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Journal of Electroceramics
ISSN 1385-3449
Volume 30
Number 3
J Electroceram (2013) 30:119-128
DOI 10.1007/s10832-012-9772-x
High dielectric permittivity of
SrBi2Nb2O9(SBN) added Bi2O3 and La2O3
E.O.Sancho, P.M.O.Silva,
G.F.M.Pires Júnior, H.O.Rodrigues,
D.B.Freitas & A.S.B.Sombra
1 23
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High dielectric permittivity of SrBi
2
Nb
2
O
9
(SBN) added Bi
2
O
3
and La
2
O
3
E. O. Sancho &P. M. O. Silva &G. F. M. Pires Júnior &
H. O. Rodrigues &D. B. Freitas &A. S. B. Sombra
Received: 30 May 2012 /Accepted: 16 November 2012 / Published online: 27 December 2012
#Springer Science+Business Media New York 2012
Abstract In this paper, the structural and dielectric proper-
ties of SrBi
2
Nb
2
O
9
(SBN) as a function of Bi
2
O
3
or La
2
O
3
addition level in the radio (RF) and microwave frequencies
were investigated. The SBN, were prepared by using a new
procedure in the solid-state reaction method with the addi-
tion of 3; 5; 10 and 15 wt.% of Bi
2
O
3
or La
2
O
3.
A single
orthorhombic phase was formed after calcination at 900 °C
for 2 h. The analysis by x-ray diffraction (XRD) using the
Rietveld refinement confirmed the formation of single-
phase compound with a crystal structure (a05.5129 Å, b0
5.5183 Å and c025.0819 Å; α0β0γ090°). Scanning
Electron Microscope (SEM) micrograph of the material
shows globular morphologies (nearly spherical) of grains
throughout the surface of the samples. The Curie tempera-
ture found for the undoped sample was about 400 °C, with
additions of Bi
3+
, the temperature decreases and with addi-
tions of La
3+
the Curie temperature increased significantly
above 450 °C. In the measurements of the dielectric prop-
erties of SBN at room temperature, one observe that at
10 MHz the highest values of permittivity was observed for
SBN5LaP (5%La
2
O
3
) with values of 116,71 and the lower
loss (0.0057) was obtained for SBN15LaP (15%La
2
O
3
). In
the microwave frequency region, Bi
2
O
3
added samples have
shown higher dielectric permittivity than La
2
O
3
added sam-
ples, we highlight the SBN15BiG (15 % Bi
2
O
3
) with the
highest dielectric permittivity of 70.32 (3.4 GHz). The dielec-
tric permittivity values are in the range of 28–71 and dielectric
losses are of the order of 10
−2
. The samples were investigated
for possible applications in RF and microwave components.
Keywords Radio-frequency .Ferroelectrics
1 Introduction
The family of bismuth layer structured ferroelectrics (BLSFs)
has been investigated extensively, because of its potential use
in ferroelectric random access memories [FeRAMs] applica-
tions [1,2].Bismuth layered perovskite of SrBi
2
Nb
2
O
9
(SBN)
belongs to the Aurivillius family type structures, which gen-
eral formula is Bi2O2
ðÞ
2þAn1BnO3nþ1
ðÞ
2; where the A sites
are occupied by larger cations, while the cations with
high valency are located on B sites and n is the number
of octahedral layers sandwiched between (Bi
2
O
2
)
2+
layers. The presence of Bi
2
O
3
layers has been thought
to serve as the shock absorber for enduring the fatigue
of polarization and preserve the stability of bismuth
layer structured ferroelectrics.
Various properties make SBN a good alternative to PZT,
presenting large remanent polarization, low coercive field,
high Curie temperature and lower synthesizing temperature
[3–5]. The addition of vanadium resulted in an increase in
Curie temperature and it was reported that the partial re-
placement of Nb ions by ions with lower polarizability as V,
leads to an increased distortion of the octahedral Nb(V)O
6
block perovskite [6–8].
