Preparation, stability and thermodynamic properties of Nd- and Lu-doped BaCeO3 proton-conducting ceramics

Article abstract of DOI:10.1002/ejic.200800589

The preparation of BaCeO₃ doped by neodymium and lute-tium oxides (BaCe_0.8Nd_0.2O_2.9, BaCe _0.8Lu_0.2O_2.9) has been performed by solid-state reactions of BaCO₃ and CeO

Full text of DOI:10.1002/ejic.200800589

FULL PAPER
DOI: 10.1002/ejic.200800589
Preparation, Stability and Thermodynamic Properties of Nd- and Lu-Doped
BaCeO Proton-Conducting Ceramics
3
[a]
[b]
[a]
Nata I. Matskevich, Thomas Wolf, Mariya Yu. Matskevich,* and
Tatiana I. Chupakhina[
c]
Keywords: Ceramics / Rare earths / Calorimetry / Thermodynamics / Solid-state reactions
The preparation of BaCeO
tium oxides (BaCe0.8Nd0.2
performed by solid-state reactions of BaCO
3
doped by neodymium and lute-
2.9) has been
and CeO with
, respectively. The compound BaCe0.8
2.9 has been synthesized for the first time. The X-ray
2.9 (RE = Nd,
Lu) has an orthorhombic structure (space group Pnma). The
standard formation enthalpies of BaCe0.8RE0.2 2.9 have been
determined from solution calorimetry by combining the solu-
tion enthalpies of BaCe0.8RE0.2 2.9, a BaCl + 0.8CeCl
.2RECl mixture in 1 HCl with 0.1 KI at 298.15 K and
literature data. It has been determined that both of the
above-mentioned complex oxides are thermodynamically
stable with regard to their decomposition into binary oxides
at room temperature. It has been established that
O
2.9, BaCe0.8Lu0.2O
3
2
Nd
2
O
3
and Lu
2
O
3
-
Lu0.2
O
BaCe0.8Nd0.2
Al O and ZrO
2 3 2
O
2.9 and BaCe0.8Lu0.2
O
2.9 react with water,
at ambient temperatures. It has also been
shown that the reactions with Al , ZrO and water for
2.9 are more thermodynamically favoured than
those for BaCe0.8Lu0.2
measurements have showed that BaCe0.8RE0.2
O
2
O
3
2
O
BaCe0.8Nd0.2O
O .
2.9
O
2
3
+
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
0
3
M
M
Introduction
Thermodynamics may be useful in other aspects as well. In
some cases it is possible to see the direction in which func-
tional properties change on the basis of correlations be-
tween thermodynamic and conductivity properties. How-
ever, there are no thermodynamic values for compounds in
the systems BaO–CeO –RE O . There are only formation
At present the interest in perovskite-type solid solutions
based on alkaline earth cerates is large.[
1–10]
Rare-earth-
doped barium cerates with high protonic conductivity have
a wide range of technological applications in fuel cells, sen-
sors, batteries, electro catalysis devices, etc. The investiga-
tion of proton conductivity in perovskite ceramics started
more than 20 years ago. A number of reports were pub-
lished with regard to the conduction of BaCeO -based
oxides. Neodymium-doped barium cerates are believed to
be the most conductive electrolytes.
2
2
3
enthalpies, heat capacities and entropies for BaCeO , mea-
3
[6–9]
sured by authors.
Thermodynamic properties linked to
structural characteristics have been used to develop system-
atic structure-stability relationships for solid solutions of
3
BaCe1–xRE O3–δ.
x
This paper is part of our wide investigations devoted to
the synthesis and study of the thermodynamics of com-
pounds in the BaO–CeO –RE O systems. The aim is to
However, there is still a lack of studies on other proper-
ties of these materials. In particular, the thermodynamics of
2
2
3
BaCe1–xRE O
compounds has been little studied. The
x
3–δ
prepare known and unknown doped BaCeO to investigate
3
stabilities of these phases, in particular thermodynamic sta-
bility, are interesting and important[1] in order to underpin
further practical applications. The thermodynamic stability
of complex oxides may have an impact on the mechanical
stability of the microstructure of corresponding ceramics.
the thermochemistry of BaCe1–xNd O and BaCe1–xLux-
O3–δ solid solutions and to compare the stability and
thermodynamic values of these compounds.
