Materials Sciences and Applicatio ns, 2011, 2, 1349-1353
doi:10.4236/msa.2011.29183 Published Online September 2011 (http://www.SciRP.org/journal/msa)
1349
Temperature Dependence of the Magnetic and
Electric Properties of Ca2Fe2O5
Cléber Candido da Silva1,2*, Antonio S. B. Sombra1
1Telecommunications and Materials Science and Engineering Laboratory (LOCEM), Department of Physics, Federal University of
Ceará, Campus do Pici, Fortaleza, Ceará, Brazil; 2Universidade Federal do Maranhão (UFMA), Centro de Ciências Sociais, Saúde e
Tecnologia (CCSST), Departamento de Engenharia de Alimentos, Campus II, Imperatriz, MA, Brazil.
Received April 6th, 2011; revised April 25th, accepted July 5th, 2011.
ABSTRACT
Ca2Fe2O5 powder sample, were prepared to investigate the origin of the weak ferromagnetic component reported in
literature for calcium ferrite single crystals. In this work, the calcination method was used to produce nanocrystalline
powders of Ca2Fe2O5. XRD measurement has shown the presence of Fe3O4 magnetite and CaO as impurity phases. The
ferrimagnetic phase deeply influences the magnetic behavior with features very similar to those reported in literature
for Ca2Fe2O5, both powders and single crystals. Our results support the hypothesis that the weak ferromagnetic com-
ponent observed in Ca2Fe2O5 can be also due to the presence of magnetite impurity traces in the samples. The powders
were submitted to calcination processes at 50 0˚C for 2 hours and 950 ˚C for 16 hours. The sintered sample was submit-
ted at 1050˚C for 6 hours and characterized by X-Ray Powder diffraction (XRD), dielectric measurements, Magnetiza-
tion and Scanning Electron Microscopy (SEM) analysis.
Keywords: Ca2Fe2O5, Dielectric Measurements, Magnetization
1. Introduction
CF (Ca2Fe2O5) is a member of the family of com- pounds
with general formula A2B2O5 (A = Ca, Sr; B = Fe, Al),
and it finds application in the field of catalysis, when
obtained from mechano-chemical synthesis [1]. Its struc-
ture is the one known for the Srebrodolskite mineral [2,3]
and it is related to the perovskite (ABO3) structure by the
introduction of an ordered array of oxygen vacancies and
the creation of an alternate layer structure of octahedrally
and tetrahedrally coordinated transition metal cations.
The iron end-member CF [4,5] (mineral name srebro-
dolskite) adopts space group Pnma at ambient conditions
(a = 5.4, b = 14.8, c = 5.6 Ǻ). Their magnetic structures
and properties have been investigated by many authors
[6-12]. Physical properties of CF, such as electronic and
oxygen-ionic transport [13] and catalytic [14] and photo
catalytic [15] behavior, have been studied. Usage as
catalyst for the combustion of volatile organic com-
pounds [16,17] and for direct decomposition of NOx in
exhaust streams [18,19] has been examined. Numerous
entries in patent data bases also highlight a strong inter-
esting brownmillerites for catalytic applications. Brown-
millerite type structures exhibit two different layers, al-
ternately stacked: 1) perovskite-like sheets of octahe-
drally co-ordinated B cations and 2) layers of BO4 tetra-
hedra, which are corner-linked to form parallel zweier
single chains. Mixed occupations are observed frequently.
Two phase transitions are known for the iron end-mem-
ber CF: the loss of the antiferromagnetic order at the
Neel temperature at 720K [7-9,20] and a structural phase
transition [12,20-22] at 950K. The high-temperature
phases of the end-members Ca2Fe2O5 and Ca2Al2O5
turned out to be isotypic modulated structures [6,23],
with an aperiodic sequence of tetrahedral chains. These
structures are described using the (3+1)-dimensional su-
per space approach [24]. Their super space group is
Imma(00 γ)s00. The main purpose of the work is to pre-
pare CF ceramic and study the effect of the analyses of
the magnetic momentum versus magnetic field (H) and
dielectric comportment. X-Ray diffraction and Scanning
Electron Microscopy (SEM) analysis were also done to
characterize such ceramic.
2. Experimental
CF crystalline powders were prepared by stoichiomet-
ric quantities of CaCO3 (Aldrich 99%) and Fe2O3 (Al-

