MICROSTRUCTURAL ANALYSIS OF CORE-SHELL STRUCTURED MgB2 SUPERCONDUCTING FIBERS FABRICATED BY HYBRID PHYSICAL CHEMICAL VAPOR DEPOSITION

We have deposited MgB2 thin films on the carbon fiber by hybrid physical–chemical vapor deposition (HPCVD) method which is known as the most effective technique for depositing MgB2 thin films without pore formation. By adopting carbon fiber as substrate and gas phase reaction between diborane (B2H6) gas and Mg vapor for MgB2 formation, core-shell structured MgB2/C composite fiber could be synthesized. The high quality of the prepared MgB2 fibers was confirmed with scanning electron microscopy (SEM), and the critical temperature (Tc) of the sample deposited at 590°C and 12 sccm flow rate of B2H6 was measured at ~40 K. The microstructures of MgB2 layer was characterized using transmission electron microscopy (TEM). The bright-field TEM images showed MgB2 with the grain size of several nanometers. The MgB2 thin film showed highly dense microstructure without pore and well-connected to the carbon fiber interface. High-resolution TEM (HRTEM) images and scanning transmission electron microscopy (STEM) revealed the presence of interface phase between MgB2 thin films and carbon fiber.