Epitaxial Y1Ba2Cu3O7 thin films on CeO2 buffer layers on sapphire substrates

Pulsed laser deposition has been used to deposit Y1Ba2Cu3O7 layer on CeO2 buffer layers on (1102) sapphire. Both layers are epitaxial with the (110) direction of the CeO2 layer aligned with the <2021> direction of the sapphire substrate. The c-axis Y1Ba2Cu3O7 layer has its <100> direction aligned with the <110> direction of the CeO2. Cross-sectional transmission electron microscopy shows the epitaxy to be coherent and the interfaces to be abrupt at an atomic level. The best films have a critical current of 9 e6 A/cm2 at 4.2 K and lower microwave surface resistance than copper at 77 K and at a frequency of 31 GHz.