Effect of bond valence on microwave dielectric properties of (1-x)CaTiO3-x(Li0.5La0.5)TiO3 ceramics

Article abstract of DOI:10.1016/j.materresbull.2012.05.024

The origins of microwave dielectric properties (1 - x)CaTiO _3-x(Li_0.5La_0.5)TiO₃ (0.2 ≤ x ≤ 0.8) ceramics, prepared by a conventional solid-state reaction method, were investigated based on the theory of bond valence. The XRD and SEM results showed that complete solid solutions with orthorhombic perovskite structure were formed in the whole investigated compositional range. The dielectric constant (ε_r), quality factor (Q × f) and temperature coefficient of resonant frequency (τ_f) were closely related to B-site, A-site and the difference between A-site and B-site bond valences of ABO₃ perovskite compounds, respectively. As x value increased from 0.2 to 0.8, the dielectric constant increased from 198.3 to 276.8, the Q × f value decreased from 4340 to 1880 GHz, and the τ_f value varied from +489.7 to -178 ppm/°C. For practical applications, excellent microwave dielectric properties of ε_r = 245, Q × f = 2750 GHz and τ_f = +0.75 ppm/°C were obtained for 0.4CaTiO ₃-0.6(Li_0.5La_0.5)TiO₃ ceramics.

Full text of DOI:10.1016/j.materresbull.2012.05.024

Materials Research Bulletin 47 (2012) 2375–2379
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Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
Effect of bond valence on microwave dielectric properties of
(
1 ꢀ x)CaTiO –x(Li La )TiO ceramics
3
0.5 0.5
3
a,b
b
b,
a
Jiamao Li , Yuxian Han , Tai Qiu *, Chuangui Jin
a
School of Materials Science and Engineering, Anhui University of Technology, Maanshan 243002, China
College of Materials Science and Engineering, Nanjing University of Technology, Nanjing 210009, China
b
A R T I C L E I N F O
A B S T R A C T
Article history:
The origins of microwave dielectric properties (1 ꢀ x)CaTiO –x(Li0.5La0.5)TiO3 (0.2 ꢂ x ꢂ 0.8) ceramics,
3
Received 20 November 2011
Received in revised form 13 March 2012
Accepted 21 May 2012
prepared by a conventional solid-state reaction method, were investigated based on the theory of bond
valence. The XRD and SEM results showed that complete solid solutions with orthorhombic perovskite
structure were formed in the whole investigated compositional range. The dielectric constant (
quality factor (Q ꢁ f) and temperature coefficient of resonant frequency ( ) were closely related to B-site,
A-site and the difference between A-site and B-site bond valences of ABO perovskite compounds,
respectively. As x value increased from 0.2 to 0.8, the dielectric constant increased from 198.3 to 276.8,
the Q ꢁ f value decreased from 4340 to 1880 GHz, and the value varied from +489.7 to ꢀ178 ppm/8C.
For practical applications, excellent microwave dielectric properties of
= 245, Q ꢁ f = 2750 GHz and
= +0.75 ppm/8C were obtained for 0.4CaTiO –0.6(Li0.5La0.5)TiO ceramics.
ß 2012 Elsevier Ltd. All rights reserved.
r
e ),
Available online 30 May 2012
t
f
3
Keywords:
A. Ceramics
t
f
C. X-ray diffraction
D. Dielectric properties
e
r
t
f
3
3
1
. Introduction
With the rapid progress in wireless communication technology,
value to near-zero. Recently, a number of attempts on the
modification of microwave dielectric properties of CaTiO -based
ceramics have been undertaken. A series of new dielectric ceramics
with near-zero values have been developed by mixing CaTiO to
those materials with negative values, including (Li1/2Nd1/2)TiO
Ca(Mg1/3Ta2/3)O , NdAlO , Sm(Co1/2Ti1/2)O , and Nd(Zn1/2Ti1/2)O
3
the demand for microwave components with combined dielectric
properties has been increasing. Materials for microwave applica-
tions should have three key factors, i.e., high dielectric constant
t
f
3
t
f
3
,
3
3
3
3
(
e
r
), low dielectric loss (tan
coefficient of resonant frequency (
quantified in terms of tan or the Q-factor. For microwave
d
)
and near-zero temperature
[2–5]. However, the dielectric constants for these new ceramic
systems decrease inevitably since those materials with negative
values usually have the much smaller than that of CaTiO
ceramics. Moreover, the modification of the is mainly based on
empirical approaches, such as forming solid solutions or mixed
phases with two or more compounds.