Bismuth layer structured ferroelectrics (BLSFs) have
attracted a lot of attention because of their potential use in
the manufacture of ferroelectric random access memories
E. O. Sancho
Metallurgical and Materials Engineering Department (DEMM),
Federal University of Ceará –UFC, 60455-760, Fortaleza,
CE, Brazil
P. M. O. Silva :G. F. M. P. Júnior:H. O. Rodrigues :
D. B. Freitas :A. S. B. Sombra
Teleinformatics Engineering Department (DETI), Federal
University of Ceará –UFC, 60455-760, Fortaleza, CE, Brazil
E. O. Sancho (*):P. M. O. Silva :G. F. M. P. Júnior :
H. O. Rodrigues :D. B. Freitas :A. S. B. Sombra
Telecommunications and Materials Science and Engineering
Laboratory (LOCEM), Physics Department, Federal
University of Ceará - UFC, 60455-760, Fortaleza, CE, Brazil
e-mail: emmanuellesancho@hotmail.com
URL: http://www.locem.ufc.br
J Electroceram (2013) 30:119–128
DOI 10.1007/s10832-012-9772-x
Author's personal copy
with spontaneous polarization and good piezoelectric coef-
ficients. A great deal of effort has been carried out in order
to investigate the effects of doping on the properties of the
bismuth-containing layered perovskite-type material be-
cause there is a possibility that the cation doping would lead
to modifications in the properties of the Aurivillius family.
Many research studies report on the substitution of Nb
5+
with other cations and found a significant enhancement in
dielectric and ferroelectric properties. The replacement of
cations has also been reported by some authors to introduce
changes in the Curie temperature. Therefore, significant
efforts have been made to improve the dielectric properties
and decrease the processing temperature of SBN. It has been
reported that doping can greatly affect the crystal structure,
dielectric properties and electrical conductivities of SBN
ferroelectrics. Liu et al have shown that an appropriate La
doping in SBN ceramics can lead to a big enhancement of
polarization (up to 60 %). However, there is still the absence
of a clear understanding of the mechanism for polarization
enhancement in SBN [9,10].
In the literature, it is usual to add Bi
2
O
3
in the manufac-
turing process of SBN, due to the bismuth volatilization. La
doping has also been studied. In this work, ceramics are
prepared and the structural and dielectric properties studied
in order to gain an understanding of the consequences of
adding (La
3+
or Bi
3+
) and the fabrication methodology in
the RF(Radio frequency) and microwave properties of the
SBN matrix.
2 Experimental methods
2.1 Sample preparation
SrBi
2
Nb
2
O
9
(SBN) samples were fabricated through the
solid-state reaction method. The materials with high degree
of purity Bi
2
O
3
(99.9 % purity), SrCO
3
(99.9 % purity) and
Nb
2
O
5
(99.99 % purity) were each obtained from Sigma-
Aldrich. The precursors of SBN, bismuth oxide (Bi
2
O
3
),
strontium oxide (SrCO
3
) and niobium oxide (Nb
2
O
5
), were
weighed out in an appropriate stoichiometric ratio and
mixed together by mortar and pestle until the mixture were
uniform. Previous to the first heat treatment, high-energy
ball milling of the homogeneous powder mixture was con-
ducted in a planetary ball mill (Fritsch Pulverisette 5). The
rotation speed of the disks carrying the sealed vials was
360 rpm. Milling of powder samples was done at room
temperature in a stainless steel vial (volume ~222 cm
3
)
using 24 stainless steel balls (4 g; 10 mm Ø). The time
period of the mechanical milling operation was 8 h. The
powder was calcinated at 900 °C for 2 h, in conventional
controlled furnaces (JUNG —LF0912), starting from room
temperature with a speed of 5 °C/min. After calcination,
Bi
2
O
3
and La
2
O
3
(0; 3; 5; 10 and 15 wt.%) was added. This
material was mixed to 5 wt.% glycerin or polyvinyl alcohol
(PVA, 10 vol.%) as a binder addition to reduce the brittle-
ness of the pellets. The material was pressed into cylindrical
pellets using a hydraulic press. The pellets with a diameter
of 10 mm and a thickness of 2 mm were subject to sintering
at 850 °C for 2 h to bismuth additions and 1000 °C to
lanthanum additions, being the speed ascent temperature in
the oven of 5 °C/min. The densities of sintered ceramics are
about 6.65 g/cm
3
, higher than the value reported by
Subbarao’s[11] and about 91 % of the theoretical density
of SBN (7.27 g/cm
3
). The pellets’densities were measured
using the Archimedes method. In this procedure, a pycnom-
eter was used to measure the density of the sintered samples
(solid samples). In Table 1one has the parameters obtained
from the Rietveld refinement with their densities.
