Phase equilibria and crystal structure of the complex oxides in the Sr-Fe-Co-O system

Article abstract of DOI:10.1016/j.jssc.2008.03.010

Phase relations in the Sr-Fe-Co-O system have been investigated at 1100 °C in air by X-ray powder diffraction on quenched samples. Solid solutions of the form SrFe_1-xCo_xO_3-δ (0≤x≤0.7), Sr₃Fe_2-yCo_yO_7-δ (0≤y≤0.4) and Sr₄Fe_6-zCo_zO_13±δ (0≤z≤1.6) were prepared by solid-state reaction and by the sol-gel method. The structural parameters of single-phase samples were refined by the Rietveld profile method. The variation of the lattice parameters with composition has been determined for each solid solution and a cross-section of the phase diagram at 1100 °C in air for the entire Sr-Fe-Co-O system has been constructed.

Full text of DOI:10.1016/j.jssc.2008.03.010

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Journal of Solid State Chemistry 181 (2008) 1480– 1484
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Journal of Solid State Chemistry
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Phase equilibria and crystal structure of the complex oxides in the
Sr– Fe– Co– O system
Ã
T.V. Aksenova, L.Ya. Gavrilova, V.A. Cherepanov
Ural State University, Lenin av. 51, Yekaterinburg 620083, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
Phase relations in the Sr–Fe–Co–O system have been investigated at 1100 1C in air by X-ray powder
diffraction on quenched samples. Solid solutions of the form SrFe1ꢀxCoxO3ꢀd (0pxp0.7),
Sr3Fe2ꢀyCoyO7ꢀd (0pyp0.4) and Sr4Fe6ꢀzCozO137d (0pzp1.6) were prepared by solid-state reaction
and by the sol–gel method. The structural parameters of single-phase samples were refined by the
Rietveld profile method. The variation of the lattice parameters with composition has been determined
for each solid solution and a cross-section of the phase diagram at 1100 1C in air for the entire
Sr–Fe–Co–O system has been constructed.
Received 15 November 2007
Received in revised form
14 March 2008
Accepted 14 March 2008
Available online 21 March 2008
Keywords:
Phase diagram
& 2008 Elsevier Inc. All rights reserved.
Crystal structure
Solid solution
X-ray diffraction
Thermogravimetric analysis
1. Introduction
quenched and then heat-treated below 450 1C at high oxygen
pressure. The resulting samples possessed cubic perovskite-type
structure, in good agreement with the results reported in [17].
Sr2FeO4ꢀd synthesized at 750 1C under the flowing oxygen
(200 atm), crystallizes with a tetragonal unit cell (I4/mmm space
Strontium iron oxides, especially those doped with cobalt, in
which ionic and electronic conductivity coexist, received much
interest because of their potential applications for oxygen
separating membranes and for the partial oxidation of methane
[1]. Extensive studies of preparation routes for particular
compositions, structure and physical properties have been carried
out in recent years [2–6]. The magnetic properties of these oxides
have also received special attention because of the MR effect in
Sr3Fe2ꢀyCoyO7ꢀd and SrFe1ꢀxCoxO3ꢀd [7–10]. Relatively little work,
however, has been done on the phase stability or phase equilibria
in the Sr–Fe–Co–O system [11–13].
˚
˚
group): a ¼ 3.864 A, c ¼ 12.397 A [22]. Heating above 930710 1C
leads to decomposition of Sr2FeO4ꢀd to Sr3Fe2O7ꢀd and SrO
[14,22]. Strontium ferrite Sr4Fe3O10ꢀd, like Sr2FeO4ꢀd, is unstable
under heating and decomposes into Sr3Fe2O7ꢀd and SrFeO3ꢀd
above 850725 1C [14].
Tetragonal oxygen-deficient Sr3Fe2O7ꢀd has been prepared by
the conventional ceramic technique at 1100 1C in air with
following annealing at 900 1C in flowing O2 [23]. According to
[7], single-phase Sr3Fe2ꢀyCoyO7ꢀd exists in the range
0.25pyp1.75 when prepared at 1000 1C under flowing oxygen.
