Correlation Between the Pressure Dependence of the Critical Temperature and the Reversible Strain Effect on the Critical Current and Pinning Force in Bi2Sr2CaCu2O8+x Wires

Bi2Sr2CaCu2O8+x round wires are among the most promising high-temperature superconductor candidates for making high-field magnets that operate at fields above 20 T. Owing to the brittle nature of high-temperature superconductors, their electromechanical properties need to be studied and understood prior to magnet design and construction. The irreversible degradation of the critical current at high strains has been previously correlated to damage in the microstructure of the superconductor. The origin of the much smaller reversible strain dependence of the superconducting properties of Bi2Sr2CaCu2O8+x wires has not yet been studied in detail. In this paper, we determine the cause of the reversible effect of strain on the pinning force and the critical current at temperatures ranging from 4 K to 65 K. Measurements were made as a function of tensile strain in magnetic fields up to 16 T. The irreversibility fields, determined from the macroscopic pinning force at various temperatures and strains, and the critical temperature of the Bi2Sr2CaCu2O8+x wire were found to be strain dependent. The reversible change in critical current and pinning force in Bi2Sr2CaCu2O8+x superconducting wires can be solely attributed to the dependence of the critical temperature on pressure.