To understand basic electric properties of nano-sized magnesium oxide (MgO) / low-density polyethylene (LDPE) nanocomposite under DC voltage application, the volume resistivity, the space charge distribution and the breakdown strength were investigated. By the addition of nanosized MgO filler, both the DC breakdown strength and the volume resistivity of LDPE increased. At the average DC electric field of about 85 kV/mm and more, a positive packet space charge was observed in LDPE without MgO nano-filler, whereas a little homogeneous space charge was observed in MgO/LDPE nanocomposite material at the front of electrode. From these results, it is confirmed that the addition of MgO nano-filler leads to the improvement of DC electrical insulating properties of LDPE.

A nanocomposite material, composed of nano-sized MgO-filler added to a low-density polyethylene (LDPE), was subjected to electrical property investigations under DC voltage application. The volume resistivity of LDPE, under 40-80kV/mm DC field at 90°C, increases by the power of 10 due to the addition of only a few percent of nano-filler. The amount of space charge in LDPE under high electric field is reduced and the ratio of stress enhancement by space charge becomes less due to the addition of nanosized MgO-filler. The DC breakdown strength of LDPE is increased by adding nano-sized MgO-filler. Based on these results, the mechanism where by the nano-sized MgO filler had improved DC characteristics of LDPE was discussed.

No abstract

No abstract

No abstract

No abstract

Superconducting Bi-Sr-Ca-Cu-O thin films have been prepared for the first time by chemical vapor deposition using triphenyl bismuth and fluorocarbon-based chelates such as bis(hexafluoroacetylacetonate)strontium, bis(hexafluoroacetylacetonate)calcium, and bis(hexafluoroacetylacetonate)copper. After annealing in air, x-ray diffraction data reveal that the films deposited on (001) SrTiO3 substrates have preferential orientation of their crystalline c-axis perpendicular to the substrate surface. Four-probe resistivity measurements reveal the onset of superconductivity at 80 K and zero resistivity at 50 K.The discovery of superconducting Bi-Sr-Ca-Cu-O with Tc values in the region of 105 K1 has stimulated great interest in the preparation of high quality, high Tc films, which are of interest for the fundamental study of high Tc superconductivity and also for the application to microelectronic devices. Up to now, high Tc superconducting films have been prepared mainly by physical vapor deposition such as sputtering,2 laser ablation,3 and electron beam evaporation4 or coevaporation.5 In addition, the growth of these films by chemical vapor deposition (CVD) has also been reported.6"8 Chemical vapor deposition offers the advantages of simple apparatus, amenability to large-scale processing, low deposition temperatures, and no requirements of high vacuum. Some metalorganic chelates are used as precursors in CVD. Good precursors need to have high vapor pressure. Hydrocarbon-or fluorocarbon-based chelates are sufficiently volatile to be used as precursors. The preparation of superconducting Bi-Sr-Ca-Cu-O thin films has been reported by CVD using hydrocarbon-based chelates but not using fluorocarbon-based ones. In the previous paper, we reported the successful growth of superconducting Y-Ba-Cu-O thin films by CVD using fluorocarbon-based chelates.9In this communication, a point of issue is the choice of metalorganic chelate precursors. Triphenyl bismuth [Bi(Ph)3; Bi(C6H5)3] was employed as a bismuth source in the present study, and bis(hexafluoroacetylacetonate)copper [Cu(HFA)2; Cu(C5HF6O2)2] was selected as a copper source. As strontium and calcium sources, bis(hexafluoroacetylacetonate)strontium [Sr(HFA)2; Sr(C5HF6O2)2] and bis(hexafluoroacetylacetonate)calcium [Ca(HFA)2; Ca(C5HF6O2)2] were used. For comparison, Bi-Sr-Ca-Cu-O thin films were also prepared using Bi(Ph)3, Cu(HFA)2, and hydrocarbonbased chelates such as bis(dipivaloylmethanate) strontium [Sr(DPM)2; Sr(CuH19O2)2] and bis(dipivaloylmethanate)calcium [Ca(DPM)2; Ca(CuHi9O2)2]. Here we report for the first time on the growth of superconducting Bi-Sr-Ca-Cu-O thin films by CVD using fluorocarbon-based chelates. Figure 1 shows a schematic diagram of the CVD system. Each vaporizer was heated to an appropriate temperature to volatilize the precursor. The temperature of the vaporizer was determined according to the results of thermogravimetry and differential thermal analysis of the precursor. The gas line was also heated to prevent the condensation of each vaporized pre...

No abstract