The X-ray patterns of all samples show that these solid solutions
The binary oxides SrFeO3ꢀd, Sr2FeO4ꢀd, Sr4Fe3O10ꢀd, Sr3Fe2O7ꢀd
,
Sr4Fe6O137d and SrFe12O19 in the Sr–Fe–O system have been
described in Refs. [14–28]. Several oxides with 1:1 Sr:Fe ratio with
varying oxygen content and different crystal structures are known
[14–21]. The oxygen content and stability of these oxides depends
on the temperature and oxygen partial pressure in an ambient
atmosphere. X-ray diffraction (XRD) data show that SrFeO3ꢀd has
are isostructural with the parent compound Sr3Fe2O7ꢀd
.
The incommensurate modulated structure of Sr4Fe6O137d
,
refined from single-crystal XRD data by the super-space formal-
ism, is described in [24]. A single crystal was treated at 1430 1C for
4 h, the temperature was then lowered to 800 at 2 1C/h and finally
reduced to room temperature in 12 h [24]. A precise structural
characterization of the Sr4Fe6O137d system has been carried out
by Rossell et al. [25], who found various space groups, depending
on the oxygen content. The pseudo-binary phase diagram
Sr4Fe6O137d–Sr4Co6O137d in air has been studied by Fossdal et
al. [11]. They find that Sr4Fe6O137d is stable in air above
775725 1C. The homogeneity range of Sr4Fe6ꢀzCozO137d in air
extended from z ¼ 0 to 0.9 at 1100 1C. These results conflict with
the values 0pzp1.8 in [5,30] and with 0pzp1.5 in [31]. Undoped
an ideal cubic structure when 2.88p(3ꢀd)p3 [15,17,20],
a
tetragonal structure at 2.76p(3ꢀd)p2.84 [15,16,19], an orthor-
hombic structure when (3ꢀd) ¼ 2.75 [15,16,18] and a brownmil-
lerite structure when (3ꢀd) ¼ 2.5 [17,21]. Takeda and Watanabe
[29] prepared a continuous series of solid solutions SrFe1ꢀx
CoxO3ꢀd (0pxp1), which were heat-treated above 1000 1C,
Ã
Corresponding author. Fax: +73432 507401.
E-mail address: Vladimir.Cherepanov@usu.ru (V.A. Cherepanov).
0022-4596/$ - see front matter & 2008 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2008.03.010

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1481
Sr4Fe6O13 and the solid solution Sr4Fe6ꢀzCozO137d possesses
orthorhombic structure (Iba2 space group) [25,30].
techniques. The tetragonal unit cell parameters of the ferrite
˚
SrFeO3ꢀd obtained in the present work (a ¼ 10.945(1) A,
˚
The crystal structure and some thermochemical properties of
hexagonal SrFe12O19ꢀd are described in [26–28]. The material was
prepared as single crystals by the flux method [26,27] and in
powder form by the citrate–nitrate gel combustion route, with
final annealing at 1473 K in dry air for 100 h [28].
The phase equilibria and crystal structures of the single phases
in the CoO–Fe2O3 system were described in [32]. The homo-
geneity ranges in air at 1100 1C were found to be 0pxp0.15 for
Co1ꢀxFexO (sp. gr. Fm3m), 0pyp0.03 for Fe2ꢀyCoyO3 and
0.84pzp1.38 for Fe3ꢀzCozO4.
