No abstract

We report the effectiveness of barium niobate as a needle-type vortex pinning center, as well as a change in the vortex state in Ba–Nb–O (BNO)-doped ErBa2Cu3Oy thin films. BNO doping was effective for improving critical current properties for a magnetic field direction parallel to the c axis of a matrix film and induced the generation of columnar defects with diameters of 5–25 nm. The irreversibility lines were also changed by the BNO doping and were similar to those of heavy-ion-irradiated YBa2Cu3Oy crystals in which the vortex Bose glass state was induced. It is suggested that the characteristic field relevant to crossover from the Bose glass to collective pinned glass depends on the BNO doping level. There is a possibility that Ba-based perovskite-type oxides promote the formation of nanorods universally and these nanorods play the role of one-dimensional c-axis-correlated pinning centers.

A novel one-step soft solution-processing route called the solvothermal-copolymerization technique was successfully developed for in situ fabrication of polystyrene (PS)/CdS nanocomposites embedded with CdS nanowires in ethylenediamine media at lower temperatures (80−140 °C). In this route, the polymerization of the monomers and the formation of the CdS nanocrystallites occur simultaneously in a certain temperature range. The results of X-ray powder diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy confirmed that the embedded CdS nanowires, with diameters of 4−15 nm and lengths up to several micrometers, have [001] preferential orientation. Both temperature and solvent were found to play a key role in the synthesis of the nanocomposites. The produced novel hybrid nanocomposites display obvious quantum size effects and interesting fluorescence features. The spectroscopic properties of the PS/CdS nanowire nanocomposites were found to be sensitive to synthetic conditions, including the concentrations of Cd2+ or the monomer, temperature, and reaction time.

The internal Mg diffusion (IMD) process produces a high-density MgB 2 layer with high critical current properties, which makes it an attractive and promising method for fabricating MgB 2 wires. We have obtained high critical current properties in our previous research. However, IMD-processed MgB 2 wires can have unreacted B particles remain in the reacted layer due to the long Mg diffusion distance in the B layer during heat treatment. A reduction in the amount of unreacted B particles is expected to enhance the critical current properties. In this study, we attempted to disperse Mg powder in the B layer as an additive in order to decrease the Mg diffusion distance. We found that a 6 mol% Mg powder addition to a B layer drastically decreased the amount of unreacted B particles and enhanced the critical current density to twice the value for IMD-processed MgB 2 wire with no Mg powder added. An analysis is presented that relates the microstructure to the critical current density.