Influence of microstructures and crystalline defects on the superconductivity of MgB 2

A. SERQUIS; X. Y. LIAO; Y. T. ZHU; J. Y. COULTER; J. Y. HUANG; J. O. WILLIS; D. E. PETERSON; F. M. MUELLER; N. O. MORENO; J. D. THOMPSON; S. S. INDRAKANTI; V. F. NESTERENKO

JOURNAL OF APPLIED PHYSICS

AMER INST PHYSICS

Lugar: New York; Año: 2002 vol. 92 p. 351 - 356

0021-8979

This work studies the influence of microstructures and crystalline defects on the superconductivity of MgB 2, with the objective to improve its flux pinning. A MgB 2 sample pellet that was hot isostatic pressed (HIPed) was found to have significantly increased critical current density (J c) at higher fields than its un-HIPed counterpart. The HIPed sample had a J c of 10000A/cm 2 in 50000 Oe (5 T) at 5 K. This was 20 times higher than that of the un-HIPed sample, the same as the best J c reported by other research groups. Microstructures observed in scanning and transmission electron microscopy indicate that the HIP process eliminated porosity present in the MgB 2 pellet resulting in an improved intergrain connectivity. Such improvement in intergrain connectivity was believed to prevent the steep J c drop with magnetic field H that occurred in the un-HIPed MgB 2 pellet at H>45000Oe(4.5T) and T=5K. The HIP process was also found to disperse the MgO that existed at the grain boundaries of the un-HIPed MgB 2 pellet and to generate more dislocations in the pellets. These dispersed MgO particles and dislocations improved flux pinning also at H