Comparative study regarding the formation of La1-xSr xCrO3 perovskite using unconventional synthesis methods

Article abstract of DOI:10.1007/s10973-008-9104-1

The synthesis of strontium-doped lanthanum chromite, La _1-xSr_xCrO₃ (x=0.1 and 0.3), used as an interconnect material for solid oxide fuel cells (SOFC), was investigated using two unconventional synthesis methods: (1) organic precursors' method based on the thermal conversion of complex combination resulted in the oxidation reaction of 1,2-ethanediol by La³⁺, Sr²⁺ and Cr³⁺ nitrates; (2) combustion synthesis based on the exothermic redox reaction of La³⁺, Sr²⁺ and Cr³⁺ nitrates with urea and glycine as fuels. We also used a mixture of urea and glycine as fuel. The samples were characterized by means of thermal analysis and X-ray diffraction.

Full text of DOI:10.1007/s10973-008-9104-1

Journal of Thermal Analysis and Calorimetry, 94 (2008) 2, 343–348
COMPARATIVE STUDY REGARDING THE FORMATION OF La Sr CrO
x 3
1–x
PEROVSKITE USING UNCONVENTIONAL SYNTHESIS METHODS
1
R. Ianoê , C. P²curariu , I. Laz²u , S. Ianoêev , Z. Ecsedi , R. Laz²u and P. Barvinschi
*
1
1
1
1
1
2
1
‘Politehnica’ University of Timiêoara, Faculty of Industrial Chemistry and Environmental Engineering, P-ïa Victoriei No. 2
Timiêoara 300006, Romania
2
The West University of Timiêoara, Faculty of Physics, V. P­rvan No. 4, Timiêoara, Romania
x 3
The synthesis of strontium-doped lanthanum chromite, La1–xSr CrO (x=0.1 and 0.3), used as an interconnect material for solid ox-
ide fuel cells (SOFC), was investigated using two unconventional synthesis methods: (1) organic precursors’ method based on the
3
+
2+
thermal conversion of complex combination resulted in the oxidation reaction of 1,2-ethanediol by La , Sr and Cr nitrates;
3+
3+
2+
2) combustion synthesis based on the exothermic redox reaction of La , Sr and Cr nitrates with urea and glycine as fuels. We
3+
(
also used a mixture of urea and glycine as fuel. The samples were characterized by means of thermal analysis and X-ray diffraction.
Keywords: combustion synthesis, fuel cells, interconnect material, organic precursors, perovskite
Introduction
Although the metallic interconnects are more
cost effective, they are prone to oxidation and cannot
be used at high temperatures. Thus, ceramic materials
represent a successful choice as interconnect materi-
als. Lanthanum chromite-based materials, LaCrO3,
which belong to the perovskite family, are the most
promising interconnect materials for SOFCs. The
properties of lanthanum chromite can be significantly
Solid oxide fuel cells (SOFCs) offer a new technol-
ogy that directly converts chemical into electrical en-
ergy and represent a promising alternative over the
traditional energy conversion systems. Besides the
high efficiency and fuel adaptability, SOFCs provide
many other advantages including reliability, modular-
ity, and almost entirely nonpolluting technology,
3
+
3+
improved by substituting either La or Cr in the
practically without NO and SO emissions [1].
x x
perovskite structure with different metal cations
2
+
2+
2+
2+
2+
By using only solid materials, including the elec-
trolyte, the SOFCs are more compact and can be more
easily manipulated, and thus, multiple cells can be
stacked in series to increase the energy efficiency. In
order to do this, each individual cell is electrically
connected to another cell using an interconnect mate-
rial. The role of the interconnect material is to provide
the electrical connection between adjacent cells and
to keep fuel and oxidant apart.
(e.g., Ca , Sr , Ni , Mg , Cu , etc.) as well as by
optimizing the chemical stoichiometry of dopant cat-
ions. The poor sintering behavior of these materials
can be improved by using highly reactive powders
with high surface area [3–5].
Several methods for the low-temperature synthe-
sis of doped LaCrO have been developed in order to
3
achieve the desired properties of powders: co-precipi-
tation route [6], sol–gel [7], organic precursors [8, 9],
hydrothermal synthesis [10, 11], Pechini [12] and
microwave heating technique [13]. One of the most
promising and frequently used techniques is the com-
bustion synthesis using urea [14, 15], gly-
cine [16–20], or citric acid [21, 22] as fuels. Concern-
ing the preparation of complex metal oxide nano-
crystalline powders at low temperatures, previous
studies [23, 24] have shown a number of advantages
exhibited by the organic precursors’ method as well
as by combustion synthesis [24–26].
