Phase equilibria and crystal structure of the complex oxides in the Ln-Ba-Co-O (Ln=Nd, Sm) systems

Article abstract of DOI:10.1016/j.jssc.2011.06.006

The phase equilibria in the Ln-Ba-Co-O (Ln=Nd, Sm) systems were systematically studied at 1100 °C in air. The homogeneity ranges and crystal structure of the solid solutions: Ln_2-xBa_xO _3-δ (0

Full text of DOI:10.1016/j.jssc.2011.06.006

Journal of Solid State Chemistry 184 (2011) 2083–2087
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Journal of Solid State Chemistry
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Phase equilibria and crystal structure of the complex oxides in the
Ln–Ba–Co–O (Ln¼Nd, Sm) systems
L.Ya. Gavrilova, T.V. Aksenova, N.E. Volkova, A.S. Podzorova, V.A. Cherepanov n
Department of Chemistry, Ural State University, Ekaterinburg, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
The phase equilibria in the Ln–Ba–Co–O (Ln¼Nd, Sm) systems were systematically studied at 1100 1C
Received 26 March 2011
Received in revised form
3 June 2011
in air. The homogeneity ranges and crystal structure of the solid solutions: Ln2ꢀxBaxO3ꢀ (0oxr0.1
d
for Ln¼Nd and 0oxr0.3 for Ln¼Sm), Nd3ꢀyBayCo2O7 (0.70ryr0.80), BaCo1ꢀzSmzO3ꢀ
d
(0.1rzr0.2) were determined by X-ray diffraction of quenched samples. The values of oxygen
Accepted 6 June 2011
Available online 12 June 2011
content (5þd) for slowly cooled LnBaCo2O5þ (Ln¼Nd, Sm) samples were estimated as 5.73 for Ln¼Nd,
d
and 5.60 for Ln¼Sm. The unit cell parameters were refined using Rietveld full-profile analysis. It was
shown that NdBaCo2O5.73 possesses tetragonal structure and SmBaCo2O5.60 – orthorhombic structure.
The projections of isothermal–isobaric phase diagrams for the Ln–Ba–Co–O (Ln¼Nd, Sm) systems to the
compositional triangle of metallic components were presented.
Keywords:
Cobaltates
Phase equilibria
Crystal structure
Oxygen content
& 2011 Elsevier Inc. All rights reserved.
1. Introduction
(Ba8Co6O18) (Ba8Co8O24) series prepared within the temperature
a b
range 800–875 1C [27,28].
Mixed rare earth (Nd, Sm) and barium cobaltates attract
significant attention as promising electrode materials for inter-
mediate-temperature solid oxide fuel cells [1–5]. The state-of-
the-art research is mainly devoted to the preparation procedure,
crystal structure, oxygen nonstoichiometry and physicochemical
Complex oxides with general formula Ln2BaO4 that possess
orthorhombic structure were formed in the Ln–Ba–O systems
(Ln¼Nd, Sm) [29–32]. It is also known that alkali earth metal oxides
can be partially dissolved in the rare earth sesquioxides [33].
In the quasibinary LnCoO3ꢀ –BaCoO3ꢀ (Ln¼Nd, Sm) systems
d
d
properties of so-called double perovskite phases LnBaCo2O5þ
so-called double perovskites LnBaCo2O5þ characterized by the
d
d
[2–8]. On the contrary the phase equilibria of the Ln–Ba–Co–O
systems (Ln¼Nd, Sm), that corresponds to a physicochemical
basis of every material, have not been systematically studied yet.
