(Cu1/3Nb2/3)4+ ionic substituting effects,low-temperature sintering behaviors,and improved temperature stability of Ba3Nb4Ti4O21 microwave dielectric ceramics

In this study, (Cu_1/3Nb_2/3)⁴⁺ complex cation and BaO–ZnO–B₂O₃ glass frit were adopted to solve the high sintering temperature and poor temperature stability of Ba₃Nb₄Ti₄O₂₁ ceramics. It is shown that pure Ba₃Nb₄Ti₄O₂₁ phase was formed when Ti site was partially replaced by (Cu_1/3Nb_2/3)⁴⁺ cation. The increasing number of dopants decreases the dielectric polarizability, correspondingly, the dielectric constant and temperature coefficient of the resonance frequency values are reduced consistently. The variation of the Q × f value is determined by internal ionic packing fraction and external sintering densification. The (Cu_1/3Nb_2/3)⁴⁺ cation effectively decreases the suitable sintering temperature from 1200 to 1050 °C while greatly improving the temperature stability. BaO–ZnO–B₂O₃ glass was used to further improve the low-temperature sintering characteristics of Ba₃Nb₄Ti₄O₂₁ ceramics. It is proven that the addition of glass frits effectively decreases the temperature to 925 °C with combinational excellent microwave dielectric properties: ε_r ～55.6, Q × f ～5700 GHz, τ_f ～3 ppm/^°C, making the Ba₃Nb₄Ti₄O₂₁ ceramics promising in the applications of low-temperature cofired ceramic technology.     

High Q×f values of Zn-Ni co-modified LiMg0.9Zn0.1-xNixPO4 microwave dielectric ceramics for 5G/6G LTCC modules

In this work, Zn-Ni co-modified LiMg_0.9Zn_0.1-xNi_xPO₄ (x = 0–0.1) microwave dielectric ceramics were fabricated using a solid state synthesis route. Rietveld refinement of the XRD data revealed that all ceramic samples have formed a single phase with olivine structure. SEM images showed that the samples have a dense microstructure, that agrees with the measured relative density of 97.73 %. Based on the complex chemical bond theory, Raman and infrared reflectance spectra, we postulate that ε_r is mainly affected by the ionic polarizability, lattice and bond energy, while P-O bond plays a decisive role in Q×f and τ_f value. Optimum properties of Q×f ~ 153,500 GHz, ε_r ~ 7.13 and τ_f ~ ?59 ppm/°C were achieved for the composition LiMg_0.9Zn_0.06Ni_0.04PO₄ sintered at 875 ℃ for 2 h. This set of properties makes these ceramics an excellent candidate for LTCC, wave-guide filters and antennas for 5 G/6 G communication applications.     

Completely eliminating the metal barrier cracks on Nafion for suppressing methanol crossover with anodic aluminum oxide substrates

Methanol crossover is one of the main challenges for direct methanol fuel cells (DMFCs). Depositing a metal barrier on Nafion can reduce the crossover but usually faces the metal cracking issues. This study presents a new composite membrane in which an anodic aluminum oxide (AAO) substrate is impregnated with a Nafion solution and then coated with a layer of Au. The AAO/Nafion/Au composite membrane shows an ideal metal crack-free surface. Higher and more stable voltage has been achieved for the cell with the membrane, indicating an effectively suppressed methanol-crossover. Results reveal that there is a tradeoff between suppressing the methanol crossover and increasing the ion transmission. By optimizing the membrane, it can not only suppress the methanol crossover but also enhance the output performance of DMFCs. The current density and power density of the cells can be enhanced by 59% and 52.85%, respectively, compared to the cell with a commercial Nafion 117. Overall, this work provides a new approach to designing crack-free membranes for DMFCs.     

