Cerium Oxalate Morphotypes: Synthesis and Conversion into Nanocrystalline Oxide

Article abstract of DOI:10.1021/acs.inorgchem.9b01250

Cerium dioxide is a scientifically and technologically important material with a wide range of potential applications, particularly in solid oxide fuel cells and catalysis. Herein, we report a study focusing on the synthesis of nanocrystalline cerium dioxide via thermal decomposition of the oxalate salt. Simply by changing reaction conditions (temperature, concentration, acidity, strike) during the precipitation of the cerium solution with oxalic acid, we were able to obtain different morphologies. The main reaction parameters were mapped and linked to the morphology of the final products. Additionally, it was proved that oxalate precipitation is a robust reaction proceeding at relatively extreme contitions. Moreover, the conversion of cerium oxalate to nanocrystalline oxide was followed to monitor the progress of the reaction, the texture evolution, and the grain growth. The results showed that, for unvaried heating cycle, the grain size of converted material is linked to morphology. The thinner was the original microcrystal the smaller were the CeO₂ nanocrystals after calcination. In addition, the grains were found smaller near the edges of the ex-oxalate microcrystals. In both cases, this behavior results from asymmetrical limitations of diffusion during grain growth.

Full text of DOI:10.1021/acs.inorgchem.9b01250

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Cerium Oxalate Morphotypes: Synthesis and Conversion into
Nanocrystalline Oxide
†
‡
§
∥
Vaclav Tyrpekl,*,† Pavlina Markova, Milan Dopita, Petr Brazda, and Mirko A. Vacca
́
†Department of Inorganic Chemistry, Faculty of Science, Charles University, Hlavova, 2030 Prague, Czech Republic
‡Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5,
Prague, Czech Republic
§Department of Structure Analysis, Institute of Physics of the Czech Academy of Sciences, 18221 Prague, Czech Republic
∥Department of Chemical and Geological Sciences, University of Cagliari, S.S. 554 bivio per Sestu, Monserrato, Cagliari, 09042, Italy
S
* Supporting Information
ABSTRACT: Cerium dioxide is a scientifically and technologically important material with a wide
range of potential applications, particularly in solid oxide fuel cells and catalysis. Herein, we report a
study focusing on the synthesis of nanocrystalline cerium dioxide via thermal decomposition of the
oxalate salt. Simply by changing reaction conditions (temperature, concentration, acidity, strike)
during the precipitation of the cerium solution with oxalic acid, we were able to obtain different
morphologies. The main reaction parameters were mapped and linked to the morphology of the final
products. Additionally, it was proved that oxalate precipitation is a robust reaction proceeding at
relatively extreme contitions. Moreover, the conversion of cerium oxalate to nanocrystalline oxide was
followed to monitor the progress of the reaction, the texture evolution, and the grain growth. The
results showed that, for unvaried heating cycle, the grain size of converted material is linked to
morphology. The thinner was the original microcrystal the smaller were the CeO2 nanocrystals after
calcination. In addition, the grains were found smaller near the edges of the ex-oxalate microcrystals.
In both cases, this behavior results from asymmetrical limitations of diffusion during grain growth.
More specifically, several studies on Ce3+ oxalates have
I. INTRODUCTION
described their preparation and conversion into nanocrystalline
Over the past decades, both pure and doped cerium dioxide
oxides for different applications.15−19 All authors have reported
(CeO2, ceria) have gained significant scientific and techno-
that ceria nanocrystalline agglomerates retain the morphology/
logical relevance for their surface and transport properties.