2.2 X-ray diffraction
Structural properties of sintered ceramic pellets were studied
with X-Ray diffraction (XRD) patterns. The measurements
were carried in a X-ray powder diffractometer Xpert MPD
(Panalytical). X-ray tube (Co) operated at 40 kV and 40 mA,
with 0.5° with angular range 20°–70° (2θ). The high reso-
lution diffraction is obtained with a hybrid monochromator
Table 1 Summary identification of the samples
Code Samples Binder (3 wt.%) d(theo.) (g/cm
3
)d(exp.) (g/cm
3
)Relative density (%)
SBN0 SrBi
2
Nb
2
O
9
Glycerin 7.27 6.65 91.47
SBN3BiG SrBi
2
Nb
2
O
9
+Bi
2
O
3
(3 wt.%) Glycerin 7.27 6.90 94.91
SBN5BiG SrBi
2
Nb
2
O
9
+Bi
2
O
3
(5 wt.%) Glycerin 10.95 6.98 63.74
SBN10BiG SrBi
2
Nb
2
O
9
+Bi
2
O
3
(10 wt.%) Glycerin 8.39 6.82 81.28
SBN15BiG SrBi
2
Nb
2
O
9
+Bi
2
O
3
(15 wt.%) Glycerin 7.61 6.93 91.06
SBN3LaP SrBi
2
Nb
2
O
9
+La
2
O
3
(3 wt.%) PVA 7.26 6.69 92.14
SBN5LaP SrBi
2
Nb
2
O
9
+La
2
O
3
(5 wt.%) PVA 5.70 6.73 92.69
SBN10LaP SrBi
2
Nb
2
O
9
+La
2
O
3
(10 wt.%) PVA 5.36 6.68 92.13
SBN15LaP SrBi
2
Nb
2
O
9
+La
2
O
3
(15 wt.%) PVA 5.87 6.59 91.14
120 J Electroceram (2013) 30:119–128
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for incidence beam, which consist of mirror and Ge mono-
chromator producing a parallel and highly monochromatic
beam, respectively. The data were collected with Pixcel,
Panalytical 2nd generation solid-state detection technology
[12]. The Rietveld method is successfully applied for deter-
mination of the quantitative phase abundances of sintered
specimen. The pycnometer method was used to determine
the experimental density of the sintered samples and to
compare with the theoretical values obtained from the
Rietveld refinement procedure.
2.3 Scanning electron microscope (SEM)
The microstructures of SBN samples were also studied.
Micrographs of pellet samples were recorded on different
magnification using scanning electron microscope (SEM,
VEGA II XMU) at room temperature. The aim is to learn
how SBN densified with the addition of Bi
2
O
3
and La
2
O
3
and also the morphology of grains.
2.4 Dielectric properties
To measure the electrical properties in the RF region of
frequency, the pellets were polished and electrode with a
high-quality of silver paint was applied on either side of the
faces of the samples and dried. The dielectric properties
were measured using the computer-controlled impedance
analyzer Agilent 4294A as a function of frequency
(100 Hz to 10 MHz) at room temperature (T0300 K).
