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

摘要

Yttria-stabilized zirconia (YSZ) films are deposited on CeO_2/NiW tapes by RF sputtering for (Gd) BCO-coated conductors. Surface morphology and texture developments are investigated as the O_2: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 50W. It is observed that low O_2:Ar ratio favors the growth of (200) orientation for YSZ film, while high O_2:Ar ratio favors the growth of (111) orientation. The preferential orientation (200) of the YSZ film with low O_2:Ar ratio arises from template effect of CeO_2 buffer layer. The (111) orientation of YSZ film with high O_2:Ar ratio is due to thermodynamic mechanism aiming for the lowest surface energy. The grain size and roughness of our optimal YSZ film are 10-15nm and 0.7nm, 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 CeO_2/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 J_c of 4.0 MA/cm2 at 77K.