Formation of secondary phases in YBa 2Cu 3O 7− δ/SrTiO 3 multilayers

Abstract

The YBa 2Cu 3O 7− δ (YBCO)/SrTiO 3 (STO) material system has a potential for device applications such as superconducting field effect transistors, filters and delay lines, due to the possibility to grow heteroepitaxial structures with the necessary orientation of the highly anisotropic superconductor YBCO. To investigate microstructure and formation of secondary phases in this material system, YBCO/STO multilayers were grown by DC and rf magnetron sputtering, respectively. The formation of a previously unidentified cubic (or pseudo-cubic) phase with a lattice parameter of 0.414 nm, containing Ba, Ti, O, and Y, is reported. It is suggested that this phase is Y-substituted BaTiO 3 (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 found to have a cube-on-cube orientational relationship to the LaAlO 3 (LAO) substrate, as well as to the STO and YBCO layers. Y 2O 3 inclusions were also found in the multilayers.