It is convenient, for some applications, to define the
geometrical capacitance of a capacitor in terms of the value
of capacitance that would be obtained with the same geom-
etry but with the dielectric medium being replaced by free
space (vacuum):
C0¼"0:Ad=ð1Þ
20 30 40 50 60 70
(220)
(219)
(200)
(135)
SBN
Intensity (u.a)
(degree)
Observed
Calculated
Difference
(115)
2
Fig. 2 Rietveld refinement results of SBN Powder (calcined at 900 °C
for 2 h). The measured XRD, the calculated and the difference (ob-
served−calculated) patterns
20 30 40 50 60 70
SBN15Bi
SBN3Bi
SBN10Bi
SBN5Bi
SBN
*
*
Intensity / a.u.
**
20 30 40 50 60 70
SBN
SBN10La
SBN3La
SBN15La
SBN5La
Intensity / a.u.
**
**
*
*
(a)
(b)
2 / degree
2 / de
g
ree
Fig. 1 (a) XRD pattern (JCPDS n
o
.82-280) of SrBi
2
Nb
2
O
9
added
Bi
2
O
3
*(Sr
0.6
Bi
0.305
)
2
Bi
2
O
7
and ♦Bi
3
NbO
7
,(b) XRD pattern (JCPDS
n
o
.82-280) of SrBi
2
Nb
2
O
9
added La
2
O
3
*LaNbO
4
J Electroceram (2013) 30:119–128 121
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and the relative permittivity ε
r
defined as
"r¼""
0
=ð2Þ
In general, a wave propagating in a dielectric under-
goes losses, and the permittivity of the material can no
longer be represented by a real value. These losses can
be attributed to a number of causes, including conduc-
tion, relaxation phenomena, both in the dielectric as
well as in impurities, molecular resonances, and molec-
ular structure [13]. Because of losses, the dielectric
must be represented by a complex value. The complex
dielectric permittivity of that material can be written as
follows:
"¼"0j"00 ð3Þ
Where ε′and ε″are the real and imaginary parts of the
permittivity In a dielectric, the ratio "00 "0
=¼σw"0
=
ðÞis a
direct measurement of the ratio of the conduction current to
the displacement current. For the main case of interest,
where there is only a small conductive loss, the permittivity
is often written as
-2 0 2 4 6 8 10 12 14 16
0,00
0,05
0,10
0,15
0,20
0,25
0,30
0,50
0,55
0,60
0,65
0,70
0,75
0,80
0,00
0,05
0,10
0,15
0,20
0,25
0,30
0,50
0,55
0,60
0,65
0,70
0,75
0,80
Pr ( C/cm²)
Pc
%Bi
2
O
3
Pc
Pr
0246810121416
0,00
0,05
0,55
0,60
0,65
0,70
0,75
0,00
0,05
0,55
0,60
0,65
0,70
0,75
Pr ( C/cm²)
Pc
%La
2
O
3
Pc
Pr
(a)
(b)
μ
μ
Fig. 3 The Pr (Degree of remanent polarization) value of SBN as a
function of the (a) Bi content and (b) La content
350 360 370 380 390 400 410 420 430 440 450
1,0x10
13
1,5x10
13
2,0x10
13
2,5x10
13
3,0x10
13
3,5x10
13
4,0x10
13
4,5x10
13 10kHz
'r
Temperature (ºC)
SBN0LaP
SBN3LaP
SBN5LaP
SBN10LaP
SBN15LaP
350 360 370 380 390 400 410 420 430 440 450
0,0
2,0x10
13
4,0x10
13
6,0x10
13
8,0x10
13
1,0x10
14
1,2x10
14
1,4x10
14
'
r
Temperature (ºC)
10kHz
SBN0BiG
SBN3BiG
SBN5BiG
SBN10BiG
SBN15BiG
(a)
(b)
ε
ε
Fig. 4 Dielectric permittivity (at 10 kHz) as a function of temperature
for samples (a) SBNBiG and (b) SBNLaP
Table 2 Structural parameters
of SBN (orthorhombic (α) phase
calcined at 900 °C for 2 h)
obtained from the Rietveld
method’son
Structural parameters
a 5.5129 Å b 5.5183 Å c 25.0819 Å
α90 β90 γ90
R-P (%) 11.61 R-WP (%) 16.15 R-EXPECTED (%) 10.15
S 1.59 D –W 0.07 Space group A2
1
am
122 J Electroceram (2013) 30:119–128
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"¼"01jσ
w"0
¼"01jtan dðÞ ð4Þ
where σis the electric conductivity of the material, tanδ0σ/
ωε′, and the factor, tanδ, called the loss tangent, is common-
ly used to characterize the loss at microwave and millimeter
wavelengths, even though the losses may be due to other
than conduction. In general, ε′and ε″are functions of
frequency, although in many applications they may be con-
sidered to be constant over a limited frequency band of
interest [14,15].
