The Influence of the Microstructure and Morphology of CeO 2 Buffer Layer on the Properties of YBCO Films PLD Grown on Ni Tape

Abstract

YBa2Cu3O7−δ films were deposited on CeO2-buffered nickel substrates, with different buffer thickness. Full width at half maximum of rocking curve, Δω, of CeO2 and yttrium barium copper oxide (YBCO), as well as the critical temperature, T c, of YBCO were shown to be strongly dependent on buffer thickness. They behave similarly but not proportional to the buffer thickness increase. This and the fact that Δω vs. buffer thickness and T c vs. buffer thickness for YBCO behave similar with RMS roughness vs. thickness of CeO2 indicates that the surface peculiarity of buffers is responsible for YBCO properties. More precisely, the surface of CeO2 films prepared by the chemical solution route based on propionic acid is prone to agglomerate (de-wet) and the degree of agglomeration depends in an intricate way on buffer thickness. We showed that nor RMS roughness neither (00 l) texture degree can define alone the surface suitable for c-axis YBCO nucleation. The {111} faceted grains (even in the case of high (00 l) texture) and other defects generated by agglomeration supply a low fraction of (00 l) flat terminations of buffer that affect the nucleation of c-axis-oriented YBCO phase. Moreover, the thermal instability of the surface morphology of CeO2 buffers (further development of de-wetting process, {111} faceted grains, etc. during superconducting layer deposition) influence the quality of YBCO films.