Growth of thick MgB₂ films by impinging-jet hybrid physical-chemical vapor deposition

Hybrid physical-chemical vapor deposition (HPCVD) process was used for the deposition of MgB₂ thin film. HPCVD process combined the thermal decomposition of diborane (B₂H₆) gas and the evaporation of Mg metal to provide sufficient Mg overpressure to maintain MgB₂ phase stability at elevated temperature. The HPCVD-grown thin films was shown to be epitaxially oriented on SiC and sapphire single-crystal substrates with root-mean-square (RMS) roughness. A high superconductor fraction in the wire or tape cross-section and a thick superconductor coating was required to have a high engineering critical current density over the cross-sectional area on the entire wire. Experimental results showed that the thick MgB₂ films were dense and polycrystalline with a preferred orientation. High current density values were obtained for undoped samples with thicknesses up to 10 μm and showed little degradation compared to results for thin films.