The high operating temperature of the SOFC, ap-
proximately 1000°C, imposes severe conditions for the
component materials of the cells. Because the intercon-
nect is exposed simultaneously to the reducing envi-
ronment of the anode and to the oxidizing atmosphere
of the cathode, the potential interconnect materials
must meet the most stringent requirements of all the
cell components: excellent electrical conductivity,
thermal expansion coefficient comparable to those of
the other cell components, lack of porosity in order to
avoid mixing of fuel and oxygen, good mechanical
strength as well as chemical and physical stability [2].
From this point of view, the aim of this paper is
to investigate the strontium-doped lanthanum chro-
mite, La1–xSr
CrO
(x=0.1 and 0.3), powder prepara-
x
3
*
Author for correspondence: robert_ianos@yahoo.com
1
388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
©
2008 Akadémiai Kiadó, Budapest

IANOŸ et al.
tion using two unconventional synthesis methods: or-
reaction. During the heating process ignition occurred,
followed by the combustion of the reactants’ mixture,
with the appearance of a high speed propagating flame.
The high temperature reached within the raw material
mixture led to the formation of dried fluffy foam,
which could be easily crumbled into a fine powder.
ganic precursors’ method and combustion synthesis.
Experimental
Materials
The starting raw materials were all pro analysis purity
Instrumental methods
degree: La(NO ×6H
Merck), Sr(NO ) (Merck), 1,2-ethanediol (Fluka),
3 2
)
O (Merck), Cr(NO
)
×9H
O
3
3
2
3
3
2
The as-prepared powders were annealed in an electric
furnace at temperatures ranging between 1000
and 1350°C with one-hour soaking time. The thermal
behavior of the samples was monitored using a
TG/DTA Diamond Perkin Elmer derivatograph. The
data were recorded in static air atmosphere, using Pt
(
urea (Merck), glycine (Merck).
Organic precursors’ method
The method is based on thermal conversion of the
complex combinations resulting in the oxidation of
–
1
crucible and a heating rate of 10°C min .
1
,2-ethanediol, C
2
H O
6
2+
2
, to the glyoxilate dianion,
The evolution of the phase composition of the
samples was monitored by XRD using a Bruker’s D8
2–
3+
3+
C H O , by La , Sr and Cr nitrates. The aqueous
2
2
4
3
+
2+
3+
solution of La , Sr and Cr nitrates and 1,2-ethane-
diol, with an excess of 25% of 1,2-ethanediol was
heated in air up to 100°C. During the exothermic reac-
Advanced system, CuK radiation. The average crys-
a
tallite size was determined based on the XRD pat-
terns – h k l planes 1 1 2 and 0 0 4 – using Scherrer’s
equation:
tion, the NO gases were eliminated, resulting the com-
x
plex combination as a green-black powder, which was
subsequently washed out with acetone–water mixture
and then filtered.
0
.9l
bcosq
where D is the crystallite size in nm, l is radiation
wavelength (CuK
, 0.15406 nm), b is the full width at
D =
(1)
Combustion synthesis
a
half of maximum in radians, and q is the Bragg-angle.
In the first stage, the individual reactivity of each metal
nitrate with respect to urea (CH N O) and glycine
4 2
(C H NO ) was tested (Table 1). In the second stage,
2 5 2
Results and discussion
the desired solid solutions (La Sr CrO ,
3
0.9 0.1
La Sr CrO ) were synthesized using the following
3
0.7 0.3
The main characteristics of the combustion reaction
of each metal nitrate with urea and glycine are pre-
sented in Table 1.