Temperature Dependence of the Magnetic and Electric Properties of CaFe O
1350 22 5
2
drich 98%) were the mixtures were submitted to heat-
treatment at 500˚C during 2 h and 950˚C during 16 h
both with a heating rate of 3˚C/min. Equation (1) repre-
sents the expected chemical reaction:
323 223
2CaCOFeO CaFeO2CO  (1)
X-Ray Diffraction
The X-ray diffraction (XRD) patterns data were ob-
tained at room temperature using powder samples in an
X’Pert MPD Philips difractometer (with Kα radiation, λ =
1.54056 Å) at 40 KV and 30 mA. Intensity data were
collected by the step counting method (step 0.02˚ and a
time per step of 1s) between 20˚ and 60˚ (2θ). The analy-
sis of the crystallite size (Lc) of the Ca2Fe2O5 phase has
been done using the Scherrer’s equation [A]:
cos
c
k
L



 (2)
where k is the shape coefficient (k = 1 was chosen, con-
sidering that the shape of this point is spherical), λ the
wave length, β the full width at half maximum (FWHM)
of the peak of each phase and θ the diffract- tion angle.
For this purpose, we chose the avarege of peak within the
pattern and according to Pnma space group of Ca2Fe2O5.
This peak corresponded to hkl = 141, both along the c
crystallographic axis.
VSM
The magnetization (M/H) was measured using an Ox-
ford Instruments VSM (Vibrating Sample Magne- tome-
ter) between 1.6 and 300 K, on a field-cooled sample,
under an applied field of 100 Oe.
SEM
The morphological analysis of the sample structure
was performed using the scanning electron microscopy
(SEM), Philips XL-30, operating with bunches of pri-
mary electrons ranging from 12 to 20 keV.
3. Results and Discussions
Figure 1 present XRD pattern of the CF calcinated at
950˚C. Brownmillerite or srebrodolskite (Ca2Fe2O5) [25]
was identified. This structure (Ca2Fe2O5) can be seen like
a perovskite deficient in oxygen, where as brownmillerite
(A2B2O5) is a kind of oxygen-deficient perovskite struc-
ture that is composed of perovskite-like three-dimen-
sional framework of corner-sharing BO6 octahedra alter-
nating with slabs containing rows of corner-sharing BO4
tetrahedra which are formed by the deficiency of oxygen
during the formation of the structure [26]. The little im-
purity peaks () and () indicate the formation of
Fe3O4 [25] and CaO [25] phases respectively were de-
tected in the XRD of the sample (Figure 1). In addition,
investigations of magnetic resonance are of special in-
terest, since Ca2Fe2O5 is a many-sublattice system with
Figure 1. XRD pattern of the sample. Ca2Fe2O5 (), Fe3O4
() and CaO () [25].
a nontrivial magnetic layer structure [27]. The Figure 2
exhibits the variation of
M
 with frequency for CF at
different temperatures. A well-defined relaxation mecha-
nism is observed in the temperature range of 303 - 353 K.
The relaxation peaks shift towards higher fre- quencies
with increasing on temperature. For sample, a single
peak is observed. The presence of such relaxation peaks
in the
M

 plots indicates that the samples are ionic
conductors [28]. The nature of the variation of

dc (10
KHz) vs. 1000/T and fmax (peak maximum, Figure 2) vs.
1000/T with temperature follows the Arrhenius relation 3
and 4 respectively:
exp a
o
E
ff kT






(3)
exp a
o
E
kT







(4)
where f0 and 0 is a pre-exponential factor, Ea is the
activation energy; k is the Boltzmann constant; and T
the absolute temperature [29].
The activation energy calculated from the modulus
spectrum (0.20 eV) is also comparable to the value
Figure 2. The temperature dependence of the of the Imagi-
nary Modulus of the CF sample, from 303 to 353 K.