One-step synthesis of Co2P/N-P co-doped porous carbon composites derived from soybean derivatives as acidic and alkaline HER electrocatalysts

Developing inexpensive and efficient electrocatalysts for hydrogen evolution reaction (HER) in both acidic and alkaline mediums is of great significance to the hydrogen energy industry. Hereby, we prepared a mixture of precursors with homogeneous composition by using the chelating ability of soybean protein isolate (C and N source) and phytic acid (dopant and phosphating agent) with cobalt ions, and achieved one-step synthesis and construction of Co₂P/N–P co-doped porous carbon composite by carbonization at 800 °C. The as-synthesized Co₂P/NPPC-800 electrocatalyst exhibits low HER overpotentials of 121 and 125 mV at 10 mA cm^?2 in 0.5 M H₂SO₄ and 1.0 M KOH, which are close to those of the commercial Pt/C catalyst. Additionally, the NPPC substrate surrounding the Co₂P could diminish the corrosion during the HER, and Co₂P/NPPC-800 displays good stability and durability. Furthermore, this work offers a convenient synthesis strategy for phosphide/doped porous carbon composites in other electrochemical energy technologies.     

Laser damage resistance of plasma-sprayed alumina and honeycomb skeleton/alumina composite ceramic coatings

Al₂O₃ and honeycomb skeleton-Al₂O₃ composite coatings on Titanium alloy (Ti–6Al–4V) were prepared by atmospheric plasma spraying. A laser ablation experiment on as-sprayed coatings was performed. In this paper, the laser damage resistance, microstructure, phase composition of Al₂O₃ coatings were examined. 3D Dimensional Confocal Microscopy, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Energy Dispersive Spectrometry (EDS) characterized the laser damage morphology, microstructure, phase composition, and element analysis, respectively. The influence of the honeycomb skeleton on the laser ablation damage on as-sprayed coatings was investigated by a comparative analysis of the laser damage morphology with different laser ablation times and gas flow. The results show that the honeycomb skeleton raises thermal conductivity and thermal diffusivity. Moreover, a “tower”-like dendrite was generated during the laser irradiation of the composite coating. The honeycomb skeleton refined the structure, suppressed crack propagation, and reduced the influence of gas flow on cracks. Under the same experimental laser ablation parameters, the laser damage area of the honeycomb skeleton-Al₂O₃ composite coating was smaller than that of the Al₂O₃ coating. It was demonstrated that the laser damage resistance of the honeycomb skeleton-Al₂O₃ composite coating was superior to that of the Al₂O₃ coating.     

Development and characterisation of microporous biomimetic scaffolds loaded with magnetic nanoparticles as bone repairing material

Fine-tuning of the scaffolds structural features for bone tissue engineering can be an efficient approach to regulate the specific response of the osteoblasts. Here, we loaded magnetic nanoparticles aka superparamagnetic iron oxide nanoparticles (SPIONs) into 3D composite scaffolds based on biological macromolecules (chitosan, collagen, hyaluronic acid) and calcium phosphates for potential applications in bone regeneration, using a biomimetic approach. We assessed the effects of organic (chitosan/collagen/hyaluronic acid) and inorganic (calcium phosphates, SPIONs) phase over the final features of the magnetic scaffolds (MS). Mechanical properties, magnetic susceptibility and biological fluids retention are strongly dependent on the final composition of MS and within the recommended range for application in bone regeneration. The MS architecture/pore size can be made bespoken through changes of the final organic/inorganic ratio. The scaffolds undertake mild degradation as the presence of inorganic components hinders the enzyme catalytic activity. In vitro studies indicated that osteoblasts (SaOS-2) on MS9 had similar cell behaviour activity in comparison with the TCP control. In vivo data showed an evident development of integration and resorption of the MS composites with low inflammation activity. Current findings suggest that the combination of SPIONs into 3D composite scaffolds can be a promising toolkit for bone regeneration.     