t
f
). Dielectric loss can be
t
f
d
e
r
3
dielectric materials, Q ꢁ f (quality factor) is considered to be a
constant, where f is the microwave frequency. High dielectric
constant ceramics make it possible to noticeably miniaturize
passive microwave components since the size of microwave
t
f
In fact, the
e
r
and
t
f
of ABO
3
perovskite compounds are strongly
octahedra such as
components is inversely proportional to the square root of the
e
r
.
related to the structural characteristics of BO
6
Therefore, many efforts have been made to develop microwave
ceramics with a high dielectric constant. For example, the
bond strength and bond length between octahedral-site cation and
oxygen, respectively [6,7]. On the other hand, the structural
characteristics are mainly depended on the bond valence since the
bond valence is a function of bond strength and bond length.
Hence, the dielectric properties at microwave frequencies can be
effectively evaluated by the theory of bond valence. To better
understand the relationships between microwave dielectric
microwave dielectric properties of CaTiO
skite structure were first investigated by Kell et al. [1] in the early
970s. The combination of a high dielectric constant ( = 170) and
3
ceramics with perov-
1
e
r
a moderate dielectric loss (Q ꢁ f = 3500 GHz) makes it can be used
in electronic devices, such as filters, resonators, oscillators, and
dielectric antennas. However, the
large ( = +800 ppm/8C) for practical applications.
As a result, the primary task for developing any new CaTiO
based microwave materials is to adjust its large and positive
t
f
value of CaTiO
3
ceramics is too
properties and structural characteristics of ABO
compounds, the theory of bond valence has been applied to some
3
perovskite
t
f
3
-
ceramic systems such as Ca1ꢀxSm2x/3TiO
Fe0.5(Nb1ꢀxTa 0.5]O and (1 ꢀ x)(Ca0.7Nd0.2)TiO
8–10].
Li0.5La0.5)TiO
possess high and largely negative
near-zero , combined with high
3
,
(Pb0.45Ca0.55)[-
t
f
x
)
3
3
–x(Li0.5Nd0.5)TiO
3
[
(
3
ceramics with perovskite structure is found to
[11,12]. It is expected that a
and Q ꢁ f, can be achieved by
e
r
t
f
*
Corresponding author. Tel.: +86 25 83587262; fax: +86 25 83587268.
E-mail addresses: lijiamao@ahut.edu.cn (J. Li), qiutai51@yahoo.cn (T. Qiu).
t
f
e
r
0025-5408/$ – see front matter ß 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.materresbull.2012.05.024

2
376
J. Li et al. / Materials Research Bulletin 47 (2012) 2375–2379
2
+
2+
the substitution of (Li0.5La0.5
microwave dielectric properties of (1 ꢀ x)CaTiO
ceramics were investigated as a function of (Li0.5La0.5)TiO
0.2 ꢂ x ꢂ 0.8). The effects of A-site and B-site bond valences in
ABO perovskite compounds on the microwave dielectric proper-
ties were also discussed.
)
for Ca . In this study, the
–x(Li0.5La0.5)TiO
content
given atom, i, calculated using Eqs. (4) and (5) [17],
3
3
X
V
¼
y
(4)
(5)
3
i
i j
(
3
Ri j ꢀ d
i j
yi j ¼ exp b
c
0
b
2
. Experimental procedure
where Rij is the bond valence parameter, dij is the length of a bond
between atom i and j, and b is commonly taken to be a universal
0
(
1 ꢀ x)CaTiO
prepared by a conventional solid-state reaction method using
high-purity grade powders of CaCO , Li CO , La , and TiO as
starting materials. These starting materials were weighed accord-
ing to the desired stoichiometry of CaTiO and (Li0.5La0.5)TiO , and
3
–x(Li0.5La0.5)TiO
3
(0.2 ꢂ x ꢂ 0.8) ceramics were
˚
constant equal to 0.37 A. The used bond valence parameters were
followed the values in the previous report [17].
3
2
3
2
O
3
2
3. Results and discussion
3
3
then wet ball milled in ethanol for 24 h in polyethylene bottles
with zirconia balls, respectively. After dried at 80 8C for 6 h, the two
mixed powders were calcined at 1100 8C for 3 h in air.