x
3–δ
Results and Discussion
[
a] Nikolaev Institute of Inorganic Chemistry, Siberian Branch of
In the present study we report on the preparation of
BaCeO3 doped by neodymium and lutetium oxides
(BaCe0.8Nd0.2O2.9, BaCe0.8Lu0.2O2.9) and their thermo-
chemical properties. The compound BaCe0.8Lu0.2O2.9 has
been synthesized for the first time.
the Russian Academy of Science,
Lavrentiev Prospect, 3, Novosibirsk, 630090, Russia
Fax: +7-383-3306449
E-mail: nata@che.nsk.su
[
[
b] Karlsruhe Research Center GmbH, Institute of Solid State
Physics,
Hermann-von-Helmholtz-Platz 1, Karlsruhe, 76334, Germany
c] Institute of Solid State Chemistry, Ural Branch of the Russian
Academy of Science,
Previously, we used the expensive technique from
Karlsruhe Research Center that enables one to prepare dif-
[
11–13]
Pervomaiskaya Street, 91, Ekaterinburg, Russia
ferent complex oxides of high quality.
Eur. J. Inorg. Chem. 2009, 1477–1482
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1477

N. I. Matskevich, T. Wolf, M. Y. Matskevich, T. I. Chupakhina
The solution calorimetric experiments were carried out
FULL PAPER
Phase purity and identity of BaCe0.8Nd0.2O2.9 and
BaCe0.8Lu0.2O2.9 were confirmed by X-ray powder diffrac- in an automatic calorimeter with an isothermal jacket. The
tion (XRD) using a STADI-P, Stoe diffractometer, Ger- calorimeter consists of a Dewar vessel with a brass cover
many, Cu-Kα1 and ARL ADVANTЈXP sequential X-ray (V = 200 mL). The platinum resistance thermometer, cali-
Fluorescence Spectrometer. The samples were shown to be bration heater, cooler, mixer and device to break the am-
phase-pure ceramics with an orthorhombic structure (space poules were mounted on the lid of the Dewar vessel. The
group Pnma). The refined cell parameters obtained for Ba- construction of the solution calorimeter and the experimen-
Ce0.8Nd0.2O2.9 are a = 6.222(2) Å, b = 8.791(1) Å and c = tal procedure are described elsewhere.[12,17] The resistance
6
.224(2) Å and for BaCe0.8Lu0.2O2.9 are a = 6.181(2) Å, b of the platinum resistance thermometer was measured with
8.855(1) Å and c = 6.183(2) Å. The powder pattern and a high precision voltmeter Solartron 7061. The voltmeter
cell parameters of BaCe0.8Nd0.2O2.9 agree well with the pat- was connected to the computer through an interface and
=
terns known for this phase from the literature.[
14,15]
The the program was written in Matlab
[19]
at our laboratory.
powder X-ray diffraction pattern of barium cerate doped The program allows one to measure and record the tem-
by lutetium oxide is presented in Figure 1.
perature of the vessel, calibrate the instrument with precise
injections of electrical energy and calculate calorimeter con-
stants and enthalpies. The calorimetric vessel was main-
tained at 298.15 K with a temperature drift of less than
0.0003 °C for 10 h. Dissolution of potassium chloride in
water was performed to calibrate the calorimeter. The ob-
–
1
tained dissolution heat of KCl was 17.41Ϯ0.08 kJmol
–1
(
2
1
the molality of the final solution was 0.028 molkg , T =
–
1 [20]
98.15 K). The literature data are: 17.42Ϯ0.02 kJmol ,
–1 [21]
7.47Ϯ0.07 kJmol .
The amount of substance used (BaCe0.8Nd0.2O2.9, BaCe0.8
-
Lu0.2O2.9) was about 0.08 g for each compound. All com-
pounds were stored in a dry box to prevent interaction with
moisture or CO2.
In general, three techniques are used to determine the
enthalpy of formation at 298.15 K of metal cerates: solution
calorimetry, e.m.f. measurements and mass spectrometric
[
6–9]
Knudsen cell measurements.
In our paper we used solu-
2.9
Figure 1. Powder X-ray diffractogram of BaCe0.8Lu0.2O .
tion calorimetry as an investigation method. HCl (1 )
along with KI (0.1 ) was chosen as the solvent. KI was
added to reduce Ce to Ce .
All compounds were also characterized by chemical
+4
+3
[
16,17]
analysis.
Analytical results are presented in Table 1.
