We studied the flux pinning properties of BaZrO 3 -doped YBa 2 Cu 3 O 7−x and BaSnO 3 -doped YBa 2 Cu 3 O 7−x films. We found that BaSnO 3 -doped films showed very high global pinning forces, F p , of 28.3 GN m −3 (77 K, B c) and 103 GN m −3 (65 K, B c), twice that of BaZrO 3 -doped films. Transmission electron microscopy analysis showed that, in both films, nanorods of the dopant phase were incorporated. The BaSnO 3 nanorods were nearly straight but the BaZrO 3 nanorods became curved with the increasing film thickness.

The relationships between microstructures, crystallinity and critical current properties for B4C doped MgB2 bulks, MgB2−5x(B4C)x with x = 0, 0.04, 0.1, 0.2 and 0.4, were systematically studied. Decreases of Tc and the a-axis length and deterioration of the crystallinity of MgB2 due to the carbon substitution occurred upon B4C doping. Substantially improved Jc was observed in the B4C doped MgB2 bulks especially at 5 K under high magnetic fields. Strengthened flux pinning at grain boundaries by carbon substitution was considered to contribute to the improvement of Jc. Furthermore, the reactivity of B4C with magnesium and boron was found to be much higher than that of graphite. These findings suggested that B4C is a promising carbon source dopant for MgB2 materials with excellent Jc properties, particularly under magnetic fields.

Influence of the upper critical-field anisotropy on the transport properties of polycrystalline Mg B 2

MgB2 bulks were synthesized by the solid-state reaction of Mg and B at 600 °C and their superconducting properties were compared with samples heated at 850 °C. The samples heated at 600 °C exhibited improved critical current properties up to high fields at 20 K. Poor crystallinity is found to contribute enhancement of Hc2, Hirr and Jc at high fields. On the other hand, the strongly grain connected network structure and smaller grain size are responsible for high Jc at low fields. Improved Jc up to 3.93 × 105 A cm−2 and a high μ0Hirr of  T, as for undoped MgB2 bulks, guarantees that low-temperature sintering is a promising way to fabricate MgB2 conductors with high critical current performance.

We have discovered new arsenide oxides (Fe2As2)(Sr4M2O6) (M = Sc, Cr: M-22426). These materials are isostructural with (Fe2P2)(Sr4Sc2O6), which was found in our previous study. The new compounds are tetragonal with a space group of P4/nmm and consist of the anti-fluorite-type FeAs layer and a perovskite-type blocking layer. These compounds have long interlayer Fe–Fe distances corresponding to the c-axis length; the 15.8 Å in Sc-22426 is the longest in the iron-based pnictide oxide systems. Chemical flexibility of the perovskite block in this system was probed by chromium-containing (Fe2As2)(Sr4Cr2O6). Different trends were found in bond angle and bond length of the new pnictide oxides compared to the reported systems, such as REFePnO. The absence of superconductivity in these compounds is considered to be due to insufficient carrier concentration as in the case of undoped REFeAsO.

Quantitative texture analysis of grain-aligned [ Ca 2 Co O 3 ] 0.62 [ Co O 2 ] ceramics processed by the reactivetemplated grain growth method Highly grain-aligned Ca 3 Co 4 O 9 and (Ca 2.7 Sr 0.2 La 0.1 )(Co 3.9 Cu 0.1 )O 9 ceramics were prepared by the magnetic alignment technique, and then treated by a spark plasma sintering process to increase their bulk densities. Thermoelectric properties were investigated from room temperature to 700°C in air. Grain alignment is effective in lowering the electrical resistivity and has no obvious influence on the Seebeck coefficient, thus resulting in enhancement of the thermoelectric power factor. Substitution of Sr, La and Cu does not appreciably change the electrical resistivity and Seebeck coefficient, but significantly reduces the thermal conductivity.

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BaZrO3 nanorods are known to be effective pinning centers as c-axis-correlated pinning centers. Furthermore, BaZrO3 nanorods in REBa2Cu3Oy (RE: rare-earth element) films are formed by self-assembled stacking of BaZrO3 using a target mixture of a superconductor and BaZrO3 for pulsed-laser deposition, which is a very easy fabrication technique. The density of BaZrO3 nanorods in YBa2Cu3Oy (YBCO) films can be controlled by varying the BaZrO3 content in a target. The BaZrO3 addition has two functions for superconductivity; one is the improvement of pinning forces due to the addition of pinning centers and the other is Tc degradation. The optimum BaZrO3 addition for Jc improvement in magnetic fields is found to be around 3 wt% because of a trade-off between the two functions described above. Furthermore, the length of BaZrO3 nanorods is found to be controlled using two types of target: pure YBCO and a mixture of YBCO and BaZrO3. Varying the BaZrO3 nanorod length has an effect on the pinning mechanism. In particular, magnetic field angle dependences of Jc are varied from c-axis-correlated pinning to nearly random pinning by changing the nanorod length. The magnetic field at the crossover of the pinning mechanism seems to be adjusted by the BaZrO3 nanorod length.