More or less detailed information is available for the correspond-
ing ternary systems.
ordering of cations (Ln, Ba) in A-sublattice and possible ordering of
vacancies in oxygen sublattice were described earlier [2–8]. Depend-
ing on the size of rare earth metal and oxygen content these
complex oxides crystallized either in tetragonal ap ꢁ ap ꢁ 2ap cell
(space group P4/mmm, so-called ‘‘112’’-structure), or in orthorhom-
bic ap ꢁ 2ap ꢁ 2ap cell (space group Pmmm, so-called ‘‘122’’-struc-
ture), where ap is the cubic perovskite unit cell parameter. It was
In both Ln–Co–O (Ln¼Nd, Sm) systems LnCoO3ꢀ are the only
d
phases formed at 1100 1C in air [9–14]. Both neodymium and
samarium cobaltates possess orthorhombically distorted perovs-
kite-type structure [15–17]. So-called Ruddlesden–Popper phases
Nd4Co3O10 and Nd2CoO4, where cobalt ions possesses lower
oxidation states were prepared in more reducing conditions
(lower oxygen partial pressure) [10,18–21].
shown that double perovskites LnBaCo2O5þ possess orthorhombic
d
structure in vicinity of the value of oxygen content 5.5 (approxi-
mately 5.4–5.6), while outside this interval they are crystallized in
tetragonal structure [7]. Such behavior is differing from the phase
equilibrium in LaCoO3ꢀ –BaCoO3- system [34,35], where a wide
d
d
Two complex oxides BaCoO3ꢀ and Ba2CoO4 were described in
range of La1ꢀuBauCoO3ꢀ solid solutions (0rur0.8) was found at
d
d
the Ba–Co–O system earlier [22–25] existing in air at 1100 1C.
Although there are a number of other phases in this system obtained
at the lower temperature: members of the Anþ2B’BnO3nþ3 homo-
logous series synthesized at 920 1C [26] and members of the
1100 1C in air.
Khalyavin et al. [36] found that partial substitution of neodymium
by barium can take place and as a result Nd1ꢀuBauCoO3ꢀ solid
d
solutions have formed up to u¼0.3 at 1200 1C in air. On the contrary
no homogeneity ranges had been found in the SmCoO3ꢀ –BaCoO3ꢀ
d
d
cross-section [36].
A new phase with Sm2BaCo2O3ꢀ composition, prepared by
solid state reaction at 1300 K in flowing oxygen for 2 weeks was
d
n Corresponding author.
E-mail address: Vladimir.Cherepanov@usu.ru (V.A. Cherepanov).
reported by Siwen and Yufang [37]. Gillie et al. [38] could not
0022-4596/$ - see front matter & 2011 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2011.06.006

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L.Ya. Gavrilova et al. / Journal of Solid State Chemistry 184 (2011) 2083–2087
obtain single phase sample with Sm2BaCo2O3- nominal composi-
tion at approximately same conditions but suggested that true
Table 1
d
Unit cell parameters and reliability factors (Ri)a for the Ln2ꢀxBaxO3ꢀ (Ln¼Nd, Sm)
d
solid solutions.
composition was probably close to Sm2.1Ba0.8Co2.1O7ꢀ (where
d
d
E1).
3
x
RBr (%) Rf (%) Rp (%)
˚
˚
˚
˚
V (A)
a (A)
b (A)
c (A)
This paper focuses on the phase equilibria in the Ln–Ba–Co–O
¯
(Ln¼Nd, Sm) systems at 1100 1C in air and the crystal structure of
Nd2ꢀxBaxO3ꢀ space group P3m1
d
0.05
0.075
0.1
3.828(1) 3.828(1) 5.995(1)
3.827(1) 3.827(1) 5.994(1)
3.827(1) 3.827(1) 5.991(1)
76.10(1) 1.84
76.07(1) 1.40
76.02(2) 1.37
1.55
1.51
1.41
17.1
14.3
14.4
intermediate phases. Since crystal structure of the double per-
ovskites LnBaCo2O5þ strongly depends on the oxygen content
d
the changes of
d as a function of temperature were measured.
