Growth and superconducting transition of epitaxial thin films
thin films have been grown on SrTiO3 (STO) and yttrium-stabilized ZrO2 (YSZ) substrates by pulsed laser ablation. The substrate temperature dependence of orientation and superconducting properties were systematically studied. Good quality c-axis and a-axis orientated films can be obtained on SrTiO3 solely by changing the substrate temperature. On YSZ, films with good c-axis orientation can be grown, while it is hard to grow films with good a-axis orientation by changing substrate temperature alone. The highest TC 0 is about 37 K, which is found in the films grown on YSZ with a good c-axis orientation. For the films grown on STO, however, the highest TC 0 is about 35.6 K, with a mixed orientation of c-axis and a-axis. In most of the superconducting films, the weak temperature dependence of the normal state resistivity, as characterized by small ratios, together with a weak localization behaviour just above TC, could be attributed to the essential scattering due to the localized electronic states. The superconducting transitions in a field up to 10 T along the c-axis have been measured on a c-axis oriented film grown on SrTiO3. The zero-temperature in-plane upper critical field BC 2ab(0) is estimated from the resistivity transition data.
Neutron and X-ray scattering studies of magnetism in non-superconducting PrBa2Cu3O6+x
Abstract I give a short review of neutron and X-ray scattering experiments undertaken to study the magnetic properties of non-superconducting PrBa 2 Cu 3 O 6+ x . The measurements have confirmed the magnetic ordering of the Pr sublattice at temperatures below T Pr ≈20 K, and have revealed an incommensurate magnetic structure with a long period (∼600 A) involving both the Pr and Cu spins. The Cu spins in this Pr ordered phase are found to be non-collinear. Taken as a whole, the results provide strong evidence for a substantial magnetic coupling of the pseudodipolar type between the Pr and Cu ions. The effect of this coupling is also evident in the spectrum of low energy magnetic excitations determined by neutron inelastic scattering.
EFFECT OF SAMPLE PREPARATION ON WATER TREE RESISTANCE OF XLPE/SEBS BLENDS
The effects of an aromatic polymer, such as poly[styrene-b-(ethylene-co-butylene)b-styrene] (SEBS), and its preparation processes on water tree resistance, morphology, crystallinity, dielectric constant and dielectric loss tangent of crosslinked polyethylene (XLPE)/SEBS and XLPE/SEBS/ethylene vinyl acetate (EVA) blends were investigated. The XLPE/SEBS samples were characterized by means of differential scanning calorimetry, scanning electron microscopy, dielectric spectral analysis and the accelerated water treeing experiment. The results clearly showed that although SEBS was partially compatible with LDPE and it was dispersed evenly in XLPE matrix, the blends demonstrated excellent dielectric performances, such as dielectric constant and dissipation factor. The crystallinity of XLPE/SEBS blends was decreased with increase in SEBS content and it was further decreased with the addition of EVA. SEBS could effectively improve the water-tree resistance of XLPE and both SEBS and EVA were found to improve the water tree resistance of XLPE synergistically as expected. The differences in sample preparation processes could change the phase morphology and dielectric performance of the blends, and could also influence the dispersion of SEBS in XLPE matrix as well as the crystallinity of the blends. Different preparation processes led to different water tree resistance behaviours of the samples. The improvement of SEBS dispersion in XLPE matrix helped to improve the water tree resistance of XLPE.