Abstract
In this paper influence of the excess Ca and Cu cations on the critical temperature (Tc) and critical transport current density (Jc) of high-temperature superconducting ceramics of the compositions (HTSC) Bi1.6Pb0.4Sr2Ca2.1Cu3.1Oy, Bi1.6Pb0.4Sr2Ca2.25Cu3.25Oy and Bi1.6Pb0.4Sr2Ca3Cu4Oy synthesized by the glass-ceramic method has been studied. The synthesis of superconducting ceramics was carried out on the basis of the glass phase, obtained by ultra-fast quenching of the melt. Melting of the mixture of starting components was carried out without the use of a crucible under the influence of IR radiant heating. Analysis of the elemental composition of the samples of the initial precursors showed a significant deviation from stoichiometry in oxygen (increase), as well as a decrease in calcium content. The synthesis of HTSC ceramics was carried out at a temperature of 849–850 °C for 96 h with intermediate grinding every 24 h. Studies of the phase composition of ceramic samples by X-ray diffraction have shown that HTSC ceramics consist only of a superconducting high-temperature phase Bi-2223. Studies of current-carrying characteristics by the four-point probe method according to the criterion of 1 µV/cm2 have shown that high-temperature superconducting ceramics of the compositions Bi1.6Pb0.4Sr2Ca2.1Cu3.1Oy, Bi1.6Pb0.4Sr2Ca2.25Cu3.25Oy and Bi1.6Pb0.4Sr2Ca3Cu4Oy have an increased density of critical transport current of 9.12 A/cm2, 7.62 A/cm2 and 7.26 A/cm2, respectively. At the same time, it was found that with a decrease in the content of Ca and Cu cations in HTSC ceramics, an increase in the critical current density is observed.