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We applied hot pressing to in situ powder-in-tube-processed (PIT-processed) MgB 2 tapes. We enhanced the superconducting properties by adding nanometer-sized SiC powder and ethyltoluene (C 9 H 12 ) to the mixed powder. Hot pressing was performed at 100 MPa and 630 • C in an Ar gas atmosphere for 2-10 h. Hot pressing reduced the cross-sectional area of the MgB 2 tapes from ∼0.55 mm 2 for conventionally heat-treated tapes to ∼0.44 mm 2 . This increased the MgB 2 core density from 50% to 70%. Undoped MgB 2 tapes hot pressed for 5 h exhibited a transport J c of 90 A mm −2 at 4.2 K and 10 T, which is about three times greater than that for a tape heat treated without hot pressing. The value of J c for codoped tape hot pressed for 5 h was 450 A mm −2 at 10 T, which is larger than that for codoped tape heat treated without hot pressing (280 A mm −2 ). These results clearly demonstrate that hot pressing is effective in increasing the MgB 2 core density, and hence in enhancing the J c values of PIT-processed MgB 2 tapes.

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The effects of stress-strain on the critical current, I c , of ex situ powder-in-tube (PIT)-processed Ni-sheathed MgB 2 tapes and round wires as well as in situ PIT-processed Cu-sheathed wires at 4.2 K in a magnetic field up to 5 T have been studied. The effect of In powder addition on the Ni-sheathed MgB 2 wire was not so clear compared with that in the tape, in which the irreversible strain, ε irr , for the I c degradation onset increases significantly by the addition. This is attributed to the difference in the microstructure of the core associated with cold workings. A peak and gradual degradation behaviour of I c with strain beyond ε irr was found in the wire, whereas no evident peak and a steep degradation behaviour was found in the tape. As a possible reason, the difference in the triaxial residual stress state at 4.2 K due to the difference in geometry of the cross-section is suspected. The transverse compression tests revealed that I c of the wire did not degrade up to 270 MPa. Again, the effect of In addition was minimal. The Young's modulus of MgB 2 , 31-41 GPa, at room temperature was estimated by a tensile test of Cu sheath wire using a high-accuracy extensometer and the law of mixtures. The tensile strain dependence of I c in the Cu sheath wire was similar to that in the Ni-sheathed wire, ε irr being 0.4%. However, the stress corresponding to ε irr , 50 MPa, was about 1/10 of that for the Ni-sheath wire and the irreversible transverse compressive stress, 150 MPa, was also lower. The effect of bending strain on the I c in Cu-sheathed wire was compared with that of the tensile strain.

Surface texture and interior residual stress variation induced by thickness of YBa2Cu3O7-δ thin films J. Appl. Phys. 112, 053903 (2012) New application of temperature-dependent modelling of high temperature superconductors: Quench propagation and pulse magnetization J. Appl. Phys. 112, 043912 (2012) Flux-pinning-induced interfacial shearing and transverse normal stress in a superconducting coated conductor long strip J. Appl. Phys. 112, 043908 (2012) High, magnetic field independent critical currents in (Ba,K)Fe2As2 crystals Appl. Phys. Lett. 101, 012601 (2012) Fabrication of binary FeSe superconducting wires by diffusion process

High-T c Bi-Pb-Sr-Ca-Cu oxide superconductors have been successfully synthesized through a decomposition of organic acid salts. At the intermediate stage of this process, a gel state is obtained from a homogeneous solution. The gel shows a thermoplasticity which may facilitate its fabrication into a fiber form. The offset T c of the specimen made from this process is 102 K, which is appreciably improved by an intermediate pressing between sinterings. The highest T c and J c (77 K, 0 T) so far obtained are 109 K and 810 A/cm2, respectively.