Correlation between vibrational modes of A-site ions and microwave dielectric properties in (1?x) CaTiO3?x (Li0.5Sm0.5)TiO3 ceramics

Article abstract of DOI:10.1016/j.jallcom.2017.09.198

(1-x)CaTiO₃-x(Li_0.5Sm_0.5)TiO₃ (0.7 ≤ x ≤ 0.8, CLST) ceramics with an orthorhombic perovskite structure were fabricated by a conventional solid-state reaction method. The effects of composition variation on the microwave dielectric properties were studied in detail. The permittivity (ε_r) and quality factor (Q × f) value decreased with an increase in the x value, and the temperature coefficient of the resonant frequency (τ_f) reached nearly zero. Raman and infrared reflection spectroscopy were employed to reveal the relationship between vibrational modes and microwave dielectric properties. The Raman spectra fitted with the Lorentzian model indicated that the dielectric loss deteriorates with an increase in the x value are the result of the lowered A-site cation ordering degree. The harmonic oscillator model was used to fit the infrared reflection spectra, and the obtained complex dielectric response was extrapolated down to the microwave region. The infrared reflection spectra show that the vibrational modes related to A-site cations at lower frequencies (i.e., <150 cm^?1) play the most important role in the microwave dielectric properties of CLST ceramics. The optimal microwave dielectric properties were found to be ε_r = 109.4, Q × f = 4698 GHz, and τ_f = 1.6 ppm/°C in the sample of 0.22CaTiO₃-0.78(Li_0.5Sm_0.5)TiO₃.

Full text of DOI:10.1016/j.jallcom.2017.09.198

Journal of Alloys and Compounds 729 (2017) 742e748
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
Correlation between vibrational modes of A-site ions and microwave
dielectric properties in (1ꢀx) CaTiO ꢀx (Li Sm )TiO ceramics
3
0.5
0.5
3
Fanfan Ning , Lin Gan , Shifeng Yuan , Zeming Qi , Juan Jiang , Tianjin Zhang a
a
a
a
b
a
,
*
, **
a
Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Ministry of Education Key Laboratory for the Green Preparation and
Application of Functional Materials and School of Material Science and Engineering, Hubei University, Wuhan 430062, China
b
National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 July 2017
Received in revised form
(1-x)CaTiO -x(Li0.5Sm0.5)TiO3 (0.7 ꢁ x ꢁ 0.8, CLST) ceramics with an orthorhombic perovskite structure
3
were fabricated by a conventional solid-state reaction method. The effects of composition variation on
the microwave dielectric properties were studied in detail. The permittivity (ε
value decreased with an increase in the x value, and the temperature coefficient of the resonant fre-
quency ( ) reached nearly zero. Raman and infrared reflection spectroscopy were employed to reveal the
r
) and quality factor (Q ꢂ f)
16 September 2017
Accepted 18 September 2017
Available online 20 September 2017
t
f
relationship between vibrational modes and microwave dielectric properties. The Raman spectra fitted
with the Lorentzian model indicated that the dielectric loss deteriorates with an increase in the x value
are the result of the lowered A-site cation ordering degree. The harmonic oscillator model was used to fit
the infrared reflection spectra, and the obtained complex dielectric response was extrapolated down to
the microwave region. The infrared reflection spectra show that the vibrational modes related to A-site
Keywords:
Microwave dielectric properties
Raman
Infrared reflection
Vibrational modes
ꢀ
1
cations at lower frequencies (i.e., <150 cm ) play the most important role in the microwave dielectric
properties of CLST ceramics. The optimal microwave dielectric properties were found to be ε
r
¼ 109.4,
ꢃ
Q ꢂ f ¼ 4698 GHz, and
t
f
¼ 1.6 ppm/ C in the sample of 0.22CaTiO
3
-0.78(Li0.5Sm0.5)TiO
2017 Elsevier B.V. All rights reserved.
3
.
