X-Ray Absorption Spectroscopy Study of PZT

THAI JOURNAL OF PHYSICS, SERIES 10
TJP 10, 25002 (2014)
X-Ray Absorption Spectroscopy Study of PZT-PCN Ceramics
S. Thipyorlaeh1, M. Unruan2, R. Yimnirun3 and S. Thongmee1,4*
1
Program in Nanomaterials Science, Department of Materials Science,
Kasetsart University, Bangkok, 10900, Thailand
2
Department of Applied Physics, Faculty of Sciences and Liberal Arts,
Rajamangala University of Technology Isan, Nakhon Ratchasima, 30000, Thailand
3
School of Physics, Institute of Science, Suranaree University of Technology,
Nakhon Ratchasima, 30000, Thailand
4
Department of Physics, Faculty of Science, Kasetsart University, Bangkok, 10900, Thailand
Ferroelectric PZT-PCN ceramics with the formula (1-x)Pb(Zr1/2Ti1/2)O3-(x)Pb(Co1/3Nb2/3)O3
where x = 0.1, 0.3, and 0.5, were prepared using a solid-state mixed-oxide technique. In this work,
X-ray Absorption Spectroscopy (XAS) measurement was employed to determine the oxidation
state and local structure of Co K-edge in PZT-PCN ceramics. Synchrotron x-ray absorption nearedge structures (XANES) were preformed on PZT-PCN samples, while focused on the
relationship of ferroelectric properties of the PZT-PCN ceramics at room temperature. The
XANES showed the oxidation state of Co2+ atoms for all compositions of PZT-PCN with a weak
pre-edge peak. In addition, the polarization of saturated loops increased with the different electric
fields. The maximum value of remanent polarization (Pr) was obtained for 0.7PZT-0.3PCN and
0.5PZT-0.5PCN ceramics.
Keywords: XANES, Oxidation state, Local structure, Ferroelectric properties
1. INTRODUCTION
Ferroelectric and related materials continue to be
exploited for numerous applications, including recent
concepts of smart and intelligent systems, whereby
multifunctional components are required.1 Lead zirconate
titanate or PZT ceramics have been investigated from both
fundamental and applied viewpoints.2,3 Most commercial
PZT ceramics are designed in the vicinity of the MPB with
various doping methods in order to achieve high
properties.3,4-7 Recently, many piezoelectric ceramic
materials have been developed from binary systems
containing a combination of relaxor and normal
ferroelectric materials,3 that yield high dielectric
permittivities (e.g., PZT-PNN and PZT-PMN),4,5 excellent
piezoelectric coefficients (e.g., PZT-PZN),6 and high
pyroelectric coefficients (e.g., PNN-PT-PZ).7
Lead cobalt niobate or PCN, which exhibits a perovskite
structure and a Curie temperature of -30 o C , is a relaxor
ferroelectric material with a high dielectric constant.8,9 On
the basis of the above mentioned approach, solid solutions
of PZT and PCN are expected to synergistically combine
the properties of both the normal ferroelectric PZT and
relaxor ferroelectric PCN with exhibit electrical properties
that are better than those of the single phase PZT and
PCN.8-11
X-ray absorption spectroscopy (XAS) is a very
powerful technique for resolving the local structure
surrounding a particular (absorbing) atom. Traditionally,
* Corresponding author. Tel: +66 2562 5555 ext. 3573
Fax: +66 2942 8290
; E-mail: [email protected]
XAS is divided into two regions. The first region is low
energy which covers photon energy up to about 50 eV
above the absorption edge. This region is called the x-ray
absorption near-edge structure (XANES). The second
region is high energy from 50 to 1000 eV above the
absorption edge which called the extended x-ray absorption
fine structure (EXAFS).12
X-ray absorption near-edge spectroscopy (XANES) is a
powerful technique that can be used to investigate all
elements in crystals or amorphous structures and also is
specific element. Moreover, XANES can provide
information about the local geometry around the absorbing
atom and its oxidation state.13,14 In this case, XANES was
carried out to probe the valence and coordination
environment of four substituting cations in materials. The
results can also help to resolve an issue in dispute, i.e., the
debate whether the substituting cations would exist as
incorporated into the materials lattice or as a spinel metal
oxide with material to compose solid solution. Since, they
are two main manners of incorporating cations in natural
materials15 that cannot be differentiated by XRD.
In this work, samples were prepared by solid-state
mixed-oxide technique and synchrotron x-ray absorption
near-edge structure (XANES) technique was used to
provide specific element and oxidation state of Co atoms in
PZT-PCN ceramics materials. In addition, we also focused
on the ferroelectric properties.
