| Summary: | 碩士 === 國立臺灣大學 === 化學工程研究所 === 81 === This research contains two parts of work.The first one is the
melt-texture method which produces a poly -crystalline YBa2Cu3
O7-x ( Y123 ) superconductor by long time slow-cooling after
the incongruent melting of 123. We selected the melt-texture
polycrystalline Y123 as the sample for decoration, because this
type of sample contains varieties of microstructure, such as
large area of preferred-orientation , the minute 211 particles
and the liquid phase.And we don't know the effect of these
microstructures on the critical current density (Jc) and flux
pinning. The second part of work includes the design, the
production and the search for the best operating con -ditions
for a magnetic decoration system. The deco- ration system
consists of adapted vacuum evaporating coater and adapted
cryogenics device. We find that the best operating conditions
can be achieved by adjusting temperature, pressure and
evaporating time so that contamination can be prevented.In this
case, we can directly observe the decoration patterns on the
surface of the superconductor after evaporation of
ferromagnetic particles onto the 123 surface. To obtain the
decoration patterns,the Y123 sample- s were cooled under a
fixed magnetic field with or without a current passing through
them.The decorated patterns were analyzed in order to reveal
the nature of the pinning centers in the melt-tuxture Y123 sam-
ples.
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