Properties of Bi₂Sr₂CaCu₂O₈ thick films melt-processed at temperatures up to 950 °C

Thick Bi₂Sr₂CaCu₂O₈ films have been produced by melting Bi₂Sr₂CaCu₂O₈ powder on MgO substrates at temperatures just above the melting temperature of the powder. X-ray diffraction measurements indicate enhanced c-axis alignment throughout the thickness of the films. Films melted at 900 °C show greater alignment and contain less Bi₂Sr₂CuO₆ compared to those processed at 950 °C. Both the degree of alignment and the Bi₂Sr₂CuO₆ content increase as the cooling rate is decreased. Transport measurements show that films quickly cooled from low melt-processing temperatures have the highest critical current densities (J_c = 13 kA/cm² at 30 K). The temperature dependence of J_c is best described by a flux creep model. Finally, J_c at 4.2 K (in both parallel and perpendicular magnetic fields) undergoes a sudden drop at low fields, but levels off above 0.5 T to about 30% of the zero field value.