Journal of Alloys and Compounds 578 (2013) 26–31

Contents lists available at SciVerse ScienceDirect

Journal of Alloys and Compounds

journal homepage: www.elsevier .com/locate / ja lcom

Thermal stability of Ce1�xBixO2�d (x = 0.1–0.5) solid solution

0925-8388/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.jallcom.2013.05.006

⇑ Corresponding author. Tel./fax: +381 11 3408224.E-mail address: prekajski@vinca.rs (M. Prekajski).

Marija Prekajski a,⇑, Viktor Fruth b, Cristian Andronescu b, Lidija V. Trandafilovic a, Jelena Pantic a,Aleksandar Kremenovic c, Branko Matovic a

a Vinca Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522, 11001 Belgrade, Serbiab Institute of Physical Chemistry, Romanian Academy, 202 Splaiul Independentei Street, Bucharest 060021, Romaniac Faculty of Mining and Geology, University of Belgrade, Ðušina 7, 11000 Belgrade, Serbia

a r t i c l e i n f o a b s t r a c t

Article history:Received 26 December 2012Received in revised form 19 April 2013Accepted 2 May 2013Available online 9 May 2013

Keywords:Ce1�xBixO2�d

Nanostructured materialsThermal stabilityX-ray diffractionThermal analysis

Single phase solid solution Ce1�xBixO2�d with the composition of x = 0.1–0.5 were successfully synthe-sized at room temperature using simple and fast Self Propagating Room Temperature procedure(SPRT). Thermal stability of these solid solutions with different concentration of Bi cation was investi-gated at various temperatures up to 1400 �C by applying thermogravimetric analysis (DTA/DTG/TG).Powders were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM)and Infra Red spectroscopy (IR). It was revealed that all samples with concentration of bismuth higherthan 10 at.% are unstable during thermal treatment, resulting in Bi leaving the structure of ceria andformation of b-Bi2O3 as second phase. Moreover, at a certain temperatures bismuth begins toevaporate.

� 2013 Elsevier B.V. All rights reserved.

1. Introduction

Ceria-base nanocrystalline powders have been considered asan interesting material for application in catalysis [1], fuel cells[2], ultraviolet absorbers [3], hydrogen storage materials [4], oxy-gen sensors [5], optical devices [6] polishing materials [7] andothers. In CeO2, the facile Ce4+/Ce3+ redox cycle often leads to ahigher oxygen-storage capacity with reversible addition and re-moval of oxygen in the fluorite structure of ceria. The better re-dox properties than those of CeO2 alone were obtained by theincorporation of metal ions into the CeO2 lattice forming Ce1�xMx-

Oy solid solutions, such as Al, Zr, Hf, Si, and La [8–14]. Recently,much effort has been focused on the doping with cations thathave oxidation states lower than 4+. The purpose is to modifythe chemical and physical properties by creating oxygen vacan-cies inside the parent oxide [15–17]. Surface oxygen and oxygenvacancies are involved in catalytic activity, and enhanced oxygenmobility will enable the occurrence of redox processes at lowertemperatures.

Solid solutions (CeO2)1�x(BiO1.5)x might be of a high interest forcatalytic applications [18] and integration in gas sensors [19].Moreover, system is expected to be a novel electrolyte exhibitingnew electrochemical transport properties because ceria-based so-

lid solutions doped with lower valence ions usually possess oxideion conductivity higher than yttrium-stabilized zirconia (YSZ)and because the oxide ionic conductivity of d-Bi2O3 is the highestto date [20].

Reports about CeO2–Bi2O3 compounds showed that the possi-bility of obtaining a pure single-phase solid solution was depend-ing on the synthesis route. In our previous work, nanosized solidsolution was successfully synthesized at room temperature byusing Self Propagating Room Temperature procedure (SPRT) [21].