Subsequently, the calcined powders were mixed according to
Fig. 1 shows the XRD patterns of (1 ꢀ x)CaTiO
3 3
–x(Li0.5La0.5)TiO
(
hereafter referred to as (1 ꢀ x)CT–xLLT, 0.2 ꢂ x ꢂ 0.8) ceramics
sintered at 1300 8C for 3 h. All peaks can be indexed based on CaTiO
JCPDS #42-423) with an orthorhombic perovskite structure and no
3
(
the composition of (1 ꢀ x)CaTiO
3
–x(Li0.5La0.5)TiO
3
(0.2 ꢂ x ꢂ 0.8)
second phase was detected, indicating the formation of(1 ꢀ x)CT–xLLT
solid solution. The (1 ꢀ x)CT–xLLT solid solution exhibits the same
and remilled 24 h in ethanol. Finally, the fine powders with 8 wt.%
PVA solution as a binder were uniaxially pressed at 100 MPa, and
then cold isostatically pressed into pellets with dimensions of
3 3
orthorhombic perovskite structure as CaTiO because CaTiO is
3
orthorhombic and has a GdFeO -type perovskite structure with lattice
1
2 mm diameter and 6 mm thickness under a pressure of 300 MPa.
˚
˚
˚
parameters a = 5.442 A, b = 7.6417 A and c = 5.3807 A and with space
These pellets were sintered at 1300 8C for 3 h in air. After cooled
from 1300 to 1000 8C with a rate of 2 8C/min, the ceramics were
naturally cooled inside the furnace.
The bulk densities of the sintered pellets were measured by
the Archimedes method in distilled water. The phase constitu-
groupPnma(JCPDS#42-423),though(Li0.5La0.5)TiO
3
iscubicperovskite
structure with lattice parameter a = 3.869 A with space group Pm 3¯ m
JCPDS #89-4928). This result is similar to those previous reports on
1 ꢀ x)CaTiO –x(Li0.5Sm0.5)TiO , (1 ꢀ x)CaTiO –x(Li0.5Nd0.5)TiO and
–x(Li0.5Nd0.5)TiO ceramic systems [10,18,19].
˚
(
(
3
3
3
3
(
1 ꢀ x)(Ca0.7Nd0.2)TiO
3
3
ents were identified by the X-ray diffraction method using Cu K
a
Thediffractionpeaksslightlyshifttoaloweranglewiththeincreaseofx
radiation (40 kV and 20 mA, XRD, D8 Advance, Bruker, Germany).
The lattice parameters were determined from X-ray diffraction
patterns with the least square method [13]. The microstructures
of the sintered surfaces were observed by scanning electron
microscopy (SEM, JEOL JSM 6490, Japan). All pellets for SEM
observation were polished and thermally etched at 1200 8C for
value,whichimpliesthattheunitcellvolumegraduallyincreasesdueto
2+
2+
˚
a larger effective radius of (Li1/2La1/2
)
(1.18 A) than that of Ca
1.12 A) at the same coordination number [20]. Similar result was
–x(Li0.5Nd0.5)TiO ceramic system [3].
˚
(
reported for (1 ꢀ x)CaTiO
3
3
Table 1 summarizes the lattice parameters and densities of
(
1 ꢀ x)CT–xLLT ceramics sintered at 1300 8C for 3 h. The lattice
3
0 min. The dielectric constant and unloaded Q value at
parameters were calculated from the XRD diffraction patterns
microwave frequencies were measured using the Hakki–Cole-
man dielectric resonator method, as modified and improved by
Courtney [14,15]. The temperature coefficient of resonant
using the least square method. With the increase of (Li0.5La0.5)TiO
referred to as LLT) content, the lattice parameters of a, b, c axes and
unit cell volume of (1 ꢀ x)CT–xLLT increase. The relative densities
shown in Table 1) for all compositions are higher than 96%,
3
(
f
frequency (t ) was measured in a temperature range from 25
(
to 80 8C and the
t
f
value was calculated with the following
suggesting that dense (1 ꢀ x)CT–xLLT ceramics with various x
values can be obtained after sintering at 1300 8C for 3 h. The bulk
density steadily increases with the increasing LLT content owing to
equation:
f80 ꢀ f
3
25
6
ꢄ
t f
¼
ꢁ 10 ðppm= CÞ
(1)
the larger density (4.839 g/cm obtained from JCPDS #89-4928) of
f25 ꢃ 55
where f25 and f80 are the resonant frequency at 25 and 80 8C,
respectively.