For the analysis of Nd, Ce and Lu a spectrophotometric
method (spectrophotometer SF–46) was used. Ba was de-
termined by flame photometry (air-acetylene, Hitachi Z-
BaCe0.8Nd0.2O2.9
The derivation of the enthalpy of formation of BaCe0.8
-
8000). The content of impurities was determined by spectral
Nd0.2O2.9 was done by using the following scheme of ther-
mochemical reactions (Table 2). The principal scheme is
based on the dissolution of barium cerate doped by neo-
dymium oxide as well as the mixture of barium chloride,
cerium chloride and neodymium chloride in hydrochloric
acid [HCl (sol)] with KI. The molar concentration of metal
methods (mass-spectrometer “Element”, Finnigan Mat,
Germany). The analyses indicated that impurities of Ho,
Dy, Eu, Yb, La, Tm, Er, Pr, Sm, Te, Ca, Mg, Mn, Pb and
–
3
–4
Ag metals were present at the level of 10 –10 at.%. The
oxygen contents were determined by iodometric titrations
using 0.01  Na S O ·5H O according to the method de-
2
2
3
2
[
6]
scribed in the literature.[
18]
chlorides was the same as in the literature. A mixture of
The results of the chemical
BaCl , CeCl3 and NdCl3 was prepared in a ratio of
analysis for BaCe0.8Nd0.2O2.9 and BaCe0.8Lu0.2O2.9 allow us
to conclude that these phases have the following composi-
2
1:0.8:0.2.
tions: BaCe0.81Ϯ0.03Nd0.19Ϯ0.02O2.92Ϯ0.03
Lu0.18Ϯ0.02O2.89Ϯ0.03
, BaCe0.78Ϯ0.03-
.
BaCe0.8Lu0.2O2.9
In order to determine the formation enthalpy of barium
cerate doped by lutetium oxide we chose a thermochemical
cycle in which we dissolved BaCe0.8Lu0.2O2.9 and a mixture
Table 1. Analytical results.
Compound Found (%)
Calculated (%)
of BaCl , CeCl and LuCl . A detailed scheme of the ther-
CeCl
BaCl
NdCl
LuCl
3
Ce, 56.81Ϯ 0.04
Ba, 65.93Ϯ0.05
Nd, 57.52Ϯ0.05
Lu, 61.13Ϯ0.07
Ce, 56.85
Ba, 65.95
Nd, 57.56
Lu, 61.19%
2
3
3
2
mochemical reactions for BaCe0.8Lu0.2O2.9 is given below
Table 3). The solvent was the same as that used for Ba-
Ce0.8Nd0.2O2.9, namely 1  HCl with 0.1  KI. A mixture
3
(
3
1478
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 1477–1482

3
Nd- and Lu-Doped BaCeO Proton-Conducting Ceramics
Table 2. Thermochemical cycle for the determination of the enthalpy of formation of BaCe0.8Nd0.2
Reactions
O
2.9.[a]
∆
solH°
m
[kJ]
Ref.
BaCe0.8Nd0.2
O
2.9(s) + (5.8HCl + 1.2KI)(sol) = (BaCl
O)(sol)
(s) + 0.8CeCl (s) + 0.2NdCl
(g) + 1.45O (g) + (solution 1) = 2.9H
.2KI(s) + (solution 1) = 1.2KI(sol)
2
+ 0.8CeCl
3
+ 0.2NdCl
3
+ 0.8KCl + (1)
–385.89Ϯ3.34
this work
3 2
0.4KI + 2.9H
BaCl
2
3
3
(s) + (solution 1) = (BaCl
O(sol)
2
+ 0.8CeCl + 0.2NdCl
3
3
)(sol) (2)
–144.26Ϯ0.61
–828.94Ϯ0.13
+25.00Ϯ0.53
–394.98Ϯ0.21
–121.10Ϯ0.14
+14.41Ϯ0.05
–349.17Ϯ0.13
–953.29Ϯ0.06
–855.15Ϯ1.73
–848.43Ϯ0.53
–208.11Ϯ1.26
–1631.59Ϯ4.10
this work
[
[
[
[
[
[
[
[
[
[
6]
6]
6]
6]
6]
6]
6]
6]
6]
20]
2
1
1
0
0
0
2
.9H
2
2
2
(3)
(4)
(5)
(6)
(7)
(8)
(9)
.2 K(s) + 0.6I
.4 K(s) + 0.6I
2
(s) = 1.2KI(s)
2
3
(s) + (solution 1) = 0.4KI (sol)
.8KCl(s) + (solution 1) = 0.8KCl(sol)
.8 K(s) + 0.4Cl (g) = 0.8KCl(s)
.9H (g) + 2.9Cl (g) + (solution 1) = 5.8HCl(sol)
(g) = BaCl (s)
.8Ce(s) + 1.2Cl (g) = 0.8CeCl
.2Nd(s) + 0.3Cl (g) = 0.2NdCl
2
2
2
Ba(s) + Cl
0
0
2
2
(10)
2
3
(s)
(s)
(11)
(12)
(13)
2
3
Ba(s) +0.2Nd(s) + 0.8Ce(s) + 1.45O
2
(g) = BaCe0.8Nd0.2
O2.9(s)
this work
[a] Solution 1 is a 1  solution of HCl with 0.1  KI.
