The fabrication of homo-epitaxial magnesium oxide films in buffer layers for coated conductors

The second-generation high-temperature superconducting material $\mathrm{YBa}_{2} \mathrm{Cu}_{3} \mathrm{O}_{7-\delta}$ (YBCO) has become an emergence technology due to its superior properties, such as high critical magnetic field, high critical current density, and low AC losses. The ion beam-assisted deposition (IBAD) technique has gradually become the primary buffer layer technology for YBCO films. This paper focuses on the homo-epitaxial deposition of MgO (epi-MgO) films on the IBAD-MgO substrates. The MgO self-epitaxial layer effectively reduce the defects and stress in the films and optimize the biaxial texture of IBAD-MgO. Our experiments demonstrate that epi-MgO improves the texture, crystallization quality, and surface roughness. Furthermore, an optimal film thickness of 200 nm is identified for the epi-MgO. The structure of the epi-MgO inherits well from the IBAD-MgO layer, making it highly influenced by the IBAD-MgO process parameters. However, during the homo-epitaxial process, the deposition temperature and deposition rate have minimal effects on the MgO layer.