Search

Single crystalline α-Si 3 N 4 nanowhiskers were synthesized by direct nitridation of the NH 3 -pretreated silicon powders under N 2 /H 2 atmosphere without adding any catalysts. The phase composition and microstructure of the as-obtained products were investigated. It is shown that the NH 3 pretreatment has a great influence on the phase and microstructure of the products. With NH 3 pretreatment, single crystalline α-Si 3 N 4 nanowhiskers were obtained. Whereas, the dominant β-Si 3 N 4 particles were formed without NH 3 pretreatment. The isolated α-Si 3 N 4 crystal nuclei and the relatively thick oxide layer were formed on the surface of the silicon particles after pretreating by NH 3. The growth of the α-Si 3 N 4 nanowhiskers is obeyed the vapor-solid (VS) mechanism. [ABSTRACT FROM AUTHOR]

Silicon oxynitride nanopowders were successfully prepared by thermal explosion of the Si and SiO 2 mixed powders with the different particle sizes in various molar ratio (x / y = 2.0, 1.5) under N 2 , supplemented by the subsequent gravity separation strategy. The effects of Si/SiO 2 molar ratio, preheating temperature and insulation time on the phase composition of the as-oxynitrided products in the thermal explosion strategy were investigated. Meanwhile, the effects of sedimentation time on the phase composition and oxygen content of the as-obtained products in the gravity separation strategy were also discussed. It is shown that the by-products are absent in the as-oxynitrided products with a 1.5:1 M ratio. Prolonging the insulation time or preheating temperature is beneficial to improve the content of Si 2 N 2 O phase with a 2.0:1 M ratio. All the by-product phases are disappeared in the as-oxynitrided products with a 2.0:1 M ratio after sedimentation treatment of 120 s. The as-obtained silicon oxynitride nanopowders with 58% of recovery and 16.2% of oxygen content are close to the theoretical stoichiometric ratio of Si 2 N 2 O. The preparation mechanism of silicon oxynitride nanopowders was proposed. [ABSTRACT FROM AUTHOR]

In this work, millimeter-scale Si 3 N 4 @SiO x core-shell structure nanowires were synthesized using the direct nitridation method without the use of catalysts. The silicon powders used as raw materials were pretreated at 1300 °C for 3 h under ammonia. The ammonia was then converted into a nitrogen/hydrogen gas mixture and heated at 1350 °C for another 5 h. The morphology and structure of the as-obtained nanowires were investigated in detail. The Si 3 N 4 @SiO x nanowires with a core-shell structure were composed of a crystalline α-Si 3 N 4 core and an amorphous SiO x shell. The formation of the α-Si 3 N 4 core nanowire is due to the reaction of the N 2 gas with the byproduct SiO gas. However, the formation of the amorphous SiO x shell is related to the deposition location of the samples. For the inner part of the samples, the SiO x shell derives from the deposition of the byproduct SiO gas at 1350 °C, while the SiO x shell of the external part of the samples likely derives from the oxidation of the silicon nitride core during the cooling process. [ABSTRACT FROM AUTHOR]

Dielectric materials with a high recoverable energy-storage density (W rec) and an enhanced power density are required for downsizing pulsed power electronic devices. Dielectrics with a low but temperature-stable permittivity are better suited as energy-storage materials for power devices owing to their delayed saturation polarization response. ABO 3 perovskite-structured (Bi 0. 5 Na 0.5)TiO 3 -based [(Bi 0. 5 Na 0.5) 0.93 Ca 0.07 ](Ti 0. 85 Zr 0.15)O 3 (BCZ) lead-free ceramics exhibit good dielectric temperature stability and are being investigated as viable materials for energy-storage devices. However, these materials only produced limited W rec due to the reduced breakdown strength (BDS). Herein, various advanced engineering techniques, including glass doping and the viscous polymer rolling process, were applied to the BCZ to substantially enhance the BDS of the ceramics. Our results show that the BCZ-0.75 wt% glass-additive composition achieved an ultrahigh W rec of 7.78 J/cm3 under a comparatively low electric field and remained above 4.6 J/cm3 in the temperature range of 30 °C–160 °C. This work demonstrates that the BCZ is a viable competitor for lead-free dielectrics and guides for the development of novel high-performance dielectric materials for future pulsed power devices. [ABSTRACT FROM AUTHOR]

As a lead-free material, AgNbO 3 has received a lot of attention for its potential application in the field of energy storage. Herein, Ag x NbO 2.5+ x /2 ceramics were successfully synthesized via solid state reaction with the x ranged from 1 to 0.92. The effect of silver deficiency on structure, dielectric properties and energy storage performance was investigated. As x value decreased from 1 to 0.94, the unit volume of Ag x NbO 2.5+ x /2 ceramics contracted. Meanwhile, all the compositions displayed double hysteresis loops with reduced P max , P r and enhanced transformation fields (E F and E B) as functions of silver deficiency. Silver deficiency stabilized the antiferroelectric state in the FIE (-like) phase and improved the energy storage performance of AgNbO 3 ceramics. Hence, an enhanced energy storage performance (W rec = 3.1 J/cm3, η = 49%) were achieved in Ag 0.94 NbO 2.97 ceramic. [ABSTRACT FROM AUTHOR]