shape of the original oxalate microcrystals, which is also
Accordingly, several extensive reviews have described specific
properties of ceria as a high-temperature electrolyte1,2 or as a
typically observed in An oxides prepared by oxalate
conversion.14,20−22 Additionally, cerium oxalate has shown
catalyst,3,4 among other applications. Furthermore, ceria is
often used as a nonradioactive surrogate of PuO2 or AmO2.5,6
uncommon morphologies when precipitated inside a droplet
compartment.23 Moreover, atypical agglomerate shapes of
In addition to dedicated synthetic strategies, for example,
nanocrystalline ceria were also prepared via hydrothermal
focused synthesis of one-dimensional (1D), two-dimensional
decomposition of cerium oxalate.24,25 Such a method is also
suitable for the preparation of AnO2 (An = Pu, U, Th, Np, and
their solid solutions) from its corresponding oxalates.26
(2D), and three-dimensional (3D) nanostructures,7 two simple
approaches can be used to prepare nanocrystalline oxides of
lanthanides (Ln) and actinides (An)without demanding
setups, nonaqueous solvents, or harsh conditionsand easily
scaled up. The former involves the hydrolysis of a metal salt
solution (see refs 8 and 9 for Ce), whereas the latter relies on
the precipitation of metal ions with oxalic acid, forming a
nonsoluble oxalate salt, followed by conversion into the oxide
by annealing. The present study focuses on the latter, which
uses the precipitation of oxalates to separate metal ions from
solution thanks to the low solubility products of these
compounds. The structures of the most typical and stable
hydrated oxalates are shown in Figure 1. They are represented
by M2(C2O4)3·10H2O for Ln3+ and by An3+ and M2(C2O4)2·
6H2O for An4+.10−13 In turn, appropriate annealing conditions
lead to oxalate decomposition and conversion into nano-
crystalline oxides.13
Despite the advantages advanced techniques bring, large-
scale technological procedures often restrict the choice of
possible synthetic conditions for economic reasons. Therefore,
we recently performed a study to assess the effect of basic
conditions (concentration, temperature, pH, strike) on the
morphology of Th(C2O4)2·6H2O.27 Indeed, by changing these
simple precipitation parameters, the shape of oxalate micro-
crystals changed significantly, thus making it possible to obtain
squarelike crystals, octagons, and spherical agglomerates,
among other shapes. Herein, we employed a similar strategy
for cerium. On the basis of our results, we report how the basic
Received: April 29, 2019
© XXXX American Chemical Society
A
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Figure 1. Visual representations of typical lanthanide and actinide oxalate structures. The top sketches show the lanthanide Ln(An)3+ oxalate
dekahydrate (e.g., Ce2(C2O4)3·10H2O) structure10,11 along the plane [001] on the left and along [010] on the right. The bottom figures show the
structure of An4+ oxalate hexahydrate.12 The surface of the coordination polyhedra is colored in gray. There are two groups of oxygen atoms (in
red): (i) smaller oxygen atoms, which participate in the coordination of the cations (member of the oxalate group); (ii) larger oxygen atoms, which
represent the crystalline water. The hydrogen atoms of the crystalline water are omitted for clarity.
radiation). High-temperature patterns were obtained using an Anton-
Paar heating cell (HTK 16N, TCU 2000 temperature control unit).
The crystallite size was calculated from the XRD pattern using the
Pawley method, as implemented in Jana2006,28 and the Williamson-
Hall plot.29 Transmission Electron micrographs (TEMs) were
acquired on a Philips CM120 operating at 120 kV (LaB6 cathode)
equipped with an SIS Olympus Veleta CCD camera (14-bit). The
Raman spectra were recorded on Nexus Nicolet module attached to
Nicolet 6700 spectrometer with Nd:YVO4 excitation laser (1064 nm).
Spectra were recorded between 100 and 3700 cm−1 with 4 cm−1 step,
256 scans, InGaAs detector, and 1.3 W laser power.
solution properties and precipitation conditions affect the
morphology of Ce2(C2O4)3·10H2O during the precipitation of
the Ce3+ salt with oxalic acid. Moreover, using the unusual 2D
blanket or starlike morphologies, we performed a compre-
hensive study of the oxalate conversion into nanocrystalline
CeO2 during the thermal decomposition.
II. EXPERIMENTAL SECTION
II.1. Precipitation Experiments. On the basis of our experience,
we defined a set of experiments to assess the effects of basic
precipitation parameters on the morphology of Ce2(C2O4)3·10H2O
(see Table 1). The reactant solutions were prepared using cerium(3+)
nitrate hexahydrate (Sigma-Aldrich, 99.99% purity), oxalic acid
dihydrate (Lach-Ner, >99%) and distilled water. The acidity of the
Ce3+ solution was adjusted with nitric acid (Lach-Ner, 65%). All tests
were performed using a 100 mL round-bottom flask (in water/ice
bath, if necessary) and a dropping funnel. Constant magnetic stirring
(300 rpm) was used to homogenize the solution. After precipitation,
the mixture was allowed to digest for 10 min, and the product was
subsequently collected by centrifugation (5000 rpm for 5 min).
