Synthesis and Properties of Polycrystalline MgB₂ Thin Films by a Precursor Post-annealing Process

Abstract

Unlike high-T_c oxide superconductors, the boundaries of MgB₂ grain do not have weak links. Hence, polycrystalline MgB₂ thin films have a strong potential for use in practical high-field applications. We have therefore focused on polycrystalline MgB₂ thin films fabricated on various substrates such as TiN-buffered Si and a YSZ-buffered Hastelloy tape. A low-temperature two-step process was employed for depositing of the MgB₂ thin films. The highest zero-resistance transition temperature achieved was 34 K for the MgB₂ films deposited on Si substrates. Critical current densities exceeding 10⁵ A/cm² at 4.2 K and 10T have been attained for MgB₂ films grown on Hastelloy tape. The microstructures of the films consisting of nanometer-sized grains appeared to act as strong pinning centers. Furthermore, ZrB₂ doping into MgB₂ thin films has been attempted, resulting in a slightly enhanced upper critical field.