©
1
. Introduction
dielectric ceramics that simultaneously satisfy the three required
characteristics for microwave dielectric applications because ma-
terials with high permittivity usually have a high dielectric loss and
In recent years, with the rapid development of wireless
communication and satellite communication, microwave dielectric
ceramics have been intensively studied because of their popular
applications in the fields of global positioning system (GPS) and
wireless local area network (WLAN) technology. It is known that
miniaturization, integration, and high reliability are important re-
quirements for microwave electronic devices and portable termi-
nals. Therefore, to fabricate high-performance microwave dielectric
ceramics for the applications mentioned above, a high dielectric
a large
ramics with high ε
1/2)TiO , tungsten bronze-type BaO-Ln
skite CaO-Li O-Ln -TiO or CaTiO -(Li0.5Ln0.5)TiO
3
ceramics have been developed [4e7]. Unfortunately, the high sin-
tering temperatures of tungsten bronze-type and Pb-based mate-
t
f
. In previous studies, a series of microwave dielectric ce-
, such as A-site-modified perovskite (Aþ 1/2A3þ
-TiO , complex perov-
, and Pb-based
r
3
2
O
3
2
2
2
O
3
2
3
rials, and the large positive
perovskites, hinder the application of these microwave dielectric
ceramics. Solid solutions of (1-x)CaTiO -x(Li0.5Ln0.5)TiO
(Ln ¼ Nd,
Sm, La) present promising microwave dielectric properties, which
include high ε
, superior Q ꢂ f values, and adjustable temperature
coefficient of resonant frequency [8e10]. CaTiO -(Li1/2Ln1/2)TiO
f
t values of some of the A-site-modified
constant (ε
r
), outstanding quality factor (Q ꢂ f), and near-zero
3
3
temperature coefficient of resonant frequency (
t
f
) are necessary
to achieve component miniaturization, good signal recognition,
and excellent temperature stability [1e3].
r
3
3
-
In general, it is quite challenging to fabricate microwave
based solid solutions were first reported by Ezaki et al. [6], and
temperature-stable dielectric ceramics can be obtained in a CaO-
Li
2
O-Ln
2
O
3
-TiO
2
system with ε
r
¼ 110, Q ꢂ f ¼ 4500 GHz, and
ꢃ
t
f
¼ 7.0 ppm/ C. Kim et al. [8] reported the dielectric properties of
*
Corresponding author.
the (1-x)CaTiO
3
-x(Li0.5Sm0.5)TiO
3
system, which exhibits values of
** Corresponding author.
ꢃ
E-mail addresses: jiangjuan@hubu.edu.cn (J. Jiang), zhangtj@hubu.edu.cn
ε
r
¼ 114, Q ꢂ f ¼ 3700 GHz, and
t
f
¼ 11.5 ppm/ C for x ¼ 0.7. Li et al.
(
T. Zhang).
https://doi.org/10.1016/j.jallcom.2017.09.198
925-8388/© 2017 Elsevier B.V. All rights reserved.
0

F. Ning et al. / Journal of Alloys and Compounds 729 (2017) 742e748
743
[
11] reported that Ca1-x(Li1/2Sm1/2
)
x
TiO
3
ceramics had good per-
Ettlingen, Germany) on the infrared beamline station (U4) at the
National Synchrotron Radiation Lab. (NSRL), China. Microwave
dielectric properties of the ceramics were measured with the TE01
d
formance, with microwave dielectric properties of ε
r
¼ 105.8,
ꢃ
Q ꢂ f ¼ 3170 GHz, and
t
f
¼ 0 ppm/ C when x ¼ 0.75. Gu et al. [12]
found that 0.2Ca0.8Sr0.2TiO
3
-0.8(Li0.5Sm0.5)TiO
3
solid solution ce-
shielded cavity reflection method with a network analyzer
(E5071C, Agilent, Palo Alto, CA). The temperature coefficient of the
ramics exhibit good microwave dielectric properties of ε
r
¼ 113,
ꢃ
ꢃ
ꢃ
Q ꢂ f ¼ 4400 GHz, and
t
f
¼ 8.4 ppm/ C.
resonant frequency (
t
f
) was measured at ꢀ20 C and 65 C and was
Although much work has been done to control the microwave
dielectric properties of materials that are based on CaTiO
Li0.5Sm0.5)TiO ceramics, a fundamental principles study on the
calculated using the following formula (Eq. (1)):
3
-
f
ꢀ f
ðT
2
(
3
ðT
2
Þ
1
Þ
1
6
ꢃ
t
¼
ꢂ 10 ðppm= CÞ
(1)
represent the resonant frequencies measured
Þ
f
permittivity and dielectric losses in solid solution is still needed to
reveal the responsible mechanism. The dielectric properties of
microwave dielectric ceramics mostly depend on ionic polarization
caused by lattice vibrations. Therefore, Raman and infrared spec-
troscopy are usually considered useful tools to study the relation-
ship between the dielectric properties and the vibrational modes
f
ðT ꢀ T Þ
ðT
1
Þ
where f
and f
ðT
2
ðT
1
Þ
ꢃ
ꢃ
at ꢀ20 C and 65 C, respectively.