The following parameters of the precipitation reaction were
analyzed: (i) concentration of the cerium or oxalic acid solutions
Nos. 1−4 and Nos. 9−12; (ii) temperature Nos. 5−8, Nos. 13 and 14;
and (iii) acidity from low pH Nos. 17 and 18 to very high acidity (4
M HNO3) of the cerium-containing solution Nos. 19 and 20. We
preformed both possible versions of all experiments: direct strike
(DS)oxalic acid solution dropped into the cerium nitrate
solutionand reverse strike (RS)cerium nitrate solution dropped
into the oxalic acid solution. All experiments were performed by
dropping the oxalic acid solution into the cerium nitrate solution
(DS) and then replicated the other way around (RS), maintaining the
other experimental conditions. The experimental configuration DS/
RS had a paramount effect on the morphology of the product in our
previous study.27
III. RESULTS AND DISCUSSION
III.1. Oxalate Particle Morphology and Structure. The
morphology of all samples (summarized in Table 1) was
characterized by scanning electron microscopy (SEM), as
shown in Figure 2. Various shapes and assembly morphologies
were identified, and several conclusions can be derived from
such observations. A flat, thin (5−20 μm long, 0.5−3 μm wide,
and 0.05−0.5 μm thick) needle was the most commonly found
shape of Ce2(C2O4)3·10H2O microcrystals obtained at room
temperature from medium-concentration (0.2 M) or diluted
(0.02 M) solutions (see Nos. 1−4 and Nos. 9−12 in Figure 2).
Furthermore, by combining high temperature (100 °C) with
the reverse strike configuration, we were able to obtain thin
blankets nearly transparent for SEM beam (as thin as ∼50 nm)
with lateral dimensions exceeding 20 μm. Some conditions,
namely, low temperature or high acidity with reverse strike
(No. 7 and No. 19), led to agglomeration/growth of the
needles into starlike assemblies.
All synthesized samples crystallized in the monoclinic
structure of Ce2(C2O4)3·10H2O (space group No. 14, a =
11.3470 Å, b = 9.6300 Å, c = 10.3920 Å, β = 114.52°). Large
differences in morphology significantly influenced the powder
X-ray diffraction patterns together with the preferred
orientation. The starlike morphology of the needle assemblies
(sample No. 19) showed almost ideally randomly oriented
II.2. Analytical Techniques. The morphology of the final
powders was studied under scanning electron microscopes JEOL
JSM-6510 and Philips CP XL 30. The samples were coated with a thin
Au/Pd layer or as received. Powder X-ray diffraction (XRD) was
recorded on a PANalytical X’Pert PRO diffractometer (Cu Kα
B
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Figure 2. SEM images of cerium oxalate powders. All figures contain a sample number in the top left-hand corner and information on the main
precipitation conditions in top right-hand corner. D or R represents direct or reverse strike along with the concentration or temperature value if
different from 0.2 M or from 25 °C, respectively.
microcrystals, whereas sample No. 13 with platelet morphol-
ogy, which can be easily ordered by sedimentation in
isopropanol, adopted a strong, preferred orientation with
[010] planes perpendicular to the sample support (Figure 3).
Alterations of the basic precipitation conditions affect the
oversaturation, precipitation velocity, solubility, or surface
charge/agglomeration of the particles. Since the solubility
product of cerium oxalate30,31 is very low (∼1 × 10−28) and
process of precipitation is rather fast, rigorous studies
concerning the physicochemical mechanisms of precipitate
formation and solution oversaturation are beyond the scope of
presented work. Generally, following consideration can be
adopted. Low concentrations of reagents lead to low
oversaturation, so more uniform particle growth can be
observed.27 High solution acidity affects the solubility and
can therefore shift the oversaturation conditions as well.31 On
the one hand, temperature has also an important impact on the
solubility; on the other hand, the present case is complicated
with a fact that water is not only solvent but also reagent.
