The Effect of Boron on Equilibrium of Superconducting Phases in Bi-Pb-Sr-Ca-Cu-O System

Abstract

The crystal structures of type 1234 and 2234 are not found in compositions Bi_1-xB_xSr₂Ca₃Cu₄O_y and Bi_2-xB_xSr₂Ca₃Cu₄O_y after synthesis under conditions of ambient pressure P = 1 bar and T = 835 °C for τ = 240 h. This conclusion is obtained as a result of the fact that the series of bismuth superconductors Bi_1-xB_xSr₂Ca₃Cu₄O_y, Bi_2-xB_xSr₂Ca₃Cu₄O_y, Bi_2-xB_xSr₂Ca₂Cu₃O_y, Bi_1.7-xB_xPb_0.3Sr₂Ca₂Cu₃O_y with different boron content x = 0-2 were synthesized followed by slow (rate < 10 °C/sec) cooling or quenching (< 100 °C/sec). Samples of Bi_1.7-xB_xPb_0.3Sr₂Ca₂Cu₃O_y with a boron content of x = 0.5 have a significant (> 35%) proportion of the superconducting phase 2223, regardless of the accuracy of observing the temperature modes of synthesis (in temperature ranges < ±10 °C) and cooling after it. A model of the effect of boron on phase equilibrium in Bi-Pb-Sr-Ca-Cu-O system is proposed using the process of boron-bismuth glass formation. Therefore, the boron addition during the synthesis of bismuth superconductors will increase the production process reproducibility of phase 2223. Also, this technology can be used at the synthesis of superconductors from the boron-bismuth not very enriched ores in conditions of limited available resources.