Full text of DOI:10.1007/s10973-007-8559-9

Journal of Thermal Analysis and Calorimetry, Vol. 90 (2007) 3, 955–958
ENTHALPY OF FORMATION OF BaCe0.9In0.1O3–d(s)
N. I. Matskevich*
Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, Novosibirsk 630090, Russia
Enthalpy of formation of the perovskite-related oxide BaCe0.9In0.1O2.95 has been determined at 298.15 K by solution calorimetry.
Solution enthalpies of barium cerate doped with indium and mixture of BaCl2, CeCl3, InCl3 in ratio 1:0.9:0.1 have been measured in
1 M HCl with 0.1 M KI. The standard formation enthalpy of BaCe0.9In0.1O2.95 has been calculated as –1611.7±2.6 kJ mol–1.
Room-temperature stability of this compound has been assessed in terms of parent binary oxides. The formation enthalpy of barium
cerate doped by indium from the mixture of binary oxides is DoxH0(298.15 K)= –36.2±3.4 kJ mol–1.
Keywords: BaCeO3-based perovskite, solution calorimetry, thermodynamic stability
Introduction
Experimental
Materials and methods
BaCeO3-based perovskites are potential candidates
for application in mid-temperature solid oxide fuel
cells and electrocatalysis because of their high proton
conduction [1–5]. It is generally accepted that proton
conduction is induced through the substitution of tri-
valent dopant ions on the cerium site. Solid solutions
Sample preparation
Sample of overall composition BaCe1–xInxO3–d was
prepared by solid-state reaction [9]. Appropriate
quantities of BaCO3, CeO2 and In2O3 powders
(CERAC, TM incorporated, USA, 99.9%) were
mixed and milled in a planetary mill for 12 h. The
typically form over the range BaCe1–xMxO3–x/2
,
0<x<0.2, with M=Y3+, Yb3+, Gd3+, Sm3+, Nd3+, etc.
[6]. As it has been recently shown (luminescent and
IR absorption studies) [7], doping of cerates by M3+
stabilizes the valence state +4 of Ce. The thermody-
namic stability is one of the important facts for appli-
cation [1]. The stability of cerium-based perovskites
depends on not only thermal conditions but also on
the nature of B-site doped ion [1]. It has been sug-
gested that stability increases when the dopant ion is
small and does not exhibit strong base properties. Suf-
ficient research of this has not been carried out.
powder
was
then
pressed
into
pellets
(P=3000 kg cm–2) and calcined at 1100 K for 16 h.
Following this, calcinations were performed in air at
1300 K for 5 h, 1400 K for 10 h, 1700 K for 24 h with
intermediate regrinding.
Anhydrous BaCl2 was prepared by drying BaCl2
(CERAC, TM incorporated, USA, 99.9%) in argon at
about 500 K. CeCl3 was also purchased from CERAC
(mass fraction is more than 0.999) and purified by
vacuum sublimation in order to remove the lanthanide
oxychloride impurities. For this purpose CeCl3 was
sublimated above the melting temperature (1143 K)
in a vacuum better than 10–5 Pa. InCl3 was synthe-
sized from Cl2 and In. Chlorine gas was passed over
indium at temperature about 450 K. All manipulations
with CeCl3, BaCl2 and InCl3 were performed in a dry
box (pure Ar gas).
X-ray powder diffraction was performed at room
temperature (STADI-P diffractometer; CuKa radia-
tion). The samples were found to be single phases. An
orthorhombic BaCe0.9In0.1O3–d (space group Pnma)
was prepared [8, 9]. Refined cell parameters:
a=0.6196(3) , b=0.8749(3) , c=0.6219(2) . All
compounds were also characterized by chemical anal-
ysis [10]. The content of barium was determined by
In the following, for the first time we report the
standard formation enthalpy of BaCe0.9In0.1O3–d deter-
mined by solution calorimetry and calculated
enthalpies for the reactions including this compound.
Indium is not a rare earth metal but can form solid so-
lutions on the basis of BaCeO3 [8]. The compound
has high conducting properties and can be considered
as a prospective solid electrolyte. There are no ther-
modynamic data for compounds in the Ba–Ce–In–O
system, in particular, for BaCe1–xInxO3–d
.