Nonequilibrium conditions are responsible for high solubility ofBi3+ in CeO2 lattice and it can be said that solubility of Bi3+ is highlydependent on synthesis condition, primarily temperature condi-tion. Authors who had used higher temperatures for synthesis(260–600 �C) [19,20,22] as a result had a solubility only up to10% or 15%. On the other hand, we have used room temperaturesynthesis procedure and found that solubility of Bi in CeO2 is about50%. Similar results were obtained also by Gangsehe and coauthors[23] that had used low hydrothermal synthesis route operating at240 �C.

If a compound has to be used as electrolyte material in SOFC’sthan it has to be stable in certain temperature range. However,very few data are available about the thermal stability of these so-lid solutions at higher temperatures. That is why we wanted toinvestigate thermal stability of these solid solutions synthesizedby SPRT method, with different concentration of Bi, at varioustemperatures.

M. Prekajski et al. / Journal of Alloys and Compounds 578 (2013) 26–31 27

2. Experimental

Nanocrystalline CeO2–Bi2O3 was synthesized by a SPRT method using ceriumnitrate hexahydrate (Riedel-de Haën, 99% purity), bismuth nitrate pentahydrate(Riedel-de Haën, 99% purity) and sodium hydroxide (Lach-Ner, 99% purity) as start-ing materials. Amounts of reactants for synthesis of Ce1�xBixO2�d nanopowders wascalculated according to equation:

ð1� xÞCeðNO3Þ3:6H2Oþ xBiðNO3Þ3:5H2Oþ 3NaOHþ ð1=2� dÞO2

! Ce1�xBixO2�d þ 3NaNO3 þ yH2O ð1Þ

Synthesis of nanopowders was carried out in an alumina mortar mixing reac-tants for 5–7 min, allowing rapid progress of the reaction at room temperature inthe air. After being exposed to air for 3 h, the entire volume of the powder was dis-solved in water and subjected to centrifugation at Centurion 1020D centrifuge at3000 rpm, for 10 min. Rinsing procedure was repeated four times with distilledwater and twice with ethanol, order to eliminate NaNO3 from the synthesized pow-der mixture. At the end, material was dried out at 60 �C in ambient atmosphere.

Synthesized powders were characterized and details can be found in our previ-ous work [21]. X-ray powder diffraction analysis of as synthesized samples showedthat the ceria powders with up to 50% of Bi are solid solutions with fluorite type ofstructure [21]. All synthesized powders have particle size in nanometric range (lessthan 4 nm) [21]. Raman spectral studies confirmed that all synthesized powders aresingle-phase solid solutions [21].

Samples of Ce1�xBixO2�d solid solutions with composition x = 0.1–0.5 whichwere previously obtained at room temperature, were calcinated for 1 h at differenttemperatures from 600� up to 1200 �C and then quenched to room temperature.Heating rate was 10 �C/min.

The X-ray powder analysis was used to identify the crystalline phases as well asto calculate lattice parameters of solid solutions of obtained powders. Powder XRPDpatterns of all samples heat treated at different temperatures were recorded on Sie-mens D-500 X-ray Powder Diffractometer with Ni filtered Cu Ka1,2 radiation. Themeasurements were performed in the 2h range from 20� to 80� with the step of0.02� and scanning time of 12 s per step. Calculation of the average crystallite size(D) was performed on the basis of the full width at half maximum intensity(FWHM) of the 111, 200, 220 and 311 reflections of CeO2 by using Scherrer’sformula:

Dhkl ¼Kk

b cos hð2Þ

where k is the wavelengths of the X-rays, h is diffraction angle, b is corrected half-width for instrumental broadening b = (bm � bs), bm observed half-width and bs ishalf-width of the standard CeO2 sample.

Values of lattice parameters with standard deviation [24] of all powders werecalculated based on collected XRPD data according to the formula:

4 sin2 h

k2 ¼ 1

d2hkl

¼ h2 þ k2 þ l2

a2 ð3Þ

Thermogravimetric and thermodifferential analysis (DTA/TGA) were performedusing a Mettler Toledo TGA/SDTA851e equipment at a heating rate of 10 �C/min�1,in air, with typically 20 mg sample.

