Properties of Heterophase Bi/Pb Ceramics Synthesized Using Solar Energy in the Temperature Range of 80–340 K
Abstract
For the synthesis of precursors and ceramics with the nominal composition Bi1.7Pb0.3Sr2Ca29Cu30Oᵧ, the solar gradient melt alloy quenching technology was employed. The obtained precursors and ceramics expel a magnet along the direction of the external magnetic field. This expulsion effect is also observed under the action of a directed light flux. Scanning electron microscopy (SEM) revealed a layered morphology of the precursors and ceramics, featuring caverns formed within the volume of the plate-like layers. Submicron-sized particles are located inside these caverns. X-ray diffraction (XRD) analysis confirmed the existence of superconducting homologous phases differing in stoichiometry. Such a structure can be interpreted as quasi-heterophase. Electrical resistance and magnetic properties were investigated in the temperature range of 79–460 K under ambient air conditions. Anomalous changes in resistance and magnetic induction were detected at temperatures of 280, 320, and 420 K. Ceramics are subject to thermal treatment for 1–3 h exhibit behavior characteristic of semiconductors, namely a decrease in resistance with increasing temperature. However, after thermal treatment exceeding 24 h, a transition to a superconducting-type dependence is observed. Samples that were not subject to annealing (i.e., retaining defects formed during melt quenching) demonstrate transitions at temperatures above 200 K. An explanation for the formation of high-temperature superconductivity (HTSC) is proposed based on the formation of a system of homologous phases constituting a quasi-heterophase system.