Thermodynamic properties linked to structural
data have been used to develop systematic struc-
ture-stability relationships in perovskite type oxides.
*
nata@che.nsk.su
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2007 Akadémiai Kiadó, Budapest

MATSKEVICH
Table 1 Analytical results
Compound
Found/%
Calculated/%
CeCl3
Ce, 56.81±0.04
Ba, 65.93±0.05
In, 51.94±0.03
Ce, 56.85
BaCl2
Ba, 65.95
InCl3
In, 51.91
BaCe0.9In0.1O2.95
Ba, 42.61±0.03; Ce, 39.10±0.03; In, 3.58±0.01
Ba, 42.63; Ce, 39.15; In, 3.56
Table 2 The data of dissolution enthalpies of BaCe0.9In0.1O2.95 (1 M HCl with 0.1 M KI) at 298.15 K
DsolH10 for single
The mean value with
error margin/kJ mol–1
Heat/J
experiments/kJ mol–1
m/g
0.07465
0.07412
0.07494
0.07511
0.07478
0.07415
83.580
82.340
83.935
83.983
83.129
82.366
–360.65
–357.84
–360.78
–360.17
–358.08
–357.81
–359.22±1.52
photometric method in the flame of nitrogen diox-
ide-acetylene. The content of cerium and indium was
determined by spectrophotometry. The stoichiometric
coefficient of oxygen was determined by iodometric
titration according to method described in paper [11]
with accuracy better than ±0.03. Results of chemical
analysis are presented in Table 1.
The program allows one to measure and record the
temperature of vessel, calibrate the instrument with
precise injections of electrical energy and calculate
calorimeter constants and enthalpies. The calorimet-
ric vessel was maintained at 298.15 K with tempera-
ture drift less than 0.0003°C for 10 h. Dissolution of
potassium chloride in water was performed to check
the precision of the calorimeter. The obtained dissolu-
tion heat of KCl was 17.41±0.04 kJ mol–1 (the
molality of the final solution was 0.028 mol kg–1).
The certified values are: 17.42±0.02 kJ mol–1) [14],
17.47±0.07 kJ mol–1 [15].
1 M HCl with 0.1 KI was chosen as a solvent. A
mixture of BaCl2, CeCl3, InCl3 was prepared in ratio
1:0.9:0.1. The molar concentration of CeCl3 was the
same as in paper [16].
The amount of BaCe0.9In0.1O2.95 was chosen in
such a way to have concentration of I2 and KI as au-
thors [16] used (about 0.08 g). Typical curve of calo-
rimetric experiment is presented in Fig. 1.
Calorimetric technique
Calorimetry experiments were conducted in our labo-
ratory in an automatic calorimeter with isothermal
shield of our own design and construction. Detailed
description of construction, procedure of performing
experiments and checking calorimeter are presented
in paper [12]. The measurement procedure has been
also extensively described in literature in detail [13].
The calorimeter had the reaction vessel (volume of
200 mL), the computer-controller platinum thermom-
eter and the Matlab program written at our laboratory.
298.16
298.14
298.12
298.10
298.08
298.06
298.04
298.02
298.00
297.98
Results and discussion
Calorimetric investigation
In most cases three solvents are used for dissolution
of compounds on the basis of alkaline earth and rare
earth elements: HCl, HClO4, HF. We have chosen
1 M hydrochloric acid. KI was added to reduce Ce4+
to Ce3+. This solvent was also used by Morss and
Menz [17] for determination of the enthalpy of forma-
tion of BaCeO3 and by Goudiakas et al. [18] for
BaCeO3 and SrCeO3. 1 M HCl is the most suitable
solvent for solution calorimeters [19]. We measured
0
5
10
15
20
25
30
35
Time/min
Fig. 1 Curve of calorimetric experiment
956
J. Therm. Anal. Cal., 90, 2007

FORMATION OF ENTHALPY BaCe0.9In0.1O3–d(s)
Table 3 Reaction scheme to determine the standard molar enthalpy of formation of BaCe0.9In0.1O2.95 at the temperature 298.15 K
Reaction
DsolHm0 /kJ
Ref.
