Electrical properties of MgO-ZrO₂ insulation coatings on Ag and AgMg/Bi-2212 tapes for magnet technology

High temperature MgO-ZrO₂ insulation coatings were successfully fabricated on long-length Ag and Ag/AgMg sheathed Bi₂Sr₂Ca₁Cu₂O_x (Bi-2212) superconducting tapes and wires from solutions derived from alkoxide-based precursors using a reel-to-reel, continuous sol-gel technique for 3-5 T high field insert magnets. The insulation coatings were annealed at 850 °C for 20 h under O₂ flow. The surface morphology of coatings were characterized by scanning electron microscope (SEM). Dielectric constant and high voltage breakdown of insulation on tapes was measured by a multimeter and a standard high voltage breakdown power supply. SEM observations showed that MgO-ZrO₂ insulation coatings possess homogenous and crack structures on AgMg/Bi-2212 tapes. It was found that dielectric constant and high breakdown voltage values of MgO-ZrO₂ coatings increased with increasing MgO content in ZrO₂ and coating thickness. Also, it was measured that the dielectric constant values of coatings with and without epoxy were 33 and 47, respectively. The maximum high breakdown voltage value was determined to be 1100 V in sample with 24 mol% MgO-ZrO₂ coating.