Temperature affects significantly physico-chemichal properties
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Table 1. Summary of the Tests Performed to Assess the Effect of Basic Precipitation Conditions on the Morphology of
a
Ce2(C2O4)3·10H2O
concentration oxalic acid
[M]
concentration Ce3+
[M]
temperature
additional
parameter
CeO2 grain size
[nm]
No.
strike
[°C]
final morphology
1
2
3
4
5
6
7
8
reverse
direct
reverse
direct
reverse
direct
reverse
direct
reverse
direct
reverse
direct
reverse
direct
reverse
direct
0.02
0.02
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.02
0.02
0.2
0.2
0.2
0.2
0.2
0.2
25
25
25
25
100
100
0−5
0−5
25
25
25
25
100
100
100
100
25
thin, wide needles
thin, narrow needles
thin flakes
47
53
48
70
57
100
43
48
42
36
77
67
70
86
77
77
42
55
41
38
thicker flakes
thin, large flakes
thick, solid crystals
layered flakes
thin, wide needles
starlike sharp needles
starlike sharp needles
thin, wide needles
sharp, thick stars
very thin, large flakes
thick flakes
very thin, large flakes
very thin, large flakes
thin, irregular needles
flake assemblies
starlike assemblies
thick, solid crystals
9
0.02
0.02
0.2
10
11
12
13
14
15
16
17
18
19
20
0.2
0.02
0.02
0.2
0.2
0.02
0.02
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.02
0.02
0.2
0.2
0.2
reverse
direct
reverse
direct
pH = 0.89
pH = 0.89
4 M HNO3
4 M HNO3
25
25
25
0.2
a
The table contains a brief description of the final shapes and mean grain size calculated from powder XRD after calcination to 700°C (5 °C/min
with no dwell) under air.
Figure 3. Powder XRD of samples No. 19 (left) and No. 13 (right) accompanied by SEM micrographs showing the morphology of the particles.
Sample No. 19 shows randomly oriented crystallites, whereas sample No. 13 shows a high degree of texture when sedimented on a flat surface.
Black vertical bars present the diffraction lines of monoclinic Ce2(C2O4)3·10H2O.
of water; thus, our expectation is that it affects more the
aqueous media in general than only the solubility product. In
conclusion, it is obvious that formations of cerium oxalate by
precipitation is a robust reaction, which can proceed under
relatively extreme conditions (high acidity, low/high temper-
ature).
III.2. Decomposition of the Oxalate Powder. We
performed a high-temperature XRD study of the decom-
position of cerium oxalate with the aforementioned extreme
morphologies (Nos. 13 and 19). Previously, other authors32,33
have reported that the first endothermic peak associated with
the removal of 10 water molecules has an onset at 130 °C. A
closer look at Figure 4 revealed that the decomposition of the
Ce2(C2O4)3·10H2O structure (amorphization) starts at ∼80
°C and that no diffraction maxima are present from 100 °C.
These decomposition temperatures were similar in both
morphologies. Then, nanocrystalline oxide starts to grow
from the anhydrous, decomposing oxalate. As reported for the
decomposition of U(C2O4)2·2H2O,34 the oxalate loses its
crystallinity above 270 °C, and the first UO2 peaks are already
visible at 300 °C. This represents only an interval of ∼30 °C
between the amorphous and the nanocrystalline states of the
material. In our case, the oxide starts to crystallize at a similar
temperature, which represents an interval of more than ∼210
°C, during which the material is not crystalline.
III.3. Nanocrystalline CeO2 Growth. As mentioned
earlier, at 300 °C, nanocrystalline CeO2 (fluorite structure,
̅
Fm3m) started to grow from the amorphous phase. At the
same time, anhydrous cerium oxalate decomposition started
and ended at ∼350 °C,35 whereas oxide crystallites continued
D
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Figure 4. Thermal decomposition of samples No. 19 (left) and No. 13 (right) studied by high-temperature powder XRD. Both samples show
Ce2(C2O4)3·10H2O diffraction lines; sample No. 19 is close to almost perfectly random crystallites, whereas No. 13 is a highly textured sample.
White stripes, especially visible in sample No. 13, are blind bands after removing the diffraction peaks of the platinum sample holder (37.7°, 44.9°,
and 65.5° 2θ).