1. BaCe0.9In0.1O2.95(s)+(5.9HCl+0.9KI)sol=(BaCl2+0.9CeCl3+0.1KCl+0.45I2+2.95H2O) (sol)
2. BaCl2(s)+0.9CeCl3(s)+0.1InCl3(s)=(2BaCl2+0.9CeCl3+0.1InCl3) (sol)
3. 2.95H2(g)+1.475O2(g)=2.95H2O(sol)
–359.22±1.52 This work
–137.41±0.59 This work
–843.23±0.13 [16]
+18.75±0.32 [16]
4. 0.9KI(s)+ solution 1=0.9KI(sol)
5. 0.9K(s)+0.45I2(s)=0.9KI(sol)
–296.24±0.13 [16]
+2.51±0.46 [16]
6.0.45I2(s)+solution 1=0.45I2(sol)
7. 0.9KCl(s)+solution 1=0.9KCl(sol)
+16.21±0.05 [16]
8. 0.9K(s)+0.45Cl2(g)=0.9KCl(s)
–392.81±0.12 [16]
–969.72±0.06 [16]
–855.15±1.73 [16]
–954.49±0.48 [16]
–53.72±0.84 [14]
9. 2.95H2(g)+2.95Cl2(g)+solution 1=5.9HCl(sol)
10. Ba(s)+Cl2(g)=BaCl2(s)
11. 0.9Ce(s)+1.35Cl2(g)=0.9CeCl3(s)
12. 0.1In(s)+0.15Cl2(g)=0.1InCl3(s)
13. Ba+0.1In+0.9Ce+1.475O2=BaCe0.9In0.1O2.95
–1611.66±2.64 This work
DoxH0(BaCe0.9In0.1O2.95(s), 298.15 K)=
–36.2±3.4 kJ mol–1
the dissolution enthalpy of BaCe0.9In0.1O2.95 and the
dissolution enthalpy of mixture BaCl2+CeCl3+
0.1InCl3 in this solvent, as these measurements were
not previously done. The dissolution enthalpy of bar-
ium cerate doped with indium in 1 M HCl with
0.1 M KI, DsolH0(BaCe0.9In0.1O2.95, 298.15 K)=
–359.22±1.52 kJ mol–1 is the average of six calorimet-
ric experiments (Table 2). The dissolution enthalpy of
For these calculations we have used DfH0
(BaO(s), 298.15 K), DfH0 (CeO2(s), 298.15 K), DfH0
(In2O3(s) 298.15 K) taken from [14].
The same value for BaCeO3 calculated from data
DoxH0
of
paper
[13]
is
(298.15
K)=
–51.6±2.5 kJ mol–1.
mixture
BaCl2(s)+0.9CeCl3(s)+0.1InCl3(s)
in
1 M HCl with 0.1 M KI, DsolH0 (298.15 K)=
-137.41±0.59 kJ mol–1 is the average of five calori-
metric experiments. Errors were calculated for the
95% confidence interval using the Students coeffi-
cient.
The thermochemical cycle from which the
enthalpy of formation of BaCe0.9In0.1O2.95(s) derived
is given in Table 3.
The cycle was completed with the auxiliary val-
ues for the molar enthalpies of formation of H2O(aq),
HCl(aq), BaCl2, CeCl3, KCl and InCl3 and others. The
values were taken from [14, 16].
Since entropy changes for solid-state reactions
are very small, the enthalpies of these reactions may
be used to argue that these complex oxides are more
stable than the parent binary oxides and that barium
cerate doped with indium is less stable than undoped
BaCeO3.
Conclusions
The standard molar enthalpy of formation of
BaCe0.9In0.1O2.95 obtained in the present study by so-
lution calorimetry was measured for the first time. It
was established that barium cerate doped with indium
is thermodynamically stable at room temperature with
respect to decomposition to the constituent binary ox-
ides but less stable than undoped BaCeO3.
After combining all reactions (1)–(12) we obtain
D r H103 =-D sol H10 +D sol H20 +D sol H30 -D sol H40
-D sol H50 +D sol H60 +D sol H70 +D sol H80 -D sol H90
+D sol H100 +D sol H101 +D sol H102
where DfH0 (BaCe0.9In0.1O2.95(s), 298.15 K)=
–1611.7±2.6 kJ mol–1.
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DOI: 10.1007/s10973-007-8559-9
958
J. Therm. Anal. Cal., 90, 2007