Shigeki Tokunaga

Pd addition in high Tc YBaCuO oxide

Abstract A small amount of Pd addition increases T c for the YBa 2 Cu 3 O 7− y oxide. The maximum offset, midpoint and onset temperatures of the YBa 2 (Cu 0.999 Pd 0.001 ) 3 O 7− y oxide are 92.1, 95.0 and 105 K, respectively. Excess addition of Pd decreases T c . The T c change is consistent with the results of the lattice constants.

Endurance limit of reversible Tc increase with compressive stress of YBa2Cu3O7−y oxide

Effect of compressive stress on Tc is studied for YBa2Cu3O7−y oxide. Tc increases with compressive stress for small strain, reversibly. Excess strain decreases Tc, irreversibly. We obtain a compressive stress between reversible Tc increasing and irreversible Tc decreasing as endurance limit (16.5 N/mm2). The maximum Tcoff is about 94.4 K at 16.5 N/mm2. We suggest that the YBa2Cu3O7−y oxide sample should be formed below the endurance limit of the compressive stress on sample preparation.

Formation temperature of bosons in high-Tc YBa2Cu3O7−y systems

AbstractAt different equilibrium temperatures, a precise measurement of the electrical resistivity (R) is performed for high Tc polycrystalline YBa2Cu3O7−y systems. T2 law is applied in the part of the R-T relationship far above the superconducting transition temperature. Since Landau and Pomeranchuk predicted the T2 law arising from electron-electron scattering, a higher critical temperature of T2 law is defined as a start point (Tes) of electron-electron scattering. On the other hand, we defined a lower critical temperature of T2 law as the formation temperature (Tee) of an electron-electron pair, i.e. the formation temperature of boson. Tee relates to the offset temperature of the superconducting transition

Abnormal Jc change with temperature in the high Tc YBa2Cu3O7−y system

({\rm T}_{{\text{C}}_{{\text{off}}} } )

Aging induced high Tc of Ar ion-implanted YBa2Cu3O7−y

.

HighT c of YBa2Cu3O x coated film on a nickel plate annealed for a short period

Abstract The cooling rate ( R ) dependence of J c is investigated for high T c YBa 2 Cu 3 O 7- y . J c ( J c 60 K , J c 70 K and J c 80 K ) at different temperatures depends on R . We show the existence of an approximately linear relationship between superconductive values ( J c 60 K , J c 70 K and J c 80 K ) and R .

Dependence of Tcc on the cooling conditions for liquid-quenched A15 chemical compounds☆

Abstract The temperature dependence of the superconducting critical current ( J c ) is investigated for the YBa 2 Cu 3 O 7− y system. An abnormal J c change is found from 45 to 65 K.

Stress-inducedT c increase of Bi0.7Pb0.3SrCaCu1.8O x

Etude de la variation en fonction de la vitesse de refroidissement de la temperature de transition supraconductrice