FORMATION OF SECONDARY PHASES IN YBA2CU3O7-DELTA SRTIO3 MULTILAYERS/

The YBa2Cu3O7-delta (YBCO)/SrTiO3 (STO) material system has a potentia l for device applications such as superconducting field effect transis tors, filters and delay lines, due to the possibility to grow heteroep itaxial structures with the necessary orientation of the highly anisot ropic superconductor YBCO. To investigate microstructure and formation of secondary phases in this material system, YBCO/STO multilayers wer e grown by DC and rf magnetron sputtering, respectively. The formation of a previously unidentified cubic (or pseudo-cubic) phase with a lat tice parameter of 0.414 nm, containing Ba, Ti, O, and Y, is reported. It is suggested that this phase is Y-substituted BaTiO3 (BTO), with Y in both the Ba and Ti positions of the perovskite unit cell. This new phase was observed to predominantly nucleate on the substrate surface and to be embedded in the layered structure. The precipitates were fou nd to have a cube-on-cube orientational relationship to the LaAlO3 (LA O) substrate, as well as to the STO and YBCO layers. Y2O3 inclusions w ere also found in the multilayers. (C) 1998 Elsevier Science B.V. All rights reserved.