Sm2ꢀxBaxO3ꢀ Space group C2/m
d
0.05
14.191(1) 3.628(1) 8.860(1) 449.22(2) 1.27
14.180(1) 3.626(1) 8.855(1) 448.39(1) 3.20
14.177(1) 3.625(1) 8.853(1) 448.08(1) 2.40
14.175(1) 3.625(1) 8.851(1) 447.92(2) 1.82
1.15
2.45
2.21
2.01
10.2
13.9
13.7
13.3
0.1
2. Experimental
0.2
0.3
The samples were prepared using a conventional ceramic
route and glycerin nitrate technique. In both methods rare earth
oxides Nd2O3 and Sm2O3 (with 99.99% purity), BaCO3 and Co3O4
(both of ‘‘pure for analysis’’ grade) and metallic cobalt were used
as starting materials. Metallic cobalt was obtained by reducing of
cobalt oxide in the hydrogen flow at 500–600 1C. Before weight-
ing the starting materials (oxides and barium carbonate) were
preliminary annealed in order to remove adsorbed gases and
water. Solid state synthesis was performed by stages within the
temperature range 850–1100 1C in air with intermediate grind-
ings in the agate mortar in alcohol media. According to the
glycerin nitrate technique rare earth oxides, barium carbonate
and metallic cobalt taken in appropriate ratios were dissolved in
nitric acid, and then glycerin in the amount needed for a complete
reduction of nitrate ions was added. Following heating first led to
the formation of viscous gel that subsequently transformed to
brown powder. Finally this powder was annealed at 1100 1C
during 120–240 h with intermediate grindings. All samples for
the phase equilibria study were quenched to room temperature
with cooling rate ꢂ5001/min. The samples of double perovskites
a
Here and in the next tables the reliability factors appears in the Rietveld
analysis are: RBr–Bragg factor; Rf–structural factor; Rp–profile factor.
According to the results of X-ray diffraction the homogeneity
ranges for the Ln2ꢀxBaxO3ꢀ solid solutions at studied conditions
appears within 0oxr0.1 for Ln¼Nd and 0oxr0.3 for Ln¼Sm.
The samples with larger values of barium content (0.1oxr0.6
for Ln¼Nd and 0.3oxr0.6 for Ln¼Sm) consisted of the satu-
rated solid solution (Nd1.9Ba0.1O3ꢀ or Sm1.7Ba0.3O3ꢀ , respec-
tively) and Ln2BaO4. Similarly to the parent rare earth oxide
Ln2O3 their solid solution possesses the same crystal structure:
Nd2ꢀxBaxO3ꢀ crystallized in P3m1 space group, and Sm2ꢀx
BaxO3ꢀ – in C2/m sp. gr. The unit cell parameters refined by
d
d
d
¯
d
d
the Rietveld method are presented in Table 1.
3.2. LnCoO3ꢀ –BaCoO3ꢀ system
d
d
In order to study the nature of phases existing within the
range Ln1ꢀuBauCoO3ꢀ (u¼0.0–1.0; Ln¼Nd, Sm) the samples of
d
LnBaCo2O5þ for the structural examination were slowly cooled
d
appropriate compositions with the step 0.1 were prepared using
standard ceramic and glycerin-nitrate techniques. According to
the results of XRD the only intermediate phase formed in both
from 1100 1C (cooling rate about 100 K/h) in air.
X-ray diffraction of quenched or slowly cooled powder sam-
ples were performed at room temperature using diffractometer
systems was LnBaCo2O5þ (u¼0.5, Ln¼Nd, Sm). The samples in
d
DRON-UM1 in Cu-K
chromator within the angle range 101r2
with the exposure time 5–10 s). Powder neutron profiles were
measured at the research reactor IVV-2, located near Ekaterin-
burg, Russia, on the D7A diffractometer. The wavelength
a
radiation with pyrolytic graphite mono-
r701 (scan step 0.041
the range 0ouo0.5 consisted of LnCoO3ꢀ and LnBaCo2O5þ
,
d
d
y
while in the range 0.5ouo1 LnBaCo2O5þ and BaCoO3ꢀ coex-
d
d
isted. These results for Sm containing system are in good agree-
ment with the conclusions made by Khalyavin et al. [36].
