Amorphous superconducting transformation in bismuth-base high-T-c superconducting rods

The transformation of high-resistivity amorphous (Bi1.68Pb0.32)Sr1.75Ca1.85Cu2.85Oy and (Bi1.6Pb0.4)Sr1.7Ca2.3Cu3Oy to superconductive materials has been characterized by structural, thermochemical, transport, and scanning electron microscope measurements, X-ray powder diffraction confirmed that rapid solidification of Bi-Pb-Sr-Ca-Cu-O-y yields amorphous material, In further heat treatments, sequential crystallization of three phases was identified. Differential scanning calorimetry indicated an exothermic crystallization peak at 520 degrees C with corresponding enthalpy of 62 J/g. Scanning electron microscopy studies revealed that the grain size increases with sintering time and that the formation mechanism in the interior of the bulk is different from that at the surface of the superconducting glass ceramic rods, Thermal cycling of the insulating glass to a temperature above that required for crystallization results in a transformation from an insulating to a superconducting material with a T-c (R = 0) of 105 g. It was also shown that the glass ceramic rods obtained by reheating glass rods to 850 degrees C for 120 h have a T-c (R = 0) of 105 K, whereas the disk specimens obtained by reheating the powdered glass compacts in the same way do not exhibit superconductivity above 85 K. This difference in superconductivity between the specimens is discussed in terms of the crystallization process and the amount of oxygen absorption of the specimens during heating.