MgB2 films fabricated on molybdenum substrate by hybrid physical–chemical vapor deposition for superconducting RF cavity applications

Abstract

Magnesium diboride (MgB2) is a good candidate material for superconducting RF cavities because of its higher transition temperature of ∼39 K and because of the absence of weak links between grains which prevents other high-Tc superconducting materials, such as YBCO, from being used for SRF cavities. Differently from MgB2 films fabricated on Cu or stainless steel(SS), we have fabricated MgB2 films on Mo substrate by hybrid physical–chemical vapor deposition. The films are about 0.7 µm thick and the Tc (onset) is as high as 38 K, with a corresponding transition width of 0.9 K. The upper critical field at T = 0 K, HC2(0), is extrapolated as 13.5 T and the critical current density at 5 K, JC (5 K, 0 T), is 6.5 × 105 A cm−2. Analysis results indicate that MgB2 film on molybdenum substrate has suitable superconducting properties and does not show the problems which often occur for MgB2 films fabricated on other metal substrates, such as the large cracks on SS substrate and the reaction between the substrate and the Mg on Cu substrate.