Temperature Dependence of the Magnetic and Electric Properties of CaFe O1351
22 5
obtained from the conductivity (0.18 eV) (Figure 3). The
comparable values of the activation energy of both con-
ductivity and modulus spectra indicate that the relaxation
and conductivity process may be attributed to the same
type of charge carries [30]. Figure 4 shows the magneti-
zation as a function of temperature. There is a decrease
of the magnetization with the increase in temperature
characteristic of the brownmillerite. The Ca2Fe2O5 struc-
ture is a weak antiferromagnet directed along the c-axis
[27]. This observation shows that the magnetocrystalline
anisotropy in the a-c plane is small. The influence of
Fe3O4 on the magnetic behavior not is observed. The
micrographics (Figure 5(a) and (b)) showed particles of
the sample CF, where the micro-structures demonstrate
average grain size of 0.61 μm, while the crystallites for
that sample obtained by the diffraction of x-ray range
from 70.92 ± 3.38 nm indicating the presence of large
agglomerates of particles due to the sintering process.
The reason for this morphology depends to the sintering
Figure 3. dc (10 KHz) vs. 1000/T () and fmax (peak
maximum in Imaginary Modulos of CF) vs. 1000/T ().
Figure 4. Temperature Dependence of the Magnetization
for the CF sample, from 1.6 to 300 K.
(a)
(b)
Figure 5. SEM of the CF sample with 20.000X ((a) and (b)).
effect, where, probably, the formation of Fe3O4 phase
changes the grain size in sample.
4. Conclusions
Ca2Fe2O5 (brownmillerite) phase was obtained with the
presence of impurity phases (Fe3O4 and CaO) probably
due heat-treated at 950˚C. The comparable values of the
activation energy of both conductivity and modulus
spectra indicate that the relaxation and conductivity
process may be attributed to the same type of charge car-
ries. The VSM analysis show that the Ca2Fe2O5 structure
is a weak antiferromagnet directed along the c-axis. Be-
tween 75 and 150 K we have a decrease of the magneti-
zation with the temperature characteristic of the brown-
millerite [27]. This observation shows that the magneto-
crystalline anisotropy in the a-c plane is small. The crys-
tallites for that sample obtained by the diffraction of
x-ray (70.92 ± 3.38 nm) indicating the presence of large
agglomerates of particles due to the sintering process