Table 3. Thermochemical cycle for the determination of the enthalpy of formation of BaCe0.8Lu0.2
Reactions
O
2.9.[a]
∆
solH°
m
[kJ]
Ref.
BaCe0.8Lu0.2
O
2.9(s) + (5.8HCl + 1.2KI)(sol) = (BaCl
+ 2.9H O)(sol)
(s) + 0.8CeCl (s) + 0.2LuCl
(g) + 1.45O (g) + (solution 1) = 2.9H
.2KI(s) + (solution 1) = 1.2KI(sol)
2
+ 0.8CeCl
3
+ 0.2LuCl
3
+ 0.8KCl +
(14)
–358.40Ϯ3.71
this work
0.4KI
3
2
BaCl
2
3
3
(s) + (solution 1) = (BaCl
O(sol)
2
+ 0.8CeCl + 0.2NdCl
3
3
)(sol)
(15)
(16)
(17)
(18)
(19)
(20)
(21)
(22)
(23)
(24)
(25)
(26)
–156.98Ϯ0.61
–828.94Ϯ0.13
+25.00Ϯ0.53
–394.98Ϯ0.21
–121.10Ϯ0.14
+14.41Ϯ0.05
–349.17Ϯ0.13
–953.29Ϯ0.06
–855.15Ϯ1.73
–848.43Ϯ0.53
–197.42Ϯ0.50
–1661.11Ϯ4.25
this work
[
[
[
[
[
[
[
[
[
[
6]
6]
6]
6]
6]
6]
6]
6]
6]
20]
2
1
1
0
0
0
2
.9H
2
2
2
.2 K(s) + 0.6I
.4 K(s) + 0.6I
2
(s) = 1.2KI(s)
(s) = 0.4KI (sol)
2
3
.8KCl(s) + (solution 1) = 0.8KCl(sol)
.8 K(s) + 0.4Cl (g) = 0.8KCl(s)
.9H (g) + 2.9Cl (g) + (solution 1) = 5.8HCl(sol)
(g) = BaCl (s)
.8Ce(s) + 1.2Cl (g) = 0.8CeCl
.2Lu(s) + 0.3Cl (g) = 0.2LuCl
2
2
2
Ba(s) + Cl
0
0
2
2
2
3
(s)
(s)
2
3
Ba(s) + 0.2Lu(s) + 0.8Ce(s) + 1.45O
2
(g) = BaCe0.8Lu0.2
O2.9(s)
this work
[a] Solution 1 is a 1  solution of HCl with 0.1  KI.
of BaCl , CeCl and LuCl3 was prepared in a ratio of of different compounds and processes taken from ref.[6,20]
2
3
1:0.8:0.2.
and presented in Table 2.
The measured enthalpies of solution of BaCe0.8Nd0.2O2.9
The derivation of the enthalpy of formation of BaCe0.8-
and BaCl2 + 0.8CeCl3 + 0.2NdCl3 were determined as: Lu0.2O2.9 from the solution calorimetric data was done
–
1
∆solH° (298.15 K)
=
–385.89Ϯ3.34 kJmol
(n
= 5), using the dissolution enthalpies of barium cerate doped by
1
–
1
∆solH° (298.15 K) = –144.26Ϯ0.61 kJmol (n = 6). Errors lutetium oxide and the BaCl + 0.8CeCl + 0.2LuCl mix-
2
2
3
3
were calculated for the 95% confidence interval using stan- ture in hydrochloric acid with potassium iodide. The solu-
dard procedures for the treatment of the experimental tion enthalpies of reactions (14)–(15), namely
[
12,15,17]
–1
data.
