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F. Application of the protocol to a different
oxide system
After all of the diagnostic tests were performed on
Cu
1−x
Ce
x
O
3
, the protocol was then applied to a second
system: La
1−x
Sr
x
CoO
3−
␦
. Thermal analyses showed that
the final decomposition and reaction, from the remain-
ing SrCO
3
and LaCoO
3
to La
1−x
Sr
x
CoO
3
, occurred at
851 °C. XRD results of the La
0.5
Sr
0.5
CoO
3−
␦
indicated
that at 850 °C the perovskite had formed, and at 950 °C
some of the primary peaks were more intense, while some
peaks of SrCoO
2
and other oxides began to appear. At
these decomposition temperatures, there is little indica-
tion that organic material remains in the compound.
These higher temperatures present the problem of par-
ticle coarsening, although the particle sizes are smaller
than those measured when solid-phase syntheses are
used, which require much higher temperatures.
The BET analyses of bulk powders and oxide resin
caps exhibited less of a dependence of surface area on
composition then the Cu–Ce–O system (see Fig. 9). Such
a trend does not occur, unlike in the copper-cerium oxide
system, because while the first system examined was a
mixed oxide system, the second is a solid solution. The
strontium (ionic radius: 0.158 nm) is substituted on
the lanthanum (ionic radius: 0.150 nm) sites in the
perovskite structure, but due to the small difference in
ionic radius, there is very little distortion of the crystal
lattice. With only a slight distortion of the lattice, the
surface areas of different compositions of the system
remain nearly constant. The surface areas determined
from these samples have been compared to data reported
by Doshi, Alcock, and Carberry.
19
For comparison, the
surface area for the La
0.8
Sr
0.2
CoO
3−
␦
measured in this
study from the modified Pechini method was found to be
11.20 m
2
/g, and the stated values of their Pechini method
and solid-phase synthesis are 4.83 and 0.19 m
2
/g, respec-
tively. Finally, this library was characterized for catalytic
activity in the CO oxidation reaction. Figure 10 is a
thermal difference image of this library during the CO
reaction at a temperature of 215 °C. This corresponds to
FIG. 8. Thermal image of the library in Fig. 3 illustrating the tem-
perature changes during the CO oxidation reaction. White regions have
the highest temperature increase (25 °C).
FIG. 9. Plot of surface area measurements for the La
1−x
Sr
x
Co
3−8
sys-
tem. Measurements from both bulk samples and caps are shown. For
the x
⳱ 1 composition, the surface area is 0.001 m
2
/g.
FIG. 10. Thermal image of temperature change during oxidation re-
action over La–Sr–Co–O library at 250 °C. LaCoO
3
is in the upper left
corner, and the Sr content in the compositions follow a serpentine
pattern to the right.
H.M. Reichenbach
et al.:
Combinatorial synthesis of oxide powders
J. Mater. Res., Vol. 16, No. 4, Apr 2001
973
http://journals.cambridge.org
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IP address: 138.251.14.35
the temperature at which there is 100% conversion of CO
to CO
2
by the compound La
0.8
Sr
0.2
CoO
3−
␦
, as reported
by Carberry.
19
Using the modified Pechini method with a combina-
torial inkjet deposition technique results in powders that
have a moderately high surface area. This synthesis route
is appropriate for surface-sensitive applications such as
catalyst powders, pigments, and phosphorescent materi-
als. For other applications in which smaller quantities
and smoother surface finishes are desired, vacuum depo-
sition or ultrasonic spray deposition techniques may be
more appropriate. Similar to the vacuum and ultrasonic
spray deposition methods, the modified Pechini process
of combinatorial synthesis can easily be expanded from a
library of fifteen elements to a library of 1000 elements.
In addition to increasing the number of compositions in
the library, it is also trivial to generate not only binary
and ternary compounds, but quaternary and more com-
plex oxide compositions as well.
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