Study on the improved J_c(B) performance of polyacrylic acid-doped MgB₂ bulks

We fabricated polyacrylic acid (PAA)-doped MgB₂ bulks by wet mixing and in situ reaction process and studied the relationships between the phase formation, lattice change, microstructure, and critical properties according to the PAA doping level. The PAA doping increased the MgO amount and grain boundary area but decreased the a-axis lattice constant and critical temperature (T_c), which is indicative of the substitution of B sites by C in MgB₂. Furthermore, the critical current density (J _c) at high magnetic fields improved with the increasing PAA content to 5.99 kA/cm² for the 7 wt% PAA-doped sample, which was about 6-fold higher than that of the pure sample at 5 K and 6.6 T. This improvement was mainly attributed to the C substitution and the fine grain size due to PAA doping, suggesting that PAA is an effective dopant in improving J_c(B) performance of MgB₂.