fuels: urea (U), glycine (G), and a mixture of urea and
glycine (UG). All samples were designed assuming
(g) and N2(g) are the resulting
that CO2(g), H O
2
As can be seen in Table 1, there is a different be-
haviors of each metal nitrate with respect to urea and
glycine. From this point of view, the similar behavior
of lanthanum and strontium nitrate with respect to the
two fuels needs to be emphasized. In both cases,
glycine proves to be the only fuel that reacts with these
metal nitrates, leading to the development of an explo-
sion type combustion reaction. On the other hand,
by-products of the combustion reaction. Stoichio-
metric metal nitrate–fuel molar ratios were used. After
dissolving the desired metal nitrates in the right pro-
portion in a minimum volume of distilled water, the
required amount of fuel was added: urea, glycine and a
mixture of urea and glycine. The resulting solution was
then heated up to 300°C in order to promote water
evaporation and the initiation of the combustion
Table 1 Characteristics of the combustion reaction of metal nitrates with urea and glycine
Theoretical amount
a
Phase composition of
the resulting powders
Metal nitrate
Fuel
Reaction time/s
Experimental observations
of oxide/mol
urea
–
0
NH
white, flame explosion
NH , green, incandescence
green, smoldering combustion
NH , white, no combustion
white, flame explosion
3
, white, no combustion
LaONO
3
La(NO
Cr(NO
3
)
3
×6H
2
O
0.02
glycine
La
2
O
3
urea
15
55
3
a -Cr
a -Cr
2
2
O
3
3
)
3
×9H
2
O
0.04
0.06
glycine
O
3
urea
–
0
3
3 2
Sr(NO )
3 2
Sr(NO )
glycine
SrCO
3
a
Observed gases, color of the resulting powder and combustion reaction type
344
J. Therm. Anal. Cal., 94, 2008

x 3
FORMATION OF La1–xSr CrO PEROVSKITE
chromium nitrate reacts with both urea and glycine, en-
suring the formation of single-phase a -Cr
O .
2 3
Considering the velocity of the combustion reac-
tion, one could notice that urea reacts faster with
chromium nitrate than glycine. Based on these experi-
mental observations, in general, and on the reaction
time in particular, the different reactivities of lantha-
num, strontium and chromium nitrates with respect to
urea and glycine are pointed out. Considering the
combustion reaction velocity as a criterion for the
compatibility of metal nitrate/fuel mixtures, it is
pointed out that glycine is the most suitable fuel for
lanthanum and strontium nitrates, while urea seems to
be the most adequate fuel for chromium nitrate.
The La0.7Sr0.3CrO
synthesis reactions using
urea, glycine and the mixture of urea and glycine can
be represented by Eqs (2)–(4).
3
Fig. 1 DTA curves of the raw material mixtures designed for
the La Sr CrO combustion synthesis (samples 4U,
0.9 0.1
3
5UG and 6G)
7
La(NO ) +3Sr(NO ) +10Cr(NO ) +
3 3 3 2 3 3
action, evidenced by the presence of a strong and
sharp exothermic effect at 216°C on the DTA curve.
Unlike glycine, urea (sample 4U) does not pro-
mote the evolution of a fast and intense combustion
reaction. The broad weak exothermic effect, located
between 210 and 290°C, is in excellent consistency
with the development of the redox reaction, which
lasts considerably longer (45 s). The precursor mix-
ture containing both urea and glycine (sample 5UG)
exhibits an intermediate behavior: the combustion re-
action is significantly faster (10 s) and more exother-
mic than the sample with urea, but slower and less
exothermic than the sample with glycine.
+
95/2CH N O+3/4O ®
4
2
2
®
10La Sr CrO +95/2CO +95H O+76N (2)
0.7 0.3 3 2 2 2
7
La(NO ) +3Sr(NO ) +10Cr(NO ) +
3 3 3 2 3 3
+
95/3C H NO +3/4O ®
2
5
2
2
®
10La Sr CrO +190/3CO +
0.7 0.3 3 2
+
2
475/6H O+133/3N2
(3)
7
La(NO ) +3Sr(NO ) +10Cr(NO ) +
3 3 3 2 3 3
+
15C H NO +25CH N O+3/4O ®
2
5
2
4
2
2
®
10La Sr CrO +55CO +175/2H O+61N (4)
0.7 0.3 3 2 2 2
Figure 1 shows the DTA curves obtained for the
mixture of lanthanum, chromium and strontium ni-
trates – dosed in the stoichiometric ratio correspond-
These results emphasize once again that there is a
predilection of metal nitrates with respect to certain fu-
els. At the same time, the importance of selecting the
right fuel is pointed out in order to achieve the maxi-
mum exothermic effect of the combustion reaction.
Regarding the phase formation succession for
ing to La0.9Sr0.1CrO – with urea, glycine and the mix-
3
ture of urea and glycine, respectively.
