Crystal Structure of the New Ordered Phases Based on Y2Ba3Fe3Co2O13 + δ

Article abstract of DOI:10.1134/S0020168520010161

Abstract: New phases with an ordered structure of the composition Y₂Ba₃Fe_{5 – y}Co_yO_{13 + δ} (1.7 ≤ y ≤ 2.1) were obtained via the glycerol-nitrate technique. The regions of existence of two ty

Full text of DOI:10.1134/S0020168520010161

ISSN 0020-1685, Inorganic Materials, 2020, Vol. 56, No. 1, pp. 72–76. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Neorganicheskie Materialy, 2020, Vol. 56, No. 1, pp. 76–80.
Crystal Structure of the New Ordered Phases
1
Based on Y2Ba3Fe3Co2O13 + δ
A. S. Urusovaa, A. V. Bryuzginaa, M. Yu. Mychinkoa, A. V. Dyakovaa, and V. A. Cherepanova, *
aUral Federal University name after the First President of Russia B.N. Yeltsin, Yekaterinburg, 620002 Russia
*e-mail: v.a.cherepanov@urfu.ru
Received December 16, 2018; revised May 12, 2019; accepted June 19, 2019
Abstract– New phases with an ordered structure of the composition Y2Ba3Fe5 – yCoyO13 + δ (1.7 ≤ y ≤ 2.1)
were obtained via the glycerol-nitrate technique. The regions of existence of two types of structures were
determined by transmission electron microscopy: for 1.7 ≤ y ≤ 1.8, the structure described as ap × ap × 3ap,
and for 1.9 ≤ y ≤ 2.1, it is ap × ap × 5ap, where ap is the parameter of the ideal cubic perovskite. The unit cell
parameters for all single-phase samples were refined by the Le Bail method. The phase composition of oxides
outside the homogeneity ranges is determined.
Keywords: glycerol-nitrate technique, structure, unit cell parameters, electron microscopy
DOI: 10.1134/S0020168520010161
INTRODUCTION
site, as well as Co and Fe ions in the B site [1]. On the
other hand, it is known that in individual “double” 112
phases and “triple” 123 phases, partial replacement of
cobalt with iron LnBaCo2 – xFexO5 + δ [10, 20–25] or
iron with cobalt LnBa2Fe3 – xCoxO8 + w [26] can be
implemented.
The recently described complex oxide of the
Y2Ba3Fe3Co2O13 + δ composition [1] is a rare example
of a multiplex perovskite-like superstructure, includ-
ing the ordered arrangement of not only substantially
different in size Y and Ba cations in the A sublattice,
but also close in size and chemical nature Co and Fe in
the B sublattice. The complete separation of Y and Ba
along different alternating planes was described in the
well-known “double” perovskites YBaFe2O5 + δ [2–4],
YBaCo2O5 + δ [5–10], denoted as 112 phases, or “tri-
ple” perovskites YBa2Fe3O8 + w [11–15], designated as
123 phases.
In this work, we have made an attempt to evaluate
the effect of the Fe/Co ratio variation on the stability
of the 5-fold nanostructurally ordered superstructure
of the complex oxide Y2Ba3Fe3Co2O13 + δ
.
EXPERIMENTAL
An unusual type of ordered 5-layer structures in
which REE and barium ions are located both in
immiscible (LnO) and (BaO) layers and in mixed
(Ln/BaO) layers, which were alternating in a per-
ovskite-like structure as follows: (LnO)–(BaO)–(Ln /
BaO)–(Ln/BaO)–(BaO)–(LnO), had been obtained
for Ln = Nd, Sm, Eu [16–19]. In this case, the partial
replacement of iron by cobalt, stabilizing the forma-
tion of the 5-fold superstructure, did not lead to the
ordering of the latter. An increased difference in the
cations’ radii in the A positions in the case of Ln = Y,
Ba makes the formation of mixed (Y/BaO) layers dis-
advantageous, but leads to the formation of an inter-
growth structure with ordered alternation of the 112
phase of cobaltite and 123 phase of ferrite, which
ensures complete separation of Y and Ba ions in the A
Samples for study were obtained by the glycerol-
nitrate technique. The starting reagents used were
yttrium oxide Y2O3 (ItO-B qualification), barium car-
bonate BaCO3 (of “special purity” grade), preliminary
calcined to remove adsorbed moisture and gases, iron
oxalate FeC2O4 ⋅ 2Н2О (of “pure for analysis” grade)
as well as metallic cobalt Co, nitric acid HNO3 (of
“pure for analysis” grade) and glycerin C3H8O3 (of
“pure for analysis” grade). Metallic cobalt was
obtained by reduction of Co3O4 oxide at 673 K in a
flow of hydrogen.
The powders were annealed stepwise at tempera-
tures of 1073–1373 K. The final annealing was carried
out at 1373 K in air for 60 h (with intermediate grind-
ings in ethanol every 12 h). After annealing, the sam-
ples were quenched on a massive metal plate at room
temperature with a cooling rate of 500 K/min. Some
samples were then annealed in an atmosphere with
1
The work was presented at 16th International IUPAC Confer-
ence on High Temperature Materials Chemistry (HTMC-XVI),
July 2–6, 2018, Yekaterinburg, Russia.
72

