The effect of polymer type on electric breakdown strength on a nanosecond time scale

Based on the concepts of fast polarization, effective electric field and electron impact ionization criterion, the effect of polymer type on electric breakdown strength （EBD） on a nanosecond time scale is investigated, and a formula that qualitatively characterizes the relation between the electric breakdown strength and the polymer type is derived. According to this formula, it is found that the electric breakdown strength decreases with an increase in the effective relative dielectric constants of the polymers. By calculating the effective relative dielectric constants for different types of polymers, the theoretical relation for the electric breakdown strengths of common polymers is predicted. To verify the prediction, the polymers of PE （polyethylene）, PTFE （polytetrafluoroethelene）, PMMA （organic glass） and Nylon are tested with a nanosecond-pulse generator. The experimental result shows EBD （PTFE） 〉 EBD （PMMA） 〉 EBD （Nylon） 〉 EBD （PE）. This result is consistent with the theoretical prediction.

Regulating local electric field to optimize the energy storage performance of antiferroelectric ceramics via a composite strategy

Electrostatic energy storage technology based on dielectrics is the basis of advanced electronics and high-power electrical systems.High polarization(P)and high electric breakdown strength(Eb)are the key parameters for dielectric materials to achieve superior energy storage performance.In this work,a composite strategy based on antiferroelectric dielectrics(AFEs)has been proposed to improve the energy storage performance.Here,AlN is selected as the second phase for the(Pb_(0.915)Ba_(0.04)La_(0.03))(Zr_(0.65)Sn_(0.3)Ti_(0.05))O_(3)(PBLZST)AFEs,which is embedded in the grain boundaries to construct insulating networks and regulate the local electric field,improving the Eb.Meanwhile,it is emphasized that AFEs have the AFE–FE and FE–AFE phase transitions,and the increase of the phase transition electric fields can further improve the recoverable energy density(Wrec).As a result,the Eb increases from 180 to 290 kV·cm−1 with a simultaneous increase of the phase transition electric fields,magnifying the Wrec to~144%of the pristine PBLZST.The mechanism for enhanced Eb and the phase transition electric fields is revealed by the finite element simulation method.Moreover,the PBLZST:1.0 wt%AlN composite ceramics exhibit favorable temperature stability,frequency stability,and charge–discharge ability,making the composite ceramics a promising candidate for energy storage applications.

Investigation on the Structure and Performance of Polypropylene Sheets and Bi-axially Oriented Polypropylene Films for Capacitors

Polypropylene(PP) sheets are cast with various chill roll temperatures and rates, which are studied with differential scanning calorimetry, wide angel X-ray diffraction, scanning electronic microscopy and dielectric withstand voltage test system. The results show that increasing the chill roll temperature and cast rate can promote the increase of crystallinity and the growth of β-form. The PP sheets have asymmetric skin layer structures. The lower the chill roll temperature, the thicker the skin layer, the smaller the spherulite size. The electric breakdown strength(Eb) of PP sheets is mainly affected by the crystallinity but not the morphology. The PP sheets are further stretched to prepare bi-axially oriented PP(BOPP) films with various heat setting time. Our results indicate that the structure of PP sheets affects the properties of BOPP films. The as prepared BOPP films from the sheets cast at high chill roll temperature and rate have the highest crystallinity and Eb. Heat setting time has profound effect on the crystallinity and Eb, which increase first and then decrease with the heat setting time. It is expected that our study can provide guidance for optimizing process parameters.