MgB₂ thick film with T_C = 40.2 K deposited on sapphire substrate

Abstract A thick MgB₂ film has been successfully deposited on a (001) crystalline surface of sapphire by the method of hybrid physical–chemical vapor deposition (HPCVD). The film thickness is about 1.3 μm, having a dense and interlaced structure. The film surface, as shown by scanning electron microscopy, is stacked with MgB₂ microcrystals. Transport measurements using the four‐probe technique demonstrate that its critical temperature is about 40.2 K, with a sharp transition width of 0.15 K. The transition is higher by 1 K than those commonly reported at 39 K. The residual resistivity ratio (RRR) is about 11. By extrapolation, H _C2(0) is determined as 13.7 T from magneto‐transport measurements. Also, from hysteresis measurements and applying the Bean model, the critical current density is estimated as 5 × 10¹⁰ A/m² in zero magnetic field. The investigation demonstrates that HPCVD is an effective technique to fabricate MgB₂ thick films with decent superconducting properties. Hence, it is important for future superconducting applications, in particular as a crucial preliminary stage in the fabrication of superconducting tape. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)