Microstructure and superconducting properties of hot-pressed Bi–Pb–Sr–Ca–Cu–O thick film

Abstract

Superconducting Bi_1.84Pb_0.34Sr_2.03Ca_1.9Cu_3.06O_y thick films were prepared on MgO substrates by screen printing with the powder consisting almost entirely of the 110 K phase. The thick film sandwiched between the two MgO substrates was then hot-pressed in air under various conditions. The thickness of the film was 20–40 μm. The degree of grain orientation was quantitatively evaluated through the image analysis on the SEM micrographs for the chemically etched cross sections of the samples. The degree of grain orientation and the critical current density (J_c) increased with increasing hot-pressing temperature. When hot-pressed at 855 °C under a constant pressure of 500 kg/cm² for 270 min, the J_c had a maximum value of 9500 A/cm² (77 K, 0 Oe), and the critical temperature was 110 K. When the hot-pressing pressure was higher than 200 kg/cm², the degree of grain orientation was almost independent of hot-pressing pressure. Nevertheless, the J_c increased with increasing hot-pressing pressure. The relationship between the magnetic field dependence of J_c and hot-pressing conditions was examined.