∆solH° (298.15 K) = –358.40Ϯ3.71 kJmol
(n = 5),
14
The measured enthalpies of dissolution were used for cal- ∆solH°15 (298.15 K) = –156.98Ϯ0.61 kJmol–1 (n = 6), allow
culating the enthalpy of the reaction below
one to calculate the enthalpy of the reaction below.
Ba(s) + 0.2Nd(s) + 0.8Ce(s) + 1.45O (g) = BaCe0.8Nd0.2
-
Ba(s) + 0.2Lu(s) + 0.8Ce(s) + 1.45O (g) = BaCe0.8Lu0.2
-
2
2
O2.9(s)
O2.9(s) + ∆ H°
r
according to the equation
∆ H°(298.15 K) = ∆ H° (BaCe0.8Lu0.2O2.9, s, 298.15 K) =
r
f
∆rH ° = –∆ H ° + ∆ H ° + ∆ H ° –∆ H ° – ∆solH5° –1661.11Ϯ4.25 kJmol–1 is the standard formation enthalpy
13
sol
1
sol
2
sol
3
sol
4
+
∆solH ° + ∆ H ° + ∆ H ° – ∆ H ° + ∆ H ° + of BaCe0.8Lu0.2O2.9 calculated taking into account the
6 sol 7 sol 8 sol 9 sol 10
∆solH ° + ∆ H °.
scheme presented in Table 3. The standard formation en-
11
sol 12
Here, ∆ H ° = ∆ H°(BaCe0.8Nd0.2O2.9, s, 298.15 K) = thalpy is the enthalpy at P = 1 atm, T = 298.15 K.
r
13
f
–
1
–
1631.59Ϯ4.10 kJmol is the standard formation enthalpy
Literature data for the formation enthalpies of BaO,
[
20]
of barium cerate doped by neodymium oxide.
CeO , Nd O and Lu O taken from ref.
were used to
2
2
3
2
3
To calculate this value we used experimental data mea- calculate the enthalpies of formation of BaCe0.8Lu0.2O2.9
sured by us and literature data for the formation enthalpies and BaCe0.8Nd0.2O2.9 from binary oxides as following:
Eur. J. Inorg. Chem. 2009, 1477–1482
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1479

N. I. Matskevich, T. Wolf, M. Y. Matskevich, T. I. Chupakhina
FULL PAPER
BaO(s) + 0.8CeO
2
(s) + 0.1Nd
2
O
3
(s) = BaCe0.8Nd0.2
O
2.9(s)
(27) BaCe0.8RE0.2
.1RE (s)
O
2 3 2 4 2
2.9(s) + Al O (s) = BaAl O + 0.8CeO (s) +
0
2
O
3
(30)
(31)
∆oxH°(298.15 K) = –30.44Ϯ4.83 kJmol–1
BaCe0.8RE0.2
2 3 2
O2.9(s) + ZrO (s) = BaZrO + 0.8CeO (s) +
BaO(s) + 0.8CeO
2
(s) + 0.1Lu
2
O
3
(s) = BaCe0.8Lu0.2
O
2.9(s)
(28)
2 3
0.1RE O (s)
∆oxH°(298.15 K) = –52.97Ϯ5.01 kJmol–1
The possibility of the interaction was estimated using our
In order to understand whether the BaCe0.8Nd0.2O2.9 or
BaCe0.8Lu0.2O2.9 phases are stable or unstable with regard
to decomposition to BaO + 0.8CeO + 0.1Nd O or BaO(s)
experimental data, formation enthalpies of the solid phases,
namely CeO (s), Nd O (s), Lu O (s), Ba(OH) (s), BaAl O ,
2
2
3
2
3
2
2
4
2
2
3
BaZrO , and the formation enthalpy of the gas phase
3
+
0.8CeO + 0.1Lu O mixtures it is necessary to know the
[20,23]
2
2
3
H O(g) taken from ref.
