  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.
