Preparation of oriented thick HTSC films by cryoelectrophoretic technique

Abstract

A new technique, specifically designed for the preparation of preferentially oriented HTSC (YBCO and BSCCO) films on metallic substrates has been developed. The method, named cryoelectrophoresis, is essentially based on the transport by electric fields (of the order of 1 kV/cm) of charged superconducting powders kept in a cryogenic fluid (liquid nitrogen). We show that, in these conditions, it is possible to deposit the HTSC grains with a desired orientation upon the application of an appropriate magnetic field. So far conventional electrophoretic oriented deposition was made using the weak normal-state paramagnetic moment, which required the application of magnetic fields of about 9 T. In the method that we introduced, the more intense diamagnetic moment due to the superconducting state yields comparable orientation in a small field, of about 90 G. The orientation degree is pointed out through XRD measurements, from which the fraction of grains with a particular orientation with respect to the substrate is inferred: we show that, in a film deposited with an orienting magnetic field of 90 G the number of grains with the (a, b)-planes parallel to the substrate is 2–5 times greater than in samples obtained without magnetic field and an average misorientation angle of about 25 degrees is estimated.