2.5 Microwave dielectric properties
Dielectric properties at microwave frequencies were mea-
sured in the 3–6 GHz frequency range. The end-shorted
method proposed by Hakki and Coleman and later modified
by Courtney [16] was employed for the evaluation of the
dielectric permittivity "0
rand loss tg(δ)using the TE
011
mode.
3 Results and discussion
3.1 XRD and polarization results
Figure 1(a) and (b) shows the X-ray diffractograms in the 2θ
range (20–70°) of sintered samples with 0,3,5,10 and
15 wt.% of bismuth and lanthanum respectively. The for-
mation of desired layered perovskite phase is confirmed in
all the samples. All samples show a layered perovskite
structure without the presence of any secondary phase,
indicating that Bi
3+
and La
3+
is completely incorporated
into the crystal lattice.
The peaks correspond to those of the desired perovskite
SBN, matches with the JCPDF card n. 82-280. The XRD
patterns of the SBN sample is shown in Fig. 2in the 2θ
range of 20–70° and Table 2shows the structural parameters
of the SBN (orthorhombic (α) phase) refined by the
Rietveld method’s (calcined material at 900 °C for 2 h).
The data from the X-ray refinement of calcined SBN and the
obtained parameters, R–P (%), R–WP (%) (weighted resid-
ual error), D–W (Durbin–Watson D-statistic) and S (quality
factor “goodness of fit”), are presented there. From the
mathematical standpoint, R–WP is the statistically most
meaningful indicator of the overall fit, in the sense that its
numerator is the residual that is minimized. For the same
reason, it is also the one that best reflects the progress of
refinement. Another useful numerical criterion is the S value
or the “goodness of fit”. However, R–WP (16.15 %) and S
(1.59) values showed that the refinement was effective.
Defining the degree of preferred c-axis orientation as Pc,
the calculated Pc, together with the obtained remanent po-
larization for SBNBi ceramics, are shown in Fig. 3(a). it can
Fig. 5 SEM Micrographs of SBN added Bi
2
O
3
(a) 0 wt.%, (b) 5 wt.%
and (c) 10 wt.%
J Electroceram (2013) 30:119–128 123
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be seen that the remanent polarization Pr of SBN decreases
slightly with increasing Bi content 0, 3 and 5 wt.% (0.044;
0.041; 0.035) respectively, it increases with a further in-
crease in the Bi content (x015 wt.%). Since polarization P
Fig. 6 SEM Micrographs of
SBN added La
2
O
3
(a) 0 wt.%,
(b) 3 wt.%, (c) 5 wt.%,
(d)10 wt.% and (e) 15 wt.%
124 J Electroceram (2013) 30:119–128
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is along the a-axis (P||a) in SBN, the increase in Pr cannot be
simply ascribed to the orientation effect (increasing no c-
axis orientation usually increases polarization) as well as is
also assigned to reduced in processing temperature in ion
doped Bi-layered ferroelectrics materials. The Bi
3+
ion has
the same valence, but the effect on Tc is opposite to that of
La
3+
ion, as we see in Fig. 3(b) for samples containing La
3+
the remanent polarization Pr of SBN increase with increas-
ing La content 5, 10 and 15 wt.% (0.002; 0.01; 0.083)
respectively.