The calculated heats of reac-
2
Gibbs energies (∆G = ∆H – T∆S). There are no entropy
values for the BaCe0.8Nd0.2O2.9 and BaCe0.8Lu0.2O2.9
tions (32)–(37) are:
phases in the literature. These values were estimated using BaCe0.8Nd0.2
2 2 2
O2.9(s) + H O (g) = Ba(OH) (s) + 0.8CeO (s) +
entropies of Nd O , Lu O , BaCeO , CeO taken from 0.1Nd (s)
2
O
3
(32)
(33)
(34)
(35)
(36)
(37)
2
3
2
3
3
2
ref.[
and (28), the Gibbs energies for the processes (27) and (28)
were estimated as: ∆ G°(298.15 K) = –33.48Ϯ4.83 kJ
6,22]
Using the formation enthalpies of reactions (27)
∆rH°(298.15 K) = –122.11Ϯ4.83 kJmol–1
ox
BaCe0.8Lu0.2
0.1Lu O (s)
2 2 2
O2.9(s) + H O (g) = Ba(OH) (s) + 0.8CeO (s) +
–
1
–1
mol and ∆ G°(298.15 K) = –52.97Ϯ5.01 kJmol .
ox
2
3
As can be seen, both of the above-mentioned complex
oxides are thermodynamically stable with regard to their
decomposition into binary oxides at room temperature. It
is not an obvious result for this class of compounds because
there is a discussion about the thermodynamic stability of
∆rH°(298.15 K) = –99.58Ϯ5.01 kJmol–1
2 3 2 4 2
BaCe0.8Nd0.2O2.9(s) + Al O (s) = BaAl O + 0.8CeO (s) +
2 3
0.1Nd O (s)
[
6–9]
H°(298.15 K) = –74.26Ϯ4.83 kJmol–1
r
BaCeO3.
unstable with regard to its decomposition into BaO and
There is a paper that claims that BaCeO is
∆
3
2 3 2 4 2
BaCe0.8Lu0.2O2.9(s) + Al O (s) = BaAl O + 0.8CeO (s) +
[
7]
CeO2. It is interesting to mention that usually the en-
thalpy of formation of complex oxides from binary oxides
2 3
0.1Lu O (s)
is close to zero [for example, ∆ H(298.15 K, CdSiO ) = ∆ H°(298.15 K) = –51.63Ϯ5.02 kJmol–1
ox
3
r
–
1
–
5
6.28 kJmol ]. In our case we have values at the level –30–
0 kJmol , which are higher than the usual values for com-
–
1
2 3 2
BaCe0.8Nd0.2O2.9(s) + ZrO (s) = BaZrO + 0.8CeO (s) +
2 3
0.1Nd O (s)
plex oxides but lower than formation enthalpies from bi-
nary oxides for HTSC materials [∆ H for REBa Cu O
–1
ox
2
3
7–x
∆ H°(298.15 K) = –68.26 Ϯ4.42 kJmol
r
–1
phase (RE = rare earth element) is about –200 kJmol ].
2 3 2
BaCe0.8Lu0.2O2.9(s) + ZrO (s) = BaZrO + 0.8CeO (s) +
In accordance with increasing Gibbs energies one therefore
2 3
0.1Lu O (s)
observes an increasing stability in the order BaCeO doped
3
by neodymium oxide to BaCeO doped by lutetium oxide.
Hence, barium cerate doped by lutetium oxide is more ther-
∆rH°(298.15 K) = –45.63Ϯ4.62 kJmol–1
3
It is necessary to note that the direction of any chemical
transformation is determined by the sign of the Gibbs en-
ergy ∆G° = ∆H° – T∆S°. Below we will calculate the Gibbs
energies for reactions (32)–(37). As it was mentioned earlier
the values of the entropies of BaCe0.8Nd0.2O2.9 and BaCe0.8-
Lu0.2O2.9, which were absent in the literature, were esti-
mated using entropies of Nd O , Lu O , BaCeO and CeO
2
modynamically stable than BaCeO doped by neodymium
3
oxide.
As some researchers have pointed out, a concern for Ba-
[3,23,24]
CeO is its stability in the external atmosphere.
The
3
compound reacts with water vapour to decompose into bar-
ium hydrate and cerium oxide according to the reaction:
2
3
2
3
3
[24]
BaCeO + H O = Ba(OH) + CeO .
It is also known
[6,22]
3
2
2
2
taken from ref.
The Gibbs energies for processes (32)–
that when pellets of BaCeO were sintered in alumina or
3
(
37) were calculated as
zirconia containers, XRD patterns of the contact substrates
showed that BaAl O was formed on the alumina and
–1
∆rG°(298.15 K) = –73.32Ϯ4.83 kJmol [for (32)],
∆rG°(298.15 K) = –50.79Ϯ5.01 kJmol [for (33)],
∆rG°(298.15 K) = –72.37Ϯ4.83 kJmol [for (34)],
∆rG°(298.15 K) = –49.74Ϯ5.02 kJmol [for (35)],
∆rG°(298.15 K) = –65.91 Ϯ4.42 kJmol [for (36)],
∆rG°(298.15 K) = –43.26Ϯ4.62 kJmol [for (37)].