Cold sintered,temperature-stable CaSnSiO5-K2MoO4 composite microwave ceramics and its prototype microstrip patch antenna

Dense (1-x)wt%CaSnSiO₅-xwt%K₂MoO₄ (CSSO-KMO) composite ceramics were fabricated by the cold sintering process at 180 °C under 400 MPa for 60 min. X-ray diffraction, Energy dispersive X-ray and Raman spectroscopy confirmed that CSSO and KMO coexisted without intermediate phases. As KMO weight fraction increased, relative permittivity (ε_r) and temperature coefficient of resonant frequency (τ_f) decreased and the microwave quality factor (Q×f, where f is resonant frequency) increased. Near-zero τ_f (-0.5 ppm/°C) was obtained for 65 wt%CSSO-35 wt%KMO with ε_r ～ 9.2 and Q×f ～ 6240 GHz. No chemical reaction between ceramic composites and silver was observed, demonstrating potential for cofiring with Ag-paste. A prototype antenna was fabricated from 65 wt%CSSO-35 wt%KMO composite ceramic with a bandwidth of 144 MHz @ -10 dB, a gain of 5.7 dBi and a total efficiency of 88.4 % at 5.2 GHz, suitable for 5 G mobile communication systems.     

Good dielectric performance and broadband dielectric polarization in Ag,Nb co-doped TiO2

Due to the demand of miniaturization and integration for ceramic capacitors in electronic components market, TiO₂-based ceramics with colossal permittivity has become a research hotspot in recent years. In this work, we report that Ag⁺/Nb⁵⁺ co-doped (Ag_1/4Nb_3/4)_xTi_1−xO₂ (ANTOx) ceramics with colossal permittivity over a wide frequency and temperature range were successfully prepared by a traditional solid–state method. Notably, compositions of ANTO0.005 and ANTO0.01 respectively exhibit both low dielectric loss (0.040 and 0.050 at 1 kHz), high dielectric permittivity (9.2 × 10³ and 1.6 × 10⁴ at 1 kHz), and good thermal stability, which satisfy the requirements for the temperature range of application of X9R and X8R ceramic capacitors, respectively. The origin of the dielectric behavior was attributed to five dielectric relaxation phenomena, i.e., localized carriers' hopping, electron–pinned defect–dipoles, interfacial polarization, and oxygen vacancies ionization and diffusion, as suggested by dielectric temperature spectra and valence state analysis via XPS; wherein, electron-pinned defect–dipoles and internal barrier layer capacitance are believed to be the main causes for the giant dielectric permittivity in ANTOx ceramics.     

Silica-based ceramics toward electromagnetic microwave absorption

Silica-based ceramics have been explored extensively as a class of versatile materials for various applications in architecture, catalysis, energy, machinery, and biomedical engineering. Nevertheless, comprehensive information on silica-based ceramic and electromagnetic microwave (EMW) absorption is scarce, although excellent progress has been made in this field. Here, recent progress in the investigation of silica-based ceramics toward EMW absorption is reviewed. We first introduced the basis of ceramics (characteristics, classification, synthetic methods, potential applications). Subsequently, the silica-based ceramics, including Si-based oxides and alloys, SiOC/SiC/Si₃N₄/SiCN-based composite, Ti₃SiC₂ and composite for EMW absorption were systematically summarized. Notably, the fabrication strategies, absorption properties, and mechanisms of silica-based ceramics are described in detail, with a focus on structure and component design. Lastly, the prospects and ongoing challenges of this field in the future are presented. This review is expected to learn from the past and achieve progress toward the future of silica-based ceramic for EMW absorption.     

Investigation of the microwave dielectric properties of the Li4x/3Zn2−2xTi1+2x/3O4 system by P–V–L theory and vibration spectroscopy

Li_4x/3Zn_2–2xTi_1+2x/3O₄ microwave dielectric ceramics with a spinel phase were prepared via a high-temperature solid-phase method. P–V–L theory, vibration spectra, and XPS were utilized to establish the links between the intrinsic and extrinsic factors and the microwave dielectric properties. According to the characterization, the change in permittivity (ε_r) was ascribed to the increase in the average bond ionicity of Ti–O(Af_iTi-O) and the polar mode of the lattice vibration; the change in quality factor(Q × f) resulted from the change in the Ti–O lattice energy (AU_Ti-O) and existence of oxygen vacancy; the increase in temperature coefficient of the resonance frequency (τ_f) was triggered by the increase in the Ti–O bond energy. The Li_0.6Zn_1.1Ti_1.3O₄ ceramics (x = 0.45) sintered at 1125 °C finally obtained optimal microwave dielectric constants of ε_r = 17.3, Q × f = 76,318 GHz and τ_f = -58 ppm/°C.