In Fig. 4(a) and (b) (with trivalent Bi
3+
and La
3+
ions), Tc
decrease with the increase of the concentration of the Bi
3+
ion, but increase with La
3+
ion. With smaller ion addition of
the constituent ions, Tc is increasing. This result implies that
the valence of doped ion is not an important factor for
ferroelectricity in SBN ceramics.
Ferroelectric transition temperature (Tc≈400 °C) of SBN
is slightly lower than the previously reported value because
of the non-stoichiometic composition of our SBN ceramics,
unlike some authors that uses about 4–4.5 wt.% excess
Bi
2
O
3
to compensate for weight loss of Bi
2
O
3
during sinter-
ing and the calcination to promote the solid-state reactions
among the constituent compounds [8,9]. The SBN ceramic
was a Bi-deficient phase due to the volatility of Bi during
the sintering process at 1000 °C, compared to SBN ceramics
synthesized by chemical route [17].
3.2 SEM
SEM micrograph of the material shows globular morpholo-
gies (nearly spherical). In Fig. 5with increasing the addition
of Bi
2
O
3
some voids or pores were found in the SBN
ceramic. This phenomenon indicates that big additions into
SBN may restrain the formation of the layered perovskite
phase, which is consistent with the results. The dopant is
added in small quantities used to reduce the porosity and
promote uniform grain growth by preventing the growth of
crystallites in preferential directions, resulting in a uniform
microstructure [18].
The samples are relatively dense, while small pores or
voids were found in all samples. With increasing Bi
2
O
3
addition, the growth in all three directions contributes to
the formation of cubic crystals. It can be stated that the use
of organic ligands, with respect to the addition of bismuth
oxide, did not affect the microstructure of the samples.
In Fig. 6we have the SEM micrographs of the SBN
surface samples with increased La
2
O
3
content. The SEM
micrographs reveal a microstructure comprising grains of
varying size with well defined contours indicating the nature
of the polycrystalline material. For sample SBN0La, one
observed that the grain morphology is spherical and is
distributed evenly and densely across the sample surface.
In additions of 3 and 5 wt.% La
2
O
3
, a modified type of
morphology changed from globular to lamellar, with a pre-
ferred direction, the grain size of the samples increased in
different proportions. Additions of 10 and 15 wt.% of lan-
thanum oxide is leading to more orderly and uniform mor-
phology with cubic grains geometry.
Addition with cations sometimes results in reduction in
grain size in isotropic perovskite ceramics. This is usually
difficult because the dopant diffusion, results in reduced
grain growth, during sintering. This phenomenon is ob-
served in La
2
O
3
doped samples. Another reason for the
change in microstructure may be due to preferred orientation
along the axis c, which is common with layers of ferroelec-
tric bismuth ceramic structures, this fact is observed in 3, 5
and 10 wt.% of La
2
O
3
added samples [13].
100 1k 10k 100k 1M 10M
20
40
60
80
100
120
140
160
SBN0BiG
SBN3BiG
SBN5BiG
SBN10BiG
SBN15BiG
r
'
Frequency (Hz)
SBNBiG
ε
Fig. 7 Dielectric Permittivity( "0
r) of SBNBiG samples (sintered at
850 °C/2 h) as a function of frequency
100 1k 10k 100k 1M 10M
20
40
60
80
100
120
140
160
SBNLaP
SBN0LaP
SBN3LaP
SBN5LaP
SBN10LaP
SBN15LaP
r
'
Frequency (Hz)
ε
Fig. 8 Dielectric Permittivity( "0
r) of SBNLaP samples (sintered at
1000 °C/2 h) as a function of frequency
J Electroceram (2013) 30:119–128 125
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3.3 Dielectric analysis
The variation of dielectric permittivity ("0
r) as a function of
frequency are shown in Figs. 7and 8. The SBNBiG series
shows a small decrease in the values of "0
rin the whole
frequency range, as shown in Table 3. This fact is explained
by phenomenon of dipole relaxation where at low frequen-
cies the dipoles are able to follow the frequency of the
applied field [19,20].