Temperature Dependence of the Magnetic and Electric Properties of CaFe O
1352 22 5
where the formation of Fe3O4 phase changes the grain
size in sample.
5. Acknoledgements
The authors thank this work to the Telecommunications
and Materials Science and Engineering Laboratory
(LOCEM) Physics Department, Federal, University of
Ceará-Brazil.
REFERENCES
[1] L. A. Isupova, S. W. Tsybulya, G. N. Kryukova, A. A.
Budneva, E. A. Paukshtis, G. S. Litvak, V. P. Ivanov, V.
N. Kolomiichuk, Yu. T. Pavlyukhin and V. A. Sadykov,
“Mechanochemical Synthesis and Catalytic Properties of
the Calcium Ferrite Ca2Fe2O5,” Kinetics and Catalysis,
Vol. 43, No. 1, 2002, pp. 122-128.
doi:10.1023/A:1014217716883
[2] A. A. Colville, “Structural Crystallography and Crystal
Chemistry,” Acta Crystallographica, Vol. B26, 1970, pp.
1469-1473.
[3] J. Berggren, “Refinement of the Crystal Structure of Di-
calcium Ferrite, Ca2Fe2O5,” Acta Chemica Scandinavica,
Vol. 25, 1971, pp. 3616-3624.
doi:10.3891/acta.chem.scand.25-3616
[4] E. F. Bertaut, P. Blum and A. Sagnières, “Structure du
ferrite bicalcique et de la brownmillerite,” Acta Crystallo-
graphica, Vol. 12, No. 2, 1959, pp. 149-159.
doi:10.1107/S0365110X59000433
[5] V. A. Sadykov, L. A. Isupova, S. F. Tikhov and O. N.
Kimkhai, “Synthesis and Properties of Advanced Ceramic
Materials,” Materials Research Society Symposium Series,
MRS Fall Meeting, Vol. 386, 1995, p. 293.
[6] B. Lazić, H. Krüger, V. Kahlenberg, J. Konzett and R.
Kaindl, “Incommensurate Structure of Ca2Al2O5 at High
Temperatures-Structure Investigation and Raman Spec-
troscopy,” Acta Crystallographica, Vol. B64, No. 4, 2008,
pp. 417-425.
[7] L. M. Corliss, J. M. Hastings, W. Kunnmann and E.
Banks, “Magnetic Structures and Exchange Interactions
in the Systems CaCrxFe2–xO4 and Ca2CrxFe2–xO5,” Acta
Crystallographica, Vol. 21, 1966, p. A95.
[8] R. W. Grant, S. Geller, H. Wiedersich, U. Gonser and L.
D. Fullmer, “Spin Orientation and Magnetic Properties of
Ca2FeAlO5,” Journal of Applied Physics, Vol. 39, No. 2,
1968, pp. 1122-1123. doi:10.1063/1.1656192
[9] T. Takeda, Y. Yamaguchi, S. Tomiyoshi, M. Fukase, M.
Sugimoto, H. Watanabe, “Magnetic Structure of
Ca2Fe2O5,” Journal of the Physical Society of Japan, Vol.
24, No. 3, 1968, pp. 446-452. doi:10.1143/JPSJ.24.446
[10] S. Geller, R. W. Grant and L. D. Fullmer, “Magnetic
Structures in the Ca2Fe2–xAlxO5 System,” Journal of
Physics and Chemistry of Solids, Vol. 31, No. 4, 1970, pp.
793-803. doi:10.1016/0022-3697(70)90213-1
[11] S. Geller, R. W. Grant and U. Gonser, “Crystal Chemistry
and Magnetic Structures of Substituted Ca2[Fe](Fe)O5,”
Progress in Solid State Chemistry, Vol. 5, 1971, pp. 1-26.
doi:10.1016/0079-6786(71)90015-X
[12] P. Berastegui, S. G. Eriksson and S. Hull, “A Neutron
Diffraction Study of the Temperature Dependence of
Ca2Fe2O5,” Materials Research Bulletin, Vol. 34, No. 2,
1999, pp. 303-314. doi:10.1016/S0025-5408(99)00007-0
[13] A. L. Shaula, Y. V. Pivak, J. C. Waerenborgh, P. Gac-
zyñski, A. A. Yaremchenko and V. V. Kharton, “Ionic
Conductivity of Brownmillerite-Type Calcium Ferrite
under Oxidizing Conditions,” Solid State Ionics, Vol. 177,
No. 33-34, 2006, pp. 2923-2930.
doi:10.1016/j.ssi.2006.08.030
[14] C. N. R. Rao and J. Gopalakrishnan, “New Directions in
Solid State Chemistry: Structure, Synthesis, Properties,
Reactivity, and Materials Design,” Cambridge University
Press, Cambridge, 1986.
[15] Y. Yang, Z. Cao, Y. Jiang, L. Liu and Y. Sun, “Photo-
induced Structural Transformation of SrFeO3 and
Ca2Fe2O5 during Photodegradation of Methyl Orange,”
Materials Science and Engineering: B, Vol. 132, No. 3,
2006, pp. 311-314. doi:10.1016/j.mseb.2006.03.031
[16] D. Hirabayashi, T. Yoshikawa, K. Mochizuki, K. Suzuki
and Y. Sakai, “Formation of Brownmillerite Type Cal-
cium Ferrite (Ca2Fe2O5) and Catalytic Properties in Pro-
pylene Combustion,” Catalysis Letters, Vol. 110, No. 3-4,
2006, pp. 269-274. doi:10.1007/s10562-006-0120-0
[17] D. Hirabayashi, Y. Kawamoto and K. Suzuki, “Catalytic
Decomposition of Vocs and Chlorine Fixation on Cal-
cium Ferrites with Brownmillerite Type Structure,” Jour-
nal of the Society of Inorganic Materials, Japan, Vol. 14,
No. 327, 2007, pp. 83-91.
[18] S. Shin, Y. Hatakeyama, K. Ogawa and K. Shimomura,
“Catalytic Decomposition of Nitric Oxide over Brown-
millerite-Like Compounds, Calcium Ferrate(III)
(Ca2Fe2O5) and Strontium Ferrate(III) (Sr2Fe2O5),”
Materials Research Bulletin, Vol. 14, No. 1, 1979, pp.
133-136. doi:10.1016/0025-5408(79)90241-1
[19] J. H. White, A. F. Sammells and J. D. Wander, “Catalysts
for Direct Decomposition of NOx in Exhausts,” Pro-
ceedings of the 93rd Air and Waste Management Asso-
ciation’s Annual Conference and Exhibition, Salt Lake
City, UT, United States, 2000.
[20] E. Woermann, W. Eysel, T. Hahn, “Polymorphism and
Solid Solution of the Ferrite Phase,” Proceedings of the
Fifth International Symposium on the Chemistry of Ce-
ment, Tokyo, Supplementary Paper I-54, 1968, pp. 54-
60.
[21] G. J. Redhammer, G. Tippelt, G. Roth and G. Amthauer,
“Structural Variations in the Brownmillerite Series
Ca2(Fe2–xAlx)O5: Single-Crystal X-Ray Diffraction at
25±˚C and High-Temperature X-Ray Powder Diffraction
(25±˚C · T · 1000±˚C),” American Mineralogist, Vol. 89,
2004, pp. 405-420.
[22] K. Fukuda and H. Ando, “Determination of the
Pcmn=Ibm2 Phase Boundary at High Temperatures in the
System Ca2Fe2O5-Ca2Al2O5,” Journal of the American
Ceramic Society, Vol. 85, No. 5, 2002, pp. 1300-1303.
doi:10.1111/j.1151-2916.2002.tb00263.x

