Superconducting Coupling Nature at Grain Boundaries in Bi₂Sr₂CaCu₂O_x Glass‐Ceramics

Abstract

Superconducting coupling nature at grain boundaries in BizSrzCaCuzO, glass-ceramics consisting mainly of the low-T, phase was first examined by measuring superconducting properties and temperature or ac field dependence of ac complex susceptibility. It was found from the ac loss peaks that superconducting coupling at grain boundaries was basically characterized by three types of weak links. The weak-link behaviors at grain boundaries depended strongly on cooling conditions after annealing and annealing time and temperature. Particularly, it was found that the weak links at grain boundaries were improved by prolonged annealing at 840°C. The furnace-cooled glass-ceramics obtained by annealing at 820" or 840°C for about 200 h exhibited a critical transport current density (77 K, zero magnetic field) of about 200 A/cmZ. [

Some aspects of glass-ceramic superconductors

“…We have 01ready discussed in our previous review (Chaudhuri and Som 1992) the development of superconducting wires or tapes from the glassy phases. Glass precursor approach for the preparation of high Tc superconducting fibres is very interesting (Zheng et al 1989(Zheng et al , 1991aOnishi et al 1989Onishi et al , 1990Onishi et al , 1991Komatsu et al 1990;Miller et a11990;Chaudhuri et al 1989;Bose 1994 used for making fine rods, tapes and thick films of the Bi-Sr-Ca-Cu-O or Pb-Sr-C a -C u -O glassy phases. Continuous glass fibres with diameter ~ 110/~m have been successfully drawn (Zheng et al 1991) with [4334] glass.…”

“…The J~ values for such superconducting wires are relatively small (100 to 200 A/cm2). Glass fibres of several diameters have also been drawn from the Pb doped Bi-Sr-Ca-Cu-O glassy phase (Komatsu et al 1990) with T~ as high as 109 K and Jc = 1480A/cm 2 (Komatsu et al 1990). Attempts have also been made for fabrication of long fibres from melts of 2212 phase and 1112 phase using a gas jet fibreization technique.…”

“…Dependence of Tg and T x of Bi~Pbo.4Sr2CazCu30 r glasses on their bismuth content(Komatsu et al 1990).…”

“…Values of critical temperature T c and critical current density J~ (77K, zero magnetic fieldl of Bi2Sr2CaCu2Oy glass samples annealed at 820°C in air for various times and furnace cooled(Komatsu et al 1990).…”

The effects of crystallization on the magnetic properties and critical current in Bi$ndash$Sr$ndash$Ca$ndash$Cu$ndash$O glass$ndash$ceramics

“…the glass-ceramics route, is attractive for practical applications because of the possibility of fabricating the specific shapes of high-T c superconductors such as fibres or wires. However, the values of critical current density, J c , for the Bi-based superconducting glass-ceramics are very low, for example J c = 35 A cm −2 at 77 K in zero magnetic field for Bi 2 Sr 2 Ca 1 Cu 2 O x or J c = 250 A cm −2 for (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O x [3]. To make these materials commercially useful, the values of J c should be close to 10 4 A cm −2 .…”