As can be seen in Fig. 7, SBNBiG shows an increase in
the values of "0
rwith the addition of the dopant in concen-
trations of 3 and 5 wt.% and a decrease in values of "0
rat
concentrations of 10 and 15 wt.%. This is because that the
amount of the added dopant presents a saturation region in
the SBN matrix, i.e. the number of pores in this region is
approximately equal to the number of atoms of impurities
that cause the doping [21].
In Fig. 8the SBNLaP series showed an increase in the
values of "0
rwith the increase of the addition of dopants (3
and 5 wt.%), but additions above this value (10 % and 15 %)
is lowering the "0
rvalues to lower values compared to the
pure sample. The addition of lanthanum is known to in-
crease dielectric permittivity compared to samples without
the addition. This is due to the high polarizability of the
lanthanum ion, that introduces a positive charge units in the
free structure, i.e., a strontium vacancy. Thus, the lanthanum
doping is creating openings in the structure to maintain
charge neutrality. The absence of a more pronounced polar-
ization in space charge in doped samples (with lanthanum)
is due to charge neutrality in the added sample, by having
the same valence state that strontium [22].
In Table 3one can notice that with the addition of 3 wt.%
Bi
2
O
3
, there was a decrease in values of tanδ. However the
loss is increasing with increasing concentration of Bi
2
O
3
.
Probably because the increase of the addition concentration
may have increased conductivity of the dielectric material
[23,24].
Table 3 Dielectric permittivity
("0
r) and loss (tanδ) of samples
SBNBiG (sintered at 850 °C/2 h)
and samples SBNLaP (sintered
at 1000 °C/2 h)
SBN 100 kHz 1 MHz 10 MHz
"0
rtan δ"0
rtan δ"0
rtan δ
SBN0BiG 38.21 0.0106 37.66 0.0106 37.24 0.0130
SBN3BiG 75.44 0.0069 74.68 0.0067 74.53 0.0083
SBN5BiG 111.17 0.0072 109.91 0.0075 110.85 0.0081
SBN10BiG 81.67 0.0082 80.59 0.0086 80.14 0.0101
SBN15BiG 76.16 0.0084 75.17 0.0094 75.17 0.0118
SBN0LaP 56.98 0.0103 56.11 0.0096 55.53 0.0111
SBN3LaP 87.72 0.0078 86.66 0.0124 85.90 0.0124
SBN5LaP 121.40 0.0144 118.72 0.0216 116.71 0.0216
SBN10LaP 38.70 0.0059 38.43 0.0292 38.16 0.0292
SBN15LaP 35.63 0.0051 35.47 0.0057 35.15 0.0057
051015
0,00
0,01
0,02
0,03
tan
X(%)
20
40
60
80
100
120
Bi
La
'r
10MHz
ε
δ
Fig. 9 Dielectric permittivity ("0
r) and loss (tanδ) as a function of the
addition level (X)wt.%, X 0Bi
2
O
3
or La
2
O
3
at 10 MHz frequency at
room temperature
Tab le 4 Microwave measurements obtained from Hakki-Coleman
procedure; thickness (e), diameter (D), dielectric resonant frequency
TE
011
(f
r
), dielectric permittivity ("0
r) and dielectric loss (tgδ
E
)
Sample e (mm) D (mm) f
r
(GHz) "0
rtgδ
E
SBN0BiG 8.95 17.29 4.393 28.33 0.050
SBN3BiG 7.76 15.26 3.591 57.01 0.031
SBN5BiG 7.98 15.60 3.756 49.55 0.029
SBN10BiG 8.12 16.15 3.306 60.92 0.025
SBN15BiG 7.12 15.03 3.425 70.32 0.025
SBN0LaP 8.45 17.10 3.792 42.09 0.036
SBN3LaP 7.84 15.60 3.645 53.72 0.034
SBN5LaP 7.35 14.67 3.457 67.80 0.070
SBN10LaP 7.69 17.28 5.001 26.88 0.035
SBN15LaP 8.69 17.62 5.625 17.97 0.018
126 J Electroceram (2013) 30:119–128
Author's personal copy
In the SBNLaP series, the increase in the values of loss,
well above 100 kHz is attributed to a loss due to the
resonance frequency. The loss of resonance, for the existing
materials, respond at higher frequencies (>100 kHz) as the
frequency of the applied field with the natural vibration
frequency of an ion/electron, as observed in the samples
SBN3LaP, SBN5LaP and SBN10LaP [18].