However an absence of barium solubility in NdCoO3 in the
present study (at least it has to be much less than 0.1) in contrast
to the value of homogeneity range u¼0.3, reported in [36] is
probably caused by the differences in annealing temperatures
(1100 1C in present study and 1200 1C in [36]).
˚
employed was 1.5155 A. The structural parameters were refined
by the Rietveld profile method using the Fullprof-2008 package.
The changes of oxygen content in the single phase complex
oxides were measured by TGA method (STA 409PC, Netzsch
Gmbh). The samples were placed in the TGA cell, heated up to
1100 1C and equilibrated in air at this temperature during 8 h.
The measurements performed in the cooling/heating mode (cool-
ing/heating rate 2 K/min) coincide with each other. The absolute
values of oxygen content were determined using direct reduction
The values of oxygen content for the slowly cooled samples at
room temperature were estimated from the TGA results as
(5þd)¼5.73 for Ln¼Nd, and (5þd)¼5.60 for Ln¼Sm. According
to the results of XRD analysis NdBaCo2O5.73 was found to be
tetragonal (space group: P4/mmm), and SmBaCo2O5.6—orthor-
hombic (Space group: Pmmm) that are in good agreement with
general relationship between oxygen content and crystal struc-
ture presented earlier [7]. Since the tetragonal-orthorhombic
transformation associates with the oxygen vacancies ordering the
structure of NdBaCo2O5,73 was also examined by neutron diffrac-
tion analysis. Neutron diffraction pattern of tetragonal NdBa-
Co2O5.73 is shown in Fig. 1a and XRD pattern for orthorhombic
SmBaCo2O5.6—in Fig. 1b. The results of the Rietveld refinement
for both samples are presented in Tables 2 and 3.
of LnBaCo2O5þ in hydrogen flow at 1100 1C inside the TGA cell
d
according to the following reaction:
LnBaCo2O5þd þð2:5þd dÞH2O:
ÞH2-12Ln2O3 þBaOþ2Coþð2:5þ
3. Results and discussion
3.1. Ln–Ba–O system
3.3. Ln3ꢀyBayCo2O7 system
In order to check a possibility of partial dissolution of barium
in Nd2O3 and Sm2O3 a number of samples with overall formula
Since earlier it was reported about the existence of Sm2Ba-
Co2O7 [37,38], we have checked the possibility of Ln3ꢀyBayCo2O7
(Ln¼Nd, Sm) phases formation at 1100 1C in air. Thereto the
Ln2ꢀxBaxO3ꢀ within the range 0.05rxr0.6 were prepared at
d
1100 1C in air by ceramic and glycerin-nitrate techniques.

L.Ya. Gavrilova et al. / Journal of Solid State Chemistry 184 (2011) 2083–2087
2085
Table 3
Refined atomic coordinates, unit cell parameters and reliability factors for the
SmBaCo2O5þ oxide.
d
Space group Pmmm
d
¼0.60
Atom
x
y
z
Sm
Ba
0.5
0.5
0
0.229(3)
0.5
0.250(1)
0
Co1
Co2
O1
O2
O3
O4
O5
O6
O7
0.5
0.255(2)
0.254(2)
0
0
0
0
0
0
0.5
0
0
0.5
0.5
0
0
0.5
0.5
0.5
0
0
0.239(3)
0.247(3)
0.238(2)
0.5
0.244(2)
3
˚
˚
˚
˚
a¼3.886(1) A; b¼7.833(1) A; c¼7.560(1) A; V¼230.22(2) (A) ; RBr¼10.7%;
Rf¼12.5%; Rp¼7.73%;
Fig. 1. Neutron diffraction pattern of NdBaCo2O5þ oxide (a) and XRD pattern of
d
SmBaCo2O5þ oxide (b). Points represent the experimental data and the solid
curve is the calculated profile. A difference curve is plotted at the bottom. Vertical
d
Fig. 2. XRD pattern of Nd2.25Ba0.75Co2O7ꢀ oxide. Points represent the experi-
d
mental data and the solid curve is the calculated profile. A difference curve is
plotted at the bottom. Vertical marks represent the position of allowed Bragg
reflections.
marks represent the position of allowed Bragg reflections.
