Strain induced synthesis of high temperature superconducting thin films

Abstract

Microstructures of YBa2Cu3O7−δ /BaSnO3 superlattice are analyzed by Transmission electron microscopy. YBa2Cu3O7−δ /BaSnO3 superlattices are fabricated by a pulsed laser deposition technique with in situ rotation of target materials. Typical growth conditions of substrate temperature and oxygen pressure are 710 °C and 400 mTorr, respectively. A few nm thick BaSnO3 insulating layers and YBa2Cu3O7−δ superconducting layers are sequentially deposited with total thickness of around 150 nm. Crystallographic characteristics of these superlattices are evaluated by x-ray diffractometry (XRD) and transmission electron microscopy (TEM). Several layers of YBa2Cu3O7−δ and BaSnO3 are clearly observed by TEM. The observed thickness of one layer of YBa2Cu3O7−δ and that of BaSnO3 films are 12 nm and 6.5 nm, respectively. From a high-resolution TEM observation, the strain induced by lattice length difference between YBa2Cu3O7−δ and BaSnO3 are released by introducing misfit dislocations in the YBa2Cu3O7−δ films not in the BaSnO3 films. A new insulating layer is required with small lattice mismatch to YBa2Cu3O7−δ for avoiding introduction of misfit dislocations.