FTIR spectroscopic analyses were carried out at room temperature using a Nico-let 380 spectrophotometer in the spectral range from 400 to 4000 cm�1, with a res-olution of 4 cm�1. The datasets were averaged over 200 scans.

For microstructural studies it was used JOEL JSM-6610LV scanning electronmicroscope (SEM). Semi-quantitative analysis was determinated by making a useof energy dispersive X-ray analysis (EDX) on X-Max Large Area SDD EDXspectrometer.

3. Results and discussion

The XRPD patterns of annealed CeO2 samples with concentra-tions of Bi3+ from 10% to 50% are represented at Fig. 1a–c. Severalgeneral observations can be made from Fig. 1:

– in all samples CeO2 with fluorite type of structure is principlephase,

– it is notable that with increasing temperature peaks becomemore narrow and more intense due to crystal structure arrange-ment and crystal growth,

– in samples with higher concentration of Bi3+ there is segrega-tion of additional two phases with increasing of temperature,

– further increasing of temperature leads to the disappearance ofone additional phase.

Observing the diagrams of Ce0.90Bi0.10O2�d sample (Fig. 1) itseems that the powder with 10% of Bi is stable and alwaysmonophased in investigated temperature range.

However, in sample with 20% of Bi at temperatures of 900 and1000 �C a Bi-rich secondary phase was formed (Fig. 2). That phasehas been identified as tetragonal b0 phase of Bi2O3 [19] and it ismarked with an asterisk in Fig. 1. It is interesting that at tempera-tures above 1000� there are no additional peaks that correspond tob0 phase of Bi2O3. This could be explained by evaporation of smallamount of Bi. It is known that Bi has a high vapor pressure at rel-atively low temperatures, therefore melts, and easily evaporates atexperimental condition [25].

In samples with 30% and 40% of Bi3+ onset of the second phasein the form of b0-Bi2O3 begins around 800 �C. However, at 1000 �Cthe phase evolution becomes more complex. Namely, tetragonal b-Bi2O3 appears as a third phase (filled circles in Fig. 1). Concentra-tion of this Bi phase reaches its maximum at 1100 �C, and beginsto decrease at 1200 �C due to evaporation.

Finally at very high concentrations of Bi of even 50% – segrega-tion of secondary b0 phase occurs already at 700 �C. Further in-crease in temperature leads to the formation of a third phase inthe form of b-Bi2O3 at a temperature of 900 �C. Since all analyzedsamples in these work were recorded on the same device and thesame conditions was used during recording, X-ray powder patternscan be compared with each other. In this respect, peak intensitiesshow the concentration of the given phase in the sample. Byobserving the diagram (Fig. 1c) it can be noted that with increasingtemperature there is a decrease in the intensity of the b0-Bi2O3 peakphase until their complete disappearance (asterisk in Fig. 1). Simul-taneously, peak intensities of the b-Bi2O3 increase with tempera-ture up to 1200 �C when it starts to decline (filled circles inFig. 1). It is notable that increasing concentration of b-Bi2O3 phase,amount of b0-Bi2O3 decrease, which suggest that on higher temper-atures Bi has a greater tendency to form b-Bi2O3.

It is known that CeO2 can stabilize b-Bi2O3 phase. Namely, ceriamay act as an extrinsic nucleus for the formation of b-Bi2O3 be-cause CeO2 lowers its free energy of formation compared to thatof a-Bi2O3 built on lattice vectors (2a

p2, 2a

p2, a) [23,26].

Calculated lattice parameters for all samples are shown in Ta-ble 1. In the whole temperature range the lattice parameters in-crease with increasing of Bi3+ concentration according to theVegard’s rule. According to Shannon’s compilation the ionic radiiof Ce4+ and Bi3+ for CN 8, are 0.97 and 1.17 Å, respectively [27].Thus, increasing Bi3+ concentration will keep on enlarging cell lat-tice. On the other hand, increasing of temperature leads to surpris-ing reduction in the unit cell size that can be explained by at leastby two effects. First, increasing of temperature leads to better crys-tallization of ceria with fluorite type of structure. As crystal be-comes larger, cell parameters decrease [28]. Second reason lies infact that at certain temperature Bi ion leaves the fluorite structureof Ce1�xBixO2�d and appears in the form of b0-Bi2O3 and b-Bi2O3.However, unit cell parameter of compounds with different concen-tration of Bi at each studied temperature increase with increasingof Bi content, which indicates that in the crystal lattice of CeO2