As can be seen from Fig. 1, the heating behavior
of the precursor mixtures containing the desired metal
nitrates and various fuels is quite different. The use of
glycine as a reducing agent alongside the correspond-
ing metal nitrates (sample 6G) leads to the develop-
ment of a very fast (5 s) and vigorous combustion re-
La0.7Sr0.3CrO
, lanthanum chromate (La
strontium chromate (SrCrO ) are mentioned first in
the literature [27]. However, in the case of samples
obtained directly from the combustion reaction, the
CrO ) and
3
2 6
4
Table 2 Crystalline phases identified on the XRD patterns
Designed
stoichiometry
Synthesis
method
Crystalline phases present on the XRD patterns
Sample
as-resulted
1000°C/1 h
1200°C/1 h
1350°C/1 h
La0.7Sr0.3CrO
3
3
3
3
,
,
,
La0.7Sr0.3CrO
3
3
3
,
,
,
La0.7Sr0.3CrO
3
3
3
,
,
,
3
La0.7Sr0.3CrO ,
1
U
Cr1.01LaO3±d
SrCrO
4
SrCrO
4
4
SrCrO (traces)
La0.7Sr0.3CrO
La0.7Sr0.3CrO
La0.7Sr0.3CrO
3
La0.7Sr0.3CrO ,
2
UG
La0.7Sr0.3CrO
3
Combustion
synthesis
Cr1.01LaO3±d
SrCrO
4
SrCrO
4
4
SrCrO (traces)
La0.7Sr0.3CrO
La0.7Sr0.3CrO
La0.7Sr0.3CrO
3
La0.7Sr0.3CrO ,
3
5
7
8
G
Cr1.01LaO3±d
SrCrO
4
SrCrO
4
4
SrCrO (traces)
UG
La0.9Sr0.1CrO
3
3
La0.9Sr0.1CrO
amorphous
amorphous
La0.9Sr0.1CrO
La0.7Sr0.3CrO
3
La0.9Sr0.1CrO
La0.7Sr0.3CrO
3
La0.9Sr0.1CrO
3
3
,
3
,
La0.7Sr0.3CrO
3
,
La0.7Sr0.3CrO
Organic
SrCrO
4
SrCrO
4
4
SrCrO (traces)
precursors
La0.9Sr0.1CrO
3
La0.9Sr0.1CrO
3
La0.9Sr0.1CrO
3
La0.9Sr0.1CrO
3
J. Therm. Anal. Cal., 94, 2008
345

IANOŸ et al.
Fig. 2 XRD patterns of the La0.7Sr0.3CrO
combustion synthesis (using various fuels) and organic
precursors
3
prepared via
3
Fig. 3 XRD patterns of the La0.7Sr0.3CrO powders prepared
via combustion synthesis and organic precursors’
method after annealing at different temperatures
2
+
4+
suggesting that new amounts of Cr have been pro-
main crystalline phase is the Sr -doped LaCrO3,
lacking the peaks of SrCrO (Table 2).
After annealing at 1000°C, some weak reflec-
tions of SrCrO occur, suggesting that during the
4
duced as the result of incorporation of new amounts of
2+
Sr from SrCrO into the perovskite solid solution.
4
4
Another important piece of evidence, which
stands for this reaction mechanism, is represented by
the evolution of the average crystallite size after an-
nealing samples 7 and 2UG at various temperatures.
As seen in Fig. 3, after annealing at 1200°C, the
resulting crystallites are smaller than the ones
resulting after annealing at 1000°C. This apparent
anomaly can be easily explained by considering the
development of the solid-state reaction between
2
+
combustion reaction a fraction of the Sr content was
bonded as amorphous SrCrO , which crystallized
4
when heated (Fig. 2). This finding was also sustained
by the yellow color of the samples’ washing water,
6
denoting the presence of soluble Cr .
+
The peak from 31.7°, present in all samples re-
sulting directly from the combustion synthesis
(
Fig. 2) can be attributed to a preceding phase of the
projected strontium-doped lanthanum chromite in
which the chromium oxidation state is intermediate
between 3+ and 6+. The composition attributed to this
SrCrO and the perovskite solid solution, which
4
involves a certain degree of disorganization and re-
organization of the crystalline lattice. It is very
important to notice that this behavior does not appear
phase by the JCPDS file 44-0333 is Cr1.01LaO3±d
.
2
+
In the case of using the combustion synthesis,
this evolution of the phase composition reflects very
favorable conditions for the formation of the desired
solid solution. On the basis of the low intensity of the
in the case of samples with lower Sr content
). At 1350°C in both synthesis
methods – organic precursors and combustion synthe-
sis – only small traces of SrCrO are detected, con-
firming the almost complete incorporation of SrCrO
in the LaCrO structure yielding the La0.7Sr0.3CrO
solid solution (Fig. 3).