Table 2
Table 4
Refined atomic coordinates, unit cell parameters and reliability factors for the
Unit cell parameters and reliability factors for the Nd3ꢀyBayCo2O7ꢀ solid
d
NdBaCo2O5þ oxide.
solutions.
d
Space group P4/mmm
d
¼0.73
Space group I4/mmm
3
Atom
x
y
z
y
˚
˚
˚
RBr (%)
Rf (%)
Rp (%)
a (A)
c (A)
V (A)
Nd
Ba
0.5
0.5
0
0.5
0.5
0
0.5
0.7
3.831(1)
3.833(1)
3.835(1)
20.015(2)
20.037(1)
20.069(2)
293.86(2)
294.34(3)
295.11(2)
0.974
0.72
0.712
0.71
9.68
8.58
13.3
0
0.75
0.8
Co1
O1
O2
O3
0.252(1)
0
1.96
1.90
0
0
0
0
0.5
0
0.5
0.281(2)
the main phase contained small amount of NdCoO3ꢀ n Nd2O3 as
d
impurities. The samples obtained by glycerin-nitrate technique after
120 h annealing were single phase. XRD patterns of the single phase
Nd3ꢀyBayCo2O7 (0.7ryr0.8) samples were refined by Rietveld
method within a tetragonal structure, I4/mmm space group. As an
3
˚
˚
a¼b¼3.903(1); c¼7.614(1) A; V¼116.02(2) (A) ; RBr¼5.88%; Rf¼5.61%;
Rp¼8.54%.
samples within the composition range 0.5ryr1.1 with the step
0.05 were prepared using standard ceramic route and glycerin-
nitrate technique described in Section 2. We failed to obtain
Sm2BaCo2O7, the sample of that nominal composition consisted of
SmBaCo2O5þ and Sm2ꢀxBaxO3ꢀ . On the contrary previously
example, Fig. 2 illustrates XRD pattern for the Nd2.25Ba0.75Co2O7ꢀ
oxide, and the values of structural parameters for all single phase
samples are listed in Table 4.
d
3.4. Phase equilibria in the Ln–Ba–CO–O systems (Ln¼Nd, Sm)
According to XRD patterns the samples enriched by (SmþBa)
d
d
unknown phase in the Nd3ꢀyBayCo2O7ꢀ series was detected
d
within the composition range 0.7ryr0.8. The samples prepared
by ceramic technique after annealing at 1100 1C during 240 h besides
relatively to Ln1-uBauCoO3ꢀ in the Sm–Ba–Co–O system contained
d

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L.Ya. Gavrilova et al. / Journal of Solid State Chemistry 184 (2011) 2083–2087
some previously unknown phase besides those described above.
In order to explain an appearance of unknown phase a number of
suppositions can be made. The first one is the possibility of
stabilization of Ruddlesden–Popper type phases like (Sm,Ba)2CoO4.
Furthermore Ba2CoO4 exist at studied conditions and possible
substitution of Ba by Sm could not be excluding. In order to check
this possibility a number of samples with nominal composition
(Ba1ꢀuSmu)2CoO4 with the step u¼0.1 were prepared. None of the
samples annealed at 1100 1C during more than 200 h become single
phase. Another supposition arises from the fact that the radius of
samarium ion is much smaller than that of barium ion. Earlier it was
shown that relatively small Y3þ can substitute Co ion rather than Ba
forming BaCo1ꢀxYxO3ꢀy [39]. No information concerning existence
Table 5
Unit cell parameters and reliability factors for the BaCo1ꢀzSmzO3ꢀ solid solutions.
d
3
z
RBr (%)
Rf (%)
Rp (%)
˚
˚
a (A)
V (A)
0.1
4.108(1)
4.131(1)
4.143(1)
69.33(1)
70.51(1)
71.13(2)
2.04
1.59
1.30
1.72
1.50
1.09
13.4
9.76
16.4
0.15
0.2
CoO
0.0
1.0
T = 1100°C, air
of BaCo1ꢀzLnzO3ꢀ (Ln¼Nd, Sm) had been found in the literature.
d
0.2
ξNd
ξCo
A number of samples with nominal composition corresponding to
0.8
the formula BaCo1ꢀzLnzO3ꢀ were prepared for both (Sm and Nd)
d
systems. All samples were equilibrated at 1100 1C during 200 h.