there is still a certain amount of Bi. Crystallite size values (Table 2)decreases with increasing of Bi concentration that is common phe-nomena in doped CeO2 systems [29]. Nevertheless, crystallite sizeincreases with increasing calcinations temperature owing to crys-tallization. This can be seen at the diagrams (Fig. 1) as sharpeningeffect of reflections.

TG–DTA curves of the ceria powders with concentration of Bifrom 10 to 40 mol% are shown in Fig. 2. Complete thermal processcan be divided into four stages. At the first one, DTA curves showan endothermic peak at �80 �C, followed by weight loss of �8%.This weight loss probably corresponds to the evaporation of water

Fig. 1. XRPD patterns of Ce1�xBixO2�d samples after heating at temperatures from 600 to 1200 �C: (a) Ce0.90Bi0.10O2�d, (b) Ce0.80Bi0.20O2�d, (c) Ce0.70Bi0.30O2-d, (d)Ce0.60Bi0.40O2�d and (e) Ce0.50Bi0.50O2�d. (mark ‘‘⁄’’ represents b0-Bi2O3 while and mark ‘‘d’’ represents b-Bi2O3).

28 M. Prekajski et al. / Journal of Alloys and Compounds 578 (2013) 26–31

absorbed by crystalline ceria. In the second stage, exothermal peakwith weight loss of �5% exists at about 230 to 260 �C. It was as-sumed that it comes from the decomposition of residual nitrates.

Total weight loss for these two stages is �13% (Table 3). Signif-icant weight lost indicates that as prepared samples were alsoslightly hydrated. These mass loss corresponds to the decomposi-tion of Ce(OH)3 or Ce(OH)4/CeO2�2H2O, indicating either a partiallyhydrated (CeO2�H2O) or a mixture (CeO2 + CeO2�H2O) of ceriaphases [30,31]. In addition, an exothermic peak around 270–350 �C, correlated to a weight loss of �5%, must be considered ascombination of decomposition of hydrated CeO2, the crystalliza-

tion of the residual amorphous phase and decomposition of the ni-trates group.

According to literature, Ce4+ ions could be hydrolyzed and couldform complexes with water molecules or OH� to give [Ce(OH)x(H2-

O)y](4�x)+, where x + y represent the coordination number of Ce4+.In an aqueous solution, H2O, being a polar molecule, tends to takeprotons away from coordinated hydroxide, leading to the forma-tion of CeO2�nH2O. This process can be described by the followingequations [32]:

Ce4þ þ xOHþ yH2O! CeðOHÞxðH2OÞyh ið4�xÞþ1

ð4Þ

200 400 600 800 1000 1200 1400

65

70

75

80

85

90

95

100

TG

DTA

Wei

ght l

oss

[%]

Temperature [°C]

Exo

75

80

85

90

95

100

TG

DTA

Wei

ght l

oss

[%]

Temperature [°C]

Exo

55

60

65

70

75

80

85

90

95

100

TG

DTA

Wei

ght l

oss

[%]

Temperature [°C]

Exo

55

60

65

70

75

80

85

90

95

100

TG

DTA

Wei

ght l

oss

[%]

Temperature [°C]

Exo

200 400 600 800 1000 1200 1400200 400 600 800 1000 1200 1400

200 400 600 800 1000 1200 1400

(a) (b)

(c) (d)

Fig. 2. DTA/DTG/TGA curves of the as-synthesized Ce1�xBixO2�d powders with different Bi concentration: (a) Ce0,9Bi0,1O2�d; (b) Ce0,8Bi0,2O2�d; (c) Ce0,7Bi0,3O2�d and (d)Ce0,6Bi0,4O2�d.

