism, including the optimization of electrodes, electrolytes, diaphragms, and supercapacitor structures. From the perspective of extending the theoretical voltage window, electrode functionalization, heteroatom doping, neutral electrolyte, water-in-salt electrolyte, introducing redox mediators into electrolyte, and designing asymmetric structure are effective strategies for achieving this goal. Further, the actual voltage window can be maximized by optimizing the electrode mass ratio, adjusting potential of zero voltage, and electrode functionalization. The challenge and future of expanding working voltage of aqueous supercapacitors are further discussed. Importantly, this review provides inspiration for the development of supercapacitors with high energy density.
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Microwave dielectric ceramics are vital for filters, dielectric resonators, and dielectric antennas in the 5G era. It was found that the (Cu1/3Nb2/3)4+ substitution can effectively adjust the TCF (temperature coefficient of resonant frequency) of Li2TiO3 and simultaneously increase its Q × f (Q and f denote the quality factor and the resonant frequency, respectively) value. Notably, excellent microwave dielectric properties (εr (permittivity) ≈ 18.3, Q × f ≈ 77,840 GHz, and TCF ≈ +9.8 ppm/°C) were achieved in the Li2Ti0.8(Cu1/3Nb2/3)0.2O3 (LTCN0.2) ceramic sintered at 1140 °C. Additionally, the sintering temperature of LTCN0.2 was reduced to 860 °C by the addition of 3 wt % H3BO3, exhibiting superior microwave dielectric properties (εr ≈ 21.0, Q × f ≈ 51,940 GHz, and TCF ≈ 1.4 ppm/°C) and being chemically compatible with silver. Moreover, LTCN0.2 + 3 wt % H3BO3 ceramics were designed as a patch antenna and a dielectric resonator antenna, both of which showed high simulated radiation efficiencies (88.4 and 93%) and gains (4.1 and 4.03 dBi) at the center frequencies (2.49 and 10.19 GHz). The LTCN0.2 + 3 wt % H3BO3 materials have promising future application for either 5G mobile communication devices and/or in low-temperature co-fired ceramic technology owing to their high Q, low sintering temperature, small density, and good temperature stability.
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In the present work, a series of low-temperature firing scheelite structured microwave dielectric in water-insoluble La2O3-Nb2O5-V2O5 system was prepared via the traditional solid-state reaction method. Backscattering electron diffraction, X-ray diffraction (XRD), energy-dispersive analysis, and Rietveld refinements were performed to study the phase evolution and crystal structure. In the full composition range of (1 - x)LaNbO4-xLaVO4 (0 ≤ x ≤ 0.9) ceramics, at least four typical phase regions including monoclinic fergusonite, tetragonal sheelite, B-site ordered sheelite, and composite of monoclinic LaVO4 and tetragonal sheelite phases can be detected according to XRD analysis. The variations of relative dielectric constant εr, quality factor Q × f, and resonant frequency τf could be attributed to Nb/V-O bond ionicity, lattice energy, and the coefficient of thermal expansion. Infrared reflectivity spectra analysis revealed that ion polarization contributed mainly to the permittivity in microwave frequencies ranges. Furthermore, the 0.7LaNbO4-0.3LaVO4 ceramic sintered at 1160 °C possessed excellent microwave dielectric properties with an εr of â¼17.78, a Q × f of â¼75â¯940 GHz, and a τf of ca. -36.8 ppm/°C. This series of materials might be good candidate for microwave devices.
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In this work, the (Na0.5Bi0.5)(Mo1-xWx)O4 (x = 0.0, 0.5 and 1.0) ceramics were prepared via solid state reaction method. All the samples can be well densified at sintering temperature about ~720 °C. Dense and homogeneous microstructure with grain size lying between 2~8 µm can be observed from scanning electron microscopy (SEM). Microwave dielectric permittivity of the (Na0.5Bi0.5)(Mo0.5W0.5)O4 ceramic was found to be temperature-independent in a wide range between 25~120 °C with a temperature coefficient of frequency (TCF) ~-6 ppm/°C, a permittivity ~28.9, and Qf values 12,000~14,000 GHz. Crystal structure was refined using Rietveld method and lattice parameters are a = b = 5.281 (5) Å and c = 11.550 (6) Å with a space group I 41/a (88). The (Na0.5Bi0.5)(Mo1-xWx)O4 ceramics might be good candidate for low temperature co-fired ceramics (LTCC) technology.
