Synthesis of Superconducting Perovskite by Coprecipitation of Hydroxides
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SYNTHESIS OF SUPERCONDUCTING PEROVSKITE BY COPRECIPITATION OF HYDROXIDES
I.
Valente-Campion,
and J.
P.
Barboux,
L.
Mazerolles,
D. Michel,
R.
Morineau
Livage
Chimie de la Mati~re 75005 Paris,
Condensde,
Universitd P.
et
M. Curie,
4 Place
Jussieu
France
ABSTRACT The synthesis of the superconducting perovskite YBa2Cu 3 0 7 using hydroxides as starting
precursors
has
been
investigated.
coprecipitated from mixed alcohol-water heat-treatment the perovskite phase
Hydroxides
are homogeneously
solutions without loss of barium. Upon
rapidly forms around 750°C.
However,
remains tetragonal even after long time annealing in oxygen ambient. related to an unusual microtwinning in
This
it is
the (ac) plane.
INTRODUCTION The
superconducting
sensitive
to
the
properties
microstructure
grain alignment is
the
textured films supported ZrO2 or MgO.
In
YBa 2 Cu 3 O7 perovskite are very 1
ceramics
necessary to increase
the grains of the ceramics.
SrTiO3 ,
of
of
Experience has shown that
.
the superconducting links
A simple way to achieve this is
by a substrate
that is
commonly
order to obtain large critical
between
the synthesis of an oxide such
as
currents both reaction
with the substrate and shrinkage have to be avoided by lowering the
reaction
temperature.
the
This can be achieved by
solution techniques through a better
starting
a
reagents
precipitation properties
or
allow 2
procedures .
at
"sol-gel" thin
film
However,
heat
treatment
BaCO3 , occurs. react
with
a
Moreover,
solutions
via
spin-coating
these
techniques
use
starting precursors (acetates,
phase
separation
This latter
other
of
level.
yield
deposition
most
chemical species as the
molecular
techniques
is
elements
quite
between
into
mixing of controlled
whose rheological or
dip-coating
carbon containing
carbonates...).
Upon
CuO, Y2 0 3 and barium carbonate,
unreactive 900-950°C,
and slowly a
decomposes to
temperature range where
substrate reaction and particle growth simultaneously occur. We report on the precipitation of hydroxides as a way to low temperature synthesis of textured films or simply done through addition copper
hydroxides 2
have
polarizing Ba + cation
a
ceramics. of a base to
similar
requires a too
Precipitation of hydroxides may an aqueous solution. Yttrium
precipitation high pH in
range(pH=7)
but the less
order to obtain
precipitation.
Mat. Res. Soc. Symp. Proc. Vol. 180. 01990 Materials Research Society
be and
complete
894
EXPERIMENTAL The
synthesis
has
procedure
solution by addition of NaOH 2N in
mixture.
been
discussed .
and 30%
volume acetone
a 70%
Samples are handled under argon ambient to avoid adsorption
(leading to BaCO3 ).
to be
pressure before
the
are
powders
resulting
The
vacuum.
After washing,
water of CO2
precipitate is dried at 120°C under 2 pressed into pellets under a 12t/cm
oxygen flow
heated under
three
then filtered
The precipitate is
ethanol.
The
a mixed alcohol-water
nitr
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