Microstructure studies of a-axis oriented YBa2Cu3O7-x-PrBa2Cu3O7-y heterostructures

We have studied the microstructure of epitaxial a,b-axis oriented YBCO-PrBCO heterostructures using transmission electron microscopy. These films, grown on single crystal [001] SrTiO3 or LaAlO3 by pulsed laser deposition, have a Tc,0 of 84 K as determined by DC resistivity and AC susceptibility measurements. The PrBCO layer acts as a good buffer and template layer for the subsequent growth of a-axis oriented YBCO layer. Planar sections reveal the existence of two 90° rotated variants, with a small (<5%) fraction of c-axis oriented regions. These films are relatively free of polytypoidic defects, compared to c-axis oriented films. Selected area electron diffraction patterns obtained from cross sections and planar sections reveal the orientation relationship in which the a-axis of the YBCO layer and the b-axis of the PrBCO layer are normal to the substrate surface. © 1990.