[13e15]. Dielectric losses include an intrinsic part and extrinsic
3. Results and discussion
part. The intrinsic losses may be obtained from the infrared
reflection spectra using the classical harmonic oscillator model
Fig. 1 shows the XRD patterns of the CLST ceramics with various
compositions. All diffraction peaks were indexed as an ortho-
[16]. In addition, the Raman spectra may reveal the short-range
characteristics of the ceramics, including order-disorder transi-
rhombic perovskite structure (JCPDS card No. 42-0423, CaTiO
3
,
tions [17]. Zhou et al. [18e20] reported that the Far-infrared spectra
space group Pmna), and no secondary phases were observed in all
2
þ
(
50e1000 cm-1) study showed that complex dielectric spectra
were in good agreement with the measured microwave permit-
tivity and dielectric losses in (Na0.5La0.5)MoO -(Na0.5Bi0.5)MoO
ceramics. They also reported that the infrared spectra showed that
the external vibrations of CeVO had the most remarkable effects
on the dielectric constant in the CeVO -TiO composite ceramics. In
addition, the Raman, infrared reflection, and terahertz spectra of A-
site-deficient scheelite materials (Ca1-3xBi2x )MoO : A-site va-
compositions. This result indicates that (Li0.5Sm0.5
)
ions have
diffused into CaTiO lattices and formed a solid solution. Further-
3
4
4
more, the diffraction peaks shift to a higher angle as x increases,
suggesting that the unit cell volume of the solid solution gradually
decreases with an increase in the x value as a result of the partial
4
2
þ
ions
4
2
substitution of the smaller A-site ionic radii of (Li0.5Sm0.5
(0.9995 Å) for larger Ca ions (1.1200 Å) [21].
)
2
þ
F
x
4
(
F
Fig. 2 shows SEM images of the surfaces of the CLST ceramics
with various compositions after hot corrosion treatment. A well-
densified microstructure was observed and there was no obvious
secondary phase for all compositions, which agreed well with the
XRD patterns. The average grain size of the samples was in the
cancy) were studied to evaluate the correlation between the
vibrational modes and the microwave dielectric properties.
In this work,
a
3 3
series of (1-x)CaTiO -x(Li0.5Sm0.5)TiO
(
0.7 ꢁ x ꢁ 0.8, CLST) ceramics were synthesized by a solid-state
reaction method. The effects of compositional variation on the
structure and microwave dielectric properties of the samples were
investigated in detail. Additionally, the relationship between
vibrational modes and microwave dielectric properties was dis-
cussed by fitting the Raman and the infrared reflection spectra.
range of 1e4 mm. The SEM observations suggest that there is no
significant difference in the microstructure of samples with various
compositions. In addition, the relative densities of the CLST ce-
ramics are very high (i.e., about 97%). And the relative density is
almost constant with the change of composition.
Fig. 3 presents the microwave dielectric properties of the CLST
ceramics as a function of the x value. In Fig. 3(a), the permittivity
decreases monotonously as the x value increases from 0.70 to 0.80,
which is in a good agreement with the results of Kim et al. [8] and Li
2
. Experimental procedure
(
1-x)CaTiO
were prepared by the conventional solid-state reaction method
from commercial powders of CaCO (99.0%), TiO (99.9%),
(99.99%). Initially, stoichiometric ratios of
CO3, Sm , and TiO , were respectively
balls for 12 h. After drying,
was
3
-x(Li0.5Sm0.5)TiO
3
(0.7 ꢁ x ꢁ 0.8, CLST) ceramics
2
þ
has a smaller ionic
et al. [11]. A possible reason is that (Li0.5Sm0.5
)
3
2þ
3
3
2
polarizability (2.97 Å ) than that of Ca (3.16 Å ) [22], the ionic
polarizability of the CLST ceramics decreased with the increase of x
value. According to Clausius-Mossotti equation, the ionic polariz-
ability is directly proportional to the dielectric constant [23].
Therefore, the permittivity is dependent on the ionic polarizability,
and a decrease in the ionic polarizability leads to a decrease in the
permittivity. In addition, the variation of permittivity with x value
in this study may be associated with the change in the lattice vi-
bration mode caused by the substitution of A-site ions, as will be
discussed later in the infrared spectroscopy analysis.
Li
CaCO
2
CO
3
(99.9%), and Sm
2 3
O
3
and TiO , and Li
2
2
2
O
3
2
mixed using ethanol medium and ZrO
2
ꢃ
CaTiO
3
was calcined at 1090 C for 5 h and (Li0.5Sm0.5)TiO
3
ꢃ
calcined at 1100 C for 3 h. Then, the calcined powders were
weighed according to the compositions of (1-x)CaTiO -x(Li0.5Sm0.5
TiO
(x ¼ 0.70, 0.72, 0.74, 0.76, 0.78, 0.80) and were milled again for
2 h in ethanol medium. The powers were mixed with 10 wt%
3
)
3
1
polyvinyl alcohol (PVA, 5%) solution as a binder after drying and
were uniaxially pressed into pellets 12 mm in diameter and
The Q ꢂ f value of the CLST samples also shows a downward
trend with an increase in the x value, as seen in Fig. 3(b). It is widely
known that the Q ꢂ f value depends on extrinsic factors such as the
secondary phase, impurity, grain size, and density, as well as
intrinsic losses related to the lattice vibration modes [24]. However,
the effects of extrinsic factors on the Q ꢂ f value may be negligible,
as on one hand no secondary phase or impurities were detected by
the XRD analysis (see Fig. 1), and on the other hand, dense micro-
structures and fine grain sizes were observed in the SEM images
(see Fig. 2). Therefore, the decrease in the Q ꢂ f value with x value
may be attributed to the intrinsic losses caused by the variation in
the lattice vibration mode.
