It is necessary to increase the Jc values when developing practical MgB2 superconducting wire. High Jc values even in high magnetic fields were achieved using nanometer-sized Mg powder. The highly pure nanometer-sized Mg powder was fabricated using the thermal plasma method. In addition, doping with a small amount of SiC was tried for the purpose of enhancing Jc properties. The MgB2 superconducting wires were MgB2/Fe tapes prepared from a mixture of nanometer-sized Mg, commercial amorphous B and SiC, which were fabricated using the in-situ PIT method. The Jc values of the non-doped and 10 at% SiC-doped tapes reached 90 and 250 A/mm2 at 4.2 K and 10 T, respectively. In regard to the temperature dependence of Jc, it reached at 160 A/mm2 at 20 K and 4 T which nears the practical application level.
Thermoacoustic pheomena are classified into heat-pumping, prome-mover and dream-pipe including simple heat-conduction. Necessary conditions for thermoacoustic heat-engines are discussed using the first and second laws of thermodynamics and thermoacoustic theory. These conditions restirict possible regions of the temperature gradient and the phase difference between oscillations of pressure and displacement.
A large amount of lead doping to Bi2212 superconductors is effective in decreasing their high electromagnetic anisotropy and introduces effective pinning sites, such as lamella structure interfaces due to compositional fluctuation of lead ions, resulting in greatly enhanced flux pinning properties up to high temperatures. Particularly in the high-Tc superconducting materials with lowered anisotropy, further improvement of critical current properties can be expected by doping a small amount of impurity elements, which generate locally weak superconducting regions. Based on this background, we have attempted to enhance flux pinning strength of Bi(Pb)2212 single crystals by 3d metal doping in the present study. Crystal boules with starting compositions of Bi1.6Pb0.6Sr1.8Ca(Cu1-xMx)2Oy (M = Fe, Co, Ni : x = 0, 0.001, 0.002, 0.005, 0.02) were grown by the floating zone method. Tc's of the single crystals annealed to be the carrier overdoped state were dramatically decreased with an increase of metal doping levels. Critical current performance of the 3d metal-doped Bi(Pb)2212 crystals was quite poor at high temperatures near Tc, The crystal with x= 0.001, 0.002, 0.005, however, showed improved Jc properties accompanied by larger second peak effects in the