2. EXPERIMENT
In
this
study,
the
(1-x)Pb(Zr1/2Ti1/2)O3(x)Pb(Co1/3Nb2/3)O3 ceramics (where x = 0.1, 0.3 and 0.5)
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© 2014 Thai Physics Society
S. Thipyorlaeh, et al.
were prepared from PbO, columbite CoNb2O6, and
wolframite ZrTiO4 powders by using solid-state mixedoxide technique. The pellets were sintering temperature at
°
1250 C for 2 h.16,17
To examine the local structure and oxidation state,
X-ray Absorption Spectroscopy (XAS) measurements were
conducted at ambient temperature at BL-8 of the Siam
Photon Laboratory, Synchrotron Light Research Institute
(SLRI), Thailand (electron energy of 1.2 GeV, beam
current 80-120 mA). The double-crystal monochromator
was operated with a pair of Ge (220) crystals for scanning
the energy of the synchrotron X-ray beam with energy
steps of 0.20 eV to excite the electrons in all edges. The
experiments were performed in fluorescence mode and the
signals were collected by using the 13-component
Ge-detector. The x-ray absorption near-edge structure
(XANES) measurements for the all edges were measured
for all compositions. The photon energy was calibrated by
measuring the absorption edge of Co foil and compared
with the literature. The data were processed using the
ATHENA program. The room temperature ferroelectric
hysteresis loop parameters were measured with modified
Sawyer–Tower circuit at fixed measuring frequency of 50
Hz.
3. RESULTS AND DISCUSSIONS
In this study, X-ray absorption near edge structure
(XANES) characterization was carried out to probe the
valence of the substituting cations in the synthetic samples.
In general, the energy positions of the XANES spectra
depend on the binding energy of absorbing atom, hence on
the oxidation state, but also on other parameters, such as
the nature and number of nearest neighbors.18 The linear
relationship between the edge shift and the valence state
has been established for several cations in samples with the
nearest neighbors of the same chemical species, while the
edge shift can be determined in a straightforward way only
for analogical edge profiles. In addition, different
environments of the cation, most notably with different site
symmetries, result in different K-edge profiles. Hence,
shifts of separate edge and absorption edge features have
been proposed to replace the edge shift.19 Based on this
principle, the XANES spectra in this work were evaluated
to investigate the valence of substituting metals in the
synthetic samples, by comparing the spectra of the samples
with each other, and with the spectra of reference
compounds. The reference compounds used in this study
were metal oxides with ions in single or mixed valence and
spinel standards. The absorption edge is defined as the
maximum of derivative at the absorption edge.
The oxidation state (valence) of the Co atoms was
studied by X-ray absorption near edge structure (XANES)
spectroscopy in PZT-PCN ceramics. The valence shifts for
the (1-x)Pb(Zr1/2Ti1/2)O3-(x)Pb(Co1/3Nb2/3)O3 (where x =
0.1, 0.3 and 0.5) samples, as well as the three reference
samples Co foil, CoO and Co3O4 were shown in Figure 1(a)
and 1(b).
FIGURE 1. (a) Normalized XANES spectra of Co K-edge of (1x)PZT-(x)PCN ceramics with comparison to the reference samples
with different oxidation states. (b) Pre-edge peak located in the
range from 7708 to 7710 eV.
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S. Thipyorlaeh, et al.
The results show the edge position of the samples when
compared to the reference. We found that the absorption
edge of Co foil, CoO and Co3O4 are reference for Co0, Co2+
and Co2.67+, respectively. The absorption edge shift can be
used to determine the oxidation state of Co in unknow
samples. Table 1 shows the positions of Co K-edge of
(1-x)PZT-(x)PCN ceramics and reference samples.
Figure 1(a) and 1(b) exhibits the normalized Co K-edge
XANES of (1-x)PZT-(x)PCN ceramics and Co reference
compounds. For Co foil, the shoulder peak appears
obviously at 7712.51 eV and the absorption K-edge is at
7708.41 eV. For CoO, Co2+ is six-fold coordinated by O2ions, it shows only the absorption K-edge that locates at
7719.40 eV. In case of Co3O4, Co3+ is six fold and Co2+
four-fold coordinated by O2-, the board pre-edge is shown
at 7708.91 eV, and the K-edge is obvious at 7718.60 eV
with a shoulder peak at 7723.42 eV. For Co reference
compounds (e.g., Co foil, CoO and Co3O4), a shift of
K-edge position will increase with the increasing valence
(see Figure 1 and Table 1). For 0.9PZT-0.1PCN, it shows
the board pre-edge at 7709.31 eV, and shows the
absorption edge at 7720.41 eV that is closer to CoO. In
case of 0.7PZT-0.3PCN and 0.5PZT-0.5PCN, the board
pre-edge and the absorption edge are 7709.61 eV and
7720.60 eV, respectively. All compositions of Co cations in
(1-x)PZT-(x)PCN show the absorption
K-edge (7720.41
-7720.60 eV) and peak profile there are differences with
CoO and Co3O4. When cobalt content increase, the
absorption edge peak profiles of (1-x)PZT-(x)PCN
ceramics does not changes, it reveal that the oxidation state
of Co atoms in the ferroelectric samples is mainly +2.