ꢃ
6
3
e7 mm in thickness. Finally, the pellets were heated at 550 C for
h to eliminate the binder and then sintered at 1240 C for 4 h in
ꢃ
air.
The crystal structure of the sintered samples was analyzed using
X-ray powder diffraction (XRD, D8 advance, Bruker, Germany) with
Cu K radiation. The microstructures of the ceramics were observed
a
using a scanning electron microscope (SEM, JSM-7100F, JEOL,
Japan). The Raman spectra were recorded at room temperature
using a Raman spectrometer (inVia, Renishaw, UK) excited with an
Ar ion laser (633 nm). The infrared reflection spectra were
measured using a Bruker IFS 66v FTIR spectrometer (Bruker Optics,

744
F. Ning et al. / Journal of Alloys and Compounds 729 (2017) 742e748
Fig. 1. XRD patterns of (1ꢀx)CaTiO
3
ꢀx(Li0.5Sm0.5)TiO (0.70 ꢁ x ꢁ 0.80) ceramics.
3
Fig. 2. SEM images of the surfaces of (1ꢀx)CaTiO
x ¼ 0.78; (f) x ¼ 0.80.
3
ꢀx(Li0.5Sm0.5)TiO (0.70 ꢁ x ꢁ 0.80) ceramics after hot corrosion treatment: (a) x ¼ 0.70; (b) x ¼ 0.72; (c) x ¼ 0.74; (d) x ¼ 0.76; (e)
3
The
Fig. 3(c). The
t
f
value of the ceramics as a function of x value is shown in
0.22CaTiO
Q ꢂ f ¼ 4698 GHz, and
3
-0.78(Li0.5Sm0.5)TiO
3
ceramics with
ε
r
¼
109.4,
ꢃ
ꢃ
f
t value decreases monotonously from þ66.7 ppm/ C
ꢃ
t
f
¼ þ1.6 ppm/ C. Compared to other ma-
to ꢀ10.3 ppm/ C as x increases from 0.70 to 0.80. In addition, at
terial systems with a high dielectric constant in recent years
[12,25,26], the CLST ceramics have better microwave dielectric
properties, including a higher dielectric constant and a near zero
resonant frequency temperature coefficient.
ꢃ
x ¼ 0.78, a near-zero
t
f
value of þ1.6 ppm/ C was obtained.
Compared to CaTiO
3
which is with a positive
have a negative
t
f
value of þ800 ppm/
ꢃ
ꢃ
C, (Li0.5Sm0.5)TiO
result, theoretically the
tively changed in the range from ꢀ260 to þ800 ppm/ C by
compositional tailoring. Therefore, a compromise was made and
the optimal microwave dielectric properties were achieved for the
3
t
f
value of ꢀ260 ppm/ C [4]. As a
t
f
value of the CLST system can be effec-
To investigate the relationships between the vibrational modes
and the microwave dielectric properties of the CLST ceramics,
Raman spectra, infrared reflection spectra, and group theory were
ꢃ
3
employed. It has been proved that CaTiO has an orthorhombic

F. Ning et al. / Journal of Alloys and Compounds 729 (2017) 742e748
745
Fig.
3. Microwave
dielectric
properties
of
(1ꢀx)CaTiO
3
ꢀx(Li0.5Sm0.5)TiO
3
(
0.70 ꢁ x ꢁ 0.80) ceramics as a function of x value.
Fig. 4. Raman spectra of (1ꢀx)CaTiO
3
ꢀx(Li0.5Sm0.5)TiO (0.70 ꢁ x ꢁ 0.80) ceramics.
3
perovskite structure with a space group Pmna. The phonons at the
-point of the first Brillouin zone can be described in terms of the
irreducible representations of the D2h point group:
G
G
¼ 7A
g
þ 5B1g þ 7B2g þ 5B3g þ 8A þ 10B1u þ 8B2u þ 10B3u
u
(2)
2
9
4 Raman active (7A
g
, 5B1g, 7B2g, 5B3g) and 25 infrared active (7B1u,
B2u, 9B3u) modes are to be expected [27,28]. However, in reality,
not all of these bands can be observed. It is possible that many of
the predicted bands are hidden behind other intense bands, and
may overlap or involve very low changes in polarizability, pre-
venting their bands from being seen in the spectrum [27].