Figure 5. Crystallization of CeO2 from decomposed oxalate (sample No. 13) studied by high-temperature powder XRD (left). Diffraction lines of
the platinum sample holders (37.7°, 44.9°, and 65.5° 2θ) were removed from the graphs. The variation of crystallite size as a function of
temperature was calculated using the Williamson-Hall plot from the high-temperature powder XRD data of sample Nos. 13 and 19 (right). The
change in grain size with the temperature was fitted using simple linear regression functions; 95% confidence bands are presented as well.
to growth. The growth of CeO2 from oxalate (sample No. 13)
was studied by high-temperature XRD, as shown in Figure 5,
on the left-hand side. To detect possible differences, we
followed particle growth from the textured (No. 13) and from
the “ideally random” (No. 19) sample. The two samples
showed similar growth (see Figure 5 right), albeit slightly
smaller grains in sample No. 13 (2D blankets) than in sample
No. 19. This artifact induced a further study, where all the
oxalate samples were thermally threated at 700 °C (5 °C/min
with no dwell). Crystallite size calculated from powder XRD
peak broadening (Figure 6 left) revealed that even if all the
samples were threated equally the mean size varies (see
Table1). The largest crystallites were found for the bulkiest
samples (Nos. 6 and 14) and smallest for the very thin needles
(No. 10). Generally, it can be said that the thick bulky samples
exhibit larger crystallites after calcination and that the thin
samples restricted in dimensions show the smallest (see also
high-resolution (HR) SEM images of calcined samples in
Supporting Information). Selected samples were characterized
by Raman spectrometry (Figure 6 right) to see the possible
defects in the fluorite structure and its effect on the crystallite
growth. The spectra show typical features for CeO2 as was
previously described in refs 36 and 37. Main peak can be found
at 465 cm−1 (F2g mode), while shoulder at 550 and 595 cm−1
arises with significant defects creation in the O2− lattice. The
results show no significant defect presence in the samples; the
largest defect “shoulder” can be observed in case of the sample
(No. 6). The presence of defects in this sample might be also
responsible for increased grain growth, as was observed for
ceria with dopant induced defects.38 However, separate study
would be needed for rigorous assessment of this effect.
In most cases, the samples from oxalate decomposition,
which retain the morphology of the original oxalate micro-
crystal, are not transparent for an electron beam in microscope.
Therefore, only a few particles on the edges can be studied,
and no larger areas can be mapped. Thanks to the low
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Figure 6. Mean crystallite size calculated from the XRD peak broadening by the Williamson-Hall plot is on the left. Samples of all oxalates were
treated at 700 °C (5 °C/min with no dwell). Samples were divided into group by the morphologyBulks (Nos. 6 and 14), Stars (Nos. 7, 10, 12,
19), Blankets (Nos. 5, 13, 15, 16), Needles (Nos. 1, 2, 3, 4, 9, 11, 17), and others (Nos. 8, 18, 20). On the right, selected samples (one from each
group except Other) were characterized by Raman spectrometry, spectra were normalized to the intensity of the F2g peak at 465 cm−1.
Figure 7. TEM of sample No. 13 (left) treated at 700 °C for 1 h. Image analysis of crystallite size as a function of crystallite distance from the edge
(based on a set of 110 particles). The data was fitted using the function y = a + b·exp ((k·x − 1)/k), wherein a = 18.97, b = 0.18, k = −0.008 and
the fitting parameter R = 0.35. This fitting function represents only a guide for the eye and does not represent any explicit physical law.
thickness of the oxalate microcrystals with 2D blanket
morphology, we were able to perform TEM measurements
on nanocrystalline CeO2 derived from oxalate decomposition.
On the left-hand side, Figure 7 shows the TEM micrograph of
sample No. 13 treated at 700 °C for 1 h in air. Interestingly,
the particle size varies with the position of the particle in the
sample. Close to the edges, the particles are smaller than in the
interior of the sample. This can be explained by asymmetric
diffusion or simply limited diffusion of material close edges of
original oxalate microcrystal during the CeO2 crystallite
growth.
The exact description of grain growth in porous confined
ceramic is not well-described in the literature, thus making it
difficult to compare our results with theoretical predictions or
with previously published data. However, the decrease in grain
size close to the particle edges follows the general trend of
grain growth limitation in early stages of sintering in porous or
two-phase ceramics.39,40
show that no texture remains in the sample (see Supporting
Information). Therefore, for Ce2(C2O4)3·10H2O, the orienta-
tion of oxalate microcrystal has no effect on the orientation of
oxide after conversion. This situation might be different for
oxalate of tetravalent ion (An(C2O4)2·6H2O) with a layered
structure (see Figure 1 bottom), which might behave
differently during the conversion into oxide.