In Fig. 9, one has a comparison of the dielectric permit-
tivity ("0
r) of SBN for different addition levels at 10 MHz.
For samples added with Bi
2
O
3
, the higher values of "0
rhas
been obtained for the SBN5BiG samples (110.85), while the
highest value of "0
rwas found with the sample added with
La
2
O
3
, SBN5LaP (116.71). Also in Fig. 9one has the
dielectric loss (at 10 MHz) for different addition levels.
The lowest values of tanδwas observed for SBN15LaP
(0.0057), but specifically for the sample with 15 % La
2
O
3
,
which is in agreement with lanthanum doping reported in
the literature [22].
3.4 Microwave properties
The variation of the dielectric permittivity ("0
r) and dielectric
loss (tgδ
E
) for SBN added Bi
2
O
3
or La
2
O
3
as function of
frequency, in the microwave region in the frequency range
of 3 GHz to 6 GHz is shown in Table 4.Bi
2
O
3
added
samples have shown a higher dielectric permittivity than
La
2
O
3
added samples, we highlight the SBN15BiG addition
sample with a dielectric permittivity of 70.32(3.4 GHz), is
the highest obtained value. The lowest loss was obtained for
the same sample SBN15LaP (0.018).
Under the same conditions, the dielectric permittivity ("0
r)
increases with the increaseof the Bi
2
O
3
addition (see Fig. 10).
For samples added with La
2
O
3
,weobservedanincreasein"0
r
to the composition of 5 % La
2
O
3
, and a considerable decrease
from this value, reaching its lowest value in the sample
SBN15LaP (17.976) which can be seen in Fig. 10.Asob-
served, dielectric permittivity values are in the range of 28–71
and dielectric losses are of the order of 10
−2
, making this
material a likely candidate for use as a microwave component.
4 Conclusions
In this paper a study of the structural and electrical charac-
teristics of the SrBi
2
Nb
2
O
9
(SBN) added with Bi
2
O
3
and
La
2
O
3
is presented. The compounds were prepared by a new
procedure in the solid-state reaction method. They were
studied using XRD, SEM micrograph, dielectric analysis
and microwave properties. The samples belong to the spatial
group A2
1
am, showing orthorhombic structure. The SEM
micrographs reveal a microstructure comprising grains of vary-
ing size with well defined contours indicating the nature of the
polycrystalline material. The dielectric analysis at 10 MHz
shows that the highest values of permittivity was observed
for SBN5LaP (5 % La
2
O
3
) with values of 116.71 and the lower
loss (0.0057) was obtained for SBN15LaP (15 % La
2
O
3
).
In the microwave frequency region, Bi
2
O
3
added samples
have shown higher dielectric permittivity than La
2
O
3
added
samples, we highlight the SBN15BiG (15 % Bi
2
O
3
) sample
with a the higher dielectric permittivity of 70.32(3.4 GHz).
The dielectric permittivity values are in the range of 28–
71 and dielectric losses are of the order of 10
−2
, making this
material a likely candidate for use as a microwave
component.
Acknowledgments This work was partly sponsored by Coordenação
de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and X-ray
Laboratory, Federal University of Ceará Process: 402561/2007-4 (Edi-
tal MCT/CNPq n
o
10/2007) and the U. S. Air Force Office of Scientific
Research (AFOSR) (FA9550-11-1-0095)
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