CRYSTAL STRUCTURE OF THE NEW ORDERED PHASES
73
010p
010p
001p
001p
[100]
[100]
Fig. 1. TEM images for Y Ba Fe
Co O
with y = 1.75 (a), y = 1.9 (b).
2
3
5 – y
y
13 + δ
low oxygen pressure. The values of oxygen partial metric composition Y2Ba3Fe3Co2O13 + δ in the range
pressure were adjusted using the Zirconia 318 device.
1.5 ≤ y ≤ 2.3 with a step of 0.05.
The phase composition of the samples was moni-
tored by X-ray phase analysis (XRD) on a Shimadzu
XRD-7000 diffractometer (CuKα radiation (λ =
1.5418 Å) in the range of angles 10° ≤ 2θ° ≤ 90° in a
step of 0.02° with exposure time at a point of 2 s).
In order to refine the structure determined by x-ray
analysis a transmission electron microscopy (TEM)
has been used. The studies were performed on a JEOL
JEM 2100 microscope with a hexaboride thermionic
emission cathode at an accelerating voltage of 200 kV.
The resolution is 0.17 nm.
According to the XRD results, cobalt-free
Y2Ba3Fe5O13 + δ is formed only at oxygen partial pres-
sures lower than in air. At log( /atm) = –6 small
p
O2
amount of yttrium and barium ferrites YFeO3 – δ and
BaFeO3 – δ which content did not exceed 5% were pre-
sented in equilibrium with the main phase. In the pro-
cedure of Y2Ba3Fe5O13 + δ synthesis in air, the sample
appears to be an equilibrium mixture of three phases:
YFeO3 – δ, Y3Fe5O12, BaFe0.9Y0.1O3 – δ, which is in good
agreement with the results of [4].
Partial replacement of iron by cobalt led to the for-
mation of two types of solid solutions with tetragonal
symmetry: for y varying from 1.7 to 1.8, the structure
was described as ap × ap × 3ap, and for 1.9 ≤ y ≤ 2.1 it
was ap × ap × 5ap, where ap is the unit cell parameter
for the ideal cubic perovskite.
Powdered samples for TEM studies were ground in
an agate mortar with the addition of ethanol, and the
resulting suspension was applied to a supporting cop-
per grid coated with an amorphous carbon film.
RESULTS AND DISCUSSION
XRD patterns of all single-phase oxides were
indexed in the framework of tetragonal symmetry
(sp. gr. P4/mmm).
Samples with the overall composition of Y2Ba3Fe5 – y
-
CoyO13 + δ were synthesized using the glycerol-nitrate
technique at 1373 K in air within the composition
range 0 ≤ y ≤ 3 with a step of 0.5, and near the stoichio-
Figure 1 illustrates TEM images for the Y2Ba3Fe5 – y
-
CoyO13 + δ samples with y =1.75 (a) and y = 1.9 (b).
Table 1. The unit cell parameters for Y2Ba3Fe5 – yCoyO13 + δ with 1.7 ≤ y ≤ 1.8 and 1.9 ≤ y ≤ 2.1 (sp. gr. P4/mmm)
V, Å3
Rp, %
Rwp, %
Rewp, %
y
a, Å
c, Å
1.70
1.75
1.80
1.90
1.95
2.00
2.05
2.10
3.904(1)
3.899(1)
3.901(1)
3.895(1)
3.879(1)
3.874(1)
3.848(1)
3.845(1)
11.699(1)
11.703(1)
11.659(1)
19.372(1)
19.249(1)
19.095(1)
18.895(1)
18.879(1)
178.31(1)
177.91(1)
177.42(1)
293.89(1)
289.63(1)
286.58(1)
279.78(1)
279.11(1)
17.6
14.5
17.3
11.1
12.1
20.7
17.4
15.3
31.5
19.9
34.7
23.3
21.7
28.1
33.1
29.5
14.66
17.78
13.92
11.17
17.66
13.86
17.93
17.02
INORGANIC MATERIALS Vol. 56 No. 1 2020