3
0.4
2
1
7
As a result single phase samples BaCo1ꢀzSmzO3ꢀ within the range
d
0.6
0.1rzr0.2 were obtained. All single phase solid solutions possess
BaCoO3−δ
0.4
NdCoO3−δ
0.6
cubic structure. XRD pattern for the single phase BaCo0.85Sm0.15O3-
,
d
8
6
as an example, is shown in Fig. 3, and unit cell parameters for all
single phase samples are listed in Table 5. The sample with
z¼0.05 corresponds to a mixture of two phases: saturated solid
solution BaCo0.9Sm0.1O3ꢀ and hexagonal BaCoO3ꢀ . The samples
9
Ba2CoO4
4
10
11
0.8
d
d
0.2
with nominal composition BaCo1ꢀzNdzO3ꢀ consisted of Nd2BaO4,
d
5
12
BaCoO3ꢀ and Ba2CoO4.
d
Overall phase equilibria in the Nd–Ba–Co–O system were
analyzed based on the results of XRD of 63 quenched samples,
and in the Sm–Ba–Co–O system – on 62 samples. Phase relations
at fixed temperature and oxygen pressure in a quaternary system
(Ln–Ba–Co–O) can be represented using a tetrahedron. A more
convenient, planar representation can be obtained using the
method of cross-sections. This method, however, is inapplicable
to the system under consideration because the oxidation states of
cobalt ions that various coexisted phases contain vary at the
studied conditions, therefore the compositions of simple oxides
and the compositions of the products do not lie in the same plane.
For this reason, we used projection onto the plane of metallic
components, an approach often used to represent such systems.
In this respect the composition in the phase triangles is repre-
sented by the mole fraction of metallic components, for example
xCo ¼ ðnCo=nLn þnBa þnCoÞ. The oxygen content of condensed
phases in each point of a projection is assumed to be equal to
the thermodynamically equilibrium value and could not be
1.0
0.0
NdO1.5
0.0
0.2
0.4
Nd2BaO4
0.6
0.8
1.0
ξBa
BaO
Fig. 4. A projection of isobaric isothermal phase diagram of the Nd–Ba–Co–O
system to the metallic components triangle (T¼1100 1C, Po2¼0.21 atm):
1–NdCoO3ꢀ
, CoO and NdBaCo2O5þ ; 2–CoO, NdBaCo2O5þ and BaCoO3ꢀ ;
d d d
d
3–melt; 4–Nd2O3, NdCoO3ꢀ and Nd2.3Ba0.7Co2O7ꢀ ; 5–Nd2ꢀxBaxO3ꢀ (0rxr0.1)
d
d
d
and Nd3ꢀyBayCo2O7ꢀ (0.7ryr0.8); 6–NdCoO3ꢀ , NdBaCo2O5þ and Nd2.3Ba0.7
d
d
d
Co2O7ꢀ ; 7–NdBaCo2O5þ and Nd3ꢀyBayCo2O7ꢀ (0.7ryr0.8); 8–NdBaCo2O5þ
,
d
d
d
d
Nd2.2Ba0.8Co2O7ꢀ and BaCoO3ꢀ ; 9–BaCoO3ꢀ , Nd2.2Ba0.8Co2O7ꢀ and Nd1.9Ba0.1O3ꢀ ;
d
d
d
d
d
10
– BaCoO3ꢀ , Nd1.9Ba0.1O3ꢀ and Nd2BaO4; 11–BaCoO3ꢀ , Nd2BaO4 and
Ba2CoO4; 12–Nd2BaO4, Ba2CoO4 and BaO.
d
d
d
calculated from the composition triangle. The compositions of
the samples taken into account are represented as points in the
phase diagrams (Figs. 4 and 5). As a result the phase triangle for
the Nd–Ba–Co–O system was divided into 12 fields (Fig. 4) and for
the Sm–Ba–Co–O system – into 13 fields (Fig. 5).
