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High-quality epi-MgO buffer layers under different O2/Ar pressure ratios are fabricated by rf magnetron sputtering on textured IBAD-MgO templates. Under the total deposition pressure remaining constant (14 Pa), the effect of changing the ratio of O2/Ar pressure from 1:4 to 3:2 on the microstructure and surface morphology of epi-MgO films is studied. The microstructure and morphology of epi-MgO are fully characterized by x-ray diffraction, atom force microscope and scanning electron microscope. The best texture quality of epi-MgO with an out-plane Δ𝜔 value of 1.8 ∘ and an in-plane ΔΦ value of 5.22 ∘ are obtained under the ratio of O2/Ar pressure 3:2. Further, the surface morphology indicates that the surface of epi-MgO is smooth with rms surface roughness about 4.7 nm at O2/Ar pressure ratio 3:2. After that, GdBa2Cu3O 7−𝛿 (GBCO) layers are deposited on the CeO2 cap layer buffered epi-MgO/IBAD-MgO templates to assess the efficiency of such a buffer layer stack. The critical current density of GBCO films (thickness of 200 nm) is higher than 3 MA/cm 2 , indicating that epi-MgO/IBAD-MgO is promising for depositing superconducting layers with a higher critical current density.

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