c ¼ 7.705(1) A) are in a good agreement with those reported
earlier [15,16]. The TGA results indicate that the oxygen content in
SrFeO3ꢀd at 1100 1C in air was determined as 2.5270.01
(d ¼ 0.4870.01), which agrees with the value reported in [18]
under the same conditions. The XRD results for quenched samples
show that single-phase solid solutions SrFe1ꢀxCoxO3ꢀd forms at
1100 1C in air within the range 0pxp0.7. Beyond this range
SrCoO2.57d was detected as a second phase. The crystal structure
of the SrFe1ꢀxCoxO3ꢀd with cobalt content 0pxp0.3 was found to
be tetragonal, space group I4/mmm. Further substitution of iron
for cobalt in crystal structure led to the change of lattice
symmetry: solid solutions with 0.3pxp0.7 have a cubic structure,
space group Pm3m. The oxygen deficiency, determined by TGA in
SrFe0.5Co0.5O3ꢀd is 0.4470.01. The XRD pattern and the refined
Rietveld profile for single-phase SrFe0.3Co0.7O3ꢀd are shown in
Fig. 1. The unit cell parameters for SrFe1ꢀxCoxO3ꢀd are listed in
Table 1. Cobalt substitution for iron in SrFe1ꢀxCoxO3ꢀd
(0.3pxp0.7) decreases the parameter a (Fig. 2) and hence the
volume of unit cell, since ionic radius for cobalt ion
The present work is a study of the phase equlibria in the
Sr–Fe–Co–O system in air at 1100 1C. The homogeneity ranges and
crystal structures have been determined and a cross-section of the
phase diagram has been constructed.
2. Experimental
Our starting materials were strontium carbonate SrCO3 of
‘‘special purity’’ grade, iron oxide Fe2O3 of ‘‘pure for analysis’’
grade, cobalt oxide Co3O4 of ‘‘pure for analysis’’ grade and metallic
iron of ‘‘pure for analysis’’ grade. All materials were preliminarily
dried in air to remove adsorbed moisture and gases: SrCO3 and
Co3O4 at 600 1C for 3 h, and Fe2O3 at 500 1C for 3 h. The metallic
cobalt was obtained by reducing Co3O4 in flowing hydrogen at
600 1C.
Several samples were prepared by solid-state reaction in air at
temperatures between 850 and 1100 1C for 240–316 h, with
intermediate grindings. Other samples were synthesized by the
sol–gel methods. Appropriate amounts of SrCO3, metallic Fe and
Co were dissolved in nitric acid, and then either crystalline citric
acid hydrate or glycerin was added to the solution. The resulting
gel was dried, decomposed at 300 1C and calcined at various
temperatures (400–1100 1C) in air for 72–120 h, with intermediate
grindings.
(r(Co3+) ¼ 0.685; r(Co4+) ¼ 0.67 A) is smaller than that for iron
˚
ion (r(Fe3+) ¼ 0.785; r(Fe4+) ¼ 0.725 A) [33].
˚
3.2. Solid solution Sr3Fe2ꢀyCoyO7ꢀd
The samples of general composition Sr3Fe2ꢀyCoyO7ꢀd with y ¼ 0,
0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.4 were prepared by the
citrate–nitrate method. The homogeneity range of the solid solutions
Sr3Fe2ꢀyCoyO7ꢀd was found to be 0pyp0.4. The XRD patterns of the
samples with 0.4pyp1.4 revealed additional reflections from
Sr3Co2O7ꢀd. The structure of undoped Sr3Fe2O7ꢀd at 1100 1C is
˚
˚
tetragonal, with unit cell parameters a ¼ 3.866(1) A, c ¼ 20.162(1) A,
(I4/mmm space group). The lattice parameters, refined from XRD
results, for single-phase tetragonal Sr3Fe2ꢀyCoyO7ꢀd, are listed in
Table 2. The profile obtained from the Rietveld analysis for
unsubstituted Sr3Fe2O7ꢀd is shown in Fig. 3.
Obtained oxides were characterized by XRD using DRON-UM1
diffractometers with CuKa radiation. A pyrolytic graphite mono-
3.3. Solid solution Sr4Fe6ꢀzCozO137d
˚
chromator was used for the reflected beam (l ¼ 1.5418 A). Silicon
was used as the external standard. The full-profile Rietveld
analysis (‘‘Fullprof 2006’’) was used for the crystal structure
refinement. Intensity data were collected point by point over the
angular range 101p2yp701, with 0.021 steps for 1–10 s. Conver-
gence between experimental XRD data and the calculated profile
was estimated by a set of standard factors: Rwp—the weighed
profile factor Rp—the profile factor, Rf—the structural factor,
Examination of annealed Sr4Fe6ꢀzCozO137d samples with
0pzp1.8 shows that solid solutions exist in the range z ¼ 0–1.6.
RBr—the Bragg-factor and Rexp—the expected factor.