The observed ionic polarizability (aobs) of the sintered
samples was determined by the unit-cell volume obtained from
lattice parameter and measured dielectric constant using the
Clausius–Mossoti equation of Eq. (2) [16]. The theoretical ionic
polarizability (atheo) was calculated by the additive rule of Eq. (3)
with ionic polarizabilities of cation and oxygen, as reported by
Shannon [16].
V
m
ð
e
r
ꢀ 1Þ
aobs
¼
(2)
bð
e
r
þ 2Þ
atheoðABO
3
Þ ¼
a
A
þ
a
B
þ 3
a
O
(3)
where
abilities;
oxygen;
volume and b is a constant of 4
of atom i, V
a
obs and
a
theo are the observed and theoretical polariz-
, and the ionic polarizability of A-site, B-site and
is the measured dielectric constant, V is the molar
/3, respectively. The bond valence
, was defined as the sum of all the valences ij from a
a
A
,
a
B
a
O
e
r
m
p
Fig. 1. X-ray diffraction patterns of (1 ꢀ x)CaTiO –x(Li0.5La0.5)TiO3 ceramics
3
sintered at 1300 8C for 3 h.
i
n

J. Li et al. / Materials Research Bulletin 47 (2012) 2375–2379
2377
Table 1
Lattice parameters and densities of (1 ꢀ x)CaTiO
3 3
–x(Li0.5La0.5)TiO ceramics sintered at 1300 8C for 3 h.
x (mol)
Lattice parameter ( A˚ )
Unit cell volume ( A˚ 3
)
Bulk density (g/cm )
3
Relative density (%)
a
b
c
0.2
0.4
0.6
0.8
5.4502
5.4638
5.4839
5.4974
7.6511
7.6634
7.6835
7.7236
5.3705
5.3755
5.3848
5.3900
223.95
225.08
226.89
228.86
4.10
4.28
4.51
4.63
96.9
97.1
98.9
98.3
3
Table 2
LLT than that (4.036 g/cm obtained from JCPDS #42-0423) of
CaTiO (referred to as CT).
Theoretical and observed polarizabilities of (1 ꢀ x)CaTiO
3 3
–x(Li0.5La0.5)TiO ceram-
3
ics.
Fig. 2 illustrates the dielectric constant and Q ꢁ f value of
1 ꢀ x)CT–xLLT ceramics sintered at 1300 8C for 3 h with different x
x (mol) Theoretical
a
theo Observed
D
% (
a
obs
ꢀ
a
theo)/
a
obs ꢁ 100
(
values. It can be found that the dielectric constant increases
steadily from 198.3 to 276.8 with the increase of LLT content.
Generally, the dielectric constant is strongly dependent on the
ionic polarizability, density, and secondary phase of a material
er
Vm
Z aobs
0
.2
.4
12.215
12.31
12.405
12.5
198.3 223.95 4 13.1436 7.07
220.8 225.08 4 13.2525 7.11
245.0 226.89 4 13.3770 7.27
276.8 228.86 4 13.5121 7.49
0
0.6
.8
0
[
21]. For the present (1 ꢀ x)CT–xLLT solid solutions, the dielectric
constant is not significantly affected by the density due to the
higher relative densities than 96%. In addition, no secondary phase
is detected through the investigated compositional range, as
confirmed in Fig. 1. As a result, the dielectric constant is largely
depended on the ionic polarizability. According to Table 2, the
extrinsic factors such as density, impurity, secondary phase, and
grain size, as well as the intrinsic factor due to lattice
anharmonicity [23]. The relative densities of (1 ꢀ x)CT–xLLT
ceramics with various x values are above 96%, the effect of density
on the Q ꢁ f value can be neglected because the Q ꢁ f value is
independent of relative density greater than 95% [24]. In addition,
the effects of impurity and secondary phase on the Q ꢁ f value
might be neglected since no impurity and secondary phase are
observed from the XRD patterns. Therefore, the decrease in the
Q ꢁ f value is related to grain size and lattice anharmonicity.
The typical SEM micrographs for (1 ꢀ x)CT–xLLT ceramics
sintered at 1300 8C for 3 h are shown in Fig. 4. It can be observed
that all the compositions have dense and well-developed
microstructures. It was reported that the lattice defects and
dielectric losses of dielectric ceramics were dependent on the
homogeneous grain size [25]. The grains are angular in sharp and
tend to increase in size as the amount of LLT increases. Large grains
in dielectric ceramics usually contain more defects, such as
dislocations, planar defects, and even the dislocation networks,
which lead to the decrease of the Q ꢁ f value to some extent.