2
4
–1
BaZrO was formed on the zirconia. It was thus concluded
–1
3
that BaCeO reacts with Al O or ZrO and decomposes
–1
3
2
3
2
through the following reactions: BaCeO3 + Al O3
=
+
–1
2
BaAl O + CeO2 and BaCeO3 + ZrO2 = BaZrO3
–1
2
[
4
24]
CeO2.
Taking into account the Gibbs energies of reactions (32)–
With regard to this it was interesting to discover that
BaCe0.8Nd0.2O2.9 and BaCe0.8Lu0.2O2.9 react with water
vapour, Al O or ZrO . For this reason we considered the
(37) it is possible to say that both complex oxides (Ba-
Ce0.8Nd0.2O2.9, BaCe0.8Lu0.2O2.9) react with water, Al O3
2
2
3
2
and ZrO at ambient temperature. Usually the zirconia cru-
2
following reactions:
cibles are preferable for the synthesis of barium cerates,
2 2 2 3
O(g) = Ba(OH) (s) + CeO (s) + RE O
(s) however, they are more expensive than the alumina cruci-
BaCe0.8RE0.2
O2.9(s) + H
2
(
29) bles. The enthalpies of the reactions of BaCe0.8RE0.2O2.9
1480
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 1477–1482

Nd- and Lu-Doped BaCeO
3
Proton-Conducting Ceramics
(
RE = Nd, Lu) with ZrO and Al O are practically the nide oxychloride impurities. For this purpose CeCl was sublimated
3
2
2
3
above the melting temperature (1143 K) in a vacuum at more than
same, so it is unnecessary to use the expensive ZrO cruci-
2
–
5
10
Pa. NdCl
3 3 2 3
and LuCl were prepared from Nd O and Lu.
bles. It should also be noted that the reactions with Al O ,
2
3
Nd
2
3
O (99.99%, Purathem, STREM Chemicals, New buryport,
ZrO or water for BaCe0.8Nd0.2O2.9 are more thermody-
2
USA) and Lu (99.999%, Chempur, Chem. Pur Feinchemikalen und
Forschungsbedart GmbH, Karlsruhe) were dissolved in an excess
of hydrochloric acid. Purified chlorine gas was bubbled through the
solutions. Each solution was then evaporated. Further drying was
accomplished by evaporation under vacuum at about 350 K until
the remaining chloride crystals appeared in composition. Final dry-
ing was accomplished by slow heating, in a hydrogen chloride at-
mosphere, to a final temperature of 600 to 700 K. All manipula-
namically favoured than those for BaCe0.8Lu0.2O2.9
There is also a second type of reaction for the doped-
BaCeO with water. It can be written as follows.
.
3
BaCe0.8RE0.2
O2.9(s) + xH
2
O = BaCe0.8RE0.2
O2.9–x(OH)2x
(38)
Unfortunately there is no thermodynamic data for Ba-
Ce0.8RE0.2O2.9–x(OH)2x in the literature. For this reason we
can not estimate the Gibbs energies for processes (38).
3 2 3 3
tions with CeCl , BaCl , NdCl and LuCl were performed in a
dry box (pure Ar gas).
Conclusions
Acknowledgments
In this paper, for the first time we have synthesized the
compound BaCe0.8Lu0.2O2.9 by a solid-state reaction. We
This work is supported by the Deutsche Forschungsgemeinschaft
also prepared BaCeO doped by neodymium oxide (Ba- (DFG) (grant LO 250/24-1), the Forschungszentrum Karlsruhe and
3
Ce0.8Nd0.2O2.9) and determined its structure parameters, the Program of Fundamental Investigation of the Siberian Branch
which are in good agreement with the literature data. Both of the Russian Academy of Sciences.
compounds have an orthorhombic structure (space group
Pnma). We also measured the standard formation enthalp-
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Eur. J. Inorg. Chem. 2009, 1477–1482
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1481

N. I. Matskevich, T. Wolf, M. Y. Matskevich, T. I. Chupakhina
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Published Online: March 10, 2009
1482
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 1477–1482