Oxygen content in some samples was determined by reduction
at hydrogen flux in TGA equipment at 1100 1C. X-ray powder
diffraction of the samples after reduction confirms that only SrO,
Fe and Co were present as the products. The accuracy of the
oxygen content determination was within 70.01.
3. Results and discussion
The phase equilibria in the Sr–Fe–Co–O system were studied at
1100 1C in air using 68 samples with various compositions.
3.1. Solid solution SrFe1ꢀxCoxO3ꢀd
In order to determine the homogeneity range of the solid
solution SrFe1ꢀxCoxO3ꢀd, samples with x ¼ 0, 0.1, 0.2, 0.3, 0.4, 0.5,
0.6, 0.7, 0.8, 0.9, 0.95 and 1 were prepared. The syntheses
were performed by the citrate–nitrate and standard ceramic
Fig. 1. Rietveld refinement profile for the single-phase solid solution
SrFe0.3Co0.7
O3ꢀd: open circles—experimental XRD data, upper continuous line is
the calculated profile, lower continuous line is the difference plot.

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T.V. Aksenova et al. / Journal of Solid State Chemistry 181 (2008) 1480–1484
Table 1
Structural parameters for SrFe1ꢀxCoxO3ꢀd solid solution quenched from 1100 1C in
air
˚
˚
˚
x
a (A)
b (A)
c (A)
Refinement parameters
RBr
Rf
Rp
I4/mmm
0
10.945(1)
10.917(2)
10.920(1)
10.945(1)
10.917(2)
10.920(1)
7.705(1)
7.730(1)
7.734(1)
0.541
0.745
1.28
1.06
1.50
1.94
10.8
12.2
11.2
0.1
0.2
Pm3m
0.3
3.870(1)
3.867(1)
3.865(1)
3.864(1)
3.863(1)
3.870(1)
3.867(1)
3.865(1)
3.864(1)
3.863(1)
3.870(1)
3.867(1)
3.865(1)
3.864(1)
3.863(1)
1.94
4.90
3.69
5.20
1.11
1.94
4.98
4.13
5.88
1.14
10.6
14.0
13.6
14.3
7.8
0.4
0.5
0.6
0.7
Fig. 3. Rietveld refinement profile for the single-phase Sr3Fe2O7ꢀd
: open
circles—experimental XRD data, upper continuous line is the calculated profile,
lower continuous line is the difference plot.
Table 3
Structural parameters for Sr4Fe6ꢀzCozO137d solid solution quenched from 1100 1C
in air (Iba2 space group)
3
˚
˚
˚
˚
x
a (A)
b (A)
c (A)
V (A)
Refinement parameters
RBr
Rf
Rp
0a
11.107(2) 18.949(2) 5.580(1) 1174.65(2) 1.61
1.47
1.40
2.85
1.93
1.80
1.95
1.77
2.69
1.63
1.50
1.31
12.1
11.3
10.6
10.8
10.5
0.1b 11.103(1) 18.960(2) 5.578(1) 1174.43(2) 1.51
0.2a 11.095(1) 18.960(2) 5.577(1) 1173.27(1) 1.75
0.3b 11.081(1) 18.970(2) 5.572(1) 1171.06(2) 1.42
0.4a 11.080(1) 18.977(2) 5.570(1) 1171.43(1) 1.63
0.6a 11.062(1) 18.996(2) 5.565(1) 1169.48(1) 1.26
0.8a 11.062(1) 18.987(2) 5.565(1) 1169.14(3) 1.37
9.71
10.6
10.4
10.6
Fig. 2. The unit cell parameters for the solid solution SrFe1ꢀxCoxO3ꢀd
.
1a
11.061(1) 18.993(2) 5.565(1) 1169.63(2) 1.65
1.2a 11.047(1) 19.000(2) 5.558(1) 1166.81(2) 1.34
1.4a 11.038(1) 19.001(2) 5.554(1) 1165.06(3) 1.27
1.6a 11.039(1) 19.006(2) 5.552(1) 1165.13(3) 1.29
9.92
10.7
Table 2
Structural parameters for Sr3Fe2ꢀyCoyO7ꢀd solid solution quenched from 1100 1C in
air (I4/mmm space group)
a
Samples obtained by the glycerin–nitrate technique.