PLZST-based antiferroelectric (AFE) ceramics with high recoverable energy density (W re) and efficiency (η) can be applied to pulsed power electronic devices. However, this application is constrained by the high sintering temperature (ST, 1250–1320 °C) of the ceramics per se. In this context, this study introduced a new glass phase of Ba 2 CO 3 –Al 2 O 3 –SiO 2 –K 2 CO 3 (BASK) into Pb 0.95 La 0.02 Sr 0.02 (Zr 0.50 Sn 0.40 Ti 0.10)O 3 (PLSZST) AFE ceramics by using a traditional solid-state method. By doping 0.5 wt% BASK, the ST of PLSZST ceramics was significantly reduced from 1300 °C to 1020 °C and a high W re of 3.54 J/cm3 and a high η of 86% were yield, when the electric breakdown strength increased to 230 kV/cm. In addition, a pulse discharge energy density of 2.47 J/cm3, and an extremely fast discharge speed (<0.5 μs), as well as acceptable thermal stabilities of both W re and η within 30–110 °C temperature range, were achieved. Conclusively, this AFE ceramic composition with glass additives has a great potential to be used in base metal inner-electrode multilayer ceramic capacitors for pulse power applications. [ABSTRACT FROM AUTHOR]

SrTiO 3 is recognized as one of the most promising candidate materials for colossal permittivity. However, the origin of colossal permittivity is still not well understood. In this work, SrTi 0.998 Nb 0.002 O 3 ceramics (SNT) were synthesized via typical solid-state reaction process and sintered in air, N 2 , and N 2 –H 2 atmospheres (labelled as SNT-Air, SNT-N 2 and SNT-H 2). The SNT-H 2 ceramic achieves a colossal permittivity of 89254 and a dielectric loss of 0.013 at 1 kHz and maintains a colossal permittivity (∼8 × 104) with a low dielectric loss (<0.1) throughout a wide temperature (50 °C–300 °C) and frequency (100 Hz-1 MHz) range. The mechanism of the outstanding properties of SNT-H 2 ceramics was investigated by X-ray photoelectron spectroscopy (XPS), impedance spectrum and activation energy analysis. The T i T i ′ − V O ⋅ ⋅ − T i T i ′ defect dipole and V O ⋅ ⋅ − 3 T i T i ′ − N b T i ⋅ defect dipole clusters exist in SNT ceramics by sintering in the reducing atmosphere of H 2. Otherwise, the grain is semi-conducting, and the grain boundary is insulating in SNT-H 2 ceramics by impedance spectrum analysis. In conclusion, the defect dipole and clusters localized in the grain could be the fundamental cause for the ultra-dielectric properties. As a result, The SNT-H 2 ceramic exhibits the colossal permittivity with low dielectric loss, as well as good temperature and frequency stability, potentially aiding in the development of colossal materials. [ABSTRACT FROM AUTHOR]

In this study, a novel boehmite (AlOOH) nanowhiskers/polyethylene (PE) separator was initially prepared by the AlOOH nanowhiskers coating on the commercial PE separator using dip-coating method, in which the AlOOH nanowhiskers were directly synthetized by a facile hydrothermal method. It is shown that the needle-like AlOOH nanowhiskers with the rough surfaces have been successfully obtained. Meanwhile, according to the performance characterization of separators, the AlOOH nanowhiskers/PE separator exhibits higher porosities of 60.1% and excellent mechanical properties with the tensile strength of 145.1 MPa and the elongation of 130.1%, owing to the integrally three-dimensional (3D) structure of AlOOH nanowhiskers coating layer. Also, benefiting from the spindly and rough surficial morphology of AlOOH nanowhiskers, the PE separator coating with AlOOH nanowhiskers has a smaller contact angle of 8.6° and higher electrolyte uptake of 173.1% than that coating with AlOOH nanoparticles. As expected, the LiFePO 4 /Li cell with AlOOH nanowhiskers/PE separator presents superior cycle stability and rate capacity. Then the SEM images of the lithium metal anode, disassembled from the cell with AlOOH nanowhiskers/PE separator after 200 cycles, show that the 3D structure of AlOOH nanowhiskers layer can suppress the growth of lithium dendrites. Image 1 • The commercial PE separator was coated with the ceramic AlOOH nanowhiskers using simply dip-coating method. • The influence of different AlOOH morphologies on the LIBs separator's overall performance was studied. • AlOOH nanowhiskers-coated PE separator shows better overall performance than AlOOH nanoparticles-coated one. • The 3D network layer of AlOOH nanowhiskers can suppress the growth of lithium dendrites. [ABSTRACT FROM AUTHOR]

Sodium niobate (NaNbO 3 , NN)-based ferroelectric ceramics have been extensively studied owing to their antiferroelectric (AFE) nature. However, the dielectric properties of NN-based ceramics, which would be beneficial to capacitor devices, gain less research interest. In this study, (1− x)NaNbO 3 - x Bi(Mg 0.5 Ti 0.5)O 3 (NN- x BMT, x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) ferroelectric ceramics were manufactured by a traditional solid state method. Structure and dielectric/ferroelectric properties were studied in detail by X-ray diffraction, dielectric spectrum as well as polarization-electric field hysteresis loops. All ceramic samples show an AFE P phase in the doping range. As x increases, the grain size of studied compositions gradually decreases from 5.36 μm in x = 0 to 2.05 μm in x = 0.05. In addition, the incorporation of BMT plays a regulatory role to the Curie temperature T C of ceramic samples, which decreases almost linearly from 375 °C x = 0 to 216 °C x = 0.05 at a rate of 33 °C/1 at. %. However, the degree of diffusion for each composition does not change significantly. More importantly, ultra-high thermally stable dielectric responses in a wide temperature range are obtained in NN- x BMT. Especially in x = 0.03, its permittivity is around 500 at room temperature and shows a variation less than 4.4% from 30 to 150 °C. Our results may have some guiding significance for the preparation of NN-based ceramics with specific T C , and are significantly important for capacitor applications requiring a wide temperature range stability. [ABSTRACT FROM AUTHOR]