Therefore, the decrease in the Q ꢁ f value may be partly due to the
grain size.
theoretical ionic polarizability (
ability ( obs) and the deviation of
increasing LLT content. Moreover, the
higher than the theo value, resulting from the rattling effect of B-
site ion in ABO perovskite materials. These results can be
a
theo), the observed ionic polariz-
obs from theo increase with
obs value is obviously
a
a
a
a
a
3
explained by the decrease of the B-site bond valence because B-
site bond valence and rattling effect are a function of bond strength
9]. The rattling (or tilting) causes the B cation–anion bond from an
octahedron to a neighboring octahedron in an opposite direction,
thus giving rise to a doubling of the repeat distances perpendicular
to the tilt axis [22]. At the same time, if the B cation–anion bond
distance maintains, then the B cation–B cation distance (bond
length) will become shorter and hence influence the bond strength.
[
As a result, the deviation between
atheo and aobs is depended on the
B-site bond valence of ABO perovskite materials, as shown in
3
Fig. 3. Obviously, the increase in dielectric constant for (1 ꢀ x)CT–
xLLT ceramics with the increasing x value is due to not only the
˚
˚
larger ionic polarizability of LLT (12.60 A) than that of CT (12.12 A)
but also the decrease of the B-site bond valence resulting in the
increase of rattling effect.
On the other hand, the change of Q ꢁ f value for ABO
3
perovskite
is related to the change of the external vibration mode between the
The Q ꢁ f value of (1 ꢀ x)CT–xLLT ceramics with different x
values sintered at 1300 8C for 3 h decreases with the increase of LLT
content, as shown in Fig. 2. As reported, the Q ꢁ f value depends on
3
Fig. 2. Dielectric constant and Q ꢁ f value of (1 ꢀ x)CaTiO –x(Li0.5La0.5)TiO
ceramics sintered at 1300 8C for 3 h.
3
Fig. 3. Deviations of the ionic polarizability and B-site bond valence of
(1 ꢀ x)CaTiO
3 3
–x(Li0.5La0.5)TiO ceramics sintered at 1300 8C for 3 h.

2
378
J. Li et al. / Materials Research Bulletin 47 (2012) 2375–2379
3 3
Fig. 4. SEM micrographs of (1 ꢀ x)CaTiO –x(Li0.5La0.5)TiO ceramics sintered at 1300 8C for 3 h: (a) x = 0.2; (b) x = 0.4; (c) x = 0.6; (d) x = 0.8.
0
1
.2 to 0.8, the bond valence of A-site decreases from 1.5048 to
.1256, the Q ꢁ f value decreases from 4340 to 1880 GHz
Table 3
A-site bond valence of (1 ꢀ x)CaTiO
3
3
–x(Li0.5La0.5)TiO ceramics sintered at 1300 8C
simultaneously. Therefore, the Q ꢁ f value of (1 ꢀ x)CT–xLLT
ceramics is also closely related to the A-site bond valence.
It is well known that the temperature coefficient of resonant
for 3 h.
x (mol)
R
A–O
D
A–O
b
n
A–O
V
A–O
0.2
0.4
0.6
0.8
1.937
1.908
1.878
1.849
2.7051
2.7096
2.7169
2.7247
0.37
0.37
0.37
0.37
0.1254
0.1146
0.1036
0.0938
1.5048
1.3752
1.2432
1.1256
frequency (
f
t ) is a function of the temperature coefficient of
dielectric constant (te) and the linear thermal expansion coeffi-
cient (
a
L
), as given by Eq. (6):
ꢀ
ꢁ
t
2
e
t f ¼ ꢀ
þ
a
L
(6)
6
A-site cation and the TiO octahedron within the solid–solution
the value of
a
L
is often taken as a constant of ꢅ10 ppm/8C [27].