74
URUSOVA et al.
Table 2. Phase composition of the samples Y2Ba3Fe5 – yCoyO13 + δ
y
Phase composition
YFeO3 – δ, Y3Fe5O12, BaFe0.9Y0.1O3 – δ
0
YBa2Fe3 – nConO8 + w, YFe1 – xCoxO3 – δ (0 ≤ x ≤ 0.45)
YBa2Fe3 – nConO8 + w and Y2Ba3Fe5 – yCoyO13 + δ
0.5 < y < 1.65
1.8 < y < 1.9
2.15 < y < 3.0
Y2Ba3Fe5 – yCoyO13 + δ (1.9 ≤ y ≤ 2.1),BaFe0.9 – zY0.1CozO3 – δ (0.0 ≤ z ≤ 0.15)
Presented in Fig. 1 electron diffraction images
along the [100] axis were indexed in the framework of
cubic syngony (sp. gr. Pm3m, ap ≈ 3.9 Å). It can be seen
that the sample of the nominal composition
Y2Ba3Fe3.25Co1.75O13 + δ has a triple c parameter com-
pared to the ap for the ideal simple perovskite structure
and, therefore, it refers to the 123 phase, and its formula
should be represented as Y1 + εBa2 – εFe1.95Co1.05O8 + w
(ε = 0.2). For the Y2Ba3Fe3.1Co1.9O13 + δ sample, the for-
mation of the ordered five-fold structure is observed.
The XRD pattern for the Y2Ba3Fe3.1Co1.9O13 + δ
sample refined by the Le Bail method is shown in Fig. 2,
as an example.
Substitution of iron ions (
= 0.785 / 0.92 Å,
rFe3+
Fe2+
CN = 6) with smaller cobalt ions (
= 0.75/
rCo3+
Co2+
0.885, CN = 6) [27] leads to a gradual decrease in the
length of the B – O bond and, as a result, to a decrease
in the unit cell size.
The phase composition of samples located outside
the homogeneity range is presented in Table 2.
The unit cell parameters for all single-phase samples
refined by the Le Bail method are listed in Table 1.
7000
6000
5000
4000
3000
2000
1000
0
20
30
40
50
2θ, deg
60
70
80
90
Fig. 2. XRD pattern for Y Ba Fe Co
O
, refined by the Le Bail method: points are obtained experimentally, line is the
2
3
3.1
1.9 13 + δ
theoretical profile, solid bottom line is the difference between experimental results and theoretical profile.
INORGANIC MATERIALS Vol. 56
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2020

CRYSTAL STRUCTURE OF THE NEW ORDERED PHASES
75
pp. 355–363.
The ratio of iron and cobalt in each of the coexist-
ing phases in the samples with 0.5 <y <1.65 was not
determined, and it may not coincide with the overall
composition of the initial sample due to redistribution.
https://doi.org/10.1006/jssc.2000.9006
7. Aurelio, G., Curiale, J., and Sanchez, R.D., Effects of
oxygen nonstoichiometry on the physical properties of
the YBaCo2O5 + δ layered cobaltites, Phys. B (Amster-
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CONCLUSIONS
8. Aksenova, T.V., Gavrilova, L.Ya., Tsvetkov, D.S., Vo-
ronin, V.I., and Cherepanov, V.A., Crystal structure
and physicochemical properties of layered perovskite-
like phases LnBaCo2O5+δ, Russ. J. Phys. Chem. A, 2011,
vol. 85, no. 3, pp. 427–432.
It is shown that the Fe/Co ratio is a critical param-
eter for the formation of a five-fold ordered structure
of Y2Ba3Fe3Co2O13 + δ. The deviation from the stoi-
chiometric composition in terms of cobalt content
does not exceed 0.1. A decrease in the cobalt content
to 1.7 ≤ y ≤ 1.8 leads to the formation of triple (ap ×
ap × 3ap) perovskites YBa2Fe3 – nConO8 + w, and then
https://doi.org/10.1134/S0036024411030022
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disordered perovskite YFe1 – xCoxO3 – δ
.
The unit cell parameters for all single-phase sam-
ples were refined by the Le Bail method. It was found
that the unit cell volume in the studied oxides
decreases with the increase in the cobalt content,
which is associated with the size effect. The phase
composition of oxides outside the homogeneity range
is determined.
https://doi.org/10.1016/j.jssc.2013.03.037
10. Urusova, A.S., Cherepanov, V.A., Lebedev, O.I., Ak-
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ACKNOWLEDGMENTS
The work was financially supported by the Russian Sci-
entific Foundation, project no. 18-73-00030.
netic structures of oxidized and reduced YBa2Fe3O8 + w
J. Solid State Chem., 2003, vol. 174, pp. 87–95.
https://doi.org/10.1016/S0022-4596(03)00180-4
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