Table 1Calculated unit cell parameters of Ce1�xBixO2�d (x = 0.1–0.5) samples calcinated at different temperatures. Values are given in nanometers.

Sample 600 �C 700 �C 800 �C 900 �C 1000 �C 1100 �C 1200 �C

Ce0.9Bi0.1O2�d 0.5422(3) 0.5423(3) 0.5421(2) 0.5416(1) 0.5411(6) 0.5405(8) 0.5404(8)Ce0.8Bi0.3O2�d 0.5439(2) 0.5433(3) 0.5428(9) 0.5429(3) 0.5417(4) 0.5405(7) 0.5404(8)Ce0.7Bi0.3O2�d 0.5447(4) 0.5444(4) 0.5431(7) 0.5428(5) 0.5417(6) 0.5409(5) 0.5407(5)Ce0.6Bi0.4O2�d 0.5462(5) 0.5457(1) 0.5449(4) 0.5432(5) 0.5425(7) 0.5417(9) 0.5414(1)Ce0.5Bi0.5O2�d 0.5477(7) 0.5463(6) 0.5459(6) 0.5438(2) 0.5424(9) 0.5412(3) 0.5415(1)

Table 2Calculated crystallite size of Ce1�xBixO2�d (x = 0.1–0.5) samples calcinated at different temperatures. Values are given in nanometers.

Sample 600 �C 700 �C 800 �C 900 �C 1000 �C 1100 �C 1200 �C

Ce0.9Bi0.1O2�d 10 14 27 40 66 124 158Ce0.8Bi0.3O2�d 8 12 19 26 44 118 153Ce0.7Bi0.3O2�d 9 11 16 22 37 96 154Ce0.6Bi0.4O2�d 10 12 19 22 36 79 133Ce0.5Bi0.5O2�d 9 12 16 18 54 90 142

Average value 9 12 19 26 47 102 148

Table 3Weight loss of samples Ce1�xBixO2�d with composition x = 0.1–0.4 during the thermaltreatment.

Weight loss (%) Total weight loss (%)

30–450 �C 1200–1400 �C

Ce0.9Bi0.1O2�d 13.6 8.7 22.3Ce0.8Bi0.3O2�d 13.3 18.1 31.4Ce0.7Bi0.3O2�d 15.7 28.0 44.0Ce0.6Bi0.4O2�d 11.2 28.9 40.1

M. Prekajski et al. / Journal of Alloys and Compounds 578 (2013) 26–31 29

CeðOHÞxðH2OÞyh ið4�xÞ

þH2O! CeO2 � nH2Oþ nH2OÞ þH3Oþ ð5Þ

On the other hand, presence of residual nitrates is not surpris-ing, forasmuch synthesis procedure in which metal nitrates wereused as starting materials. In these stages, major weight loss hasoccurred up to �200 �C, but much higher temperature of �500 �Cseems necessary for a complete dehydration. During heating of hy-drated samples, it comes to the decomposition of adsorbed watermolecules and residual nitrates. Resulting gases are released byevaporation. After the temperature reaches 500 �C, the mass ofthe sample keeps invariableness up to 1200 �C.

4000 3500 3000 2500 2000 1500 1000 500

440

1636

836

1035

1461

1306

590 °C

230 °C

85 °C

Inte

sity

(a.

u.)

Wavenumbers (cm-1)

as-prepared

3237

Fig. 3. FTIR patterns of Ce0,7Bi0,3O2�d sample calcined under different temperatures,according to the DTA/TG measurements.

Table 4EDX microanalysis of the as-prepared Ce0.5Bi0.5O2�d sample and calcinated atdifferent temperatures.

Nominal chemical composition EDX determinated chemical composition

Ce0.50Bi0.50O2�d as-prepared Ce0.48Bi0.52O1.74

Ce0.50Bi0.50O2�d at 700 �C Ce0.50Bi0.50O1.75

Ce0.50Bi0.50O2�d at 1000 �C Ce0.60Bi0.40O1.80

Ce0.50Bi0.50O2�d at 1200 �C Ce0.90Bi0.10O1.95

30 M. Prekajski et al. / Journal of Alloys and Compounds 578 (2013) 26–31

The third stage shows small exothermic reactions in the tem-perature region from 200 to 700 �C with maximum at�550 �C. Thisreaction is not accompanied by any changes in the mass. Based onXRPD diagrams it can be attributed to the crystallization reactionof Bi reach secondary phases.

