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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]

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]