Metal-Insulator Transition Behavior of (Pr1-yREy)1-xCaxCoO3 for Quench Protection of High Field Superconducting Magnets

REBa₂Cu₃O_y (REBCO) tapes are promising materials for high-field magnet applications due to their high critical current density and mechanical properties under high magnetic fields. However, REBCO coil has a problem of quench protection because of the low normal zone propagation velocity. This work explores the use of smart insulation (SI) coils utilizing metal-insulator transition (MIT) materials as turn-to-turn insulation to address quench protection challenges in REBCO coils. Specifically, perovskite-type cobalt oxides, (Pr_1-yRE_y)_1-xCa_xCoO₃ (RE = Sm and Y), were investigated as MIT materials for their potential application in quench protection systems. Samples were fabricated via the sol-gel method and were evaluated for their electrical resistivity ρ and MIT temperature T_MIT under high magnetic fields of up to 19 T. The results show that at certain temperatures (e.g., 62.3 K in 19 T for (Pr_0.8Sm_0.2)_0.6Ca_0.4CoO₃) ρ decreases significantly, confirming MIT behavior. The compound (Pr_0.8Sm_0.2)_0.6Ca_0.4CoO₃ showed the lowest T_MIT. Additionally, the contact resistance R_ct between the layers of the SI coil was estimated from the ρ values. The R_ct changed ratio by over three orders of magnitude as the temperature increased from 10 K to 270 K.