Fig. 4 shows the room-temperature Raman spectra of the CLST
ꢀ
1
ceramics in the range of 100e1000 cm . As indicated by previous
XRD analysis, the CLST ceramics possess an orthorhombic perov-
skite structure, which is identical to the structure of orthorhombic
3 3
CaTiO . Therefore, CLST and CaTiO should have similar vibrational
spectra. Clearly, in the Raman spectra of the CLST samples, eight
Raman bands can be observed, at 152, 225, 287 355, 479, 545, 767,
ꢀ1
and 829 cm , respectively. The broad and weak bands at 829 and
ꢀ
1
7
5
67 cm
are associated with lattice defects, and the band at
ꢀ1
45 cm is close to that of pure TieO symmetric stretching vi-
ꢀ1
bration [29]. The 479 cm band may be assigned to TieO torsional
modes (bending or internal vibration of the oxygen cage). The
ꢀ1
bands in the region of 355e225 cm should be attributed to the
modes associated with rotations of the oxygen cage, and that at
Fig. 5. Raman spectra of (1ꢀx)CaTiO
3
ꢀx(Li0.5Sm0.5)TiO (x ¼ 0.70, 0.80) ceramics. Black
3
ꢀ1
152 cm to the motion of A-site ions [30,31].
dots are experimental data, and solid lines are the Lorentz modes.
To clearly observe the changes in the Raman spectra of the
samples with an increase in the x value, the peaks were fitted by a
Lorentzian model. Fig. 5 shows the Raman spectra of CLST (x ¼ 0.70
and 0.80) ceramics de-convoluted into eight peaks. The wave
number and full width at half maximum (FWHM) of the de-
convoluted peaks of these two samples are listed in Table 1. The
Raman spectra of the other samples were also fitted by the Lor-
entzian model, and the frequencies and the FWHM values of all the
samples obtained from the fitting treatment are shown in Fig. 6. We
focus on the vibrational modes of the three strongest peaks (mode-
1, mode-2, and mode-6). As the x value increases, there is no
obvious variation in the frequencies of these three vibration modes,
as is shown in Fig. 6(a). Additionally, from Fig. 6(b), the FWHM
values of mode-2 and mode-6 vary randomly with an increase in
ꢀ
1
the x value, expect the vibrational mode at 152 cm (mode-1). The
FWHM values of mode-1 showed a monotonous increase with an

746
F. Ning et al. / Journal of Alloys and Compounds 729 (2017) 742e748
Table 1
Parameters of the Lorentzian model obtained by fitting the Raman spectra of (1ꢀx)CaTiO
3
ꢀx(Li0.5Sm0.5)TiO
3
(x ¼ 0.70, 0.80) ceramics.
x ¼ 0.80
Mode
Vibration mode
x ¼ 0.70
Wavenumber(cm 1
ꢀ
)
FWHW
Wavenumber(cm
ꢀ1
)
FWHW
1
2
3
4
5
6
7
8
motion of A-site ions
OeTieO bending mode
OeTieO bending mode
OeTieO bending mode
TieO torsional mode
symmetric stretching mode of TiO
lattice defect
152.0
225.4
286.7
355.0
479.4
544.9
766.8
829.4
58.3
113.0
85.7
89.6
25.5
69.1
26.4
77.2
155.5
233.0
291.5
356.0
479.9
547.6
775.5
832.8
61.4
111.0
79.0
81.4
26.5
73.4
39.7
60.2
6
octahedral
lattice defect
Fig. 6. Raman mode parameters-frequencies and FWHM values of (1ꢀx)CaTiO
3
ꢀx(Li0.5Sm0.5)TiO (0.70 ꢁ x ꢁ 0.80) ceramics obtained by the Lorentz model.
3
increase in the x value, which is due to the decrease in the order
þ
3þ
2þ
degree of A-site ions (i.e., Li , Sm , and Ca ). While the disor-
dered distribution of A-site ions have considerable effects on the
dielectric behaviors of microwave dielectric ceramics, because the
disordered A-site ions may break the periodic arrangement of
charges and then increase the dielectric losses [32,33]. In this study,
the disordered distribution of A-site ions in the CLST system
resulted in the broadening of the Raman spectra of mode-1 and an
increase in its FWHM value, which deteriorates the Q ꢂ f values of
CLST ceramics as the x value increases.