IV. CONCLUSION
Ceria belongs to a group of technologically important
materials, which are highly desired in nanocrystalline form
for catalytic applications or in a dense, compact form for high-
temperature applications. For both applications, the oxalate salt
has been widely used as a precursor for high surface area and
sinteractive ceria. In this study, we demonstrated that no
demanding synthetic strategies are necessary, the morphology
of the oxalate product during precipitation can be affected by
simple and mild conditions (strike, temperature, concentration,
and solution acidity). Additionally, cerium oxalate precipitation
is a robust reaction that proceeded even at relatively harsh
conditions (high/low temperature, high acidity). We followed
the conversion of different morphotype into nanocrystalline
ceria. The results showed that the grain size is linked with the
Lastly, we studied the possibility of full or partial texture
conservation during the oxalate conversion. For such purpose,
we performed an omega scan on texture sample No. 13, which
was sedimented on a platinum holder (similarly as on Figure 3
left) and converted into oxide at 400 °C for 1 h. The results
F
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(12) Duvieubourg-Garela, L.; Vigier, N.; Abraham, F.; Grandjean, S.
Adaptable coordination of U(IV) in the 2D-(4,4) uranium oxalate
network: from 8 to 10 coordinations in the uranium (IV) oxalate
hydrates. J. Solid State Chem. 2008, 181, 1899−1908.
morphology of the initial oxalate. Moreover, nonhomogeneous
crystallite growth was observed within the agglomerates that
retained the original oxalate shape. Smaller crystallites were
found near the edges of the agglomerate, which may be
explained by diffusion restrictions.
(13) Abraham, F.; Arab-Chapelet, B.; Rivenet, M.; Tamain, C.;
Grandjean, S. Actinide oxalates, solid state structures and applications.
Coord. Chem. Rev. 2014, 266−267, 28−68.
ASSOCIATED CONTENT
* Supporting Information
■
(14) Tyrpekl, V.; Vigier, J.-F.; Manara, D.; Wiss, T.; Dieste Blanco,
O.; Somers, J. Low temperature decomposition of U(IV) and Th(IV)
oxalates to nanograined oxide powders. J. Nucl. Mater. 2015, 460,
200−208.
(15) Heintz, J. M.; Bernier, J. C. Synthesis and sintering properties of
cerium oxide powders prepared from oxalate precursors. J. Mater. Sci.
1986, 21, 1569−1573.
(16) Zhang, D.-E.; Ni, X.-M.; Zheng, H.-G.; Zhang, X.-J.; Song, J.-M.
Fabrication of rod-like CeO2: Characterization, optical and electro-
chemical properties. Solid State Sci. 2006, 8 (11), 1290−1293.
(17) Zhao, P.; Song, J.; Xia, M.; Wang, Y.; Meng, D.; Wang, H.; Li,
R. Photocatalytic and electrochemical properties of CeO2 with
lamellar structure inherited from cerium oxalate complex. J. Porous
Mater. 2017, 24 (4), 1089−1094.
(18) Li, M.; Wang, M.; Liu, Z.; Hu, Y.; Wu, J. Cerium dioxide with
large particle size prepared by continuous precipitation. J. Rare Earths
2009, 27 (6), 991−996.
(19) Maslennikov, D. V.; Matvienko, A. A.; Chizhik, S. A.;
Sidelnikov, A. A. Synthesis and structural characterization of ceria
nanoparticle agglomerates with shape inherited from an oxalate
precursor. Ceram. Int. 2019, 45 (3), 4137−4141.
(20) Wangle, T.; Tyrpekl, V.; Cagno, S.; Delloye, T.; Larcher, O.;
Cardinaels, T.; Vleugels, J.; Verwerft, M. The effect of precipitation
and calcination parameters on oxalate derived ThO2 pellets. J. Nucl.
Mater. 2017, 495, 128−137.
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.9b01250.