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A series of (Bi1-x Y x )VO4 (0.4 ≤ x ≤ 1.0) ceramics were synthesized using the traditional solid-state reaction method. In the composition range of 0.4 ≤ x ≤ 1.0, a zircon-type solid solution was formed between 900 and 1550 °C. Combined with our previous work (scheelite monoclinic and zircon-type phases coexist in the range of x < 0.40), a pseudobinary phase diagram of BiVO4-YVO4 is presented. As x decreased from 1.0 to 0.40, the microwave permittivity (εr) of (Bi1-x Y x )VO4 ceramics increased linearly from 11.03 to 30.9, coincident with an increase in the temperature coefficient of resonant frequency (TCF) from -61.3 to +103 ppm/°C. Excellent microwave dielectric properties were obtained for (Bi0.3Y0.7)VO4 sintered at 1025 °C and (Bi0.2Y0.8)VO4 sintered at 1075 °C with εr â¼ 19.35, microwave quality factor (Qf) â¼ 25 760 GHz, and TCF â¼ +17.8 ppm/°C and εr â¼ 16.3, Qf â¼ 31 100 GHz, and TCF â¼ -11.9 ppm/°C, respectively. Raman spectra, Shannon's additive rule, a classical oscillator model, and far-infrared spectra were employed to study the structure-property relations in detail. All evidence supported the premise that Bi-based vibrations dominate the dielectric permittivity in the microwave region.
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x(Ag(0.5)Bi(0.5))MoO4-(1 - x)BiVO4 (0.0 ≤ x ≤ 1.0) ceramics were prepared by using the solid-state reaction technique. Ceramics with x < 0.10 had a monoclinic scheelite structure, while those with ≥0.10 were tetragonal scheelite solid solutions. This indicates that the phase transformation temperature of BiVO4 was lowered through the formation of a solid solution. The thermal expansion data of the x = 0.08 sample showed that the thermal expansion coefficient was increased suddenly from +8 to +15 ppm/°C at about 60.6 °C due to the phase transition. Similarly, a maximum value of microwave dielectric permittivity was revealed at about 65 °C for the x = 0.08 sample. All of the ceramics could be well sintered below 700 °C. Good microwave dielectric behaviors, with relative permittivity >75 and Q(f) > 9000 GHz, were obtained in ceramics with compositions near x = 0.10. Both the THz data and the infrared spectra were used to study the intrinsic dielectric behavior of the materials at microwave frequencies.
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In the present work, the microwave dielectric ceramic (Ag0.5Bi0.5)(Mo0.5W0.5)O4 was prepared by using the solid-state reaction method. (Ag0.5Bi0.5)(Mo0.5W0.5)O4 was found to crystallize in the scheelite structure, in which Ag(+) and Bi(3+) occupy the A site randomly with 8-coordination while Mo(6+) and W(6+) occupy the B site with 4-coordination, at a sintering temperature above 500 °C, with lattice parameters a = b = 5.29469(2) Å and c = 11.62114(0) Å, space group I4(1)/a (No. 88), and acceptable Rp = 9.38, Rwp = 11.2, and Rexp = 5.86. High-performance microwave dielectric properties, with permittivity â¼26.3, Qf value â¼10,000 GHz, and temperature coefficient â¼+20 ppm/°C, were obtained in the sample sintered at 580 °C. Its chemical compatibility with aluminum at its sintering temperature was revealed and confirmed by both X-ray and energy dispersive spectrometer analysis. This ceramic could be a good candidate for ultralow-temperature cofired ceramics.
