The electrical and magnetic transport behaviour of composite samples of (1 − x)La 0.67 Ca 0.33 MnO 3 + xFe 3 O 4 with x = 0, 0.1%, 1% and 2% were studied in a temperature interval 10-300 K and for magnetic fields H = 0, 0.3, 0.5, 1 and 3 T. The temperature and magnetic field dependence of resistivity of composites show that the low Fe 3 O 4 doping levels have important effects on electrical and magnetic transport behaviour of La 0.67 Ca 0.33 MnO 3 . Especially, compared to pure La 0.67 Ca 0.33 MnO 3 , a new insulator-metal (I-M) transition was observed at a lower temperature T P2 in all Fe 3 O 4 doped La 0.67 Ca 0.33 MnO 3 composites, which may result from the existence of a new phase related to Fe 3 O 4 dopant at grain boundaries and surfaces of La 0.67 Ca 0.33 MnO 3 phases. It is of interest to note that the new I-M transition temperature, T P2 , is almost independent of the magnetic field. Meanwhile, an obvious magnetoresistance effect was observed between temperatures T P1 and T P2 . The results were discussed by considering the results of scanning electron microscopy, x-ray diffraction, dielectric relaxation and susceptibility analysis.

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The grain-boundary structure and the temperature dependence of resistivity were investigated for (1-x)LCMO + xYSZ, where LCMO and YSZ represent La2/3Ca1/3MnO3 and yttria-stabilized zirconia, respectively. It is shown that the YSZ doped samples for x<2% show transport and low-field magnetoresistance (LFMR) behaviours different from that for x>2%. The metal-insulator transition temperature (Tp) decreases for x<2% but increases for x>2% as x is increased. LFMR increases with x for x<2% but decreases for x>2%. The experimental observations are discussed on the basis of scanning electron microscopy (SEM) analysis, which reveals YSZ appearing at the grain boundaries of LCMO for x<2%, while presenting itself within the sample in the form of clusters for x>2%.

Thermo‐responsive dielectric materials are in urgent demand owing to the rapid development of smart electronic/electrical systems. Although different types and structures of thermally responsive dielectric materials have been continuously reported, their dielectric response behaviors all originate from thermodynamic phase transitions. Herein, it is demonstrated that structural relaxation in poly(vinylidene fluoride) (PVDF), a non‐thermodynamic phase transition, can induce a significant thermal dielectric pulse at room temperature. The dielectric pulse strength of up to 6.3 × 105 at 20 Hz, with a dielectric pulsing temperature of 24 °C, is achieved from polyethylene glycol (PEG)‐PVDF coaxial nanofibrous films (PVDF@PEG), fabricated via a continuous blow spinning method. Moreover, the films exhibit excellent flexibility, adjustable strength and toughness, switchable hydrophilicity/hydrophobicity, and effective thermal management capability. The relaxation‐induced dielectric pulsing effect, outstanding multifunctionality, and simple preparation combine to promote further scalability and prospects of PVDF@PEG. In particular, the work contributes to the discovery of the relaxation‐induced dielectric response mechanism, which provides a new strategy for the generation of thermo‐responsive dielectric materials.

DHPeng Department of EJedrlcal EngIneering, Huazhong UnlVf!tSity 0/5dence 9 redltlOiogy ZYLI Department 0/ Bedrlcal Engineering, Huozhong University ofScience 8 Technology J M K MacAlpIne MA PhD Department 0/Electtfcal Engineering. Hong Kong Potytechnlc unIversity Measurements have been made Of dc corona onset and breakdown voltages for both positive and negative point/plane eledrode systems in compressed sulphur hexafluoride in the presence of water vapour. The presence Of moisture lowered the onset voltages and raised the breakdown voltages significantly. The effect af maisture onflashover voltages in the presence of metallic particles was also Investigated and the results showed that there was little effed except when moisture was likely to be condensing of the spacer surface; If the moisture froze there was again little effed.The redudlon In flashover voltage due to moisture was Independent Of and In addition to the effed Of the presence Of a metallic particle.