Pulsed laser deposition of YBa2Cu307-x superconducting thin films : correlation between preparation conditions and structural and electrical properties

Abstract : YBa2Cu307-x thin films were obtained on MgO single crystals using pulsed laser deposition with a KrF excimer laser (248 nm) operated at 10 Hz with a laser fluence of 3 J/cm 2. Substrate temperature was monitored at 790°C with an halogen lamp and oxygen pressure was maintained at 0.3 mbar. Structural parameters were systematically investigated by X-ray diffraction. Electrical properties were characterized using a dc four probes method (25 to 300 K). In order to understand parameters which may lead to epitaxial thin films with high superconducting properties (i.e. transition temperature as high as 90 K, low transition width and critical current density of about 105 to 106 A/cm2), the role of cooling process was studied for purely c-axis oriented films using different cooling gases (oxygen or argon) and different cooling pressures. The effects of cooling process were checked by systematic study of cell parameters, rocking curves, critical temperature and transition width. Optimum cooling pressure led to thin films with a transition width of about 0.5 K and critical current density of about 106 A/cm 2 at 80 K.