TABLE 1
Positions of Co K-edge of (1-x)PZT-(x)PCN ceramics and
reference samples.
Samples
Edge position (eV)
Co foil
7708.41
CoO
7719.40
Co3O4
7718.60
0.9PZT-0.1PCN
7720.41
0.7PZT-0.3PCN
7720.60
0.5PZT-0.5PCN
7720.60
Figure 2 shows the saturated loops of (1-x)PZT–(x)PCN
ceramics with (a) x = 0.1, (b) x = 0.3 and (c) x = 0.5
samples, respectively with difference electric fields
strengths. The shape of hysteresis loop varies with the
electric field. In addition, the results of each condition
(0.1, 0.3 and 0.5) is not reach the PCN applying the electric
field.
FIGURE 2. Polarization of the (1-x)PZT-(x)PCN ceramics
with (a) x = 0.1, (b) x = 0.3 and (c) x = 0.5 by applying
electric field 6, 8, 10 and 12, respectively.
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S. Thipyorlaeh, et al.
The hysteresis loop of Figure 2(b) and 2(c) are larger
than Figure 2(a). This is because higher doping can lead to
increase the electrical properties of PZT.
FIGURE 3. Hysteresis loops of the (1-x)PZT-(x)PCN ceramics
with x = 0.1, 0.3 and 0.5 measured at 12 kV/cm.
The polarization-electric field (P-E) hysteresis loops of
(1-x)PZT-(x)PCN ceramics are presented in Figure 3. The
P-E curves of the samples with x = 0.1, 0.3 and 0.5
measured at 12 kV/cm. At x = 0.1, it can be seen that the
P-E loop is small with remanent polarization value. This
curve suggests that the most of the aligned dipole moments
switch back to a randomly oriented state upon removal of
the field. For x = 0.3 and 0.5, they show a symmetry shape.
This reveals the rectangular hysteresis loops. From the fully
saturated loops, the remanent polarization Pr and coercive
field Ec were determined. The values of Pr and Ec for
composition x = 0.3 are 30.70 µ C/ cm2 and 8.09 kV/cm,
respectively, whereas the composition x = 0.5, the remanent
polarization Pr is 32.09 µ C/cm2. At the composition 0.1
≤ x ≤ 0.5, the hysteresis loop has a typical square form
stipulated by switching of a domain structure in an
electrical field, which is typical of a phase that contains
long-range cooperation between dipoles. This is the
characteristic of a ferroelectric micro-domain state. At
room temperature, the values of Pr are ≈ 4.81, 30.70 and
32.09 µ C/cm2 for composition x = 0.1, 0.3 and 0.5
samples, respectively. The results of the other compositions
are also listed in Table 2.
Table 2
Polarization hysteresis data as a function of x in the (1-x)PZT(x)PCN ceramics system.
Compositions
Ps
(
µC / cm
E c (kV/cm)
Pr
2
)
( µC
/ cm
2
)
x = 0.1
9.04
4.81
5.43
x = 0.3
32.49
30.70
8.09
x = 0.5
32.50
32.09
7.20
From Table 2, it is seen that the samples with
compositions x = 0.3 and 0.5 exhibit the highest saturation
and remanent polarization. For the composition x = 0.1
show the small saturation and remanent polarization in the
ceramics studied. All of these results are studies from
XANES.
4. CONCLUSION
In this work, ferroelectric (1-x)PZT-(x)PCN ceramics,
were prepared by solid-state mixed-oxide technique. This
study employed XANES as an effective tool to investigate
the valences and site occupancies of substituting metal
cations in ferroelectric materials. The presented results
reveal that Co cations in the oxidation state (valence) of +2
occupy in symmetry perovskite structure, which its exhibits
a perovskite structure with a relaxor ferroelectric material
with Co2+ of PCN relaxor in ferroelectric PZT-PCN
ceramics. The hysteresis loops of x = 0.3 and 0.5 measure
at room temperature show high P-E loops with remanent
polarization values.
ACKNOWLEDGMENTS
The authors would like to thank the Synchrotron Light
Research Institute (SLRI) for XAS measurement. This
work was also supported by the School of Physics, Institute
of Science, Suranaree University of Technology, for the use
of equipment and wishes to thank Dr. Muangjai Unruan for
the samples and method of electrical properties
measurement.