It should be noted that similarly to the La–Ba–Co–O system
[34,35] the melt regions (field 3 in Figs. 4 and 5) were detected
in the vicinity of cobalt oxide content approximately 60–80% at CoO–
BaO side for both Nd–Ba–Co–O and Sm–Ba–Co–O systems. Since no
systematic study of melt regions has been performed in the present
work these fields are shown schematically in the phase triangles.
4. Conclusion
The systematic study of phase equilibria in the Nd–Ba–Co–O
and Sm–Ba–Co–O systems show the similarity in the composi-
tional range nCo/(nLnþnBa)Z1. In both systems the formation of
so-called double perovskite LnBaCo2O5þ takes place. However
d
the difference in oxygen content in these complex oxides leads to
the different crystal structure – tetragonal (space group P4/mmm)
for NdBaCo2O5.73
, and orthorhombic (space group Pmmm)
for SmBaCo2O5.60. The phase equilibria in the compositional
range nCo/(nLnþnBa)o1 differ significantly. The formation of
Nd3ꢀyBayCo2O7ꢀ solid solutions within the compositional range
d
Fig. 3. XRD pattern of BaCo0.85Sm0.15O3ꢀ oxide. Points represent the experimental
data and the solid curve is the calculated profile. A difference curve is plotted at the
d
0.7ryr0.8 was detected in neodymium containing system and
single phase BaCo1ꢀzSmzO3ꢀ solid solutions were found to be
bottom. Vertical marks represent the position of allowed Bragg reflections.
d

L.Ya. Gavrilova et al. / Journal of Solid State Chemistry 184 (2011) 2083–2087
2087
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7
SmCoO3−δ
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1.0
0.0
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Sm2BaO4
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0.8
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1.5
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Fig. 5. A projection of isobaric isothermal phase diagram of the Sm–Ba–Co–O system
to the metallic components triangle (T¼1100 1C, Po2¼0.21 atm): 1–SmCoO3ꢀ , CoO
d
and SmBaCo2O5þ
; 2–CoO, SmBaCo2O5þ and BaCoO3ꢀ ; 3–melt; 4–Sm2O3,
d d d
SmCoO3ꢀ and SmBaCo2O5þ ; 5–SmBaCo2O5þ and Sm2ꢀxBaxO3ꢀ (0rxr0.3);
d
d
d
d
6–SmBaCo2O5þ , BaCoO3ꢀ and BaCo0.9Sm0.1O3ꢀ ; 7–SmBaCo2O5þ , BaCo0.9Sm0.1
d
d
d
d
O3ꢀ and Sm1.7Ba0.3O3ꢀ ; 8–Sm1.7Ba0.3O3ꢀ and BaCo1ꢀzSmzO3ꢀ (0.1rzr0.2);
d
d
d
d
9–Sm1.7Ba0.3O3ꢀ
,
d
Sm2BaO4 and BaCo0.8Sm0.2O3ꢀ
;
d
10–BaCoO3ꢀ
,
Ba2CoO4 and
d
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d
d
Ba2CoO4 and BaCo0.8Sm0.2O3ꢀ ; 13–Sm2BaO4, Ba2CoO4 and BaO.
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´
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system. Although the difference in the value of ionic radii of
˚
neodymium and samarium ions is not very large (
Dr¼0.03 A [40])
they reveal different character of phase relations. Even their
simple oxides crystallized in different space groups and homo-
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This work was financially supported in parts by the Russian
Foundation for Basic Research (project no. 09-03-00620) and the
Ministry for Education and Science of the Russian Federation
within the Federal Target Program ‘‘Research and Teaching Stuff
of Innovative Russia for 2009–2013’’.
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