The role of Ag in the pulsed laser growth of YBCO thin films

We have studied systematically the role of silver in improving microstructu re and properties of Y1Ba2Cu3O7-delta (YBCO) thin films. We have more than doubled the grain size to nearly 1.8 mu m and reduced processing temperatur es by incorporating Ag in the YBCO films, which is accomplished by using a composite target containing 15% by weight of Ag. These films show approxima tely four times higher J(c) than the best films obtained on MgO(001) substr ates deposited from stoichiometric Y1Ba2Cu3O7-delta targets. Study of the s ilver content in the film as a function of the deposition temperature shows clearly a decreasing concentration with increasing temperature and a segre gation of the Ag to the surface. The increased oxygen content in the films is also observed at lower processing temperatures, providing strong support for the efficient oxygenation of YBCO via the presence of silver. A qualit ative model suggests that the formation of silver oxide, rapid surface diff usion of Ag on MgO surfaces, and the nonreactivity of Ag with YBCO are the key aspects to the improvement in microstructure. The possibility of extend ing these ideas to the growth of oxides is also discussed, along with the f abrication of in-situ superconducting-metal junctions with 3D geometries. ( C) 1999 American Institute of Physics. [S0021-8979(99)00809-9].