1. Haertling, G.H., Ferroelectric ceramics: History and
technology, J. Am. Ceram. Soc., Vol. 82, pp. 797-818, 1999
2. Moulson, A.J. and Herbert, J.M., Electroceramics: Materials
Properties Applications, Wiley, Chichester, UK, 2003
3. Cross, L.E., Ferroelectric materials for electromechanical
transducer applications, Materials Chemistry and Physics,
Vol. 43, pp. 108-115, 1996
4. Vittayakorn, N., Rujijanagul, G., Tan, X., Marquardt, M.A.,
and Cann, D.P., The morphotropic phase boundary and
dielectric
properties
of
the
xPb(Zr1/2Ti1/2)O3(1−x)Pb(Ni1/3Nb2/3)O3 perovskite solid solution, Journal of
Applied Physics, Vol. 96, no. 9, pp. 5103-5109, 2004.
5. Yimnirun, R., Ananta, S. and Laoratanakul, P., Dielectric and
ferroelectric properties of lead magnesium niobate-lead
zirconate titanate ceramics prepared by mixed-oxide method,
Journal of the European Ceramic Society Vol. 25, pp. 32353242, 2005
6. Fan, H., Park, G.T., Choi, J.J., Ryu, J. and Kim, H.E.,
Preparation and improvement in the electrical properties of
lead zinc-niobate-based ceramics by thermal treatments, J.
Mater. Res., Vol. 17, pp. 180-185, 2002
7. Luff, D., Lane, R., Brown, K.R. and Marshallsay, H.J., Trans.
J. Br. Ceram. Soc., Vol. 73, pp. 251, 1974
8. Unruan, M., Vittayakorn, N., Wongmaneeruang, R.,
Prasatkhetragarn, A., Ananta, S. and Yimnirun.R., Synthesis
and properties of Pb(Co1/3Nb2/3)O3 ceramics, Journal of Alloys
and Compounds, Vol. 466, pp. 264-267, 2008
9. Hachiga, T., Fujimoto, S. and Yasuda. N., The pressure and
temperature dependence of the dielectric properties of
Pb(Co1/3Nb2/3)O3, J. Phys. D, Vol 20, pp. 1291-1296, 1987
25002-4
S. Thipyorlaeh, et al.
10. Kudo,T., Yazaki, T., Naito, F. and Sugaya, S., Dielectric and
piezoelectric properties of Pb(Co1/3Nb2/3)O3-PbTiO3-PbZrO3
solid solution ceramics J. Am. Ceram. Soc., Vol. 53, pp. 326,
1970
11. Brankovic, Z., Brankovic, G. and Varela, J.A., PZT ceramics
obtained from mechanochemically synthesized powders, J.
Mater. Sci., Vol. 14, pp. 37-41, 2003
12. Koningsberger, D.C. and Prins, R., X-ray Absorption:
Principles, Applications, Techniques of EXAFS, SEXAFS,
and XANES, Wiley, New York, Vol. 92, pp. 3–4, 1988
13. Hagen, A., In situ XANES cell used for the study of
lanthanum strontium cuprate deNOx catalysts, Chem. Phys.
Lett. Vol. 502, pp. 235-240, 2011
14. van Bokhoven, J.A., Louis, C., Miller, J.T., Tromp, M.,
Safonova, O.V. and Glatzel, P., Activation of Oxygen on
Gold-Alumina Catalysts: In-Situ High Energy Resolution
Detection and Time-Resolved X-ray Spectroscopy, Angew.
Chem. Int., Ed. 45 Vol. 28, pp. 4651-4654, 2006
15. Zhou, M.F., Wang,C.Y., Pang, K.N., Shellnutt, G.J. and Ma,
Y., Mineral Deposit Research: Meeting the Global Challenge,
Vol. 1-2, pp. 511-513, 2005
16. Prastkhetragarn, A., Vittayakorn, N., Ananta, S., Yimnirun, R.
and Cann, D.P., Synthesis and dielectric and ferroelectric
properties
of
ceramics
in
(1-x)Pb(Zr1/2Ti1/2)O3(x)Pb(Co1/3Nb2/3)O3 system, Japan. J. Appl. Phys., Vol. 48,
pp. 998-1002, 2008
17. Unruan, M., Prasatkhetragarn, A., Laosiritaworn, Y., Ananta,
S. and Yimnirun, R., Dielectric properties of PZT-PCN
ceramics under compressive stress, Phys. Scr., Vol. 77, pp.
045702(1-4), 2008
18. Pantelouris, A., Modrow, H., Pantelouris, M., Hormes, J. and
Reinen, D., The influence of coordination geometry and
valency on the K-edge absorption near edge spectra of
selected chromium compounds, Chem. Phys., Vol. 300, pp.
13-22, 2004
19. Arcon, I., Kolar, J., Kodre, A., Hanzel, D. and Strlic, M.,
XANES analysis of Fe valence in iron gall inks, X-ray
Spectrom, Vol. 36, pp. 199-205, 2007
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