Temperature Dependence of the Magnetic and Electric Properties of Ca2Fe2O5
1353
[23] H. Krüger and V. Kahlenberg, “Incommensurately
Modulated Ordering of Tetrahedral Chains in Ca2Fe2O5 at
Elevated Temperatures,” Acta Crystallographica Section
B, Vol. 61, No. 6, 2005, pp. 656-662.
[24] T. Janssen, A. Janner, A. Looijenga-Vos and P. M. de
Wolff, “Mathematical, Physical and Chemical Tables, In-
commensurate and Commensurate Modulated Struc-
tures,” Kluwer Academic Publishers, Dordrecht, 2004.
[25] JCPDS—Pattern 38-0408 (Ca2Fe2O5), 03-0863 (Fe3O4)
and 82-1690 (CaO).
[26] I. G. Minyaylova, I. A. Presnyakov, K. V. Pokholok, A.
V. Sobolev, A. V. Baranov, G. Demazeau, G. A. Govor
and A. K. Vetcher, “Hyperfine Interactions and Dynamic
Characteristics of 119Sn Dopant Atoms in Ca2Fe2O5,”
Journal of Solid State Chemistry, Vol. 151, No. 2, 2000,
pp. 313-316. doi:10.1006/jssc.2000.8660
[27] C. Brotzeller, R. Geick and P. Marchukov, “Magnetic
Excitations in Dicalcium Ferrite,” Solid State Communi-
cations, Vol. 82, No. 11, 1992, pp. 923-925.
doi:10.1016/0038-1098(92)90721-K
[28] B. Yang, J. Zhou, Z. Gui, Z. Yue and L. Li, “Preparation
and Magnetic Characterization of Y-Type Hexaferrites
Containing Zinc, Cobalt and Copper,” Materials Science
and Engineering B, Vol. 99, No. 1-3, 2003, pp. 266-269.
doi:10.1016/S0921-5107(02)00545-7
[29] K. P. Padmasree, D. K. Kanchan, A. R. Kulkami, “Im-
pedance and Modulus Studies of the Solid Electrolyte
System 20CdI2-80[xAg2O-y(0.7V2O5-0.3B2O3)], Where 1
≤ x/y ≤ 3,” Solid State Ionics, Vol. 177, No. 5-6, 2006, pp.
475-482
[30] S. K. Barik, P. K. Mahapatra, R. N. P. Ghoudhary,
“Structural and Electrical Properties of Na1/2La1/2TiO3
Ceramics,” Applied Physics A: Materials Science &
Processing, Vol. 85, 2006, pp. 199-203.