ABSTRACT
Systematic experiments were performed by in situ observation of the YBa(2)Cu(3)O(z) (Y123 or YBCO) melting. Remarkably, the superheating phenomenon was identified to exist in all commonly used YBCO thin films, that is, films deposited on MgO, LaAlO(3) (LAO), and SrTiO(3) (STO) substrates, suggesting a universal superheating mode of the YBCO film. Distinctively, YBCO/LAO films were found to possess the highest level of superheating, over 100 K, mainly attributed to the lattice match effect of LAO substrate, that is, its superior lattice fit with Y123 delaying the Y123 dissolving and inferior lattice matching with Y(2)BaCuO(5) (Y211) delaying the Y211 nucleation. Moreover, strong dependence of the thermal stability on the substrate material for Y123 films was also found to be associated with the substrate wettability by the liquid and the potential element doping from the substrate. Most importantly, the understanding of the superheating behavior is widely valid for more film/substrate constructions that have the same nature as the YBCO film/substrate.
ABSTRACT
The melting process of YBa(2)Cu(3)O(x) (YBCO or Y123) films under an oxygen atmosphere was observed in situ by means of high-temperature optical microscopy. The films were classified by pole figure measurement as c-axis oriented, with two different in-plane orientations (denoted as 0 and 45 degrees). In the 45 degrees-oriented films, electron diffraction and high-resolution transmission electron microscopy (HRTEM) detected an intermediate Cu(2)O nanolayer in the vicinity of the interface. The melting mode and the thermal stability of the YBCO thin films with different in-plane orientations were greatly influenced by oxygen partial pressure. Notably, the thermal stability of the 45 degrees-oriented YBCO films dramatically grew with increasing oxygen partial pressure. We attributed this effect to a change in the intermediate Cu(2)O nanolayer thermal stability. We conclude and suggest that the thermal stability of YBCO films can be significantly enhanced by inserting a Cu(2)O buffer nanolayer.