Fig. 7 illustrates the infrared reflection spectra of the CLST
ꢀ1
samples ranging from 50 to 1200 cm . The infrared reflection
spectra were fitted with 12 resonant modes using the classical
oscillator model. The fitted results (black lines) are quite consistent
with the measured spectra (red circles). The phonon parameters
obtained from the fitting treatment of the infrared reflection
spectra of the CLST ceramics are listed in Table 2. The infrared
reflection spectra of the CLST ceramics can be divided into three
wavenumber regions, corresponding to those for a simple perov-
ꢀ
1
skite structure [34]. The modes below 150 cm are due to the
external vibration mode of the A-site cations. The modes in the
ꢀ
1
range of 150e500 cm should be ascribed to TieOeTi bending
ꢀ1
modes, and the modes above 500 cm should be attributed to
TieO stretching modes [28]. These classifications are basically
consistent with Raman results.
According to the Fresnel equation (Eq. (3)), the dielectric func-
tion ε*(u) is associated with the infrared reflectance R(u); thus, the
Fig. 7. Measured (red circles) and fitted (black lines) infrared reflection spectra of
complex dielectric response of the CLST ceramics can be obtained
from the fitting of the infrared spectra using the Lorentz oscillator
(1ꢀx)CaTiO ꢀx(Li0.5Sm0.5)TiO3 (0.70 ꢁ x ꢁ 0.80) ceramics. (For interpretation of the
3
references to colour in this figure legend, the reader is referred to the web version of
this article.)

F. Ning et al. / Journal of Alloys and Compounds 729 (2017) 742e748
747
Table 2
Phonon parameters obtained from fitting the infrared reflection spectra of (1-x)CaTiO
3
-x(Li0.5Sm0.5)TiO
3
(0.70 < x < 0.80) ceramics.
Mode
x ¼ 0.72 ε
∞
¼ 4.84
x ¼ 0.74 ε
∞
¼ 5.05
x ¼ 0.76 ε
∞
¼ 5.54
x ¼ 0.78 ε
∞
¼ 4.65
u
oj
u
pj
g
j
△ ε
j
u
oj
u
pj
g
j
△ ε
j
u
oj
u
pj
g
j
△ ε
j
u
oj
u
pj
g
j
△ ε
j
1
2
3
4
5
6
7
8
9
94
578
579
551
605
584
464
304
210
155
127
616
248
51
43
36
33
35
44
44
38
33
23
52
104
37.8
17.9
10.1
9.1
6.5
3.2
0.9
0.3
0.2
0.1
93
569
597
681
668
564
340
194
110
88
68
59
50
46
55
53
37
24
17
53
56
159
37.4
17.4
13.0
9.0
4.8
1.2
0.3
0.1
0.04
1.1
0.3
94
574
577
530
600
559
532
342
305
268
206
702
292
80
51
37
34
34
41
43
41
46
39
46
107
37.3
16.3
8.4
7.9
5.4
3.9
1.2
0.8
0.6
0.2
1.6
0.1
92
546
561
558
602
593
483
296
241
234
161
647
254
54
46
38
35
36
44
43
39
44
34
51
99
35.2
16.5
10.0
8.5
6.4
3.3
0.9
0.5
0.4
0.2
137
173
201
229
260
322
357
389
418
550
782
143
189
223
257
309
372
402
421
548
689
778
143
183
213
240
270
316
345
377
416
556
785
138
176
206
234
265
316
344
377
415
552
783
10
11
12
575
380
329
1.3
0.1
1.4
0.1
0.2
The bold numbers are calculated values, which need to be emphasized.
model (Eq. (4)).
n
n
2
u
X
X
ε0 ¼ ε
þ
D
εj ¼ ε
þ
pj
(5)
∞
∞
2
u
j¼1
j¼1
oj
ꢀ
ꢀ
ꢀ
ꢀ
pffiffiffiffiffiffiffiffiffiffiffi
2
*
ꢀ
Þ ¼ ꢀ
ꢀ
1 ꢀ ε ð
u
Þꢀ
Rð
u
pffiffiffiffiffiffiffiffiffiffiffiꢀ
(3)
(4)
00
n
X
Dε g
j
j
*
ꢀ
ε
1
þ
ε ð
uÞ
tand
¼
¼
u
ꢁ
ꢂ
(6)
0
P
n
j¼1
ε
2
j¼1
u
ε
∞
þ
Dε
j
oj
where △ε
j
is the contribution of a phonon to the permittivity from
n
2
the j-th Lorentz oscillator. In the CLST ceramics, the value of △ε
j
represents the mode that contributes to the permittivity.
