Microstructures of 123 thick films grown on various substrates by liquid phase epitaxy

Abstract

Microstructures of Y123 thick films grown on various substrates by liquid phase epitaxy were studied by transmission electron microscopy. We found a unique microstructure of 123 thick films on MgO substrate, that is, there exist many small angle grain boundaries (with average grain size of several µm, misorientation less than 1°) which appeared down to the substrate film interface. The appearance of these high density small angle grain boundaries can be partially responsible for no cracks and high Jc of the 123 film on MgO substrate. After analyzing the atomic microstructures between film and substrates, we found that the strain in the film on MgO substrate is the lowest among several commonly used substrates. Relatively large mismatch can result in an incoherent interface and nearly all strain between film and substrate is relieved at the interface. Small angle grain boundaries result from such a pseudo-epitaxy of 123 on MgO substrate due to the weak interaction. Growing a MgO buffer layer on SrTiO3 substrate can introduce small angle grain boundaries and increase critical thickness to avoid cracks.