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 △ω value of 1.8° and an in-plane △ Φ 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,GdBa2Cu3O7-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 200nm) is higher than 3 MA/cm2,indicating that epi-MgO/IBAD-MgO is promising for depositing superconducting layers with a higher critical current density.