X
u
*
pj
ε ð
u
Þ ¼ ε
∞
þ
2
2
u
ꢀ
u
ꢀ igju
0
00
j¼1 oj
The complex dielectric responses (ε and ε ) of the CLSTceramics
obtained from the fitting treatment of the infrared reflection
spectra and corresponding experimental microwave data are
shown in Fig. 8. The calculated permittivities are slightly lower than
the measured ones in the microwave range. Meanwhile, the
calculated dielectric losses are quite consistent with the values
where ε
tronic polarization;
∞
is the high-frequency permittivity caused by the elec-
oj, and are the plasma frequency, the
u
pj
,
u
g
j
eigenfrequency, and the damping coefficient of the j-th Lorentz
oscillator, respectively; and n is the number of phonon modes. In
the microwave frequency region (
u
«
u
pj), ε’ (Eq. (5)) and tan
d
(Eq.
d
measured using the TE01 method. Therefore, it can be concluded
(
6)) can be derived from the Lorentzian formula. Therefore, the
that the dielectric polarization of the CLST ceramics in the micro-
wave region is dominated by the phonons in the infrared region
[20].
contributions of each phonon to the microwave dielectric proper-
ties can be calculated:
Fig. 8. The real (a) and imaginary (b) parts of the complex dielectric response of (1ꢀx)CaTiO
3
ꢀx(Li0.5Sm0.5)TiO
3
(0.70 < x < 0.80) ceramics. Red dots are experimental microwave
data; solid lines are the results from fitting the infrared spectra. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this
article.)

748
F. Ning et al. / Journal of Alloys and Compounds 729 (2017) 742e748
Phonon parameters obtained from the fitting of the infrared
reflection spectra of the CLST ceramics are given in Table 2. The
administrators in the IR beamline workstation of National Syn-
chrotron Radiation Laboratory (NSRL), University of Science and
Technology of China, for their help in the IR measurements.
permittivity contributions of the modes at low frequencies, below
ꢀ
1
1
50 cm , are much larger than that of other modes in the CLST
ceramics, and the permittivity contributions decrease with an in-
crease in the x value. In addition, the sum of the contribution of the
vibrational modes to the dielectric constant also decreases with
increasing x value. Therefore, the permittivity of the CLST ceramics
decreased as the x value increased, which is consistent with the
measured results. In this study, the external vibration modes at low
frequencies related to the A-site ions play an important role in the
microwave dielectric properties of the CLST ceramics. When the x
value increased, the permittivity contributions of the external vi-
bration modes at low frequencies related to the A-site cations
decreased. This took a significant effect on the decrease in the
dielectric constant of the CLST ceramics. It indicates that the
dielectric properties of the CLST materials can be effectively
tailored by A-site substitutions.
References
[1] I.M. Reaney, D. Iddles, J. Am. Ceram. Soc. 89 (2006) 2063e2072.
[2] B. Ullah, W. Lei, Z.-Y. Zou, X.-H. Wang, W.-Z. Lu, J. Alloy. Compd. 695 (2017)
648e655.
[3] Z.-Y. Shen, Q.-G. Hu, Y.-M. Li, Z.-M. Wang, W.-Q. Luo, Y. Hong, Z.-X. Xie, R.-
H. Liao, X. Tan, J. Am. Ceram. Soc. 96 (2013) 2551e2555.
[4] H. Takahashi, Y. Baba, K. Ezaki, Y. Okamoto, K. Shibata, K. Kuroki, S. Nakano,
Jpn. J. Appl. Phys. 30 (1991) 2339.
[5] J. Mercurio, M. Manier, B. Frit, Ferroelectrics 127 (1992) 35e40.
[
6] K. Ezaki, Y. Baba, H. Takahashi, K. Shibata, S. Nakano, Jpn. J. Appl. Phys. 32
1993) 4319.
7] J. Kato, H. Kagata, K. Nishimoto, Jpn. J. Appl. Phys. 30 (1991) 2343.
(
[
[8] E.S. Kim, K.H. Yoon, J. Eur. Ceram. Soc. 23 (2003) 2397e2401.
9] K. Yan, M. Fujii, T. Karaki, M. Adachi, Jpn. J. Appl. Phys. 46 (2007) 7105e7107.
[
[
[
10] J. Li, Y. Han, T. Qiu, C. Jin, Mater. Res. Bull. 47 (2012) 2375e2379.
11] Y.M. Li, T.T. Song, F. Hu, R.H. Liao, B. Zhang, Adv. Mater. Res. 105e106 (2010)
2
38e241.
[12] F.-f. Gu, G.-h. Chen, C.-l. Yuan, C.-r. Zhou, T. Yang, Y. Yang, Mater. Res. Bull. 61
2015) 245e251.
4
. Conclusion
1-x)CaTiO -x(Li0.5Sm0.5)TiO
(
[13] A. Dias, L.A. Khalam, M.T. Sebastian, M.M. Lage, F.M. Matinaga, R.L. Moreira,
(
3
3
(0.7 ꢁ x ꢁ 0.8) ceramics were
Chem. Mater. 20 (2008) 259e269.