3
b
˚
˚
˚
x
a (A)
c (A)
V (A )
Refinement parameters
Samples obtained by the citrate–nitrate technique.
RBr
Rf
Rp
3.4. Solid solution SrFe12ꢀuCouO19ꢀd
0
3.867(1)
3.866(1)
3.863(1)
3.861(1)
3.859(1)
20.156(1)
20.152(2)
20.151(2)
20.155(1)
20.153(1)
301.37(2)
301.23(3)
300.82(2)
300.52(2)
300.13(2)
4.86
4.79
9.48
9.71
9.28
9.08
8.94
0.1
0.2
0.3
0.4
1.93
1.56
The citrate–nitrate route was used to prepare SrFe12O19ꢀd and
SrFe12ꢀuCouO19ꢀd with u ¼ 0.1. Strontium hexaferrite SrFe12O19ꢀd
is isomorphous with the magnetoplumbite BaFe12O19ꢀd (space
group P63/mmc). All reflections of single-phase SrFe12O19ꢀd
quenched from 1100 1C in air were indexed in the P63/mmc space
group. The hexagonal lattice parameters obtained for SrFe12O19ꢀd
1.70
1.67
0.845
0.992
0.915
0.999
The preparation technique for each sample is appended to Table 3.
The maximum value of Co substitution for Fe lies between z ¼ 1.6
and 1.7, which is slightly smaller the values reported in [5,11]. This
can be explained by the fact that our samples were prepared at a
higher temperature (1100 1C) than those used in [5,11]
(850–900 1C). Our XRD pattern for Sr4Fe6O137d is identical to that
˚
˚
were a ¼ b ¼ 5.878(2) A, c ¼ 23.045(3) A, in good agreement with
those obtained in [26,27]. According to X-ray data, the sample
with overall composition SrFe11.9Co0.1O19ꢀd consisted of three
phases: SrFe12O19ꢀd, Sr4Fe6ꢀzCozO137d solid solution and CoFe2O4.
We conclude any range of z for which Sr4Fe6ꢀzCozO137d is
homogeneous is significantly less than 0.1.
˚
reported in [5] (orthorhombic unit cell parameters a ¼ 11.107(2) A,
˚
˚
b ¼ 18.949(2) A, c ¼ 5.580(1) A, space group Iba2). The introduc-
tion of cobalt into the structure of Sr4Fe6ꢀzCozO137d leads to
monotonic variations in the unit cell parameters with increase of
cobalt content (Fig. 4). The volume of unit cell decreases with z
because ionic radius of cobalt is smaller than that of iron. The unit
cell parameters obtained for single-phase Sr4Fe6ꢀzCozO137d are
given in Table 3.
3.5. Phase diagram of the Sr– Fe– Co– O system in air at 1100 1C
A convenient plane representation of the quaternary Sr–Fe–
Co–O system can be made in triangular form if the composition is
expressed in terms of the molar fraction of the metallic

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1483
Table 4
Phase composition within the fields of the cross-section of phase diagram of
Sr– Fe– Co– O system (Fig. 5)
Fields on the diagram Phase composition
1
2
3
4
5
CoO, SrCoO2.57d, SrFe0.3Co0.7O3ꢀd
Co1ꢀyFeyO (0pyp0.15), SrFe1ꢀxCoxO3ꢀd (0.38pxp0.7)
Co0.85Fe0.15O, SrFe0.62Co0.38O3ꢀd, Sr4Fe4.4Co1.6O137d
Co0.85Fe0.15O, Sr4Fe4.4Co1.6O137d, Co1.38Fe1.62O4
Sr4Fe6ꢀzCozO137d (0.3pzp1.6), CouFe3ꢀuO4
(0.84pup1.38)
6
Sr4Fe5.7Co0.3
Co0.84Fe2.16O4, SrFe12
SrFe12
O
137d, Co0.84Fe2.16O4, SrFe12O19ꢀd
7
O
19ꢀd, Fe1.97Co0.03O3
8
O
19ꢀd, Fe2ꢀxCoxO3 (0pxp0.03),
9
SrFe12O19ꢀd, Sr4Fe6ꢀzCozO137d (0pzp0.3)
10
11
12
13
14
15
Sr4Fe6ꢀzCozO137d (0pzp1.6), SrFe1ꢀxCoxO3ꢀd (0pxp0.38)
SrFe1ꢀxCoxO3ꢀd (0pxp0.7), Sr3Fe2ꢀyCoyO7ꢀd (0pyp0.4)
SrFe0.3Co0.7
O
3ꢀd, Sr3Fe1.6Co0.4
O7ꢀd, Sr3Co2O7ꢀd
Sr3Co2O7ꢀd, SrFe0.3Co0.7
O
3ꢀd, SrCoO2.57s
SrO, Sr3Co2O7ꢀd, Sr3Fe1.6Co0.4O7ꢀd
SrO, Sr3Fe2ꢀyCoyO7ꢀd (0pyp0.4)
Fig. 4. The lattice parameters for Sr4Fe6ꢀzCozO137d versus composition of solid
solution: open symbols—data reported in [4], filled symbols—data obtained in this
study.
