A new epitaxial BaSnO3 buffer layer for YBa2Cu3O7-delta thin films on MgO substrates

45 degrees grain boundaries, which drastically increase surface resistance (R-S) in superconducting YBa2Cu3O7-delta films for microwave devices on MgO substrates, are eliminated using a new buffer layer of BaSnO3. BaSnO3 buff er layers and YBa2Cu3O7-delta films are grown by ArF pulsed laser depositio n. Epitaxial relationships among BaSnO3, YBa2Cu3O7-delta and MgO are confir med by x-ray phi-scanning. The Rs values of the YBa2Cu3O7-delta films are m easured using a dielectric resonator with 22 GHz TE011 mode. The epitaxial YBa2Cu3O7-delta films grown on BaSnO3 buffered MgO substrates show lower R- S than YBa2Cu3O7-delta films directly grown on MgO substrates. The BaSnO3 b uffer layer which enables YBa2Cu3O7-delta films to grow without 45 degrees grain boundaries at a optimum film growth condition is attractive for micro wave applications.