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In the present work, a full range of compositions of xBi(2/3)MoO4-(1 -x)BiVO4 (0.0 ≤ x ≤ 1.0) was prepared by the solid state reaction method. All the ceramic compositions could be readily densified to below 850 °C. As the x value increased, the monoclinic scheelite structure continuously changed to a tetragonal structure at x = 0.10, which means the ferroelastic phase transition temperature was lowered to near room temperature. In the compositional range 0.50 ≤ x < 0.70, a novel ordered scheelite phase was formed, most likely through A-site vacancy ordering. For compositions x ≥ 0.70, a composite two-phase region consisting of the ordered scheelite and Bi(2/3)MoO4 phases was formed. High microwave permittivity around 75 and Qf values around 8000 GHz could be obtained in the compositions near the phase boundaries between monoclinic and tetragonal scheelite phases. The intrinsic microwave dielectric properties were extrapolated from the far infrared reflectivity spectra, and it was found that the polarization was dominated by the Bi-O stretches when x ≤ 0.10.
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In the present work, the (Bi1-xCex)VO4 (x ≤ 0.6) ceramics were prepared via a solid-state reaction method and all the ceramic samples could be densified below 900 °C. From the X-ray diffraction analysis, it is found that a monoclinic scheelite solid solution can be formed in the range x ≤ 0.10. In the range 0.20 ≤ x ≤ 0.60, a composite region with both monoclinic scheelite and tetragonal zircon solid solutions was formed and the content of the zircon phase increased with the calcined or sintering temperature. The refined lattice parameters of (Bi0.9Ce0.1)VO4 are a = 5.1801(0) Å, b = 5.0992(1) Å, c = 11.6997(8) Å, and γ = 90.346(0)° with the space group I112/b(15). The VO4 tetrahedron contracts with the substitution of Ce for Bi at the A site, and this helps to keep the specific tetrahedron chain stable in the monoclinic structure. The microwave dielectric permittivity was found to decrease linearly from 68 to about 26.6; meanwhile, the quality factor (Qf) value increased from 8000 GHz to around 23900 GHz as the x value increased from 0 to 0.60. The best microwave dielectric properties were obtained in a (Bi0.75Ce0.25)VO4 ceramic with a permittivity of â¼47.9, a Qf value of â¼18000 GHz, and a near-zero temperature coefficient of â¼+15 ppm/°C at a resonant frequency of around 7.6 GHz at room temperature. Infrared spectral analysis supported that the dielectric contribution for this system at microwave region could be attributed to the absorptions of structural phonon oscillations. This work presents a novel method to modify the temperature coefficient of BiVO4-type materials. This system of microwave dielectric ceramic might be an interesting candidate for microwave dielectric resonator and low-temperature cofired ceramic technology applications.
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In the present work, the (K(0.5x)Bi(1-0.5x))(Mo(x)V(1-x))O(4) ceramics (0≤x ≤ 1.00) were prepared via the solid state reaction method and sintered at temperatures below 830 °C. At room temperature, the BiVO(4) scheelite monoclinic solid solution was formed in ceramic samples with x < 0.10. When x lies between 0.1-0.19, a BiVO(4) scheelite tetragonal phase was formed. The phase transition from scheelite monoclinic to scheelite tetragonal phase is a continuous, second order ferroelastic transition. High temperature X-ray diffraction results showed that this phase transition can also be induced at high temperatures about 62 °C for x = 0.09 sample, and has a monoclinic phase at room temperature. Two scheelite tetragonal phases, one being a BiVO(4) type and the other phase is a (K,Bi)(1/2)MoO(4) type, coexist in the compositional range 0.19 < x < 0.82. A pure (K,Bi)(1/2)MoO(4) tetragonal type solid solution can be obtained in the range 0.82 ≤ x ≤ 0.85. Between 0.88 ≤ x ≤ 1.0, a (K,Bi)(1/2)MoO(4) monoclinic solid solution region was observed. Excellent microwave dielectric performance with a relative dielectric permittivity around 78 and Qf value above 7800 GHz were achieved in ceramic samples near the ferroelastic phase boundary (at x = 0.09 and 0.10).