been determined. The structural parameters of the solid solutions
were refined by the Rietveld full-profile analysis and the
isobaric–isothermal cross-section of the phase diagram for the
Sr–Fe–Co–O system in air at 1100 1C has been constructed.
Acknowledgment
This work was financially supported by Russian Foundation for
Basic Researches (Project RFBR-Urals N 07-03-96079).
References
[1] U. Balachandran, T.J. Dusek, S.M. Sweeney, R.B. Poeppel, R.L. Mieville, P.S.
Maiya, M.S. Kleefisch, S. Pei, T.P. Kobylinski, C.A. Udovich, A.C. Bose, Am.
Ceram. Soc. Bull. 74 (1995) 71–75.
[2] H. Fjellva˚ g, B.C. Hauback, R. Bredesen, J. Mater. Chem. 7 (1997) 2415–2419.
[3] W. Jin, I.R. Abothu, R. Wang, T.-S. Chung, Ind. Eng. Chem. Res. 41 (2002)
5432–5435.
[4] Z.Q. Deng, W. Liu, D.K. Peng, C.S. Chen, W.S. Yang, Mater. Res. Bull. 39 (2004)
963–969.
[5] B. Ma, J.P. Hodges, J.D. Jorgensen, D.J. Miller, J.W. Richardson, U. Balachandran,
J. Solid State Chem. 141 (1998) 576–586.
[6] L. Mogni, F. Prado, A. Caneiro, Chem. Mater. 18 (2006) 4163–4170.
[7] G.M. Veith, R. Chen, G. Popov, M. Croft, Y. Shokh, I. Nowik, M. Greenblatt,
J. Solid State Chem. 166 (2002) 292–304.
Fig. 5. Isobaric–isothermal cross-section of phase diagram of the Sr–Fe–Co–O
system at 1100 1C in air.
[8] S. Ghosh, P. Adler, J. Mater. Chem. 12 (2002) 511–521.
[9] A. Maignan, C. Martin, N. Nguyen, B. Raveau, Solid State Sci. 3 (2001) 57–63.
[10] P.D. Battle, M.A. Green, J. Lago, A. Mihut, M.J. Rosseinsky, L.E. Spring,
J. Singleton, J.F. Ventre, Chem. Commun. (1998) 987.
[11] A. Fossdal, L.T. Sagdahl, M.-A. Einarsrud, K. Wiik, T. Grande, P.H. Larsen, F.W.
Poulsen, Solid State Ionics 143 (2001) 367–377.
components. However, the oxygen content in coexisting complex
oxides cannot be determined from such a diagram, its value
should be ascribed to the corresponding thermodynamically
equilibrium composition of each phase.
[12] S. McIntosh, J.F. Vente, W.G. Haije, D.H.A. Blank, H.J.M. Bouwmeester, Solid
State Ionics 177 (2006) 833–842.
[13] N. Grunbaum, L. Mogni, F. Prado, A. Caneiro, J. Solid State Chem. 177 (2004)
2350–2357.
