Texture and morphology developments of Yttria-stabilized zirconia (YSZ) buffer layer for coated conductors by RF sputtering

Yttria-stabilized zirconia (YSZ) films are deposited on CeO2/NiW tapes by RF sputtering for (Gd) BCO-coated conductors. Surface morphology and texture developments are investigated as the O2 : Ar ratio and sputtering power increase. Both the grain size and the roughness of YSZ films increase as sputtering power increases. A simple model proposed by Bartelt et al. is used to explain the results. The strain relaxation mechanism plays a major role in the sudden increase in roughness for YSZ film deposited at a sputtering power of 50 W. It is observed that low O2 : Ar ratio favors the growth of (200) orientation for YSZ film, while high O2 : Ar ratio favors the growth of (111) orientation. The preferential orientation (200) of the YSZ film with low O2 : Ar ratio arises from template effect of CeO2 buffer layer. The (111) orientation of YSZ film with high O2 : Ar ratio is due to thermodynamic mechanism aiming for the lowest surface energy. The grain size and roughness of our optimal YSZ film are 10–15 nm and 0.7 nm, respectively. The out-of-plane texture of our optimal YSZ film is 4.05°. The in-plane texture is 6.35°. The plan view and cross-section SEM images of YSZ films on CeO2/NiW tapes show a flat, dense and no micro-cracks morphology. Based on these results, (Gd) BCO films are deposited by RF sputtering, achieving self-field Jc of 4.0 MA/cm2 at 77 K.