The last phase in thermogravimetric evolution of examinedsamples is major endothermic reaction at about 1400 �C, whichrepresents melting and evaporating process of Bi compounds. Forevery analyzed sample with different concentration of Bi thesereaction starts at 1200 �C but the end of reaction depends on theconcentration of Bi. Namely, as the amount of Bi increase, end ofthe reaction is shifted towards higher temperature. The amountof evaporated bismuth is higher as its initial concentration in thesample was greater.

Fig. 4. SEM images of samples Ce0,90Bi0,10O2�d calcinated at (a) 700 �C, (

The origin of mass loss that occurs during thermal treatment upto 500 �C was tested using FTIR method. Fig. 3. shows FTIR spectraof as prepared Ce0,7Bi0,3O2�d sample, and the same sample ther-mally treated at different temperatures at which the DTA analysisreported peaks. FTIR spectrum of the as-prepared CeO2 sampleFig. 3, shows a group of strong intense bands at 3237, 1461,1306 cm�1 and below 500 cm�1. The spectrum also shows peaksof lower intensity at 1636, 1035 and 836 cm�1.

In lights of the proposed assignments of such peaks in othersimilar systems, [33–35] the observed bands can be assigned asfollows: wide band at about 3237 cm�1 is typical for OAH [30],which corresponds to the physically adsorbed water on the sample.Band at 1636 cm�1 corresponds to the d(OH) mode [33]. The exis-tence of residual or adsorbed water molecules and hydroxidegroups in the ceria-based samples is very common [36–39]. Thewide band at 1306 cm�1 consists of the symmetrical stretchingmode of N@O and the inside bending mode of NAH [36]. The out-side bending mode of NAH is at 836 cm�1. Minor mode which oc-curs at 1461 cm�1 corresponds to vibrations of CH3 molecules. Theexistence of these organic molecules is the result of processingwhere the last step is rinsing of the samples with alcohol. Intenseabsorption band that appears at wavelengths below 500 cm�1 rep-resents the stretching vibration of molecules in the structure ofcerium oxide, i.e. d(Ce–O–Bi) mode [36,40].

FTIR spectra of thermally treated samples show a gradual disap-pearance of the absorption bands, which corresponds to vibrationsof adsorbed water molecules and residual nitrates (Fig. 3). First,

b) 1200 �C and Ce0,50Bi0,50O2�d calcinated at (c) 700 �C, (d) 1200 �C.

M. Prekajski et al. / Journal of Alloys and Compounds 578 (2013) 26–31 31

there is a decrease and then loss of bands at the 3237 and1636 cm�1 which corresponds to adsorbed water. These bands al-most completely disappear at 230 �C (Fig. 3). Temperatures above500 �C lead to the decomposition of nitrates groups, and thus thedisappearance of the vibration bands that belong to them. In theend, there remains only the peak corresponding to d(Ce–Bi–O)mode (Fig. 3). The results of the FTIR analysis confirmed theassumption that the mass loss that occurs during the heat treat-ment up to 500 �C of the Ce1�xBixO2�d samples originates from ad-sorbed water (i.e. moisture) and residual nitrate.

SEM images of samples Ce0,90Bi0,10O2�d and Ce0,50Bi0,50O2�d cal-cinated at 700 and 1200 �C are represented at Fig. 4a–d respec-tively. It reveals that morphologies of powders annealed at700 �C is cemented in a form of agglomerated lumps. Further in-crease in annealing temperature changes the morphology of thepowder. Fig. 4b and d show that agglomerates in sample annealedat 1200 �C are joined into bigger body but still without clear crystalforms. The change in morphology can be ascribed to high anneal-ing temperature that provides fast diffusion necessary for crystal-lite growth. It can be roughly estimated that the particle size ofsample annealed at 1200 �C lies in the range of 100–200 nm.

