Available online at www.sciencedirect.com
Journal of the European Ceramic Society 30 (2010) 3137–3143
CeO
2
–YO
1.5
–NdO
1.5
system: An extensive phase relation study
V. Grover
a
, S.V. Chavan
a
, P. Sengupta
b
, A.K. Tyagi
a,∗
a
Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, India
b
Materials Science Division, Bhabha Atomic Research Centre, Mumbai 400 085, India
Received 9 December 2009; received in revised form 4 June 2010; accepted 15 June 2010
Available online 24 July 2010
Abstract
The sub-solidus phase relations in the CeO
2
–YO
1.5
–NdO
1.5
system have been studied. About 45 compositions in the series
Ce
1-x
(Y
0.70
Nd
0.30
)
x
O
2-0.5x
,Y
1-x
(Ce
0.50
Nd
0.50
)
x
O
1.5+0.25x
and Nd
1-x
(Ce
0.55
Y
0.45
)
x
O
1.5+0.275x
were prepared and characterized by powder XRD. In
the Ce
1-x
(Y
0.70
Nd
0.30
)
x
O
2-0.5x
series, there was a gradual transformation from the defective F-type cubic lattice to an ordered C-type phase
with increasing x, whereas in the Y
1-x
(Ce
0.50
Nd
0.50
)
x
O
1.5+0.25x
series, the C-type cubic lattice of yttria was retained over the entire range. In the
Nd
1-x
(Ce
0.55
Y
0.45
)
x
O
1.5+0.275x
system, the compositions with NdO
1.5
content greater than 95 mol% showed coexistence of hexagonal, monoclinic
and cubic phases. A biphasic region of monoclinic and C-type cubic phases was observed as NdO
1.5
decreases from 90 to 70 mol%. All the com-
positions below 70 mol% NdO
1.5
, were found to be C-type cubic solid solutions. The phase relations are distinctly characterized by an extensive
range of cubic solid solutions, stable under the slow-cooled conditions. To the best of our knowledge, this is the first detailed sub-solidus study
reported in CeO
2
–YO
1.5
–NdO
1.5
system.
© 2010 Elsevier Ltd. All rights reserved.
Keywords: Powders-solid state reaction; X-ray methods; CeO
2
1. Introduction
Cerium oxide is a candidate material for variety of potential
applications, e.g. optical glass-polishing, petroleum-cracking
catalyst, gas sensors, etc.
1
Doped ceria is a potential solid elec-
trolyte material for use in oxygen concentration cells, solid oxide
fuel cells and in controlling air-to-fuel ratio in the automobile
exhaust. In nuclear industry, CeO
2
is considered an important
material as for its use as a surrogate for PuO
2
.
2,3
A number of reports have appeared in literature during
the last few decades on alkaline-earth and rare-earth oxide
doping in CeO
2
, e.g. MgO,
4
CaO and SrO,
5
Sc
2
O
3
,
6
Y
2
O
3
,
Gd
2
O
3
, La
2
O
3
, Nd
2
O
3
, Yb
2
O
3
,
7
La
2
O
3
and Eu
2
O
3
.
8
In
order to study new doped ceria materials (solid solutions and
line compositions), several ceria based ternary phase rela-
tions have also been explored in detail. For example, ZrO
2
–
Y
2
O
3
–CeO
2
,
9,10
Nd
2
O
3
–CeO
2
–CuO, RuO
2
–Y
2
O
3
–CeO
2
,
11
Bi
2
O
3
–Y
2
O
3
–CeO
2
,
12
ZrO
2
–CeO
2
–LaO
1.5
.
13
Recently, var-
∗
Corresponding author. Tel.: +91 22 2559 5330;
fax: +91 22 2550 5050/2551 9613.
E-mail addresses: aktyagi@barc.ernet.in, aktyagi64@rediffmail.com
(A.K. Tyagi).
ious ternary relations have been reported on ceria based
mixed oxides like CeO
2
–ZrO
2
–Gd
2
O
3
, CeO
2
–ThO
2
–ZrO
2
and
CeO
2
–Gd
2
O
3
–ThO
2
under the slow-cooled conditions.
14,15
In the present study, a new ceria based ternary sys-
tem, CeO
2
–YO
1.5
–NdO
1.5
has been investigated under the
slow-cooled conditions. CeO
2
is known to have similar thermo-
physical properties as PuO
2
. Hence, CeO
2
can act as a surrogate
material for PuO
2
(fissile material) used in nuclear reactors,
whereas YO
1.5
and NdO
1.5
are the fission products.
16
Thus,
this ternary phase relation will be able to throw some light on
kinds of phase fields present in the system containing these three
components and will act as an invaluable database.
Detailed studies on the phase relations in the CeO
2
–RE
2
O
3
(RE = rare-earth) binary systems suggest that width of the two-
phase region (i.e., coexistence of F and C-type phases) decreases
with increasing RE
3+
(rare-earth ion) radius.
17,18
Here again,
it was difficult to distinguish the presence of a complete solid
solution or a biphasic region (Fluorite
ss
and C-type
ss
) by X-
ray diffraction, as the cell constants tend to converge due
to solid solution formation.
19–22
Pepin et al.
23
have deter-
mined the binary phase relations in CeO
2
–RE
2
O
3
system by
quenching and have extrapolated it to ternary regions by taking
CeO
2
–Y
2
O
3
–Nd
2
O
3
as the model reaction. It has been sug-
0955-2219/$ – see front matter © 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jeurceramsoc.2010.06.005