Omega scan measurements describing the texture and
HRSEM micrographs of cerium oxalate converted to
oxide (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: tyrpekl@natur.cuni.cz.
■
ORCID
Vaclav Tyrpekl: 0000-0001-7149-1343
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors are grateful to the Ministry of Education, Youth
and Sports, research infrastructure LM2015073 and to Dr. M.
Fridrichova for the Raman measurements.
(21) Zsabka, P.; Leinders, G.; Baena, A.; Cardinaels, T.; Binnemans,
K.; Verwerft, M. Synthesis of gadolinium-doped thorium dioxide via a
wet chemical route: Limitations of the co-precipitation method. J.
Nucl. Mater. 2017, 489, 211−221.
REFERENCES
■
(1) Inaba, H.; Tagawa, H. Ceria-based solid electrolytes. Solid State
Ionics 1996, 83 (1−2), 1−16.
(22) Ziouane, Y.; Arab-Chapelet, B.; Tamain, C.; Lalleman, S.;
Delahaye, T.; Leturcq, G. Speciation of residual carbon contained in
UO2. J. Solid State Chem. 2016, 244, 45−51.
(2) Kharton, V. V.; Marques, F. M. B.; Atkinson, A. Transport
properties of solid oxide electrolyte ceramics: A brief review. Solid
State Ionics 2004, 174 (1−4), 135−149.
̈
(23) Jehannin, M.; Charton, S.; Corso, B.; Mohwald, H.; Riegler, H.;
(3) Montini, T.; Melchionna, M.; Monai, M.; Fornasiero, P.
Fundamentals and Catalytic Applications of CeO2-Based Materials
(2016). Chem. Rev. 2016, 116 (10), 5987−6041.
Zemb, T. Structured solvent effects: Microscopically organized cerium
oxalate particles. Colloid Polym. Sci. 2017, 295 (10), 1817−1826.
(24) Liu, W.; Feng, L.; Zhang, C.; Yang, H.; Guo, J.; Liu, X.; Zhang,
X.; Yang, Y. A facile hydrothermal synthesis of 3D flowerlike CeO2 via
a cerium oxalate precursor. J. Mater. Chem. A 2013, 1, 6942−6948.
(25) Zhang, G.; Shen, Z.; Liu, M.; Guo, C.; Sun, P.; Yuan, Z.; Li, B.;
Ding, D.; Chen, T. Synthesis and Characterization of Mesoporous
Ceria with Hierarchical Nanoarchitecture Controlled by Amino Acids.
J. Phys. Chem. B 2006, 110 (51), 25782−25790.
(4) Ratnasamy, C.; Wagner, J. Water gas shift catalysis. Catal. Rev.:
Sci. Eng. 2009, 51 (3), 325−440.
(5) Sutherland-Harper, S.; Taylor, R.; Hobbs, J.; Pimblott, S.;
Pattrick, R.; Sarsfield, M.; Denecke, M.; Livens, F.; Kaltsoyannis, N.;
Arey, B.; Kovarik, L.; Engelhard, M.; Waters, J.; Pearce, C. Surface
speciation and interactions between adsorbed chloride and water on
cerium dioxide. J. Solid State Chem. 2018, 262, 16−25.
(6) Watkinson, E. J.; Ambrosi, R. M.; Williams, H. R.; Sarsfield, M.
J.; Stephenson, K.; Weston, D. P.; Marsh, N.; Haidon, C. Cerium
neodymium oxide solid solution synthesis as a potential analogue for
substoichiometric AmO2 for radioisotope power systems. J. Nucl.
Mater. 2017, 486, 308−322.
̀
̈
(26) Popa, K.; Walter, O.; Dieste-Blanco, O.; Guiot, A.; Bouexiere,
D.; Colle, J.-Y.; Martel, L.; Naji, N.; Manara, D. A low-temperature
synthesis method for AnO2 nanocrystals (An = Th, U, Np, and Pu)
and associate solid solutions. CrystEngComm 2018, 20, 4614−4622.
̌
(27) Tyrpekl, V.; Belis, M.; Wangle, T.; Vleugels, J.; Verwerft, M.
Alterations of thorium oxalate morphology by changing elementary
(7) Melchionna, M.; Fornasiero, P. The role of ceria-based
nanostructured materials in energy applications. Mater. Today 2014,
17 (7), 349−357.
precipitation conditions. J. Nucl. Mater. 2017, 493, 255−263.
