Effect of Conductive Metal Powder Incorporation on Vanadium Trioxide Insulation Between REBCO Tapes

Vanadium trioxide (V ₂ O ₃ ) exhibits a negative temperature dependency in its electrical resistivity, a phenomenon known as the metal-to-insulator transition (MIT). This study investigates the implications of this property, particularly noting that V ₂ O ₃ 's resistivity significantly decreases above approximately 150K, reaching levels comparable to metallic resistivity. Such behavior is pivotal in enabling the automatic adjustment and recovery of contact resistance ( R _ct ) in rare-earth barium copper oxide (REBCO) coils, in response to internal temperature fluctuations. By introducing V ₂ O ₃ insulation, REBCO coils can effectively combine the benefits of both insulated and non-insulated configurations. To enhance the reliability of V ₂ O ₃ insulation in REBCO applications, it is essential to ensure the compatibility of V ₂ O ₃ 's inherent properties, such as electrical and thermal conductivities, with the quench states of the REBCO coil. The primary aim of this research is to evaluate the feasibility of incorporating metallic powder (molybdenum, Mo) into V ₂ O ₃ as a potential enhancement for REBCO applications. The study measures R _ct values, reflecting MIT behavior, in REBCO conductors integrated with V ₂ O ₃ paste containing micrometer and nanometer-sized Mo powder. These measurements were conducted across various Mo concentrations within a conduction-cooled environment, spanning a temperature range of 20 to 290 K. Additionally, thermal conductivity assessments were performed to ascertain the efficacy of the V ₂ O ₃ + Mo mixture coatings. Spectrometry analysis was also conducted on the samples to examine their micro-morphological characteristics.