INFLUENCE OF THE CHARACTERISTICS OF A SRTIO3 BUFFER LAYER ON THE SUPERCONDUCTIVITY OF LASER-ABLATED YBA2CU3O7-DELTA FILMS

The superconductivity of YBa2Cu3O7-partial-derivatives (YBCO) films gr own on MgO substrate materials has been modified significantly using S rTiO3 (STO) films as buffer layers. The role of the STO layer has been examined by conventional wide-angle X-ray diffraction (XRD), by atomi c force microscopy (AFM) and by grazing-incident X-ray diffraction (GI XD) techniques and it has been found (i) to suppress the interaction b etween the films and the substrate materials and (ii) to enhance the n ucleation and growth of (001)-oriented YBCO grains. The (001) epitaxia l STO films are found to be of decisive importance to optimization of the superconductivity of the subsequently deposited YBCO films. Both t he substrate temperature (720-degrees-C) and oxygen pressure (0.02 mba r) have to be stringently controlled for this purpose. The YBCO/STO/Mg O films thus obtained possess excellent superconducting properties wit h T(c) = 90 K and transition width DELTAT = 2 K.