̌
̌
̌
(28) Petrícek, V.; Dusek, M.; Palatinus, L. Crystallographic
computing system JANA2006: general features. Z. Kristallogr. -
Cryst. Mater. 2014, 229, 345−352.
(8) Chen, P.-L.; Chen, I.-W. Reactive cerium IV oxide powders by
the homogeneous precipitation method. J. Am. Ceram. Soc. 1993, 76
(6), 1577−1583.
(29) Williamson, G.; Hall, W. X-ray line broadening from filed
aluminium and wolfram. Acta Metall. 1953, 1, 22−31.
(30) Crouthamel, C. E.; Martin, D. S. Solubility of the rare earth
oxalates and complex ion formation in oxalate solution. II.
Neodymium and cerium(III). J. Am. Chem. Soc. 1951, 73 (2), 569−
573.
(9) Reinhardt, K.; Winkler, H. Cerium Mischmetal, Cerium Alloys,
and Cerium Compounds. Ullmann’s Encyclopedia of Industrial
Chemistry 2000, DOI: 10.1002/14356007.a06_139.
(10) Dicerium trioxalate decahydrate, ICSD: 109637, Inorganic
Crystal Structure Database, http://www2.fiz-karlsruhe.de/icsd_home.
html, January 2018.
́
(31) Rodríguez-Ruiz, I.; Teychene, S.; Vitry, Y.; Biscans, B.;
Charton, S. Thermodynamic modeling of neodymium and cerium
oxalates reactive precipitation in concentrated nitric acid media.
Chem. Eng. Sci. 2018, 183, 20−25.
(11) Ollendorff, W.; Weigel, F. The crystal structure of some
lanthanide oxalate decahydrates, Ln2(C2O4)3·10H2O, with Ln = La,
Ce, Pr, and Nd. Inorg. Nucl. Chem. Lett. 1969, 5 (4), 263−269.
G
DOI: 10.1021/acs.inorgchem.9b01250
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(32) El-Houte, S.; El-Sayed Ali, M. Thermal decomposition of
cerium oxalate and mixed cerium-gadolinium oxalates. J. Therm. Anal.
1991, 37, 907−913.
(33) Altas, Y.; Tel, H. Structural and thermal investigations on
cerium oxlatae and derived oxide powders for the preparation of
(Th,Ce)O2 pellets. J. Nucl. Mater. 2001, 298 (3), 316−320.
(34) Martinez, J.; Clavier, N.; Ducasse, T.; Mesbah, A.; Audubert, F.;
Corso, B.; Vigier, N.; Dacheux, N. From uranium(IV) oxalate to
sintered UO2: Consequences of the powders’ thermal history on the
microstructure. J. Eur. Ceram. Soc. 2015, 35 (16), 4535−4546.
(35) De Almeida, L.; Grandjean, S.; Vigier, N.; Patisson, F. Insights
into the Thermal Decomposition of Lanthanide(III) and Actinide-
(III) Oxalates − from Neodymium and Cerium to Plutonium. Eur. J.
Inorg. Chem. 2012, 2012 (31), 4986−4999.
(36) Filtschew, A.; Hofmann, K.; Hess, C. Ceria and Its Defect
Structure: New Insights from a Combined Spectroscopic Approach. J.
Phys. Chem. C 2016, 120, 6694−6703.
(37) Nakajima, A.; Yoshihara, A.; Ishigame, M. Defect induced
Raman spectra in doped CeO2. Phys. Rev. B: Condens. Matter Mater.
Phys. 1994, 50, 13297−13307.
(38) Chen, P.-L.; Chen, I.-W. Grain growth in CeO2“ Dopant
effects, Defect mechanism, and solute drag. J. Am. Ceram. Soc. 1996,
79 (7), 1793−1800.
(39) Rahaman, M. N. Ceramics processing and sintering, 2nd ed.; CRC
Press, 2003.
(40) Carter, C. B.; Norton, M. G. Sintering and Grain Growth. In
Ceramic Materials; Springer: New York, NY, 2013.
H
DOI: 10.1021/acs.inorgchem.9b01250
Inorg. Chem. XXXX, XXX, XXX−XXX