[14] A. Fossdal, M.-A. Einarsrud, T. Grande, J. Solid State Chem. 177 (2004)
2933–2942.
[15] M. Takano, T. Okita, N. Nakayama, Y. Bando, Y. Takeda, O. Yamamoto,
J.B. Goodenough, J. Solid State Chem. 73 (1988) 140–150.
[16] L. Fourne`s, Y. Potin, J.C. Grenier, G. Demazeau, M. Pouchard, Solid State
Commun. 62 (1987) 239–244.
Using the XRD data from all our samples, we have divided the
isobaric–isothermal cross-section of the Sr–Fe–Co–O phase dia-
gram into 15 phase fields (Fig. 5). The compositions of the samples
are shown as points on the diagram. The phases coexisting in each
field are given in Table 4. In field 3, semi-quantitative X-ray
analysis revealed a fixed composition of SrFe1ꢀxCoxO3ꢀd with
x ¼ 0.38 coexisting with Co-saturated Sr4Fe4.4Co1.6O137d and Fe-
saturated Co0.85Fe0.15O. The same method was used to determine
the fixed composition of Sr4Fe5.7Co0.3O137d coexisting with
Co0.84Fe2.16O4 and SrFe12O19ꢀd within the field 6 (Fig. 5).
`
[17] A. Wattiaux, L. Fournes, A. Demourgues, N. Bernaben, J.C. Grenier,
M. Pouchard, Solid State Commun. 77 (1991) 489–493.
[18] M. Schmidt, J. Phys. Chem. Solids 61 (2000) 1363–1365.
[19] T.C. Gibb, J. Chem. Soc. Dalton Trans. (1985) 1455–1470.
[20] H. Taguchi, J. Mater. Sci. Lett. 2 (1983) 665–666.
[21] J.-C. Grenier, N. Ea, M. Pouchard, P. Hagenmuller, J. Solid State Chem. 58
(1985) 243–252.
4. Conclusion
[22] S.E. Dann, M.T. Weller, D.B. Currie, J. Solid State Chem. 92 (1991) 237–240.
[23] K. Mori, T. Kamiyama, H. Kobayashi, S. Torii, F. Izumi, H. Asano, J. Phys. Chem.
Solids 60 (1999) 1443–1446.
[24] O. Pe´rez, B. Mellenne, R. Retoux, B. Raveau, M. Hervieu, Solid State Sci. 8
(2006) 431–443.
The
solid
solutions
SrFe1ꢀxCoxO3ꢀd
(0pxp0.7),
Sr3Fe2ꢀyCoyO7ꢀd (0pyp0.4), Sr4Fe6ꢀzCozO137d (0pzp1.6) have
been prepared and their homogeneity ranges in air at 1100 1C have

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[25] M.D. Rossell, A.M. Abakumov, G. Van Tandeloo, M.V. Lomakov, S.Ya. Istomon,
E.V. Antipov, Chem. Mater. 17 (2005) 4717–4726.
[26] X. Obradors, X. Solans, A. Collomb, D. Samaras, J. Rodriguez, M. Pernet, M.
Font-Altaba, J. Solid State Chem. 72 (1988) 218–224.
[27] K. Kimura, M. Ohgaki, K. Tanaka, H. Morikawa, F. Marumo, J. Solid State Chem.
87 (1990) 186–194.
[28] S.K. Rakshit, S.C. Parida, S. Dash, Z. Singh, R. Prasad, V. Venugopal, Mater. Res.
Bull. 40 (2005) 323–332.
[29] T. Takeda, H. Watanabe, J. Phys. Soc. Japan 33 (1972) 973–978.
[30] Y. Xia, T. Armstrong, F. Prado, A. Manthiram, Solid State Ionics 130 (2000)
81–90.
[31] Z. Deng, G. Zhang, W. Liu, D. Peng, C. Chen, Solid State Ionics 152–153 (2002)
735–739.
[32] N.V. Proskurnina, V.A. Cherepanov, O.S. Golynets, V.I. Voronin, Inorg. Mater.
40 (2004) 955–959.
[33] R.D. Shannon, C.T. Prewitt, Acta Crystallogr. A 32 (1976) 751–753.