Epitaxial relations between in situ superconducting YBa2Cu 3O7-x thin films and BaTiO3/MgAl 2O4/Si substrates

In situ superconducting YBa2Cu3O7-x films with Tc0 up to 87 K and Jc, 77 K up to 6×10 4 A/cm2 were prepared on Si substrates with MgAl 2O4 and BaTiO3 double-buffer layers. The epitaxial relations between various layers were established by transmission electron microscopy. The MgAl2O4 layer is heavily faulted. The subsequent BaTiO3 layer stops most of the faults, provides a template for the YBa2Cu3O7-x growth, and partially screens off the stress due to different thermal expansion coefficients. The microstructure of the YBa2Cu3O 7-x layer is very similar to that of the films deposited directly on SrTiO3, exhibiting a homogeneous heavily faulted single-crystal-like structure free from secondary phases and grain boundaries. The slight degradation of the transport properties is attributed to residual thermal stress.