In the case of stoichiometry with lower Sr con-
tent (La Sr CrO ), the desired crystalline phase is
(La0.9Sr0.1CrO
3
4
SrCrO
4
reflections, it can be asserted that, already in
4
3
the samples resulting directly from the combustion
2+
3
3
+
synthesis, the projected substitution (La ® Sr ) was
largely realized and the La0.7Sr0.3CrO phase was
formed. When the temperature rises, the consumption
of SrCrO continues due to its assimilation in the
chromite phase and the oxidation number of the chro-
mium from SrCrO reduces due to the release of oxy-
gen surplus.
In fact, the dark brown color of the combus-
tion-synthesized powders reflects the simultaneous
2
+
3
0
.9 0.1
3
4
obtained more easily. As seen in Table 2, the use of
urea and glycine fuel mixture (Sample 5UG) allows
the formation of pure nanocrystalline La0.9Sr0.1CrO
directly from the combustion reaction, no additional
annealing step being required (Fig. 4).
Unlike the combustion-synthesized La0.7Sr0.3CrO
powders, which exhibit a dark brown color before an-
nealing and a black one after annealing, the
powders exhibit a brown color, which
does not change after annealing. The lighter color of
La Sr CrO powders can be explained by the lower
4
3
3
3+
4+
presence of Cr and Cr , indicating that the partial sub-
3+
2+
stitution of La by Sr has already taken place to a cer-
3+
tain extent. Considering the partial substitution of La
La0.9Sr0.1CrO
3
2
+
3+
by Sr , the oxidation of Cr to Cr is mandatory in or-
4+
der to preserve the electric neutrality of the crystalline
0
.9 0.1
3
3
+
2+
lattice; for every La cation substituted by a Sr cation,
2+
amount of doping Sr , which involves a lower
4+
amount of Cr .
3+
4+
one Cr cation oxidizes to Cr . After annealing, the
color of the powders turns from dark brown to black,
346
J. Therm. Anal. Cal., 94, 2008

x 3
FORMATION OF La1–xSr CrO PEROVSKITE
2
For lower Sr content, La0.9Sr0.1CrO , the perovs-
+
•
3
kite phase results directly from the combustion re-
action, without the necessity for additional thermal
treatments. Using the organic precursors’ method,
the formation of La0.9Sr0.1CrO
at 1000°C.
requires annealing
3
•
•
The average crystallite size of the combustion-syn-
thesized powders is directly influenced by the na-
ture of the fuel.
2+
As the Sr content increases, its inclusion into the
perovskite phase takes place more difficult and a
higher annealing temperature is required. Although
in the case of combustion synthesis the resulting
Fig. 4 XRD patterns of the La0.9Sr0.1CrO
3
prepared via
powder already contains La0.7Sr0.3CrO
3
as the main
crystalline phase, some of the Sr content is immo-
bilized in SrCrO . The inclusion of SrCrO into the
desired crystalline phase requires annealing at
350°C. From this point of view similar results were
obtained using the organic precursors’ method.
2+
combustion synthesis and organic precursors’ method,
after annealing at different temperatures
4
4
An important remark is that the brown color of the
powder cannot be assigned to the presence of residual
carbon because the losses on ignition are almost negli-
1
3+
gible (1.1%), but to the simultaneous presence of Cr
3+
4+
2+
and Cr due to the partial substitution of La by Sr .
After annealing the sample at 1000°C with one hour
soaking time, there are no modifications concerning
the color of the powder or its phase composition, ex-
cept for an improvement of the crystalline character
evidenced by the increase in the average crystallite size
References
1
O. Yamamoto, Electrochim. Acta, 45 (2004) 1423.
E. S. M. Seo, W. K. Yoshito, V. Ussui, D. R. R Lazar,
S. R. H. M. Castanho and J. O. A. Paschoal, Mater. Res.,
7 (2004) 215.
2
(
Fig. 4). All these observations point out that the partial
3 J. W. Fergus, Solid State Ionics, 171 (2004) 1.
4 N. Sakai, H. Yokokawa, T. Horita and K. Yamaji,
Int. J. Appl. Ceram. Tech., 1 (2004) 23.
3+
2+
substitution of La by Sr , which involves the partial
4+
oxidation of Cr to Cr , has already taken place dur-
3+
5
6
7
P. H. Larsen, P. V. Hendriksen and M. Mogensen,
J. Therm. Anal. Cal., 49 (1997) 1263.
ing the combustion reaction.
