Improvement of superconductivity in Bi-2212 single crystals grown by a vertical Bridgman method

Abstract

Abstract We grew Bi2Sr2CaCu2Oy (Bi-2212) single crystals by the modified vertical Bridgman method using the starting materials of Bi:Sr:Ca:Cu=x:2:1:2 (x=2–3), and investigated the optimum annealing conditions for the improvement of the superconductivity. From the results, we found that the optimum composition of starting materials for the large and plate-like Bi-2212 single crystal with good superconductivity and crystallinity was Bi:Sr:Ca:Cu=2:2:1:2, and that the Tc, the full-width-half-maximum value of (0 0 1 0 ) X-ray diffraction peak and the size of the single crystal were 82 K, 0.05° and 18 × 5 mm2, respectively. In the single crystal annealed at 600 °C for 10 h in an atmosphere of oxygen gas, the Tc of the as-grown single crystals increased with annealing time and changed from 82 to 86.3 K. On the other hand, the ΔT of the single crystal annealed at 600 °C for 5 h tended to decrease with increasing annealing time and changed from 6.2 to 4.2 K.