Interaction of La-Sr-Cu-0 and Ln-Ba-Cu-O (Ln= Y, Ho, Yb) Films With Ceramic Substrates

Abstract

In the preparation of superconducting oxide films, one frequently observes crack formation, crystal orientation, phase seperation, and chemical reaction, all of which involve interactions between superconductors and substrate. Quantitative verification of these phenomena is expected to provide useful information for the preparation and microprocessing of high Tc films. Thermal expansion behavior of representative superconductors and substrate materials has been measured by a dilatometric method. The superconductors have far greater mean thermal expansion coefficients than conventional substrate materials and the difference correspond well with the crack size observed in some of the films. The non-linear expansion of BLnCO also contain information on the kinetics of oxygen uptake and secession as well as on the phase transition temperature. The effect of lattice matching has been investigated on Ba-Yb-Cu-O films. The films were deposited by sputtering on (100) and (110) SrTiO3 and some other ceramic substrates and their orientation was measured by SEM. Furthermore, chemical interaction has been examined by heating mixed powders of superconductors and substrate materials at various temperatures. The structural variation and the reduction in superconducting volume fraction were analyzed by X-ray diffraction and ac-susceptibility measurements, respectively.