On the other hand, in the case of the organic pre-
cursors’ method, the formation of the perovskite
phase requires annealing at 1000°C. As one could ex-
pect, after annealing at 1200°C, crystallites growth
takes place, so that the average crystallites size
is 30.1 nm (Fig. 4).
M. R. Guire, S. E. Dorris, R. B. Poeppel, S. Morissette and
U. Balachandran, J. Mater. Sci., 8 (1993) 2327.
S. Bilger, G. Blaß and R. Förthmann, J. Eur. Ceram. Soc.,
17 (1997) 1027.
8 D. Berger, V. Fruth and I. Jitaru, Mater. Lett.,
58 (2004) 2418.
2
+
In case of samples with high Sr content,
9 D. Berger, I. Jitaru, N. Stanica, R. Perego and J.
Schoonman, J. Mater. Synth. Process., 9 (2001) 137.
0 L. P. Rivas-Vazquez, J. C. Rendon-Angeles,
J. L. Rodriguez-Galicia, K. Zhu and K. Yanagisawa,
Solid State Ionics, 172 (2004) 389.
La0.7Sr0.3CrO , the differences between the two synthe-
3
1
1
sis methods are insignificant, considering the same an-
nealing temperature required for the perovskite forma-
tion as a single phase. Nevertheless, it must be pointed
out that in the case of combustion synthesis, the
perovskite solid solution is the main crystalline phase,
which results directly from the combustion reaction.
1 L. P. Rivas-Vazquez, J. C. Rendon-Angeles,
J. L. Rodriguez-Galicia, C. A. Gutierrez-Chavarria, K. J. Zhu
and K. Yanagisawa, J. Eur. Ceram. Soc., 26 (2006) 81.
12 T. Lone-Wen and A. A. Lessing, J. Mater. Res.,
(1992) 511.
3 Y. S. Malghe and S. R. Dharwadkar, J. Therm. Anal. Cal.,
1 (2008) 915.
4 S. Biamino and C. Badini, J. Eur. Ceram. Soc.,
4 (2004) 3021.
5 E. P. Marinho, A. G. Souza, D. S. de Melo, I. M. G. Santos,
D. M. A. Melo and W. J. da Silva, J. Therm. Anal. Cal.,
7 (2007) 801.
6 A. S. Mukasyan, C. Costello, K. P. Sherlock, D. Lafarga
and A. Varma, Sep. Purif. Technol., 25 (2001) 117.
17 D. Kishori, A. Mukasyan and A. Varma, J. Am. Ceram. Soc.,
6 (2003) 1149.
7
1
1
1
9
Conclusions
2
•
The two unconventional synthesis methods allow
the formation of the perovskite solid solutions,
CrO (x=0.1 and 0.3), at lower tempera-
La1–xSr
x
3
8
tures than in the case of the ceramic method, based
on annealing mechanical mixtures of oxides and/or
salts.
1
8
J. Therm. Anal. Cal., 94, 2008
347

IANOŸ et al.
1
1
8 Y. Yong-Jie, W. Ting-Lian, T. Hengyong, W. Da-Qian
and Y. Jianhua, Solid State Ionics, 135 (2000) 475.
9 G. Zhu, X. Fang, C. Xia and X. Liu, Ceram. Int.,
24 C. P²curariu, I. Laz²u, Z. Ecsedi, R. Laz²u, P. Barvinschi
and G. M²rginean, J. Eur. Ceram. Soc., 27 (2007) 707.
25 R. Ianoê, I. Laz²u, C. P²curariu and P. Barvinschi,
Eur. J. Inorg. Chem., (2008) 925.
3
1 (2005) 115.
0 Z. Zhong, Solid State Ionics, 177 (2006) 757.
1 K. Zupan, D. Kolar and M. Marinëek, J. Power Sources,
6 (2000) 417.
2 K. Zupan, S. Pejovnik and J. Ma¹ek, Acta Chim. Slov.,
8 (2001) 137.
3 I. Laz²u, C. P²curariu and R. I. Laz²u, Interceram,
1 (2002) 266.
2
2
26 R. Ianoê, I. Laz²u, C. P²curariu and P. Barvinschi,
Eur. J. Inorg. Chem., (2008) 931.
8
27 A. Ianculescu, A. Br²ileanu, I. Pasuk and M. Zaharescu,
J. Therm. Anal. Cal., 66 (2001) 501.
2
2
4
DOI: 10.1007/s10973-008-9104-1
5
348
J. Therm. Anal. Cal., 94, 2008