range based on the previous report [26]. This means that the
variation in A-site bond valence will affect the Q ꢁ f value. A
smaller A-site bond valence indicates that the bond strength
between oxygen and A-site cation is weaker and the anharmonic
interaction is increased, so the Q ꢁ f value is decreased. Table 3
shows the A-site bond valence for the present ceramics calculated
using Eqs. (4) and (5). Fig. 5 displays the dependence of the Q ꢁ f
value on the A-site bond valence. As LLT content increases from
Hence, t is largely related to t that depended on the recovery
f
e
energy of structural distortion of oxygen polyhedra. Recently, B-site
bond valence has been applied to evaluate the of some perovskite
compounds such as Ca1ꢀxSm2x/3TiO [8] and (Pb0.45Ca0.55)[-
Fe0.5(Nb1ꢀxTa 0.5]O [9] and some instructive conclusions have
t
f
3
x
)
3
f
Fig. 6. Dependence of the t value on the relative difference between A-site and B-
Fig. 5. Dependence of the Q ꢁ f value on the A-site bond valence of (1 ꢀ x)CaTiO
3
–
site bond valences of (1 ꢀ x)CaTiO –x(Li0.5La0.5)TiO3 ceramics sintered at 1300 8C
3
x(Li0.5La0.5)TiO ceramics sintered at 1300 8C for 3 h.
3
for 3 h.

J. Li et al. / Materials Research Bulletin 47 (2012) 2375–2379
2379
been drawn. However, these conclusions cannot be applied in some
Acknowledgments
solid solutions of the complex perovskite compounds because the
structural distortions are too complex. The effect of structural
distortion on te must be evaluated by all of cation bond valences,
This work was supported by National Science Foundation of
China (21071003) and Project Funded by the Priority Academic
Program Development of Jiangsu Higher Education Institutions.
including A-site and B-site bond valences. The dependence of the
value onthe relativedifference of A-siteandB-site bondvalencesare
shown in Fig. 6. It can be found that the value decreases with the
t
f
t
f
increaseof thedifferencebetweenA-siteandB-site bondvalencesas
LLT content increases. The increase of the difference between A-site
and B-site bond valences means that the degree of tilting on oxygen
octahedra and the restoring force for recovering the tilting
References
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correspondingly increase. Finally, the
can be effectively evaluated by the difference between A-site and
B-site bond valences for the complex perovskite structure. At x = 0.6,
t
f
value decreases. Therefore,
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[
[
[
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t
f
a
0
near-zero
t
f
(+0.75 ppm/8C) was obtained for 0.4CaTiO
3
–
[8] K.H. Yoon, W.S. Kim, E.S. Kim, Mater. Sci. Eng. B 99 (2003) 112–115.
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[
.6(Li0.5La0.5)TiO ceramics sintered at 1300 8C for 3 h.
3
[
[
4
. Conclusions
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2
84–286 (in Chinese).
Complete (1 ꢀ x)CaTiO
3 3
–x(Li0.5La0.5)TiO solid solutions with
[
13] M.U. Cohen, Rev. Sci. Instrum. 6 (1935) 68–74.
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orthorhombic perovskite structure were obtained by a conven-
tional solid-state reaction method through the entire composi-
[
[
[
tional range (0.2 ꢂ x ꢂ 0.8). With the increase of (Li0.5La0.5)TiO
content, the dielectric constant ( ) enhanced due to the increase in
ionic polarizability and the decrease in B-site bond valence of ABO
3
e
r
[19] T. Lowe, F. Azough, R. Freer, J. Eur. Ceram. Soc. 23 (2003) 2429–2433.
3
[
[
[
20] R.D. Shannon, Acta Crystallogr. A 32 (1976) 751–767.
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perovskite compounds, resulting from the increase of unit cell
volume. The quality factor (Q ꢁ f) was dependent not only on the
grain size but also on the A-site bond valence. The
t
f
value
[23] W.S. Kim, E.S. Kim, K.H. Yoon, J. Am. Ceram. Soc. 82 (1999) 2111–2115.
[
[
[
24] D.M. Iddles, A.J. Bell, A.J. Moulson, J. Mater. Sci. 27 (1992) 6303–6310.
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[27] M.T. Sebastian, Dielectric Materials for Wireless Communication, first ed.,
Elsevier, Amsterdam, 2008.
decreased with the increase of the difference between A-site and B-
site bond valences as (Li0.5La0.5)TiO content increases. Typically,
excellent microwave dielectric properties of = 245,
Q ꢁ f = 2750 GHz, and = +0.75 ppm/8C were obtained for
.4CaTiO –0.6(Li0.5La0.5)TiO ceramics sintered at 1300 8C for 3 h.
3
e
r
t
f
0
3
3