Semi-quantitative chemical analysis was done on samplesdoped with 50% Bi, and the results are shown in Table 4. It revealedthat as prepared sample and sample thermally treated at 700 �Chave chemical composition very similar with desired one, whichis not the case with samples calcinated at higher temperatures thatare subject to significant loss of Bi. These results confirm theassumption that at high temperature (above 1000 �C) comes to aloss of Bi from the samples, by the process of evaporation.

4. Conclusions

Investigation of thermal stability of Ce1�xBixO2�d solid solutionwith the composition of x = 0.1–0.5 synthesized by SPRT method,was done. At room temperature, these solid solutions are stable.Nonequilibrium conditions are responsible for high solubility ofBi3+ in CeO2 lattice. Nevertheless, at high temperatures these solidsolutions become unstable, except the Ce0,90Bi0,10O2�d samplewhich remains monophased in investigated temperature range.Based on the X-ray powder reflection results obtained in this workit can be said that samples with higher concentration of Bi3+ attemperatures above 700 �C comes to segregation of secondaryphases in form of b0-Bi2O3 and b-Bi2O3. At temperatures above1200 �C Bi tends to completely leave the mixture by evaporating,which was confirmed by DTA/TGA analysis. According to observedresults of peak intensities analysis of powder patterns it seems thatcompounds with a higher concentration of Bi are less stable, interms of forming greater amount of undesirable secondary phases.In addition, as DTA/TGA analysis showed that concentration ofevaporated Bi is in accordance with its initial concentration inthe sample. Therefore, it can be said that as concentration of Bi in-creases, stability of CeO2–Bi2O3 solid solution at high temperaturesdecreases. Thermal instabilities, which were revealed in this paper,should be kept in mind when potential application is concerned.

Acknowledgement

This project was financially supported by the Ministry of Educa-tion and Science of the Republic of Serbia (Project Number: 45012).

References

[1] P. Bera, A. Gayen, M.S. Hegde, N.P. Lalla, L. Spadaro, F. Frusteri, J. Phys. Chem. B107 (2003) 6122–6130.

[2] G. Jacobs, L. Williams, U. Graham, D. Sparks, B.H. Davis, J. Phys. Chem. B 107(2003) 10398–10404.

[3] R.X. Li, S. Yabe, M. Yamashita, S. Momose, S. Yoshida, S. Yin, T. Sato, Solid StateIonics 151 (2002) 235–241.

[4] K. Sohlberg, S.T. Pantelides, S.F. Pennycook, J. Am. Chem. Soc. 123 (2001) 6609–6611.

[5] P. Jasinski, T. Suzuki, H.U. Anderson, Sens. Actuat. B 95 (2003) 73–77.[6] F. Goubin, X. Rocquefelte, M.H. Whangbo, Y. Montardi, R. Brec, S. Jobic, Chem.

Mater. 16 (2004) 662–669.[7] D.G. Shchukin, R.A. Caruso, Chem. Mater. 16 (2004) 2287–2292.[8] L. Li, G. Li, Y. Che, W. Su, Chem. Mater. 12 (2000) 2567–2574.[9] A. Bensalem, F. Bozon Verduraz, M. Delamar, G. Bugli, Appl. Catal. 121 (1995)

81–93.[10] R.K. Usman, G.W. Graham, W.L.H. Watkins, R.W. McCabe, Catal. Lett. 30 (1995)

53–63.[11] F. Zamar, A. Trovarelli, C. De Leitenburg, G. Dolcetti, J. Chem. Soc. Chem.

Commun. (1995) 965–966.[12] M. Luo, J. Chen, J. Lu, Z. Feng, C. Li, Chem. Mater. 13 (2001). 197–02.[13] A.I. Kozlov, D.H. Kim, A. Yezerets, P. Andersen, H.H. Kung, M.C. Kung, J. Catal.

