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

We have studied systematically the role of silver in improving microstructure 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 temperatures by incorporating Ag in the YBCO films, which is accomplished by using a composite target containing 15% by weight of Ag. These films show approximately four times higher J(c) than the best films obtained on MgO(001) substrates deposited from stoichiometric Y1Ba2Cu3O7-delta targets. Study of the silver content in the film as a function of the deposition temperature shows clearly a decreasing concentration with increasing temperature and a segregation 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 qualitative model suggests that the formation of silver oxide, rapid surface diffusion of Ag on MgO surfaces, and the nonreactivity of Ag with YBCO are the key aspects to the improvement in microstructure. The possibility of extending these ideas to the growth of oxides is also discussed, along with the fabrication of in-situ superconducting-metal junctions with 3D geometries. (C) 1999 American Institute of Physics. [S0021-8979(99)00809-9].