[14] F. Shi, H. Dong, Dalton Trans. 40 (2011) 6659e6667.
prepared by the conventional solid-state reaction method. All
ceramic samples demonstrate a pure orthorhombic perovskite
structure, and there is no apparent difference in morphology. The
microwave dielectric properties of the samples were studied by
varying the composition. As the x value increases, the permittivity
[
15] D. Zhou, L.-X. Pang, H. Wang, J. Guo, X. Yao, C.A. Randall, J. Mater. Chem. 21
2011) 18412.
16] K. Wakino, M. Murata, H. Tamura, J. Am. Ceram. Soc. 69 (1986) 34e37.
(
[
[17] H. Zheng, G.D.C. Csete de Gy o€ rgyfalva, R. Quimby, H. Bagshaw, R. Ubic,
I.M. Reaney, J. Yarwood, J. Eur. Ceram. Soc. 23 (2003) 2653e2659.
[18] W.-B. Li, D. Zhou, H.-H. Xi, L.-X. Pang, X. Yao, N. Alford, J. Am. Ceram. Soc. 99
and Q ꢂ f value decrease, and the
f
t value changes from positive
(2016) 2083e2088.
into negative. At x ¼ 0.78, the optimal microwave dielectric prop-
[19] W.-B. Li, D. Zhou, D. Guo, L.-X. Pang, G.-H. Chen, Z.-M. Qi, Q.-P. Wang, H.-C. Liu,
ꢃ
J. Alloy. Compd. 694 (2017) 40e45.
erties of ε
r
¼ 109.4, Q ꢂ f ¼ 4698 GHz, and
t
f
¼ 1.6 ppm/ C were
[20] J. Guo, C.A. Randall, D. Zhou, G. Zhang, C. Zhang, B. Jin, H. Wang, J. Eur. Ceram.
obtained. The vibrational properties of the A-site ions of the CLST
ceramics were investigated by Raman and infrared spectra ana-
lyses. As revealed by the Raman results, the Q ꢂ f value decreased
with an increase in the x value as a result of the lowered order
degree of the A-site ions. Additionally, the infrared reflectance
spectra indicate that the permittivity of the CLST ceramics is
strongly dependent on the external vibration modes at low fre-
quencies (i.e., <150 cm ), related to the A-site cations. This result
implies that A-site substitutions could be an effective method to
tailor the properties of CLST ceramic materials.
Soc. 35 (2015) 4459e4464.
[21] R.D. Shannon, Acta Crystallogr. 32 (1976) 751e767.
[
[
[
[
22] H.-H. Xi, D. Zhou, H.-D. Xie, B. He, Q.-P. Wang, N. Alford, J. Am. Ceram. Soc. 98
2015) 587e593.
(
23] Z.-M. Dou, J. Jiang, G. Wang, F. Zhang, T.-J. Zhang, Ceram. Int. 42 (2016)
6743e6748.
24] F. Liu, X.-Y. Liu, C.-L. Yuan, J.-J. Qu, G.-H. Chen, C.-R. Zhou, F. Liu, J. Eur. Ceram.
Soc. 35 (2015) 2091e2098.
25] Z.-X. Fang, B. Tang, F. Si, S.-R. Zhang, J. Alloy. Compd. 693 (2017) 843e852.
[26] H.-T. Chen, B. Tang, P. Fan, M. Wei, S.-R. Zhang, Ceram. Silik aꢀ ty 61 (2017) 1e5.
[27] H. Zheng, I.M. Reaney, G.D.C.C. De Gy
M.P. Seabra, V.M. Ferreira, J. Mater. Res. 19 (2003) 488e495.
28] K.W. Sup, Y.K. Hyun, K.E. Soo, J. Am. Ceram. Soc. 83 (2000) 2327e2329.
29] S.Y. Wu, Y. Li, X.M. Chen, J. Phys. Chem. Solids 64 (2003) 2365e2368.
ꢀ1
oꢀ rgyfalva, R. Ubic, J. Yarwood,
[
[
Acknowledgements
[30] T. Hirata, K. Ishioka, M. Kitajima, J. Solid State Chem. 124 (1996) 353e359.
[
[
[
31] U. Balachandran, N.G. Eror, Solid State Commun. 44 (1982) 815e818.
32] E. Schl o€ mann, Phys. Rev. 135 (1964) 413e419.
This work was supported by the National Science Foundation of
China (11774083). The authors would like to thank the
33] H. Tamura, J. Eur. Ceram. Soc. 26 (2006) 1775e1780.
[34] C.H. Perry, B.N. Khanna, G. Rupprecht, Phys. Rev. 135 (1964) A408eA412.