209 (2002) 417–426.[14] N. Sergent, J. Lamonier, A. Aboukaïs, Chem. Mater. 12 (2000) 3830–3835.[15] P. Bera, K.R. Priolkar, P.R. Sarode, M.S. Hegde, S. Emura, R. Kumashiro, N.P.

Lalla, Chem. Mater. 14 (2002). 3591–01.[16] P. Bera, K.R. Priolkar, A. Gayen, P.R. Sarode, M.S. Hegde, S. Emura, R. Kumashiro,

V. Yayaram, G.N. Subbanna, Chem. Mater. 15 (2003) 2049–2060.[17] K.R. Priolkar, P. Bera, A. Gayen, P.R. Sarode, M.S. Hegde, S. Emura, R. Kumashiro,

N.P. Lalla, Chem. Mater. 14 (2002) 2120–2128.[18] L. Li, B. Yan, J. Non-Cryst. Solids 355 (2009) 776–779.[19] L. Bourja, B. Bakiz, A. Benlhachemi, M. Ezahri, J.C. Valmelette, S. Villain, J.R.

Gavarri, Adv. Mater. Sci. Eng. 2009 (2009) 1–4.[20] Z.C. Li, H. Zhang, B. Bergman, Ceram. Int. 34 (2008) 1949–1953.[21] M. Prekajski, Z. Dohcevic-Mitrovic, M. Radovic, B. Babic, J. Pantic, A.

Kremenovic, B. Matovic, J. Eur. Ceram. Soc. 32 (2012) 1983–1987.[22] S. Dikmen, P. Shuk, M. Greenblatt, Solid State Ionics 112 (1998) 299–307.[23] L. Guangshe, L. Liping, F. Shouhua, W. Minqiang, Z. Liangying, Y. Xi, Adv. Mater.

11 (1999) 146–149.[24] J.C. De Wijs, Acta Cryst. 3 (1950) 394.[25] P. Rice, D.V. Ragone, J. Chem. Phys. 45 (1966) 4141.[26] X.L. Chen, W. Eysel, J. Solid State Chem. 127 (1996) 128–130.[27] A. Shannon, Acta Crystallogr. A 32 (1976) 751–767.[28] A.E. Baranchikov, O.S. Polezhaeva, V.K. Ivanov, Y.D. Tretyakov, Cryst. Eng.

Commun. 12 (2010) 3531–3533.[29] B. Matovic, Z. Dohcevic-Mitrovic, M. Radovic, Z. Brankovic, G. Brankovic, S.

Boskovic, Z.V. Popovic, J. Powder Sources 193 (2009) 146–149.[30] M.L. Dos Santos, R.C. Lima, C.S. Riccardi, R.L. Tranquilin, P.R. Bueno, J.A. Varela,

E. Longo, Mater. Lett. 62 (2008) 4509–4511.[31] H.Z. Song, H.B. Wang, S.W. Zha, D.K. Peng, G.Y. Meng, Solid State Ionics 156

(2003) 249–254.[32] M. Hirano, M. Inagaki, J. Mater. Chem. 10 (2000) 473–477.[33] M. Zawadzki, J. Alloys Comp. 454 (2008) 347–351.[34] R. Cracium, W. Daniell, H. Knozinger, Appl. Catal. A Gen. 230 (2002) 153–168.[35] R.D. Maggio, R. Campostrini, G. Guella, Chem. Mater. 10 (1998) 3839–3847.[36] X. Yu, P. Ye, L. Yang, S. Yang, P. Zhou, W. Gao, J. Mater. Res. 22 (2007) 3006–

3013.[37] M.S. Khalil, L.A. Elkabee, B. Murphy, Microporous Mesopororous Mater. 78

(2005) 83–89.[38] L. Li, Y. Chen, Mater. Sci. Eng. A 406 (2005) 180–185.[39] D. Terrible, A. Trovarelli, J. Llorca, C. Leittenburg, G. Dolcetti, J. Catal. 178

(1998) 299–308.[40] C. Ho, J.C. Yu, T. Kwong, A.C. Mak, S. Lai, Chem. Mater. 17 (2005) 4514–4522.