Microwave dielectric properties of Ba2Ca1-xSr xWO6double perovskites

Article abstract of DOI:10.1111/j.1551-2916.2011.04450.x

Ba₂Ca_1-xSr_xWO₆ (x=0-1) microwave dielectric ceramics have been prepared using the two-step solid-state reaction method. The substitution of Sr²⁺ for Sr²⁺ can effectively lower the densification temperature of the ceramics from 1500° to 1200°C. Single-phase ceramics with double perovskite structures were obtained, and structural transitions occurred in Ba₂Ca _1-xSr_xWO₆ via the phase sequence: cubic→rhombohedral→monoclinic with an increase of x. The microwave dielectric properties of the Ba₂Ca_1-xSr_xWO ₆ ceramics can be effectively tuned by tailoring x. The dielectric constant (E_r) remains almost unvaried, the quality factor (Q × f) decreases monotonically, and the temperature coefficient of resonant frequency (τ_f) changes in sign with the increase of x. A good combination of the microwave dielectric properties was obtained for Ba ₂Ca_0.975Sr_0.025WO₆ sintered at 1250°C: E_r=23.9, Q × f=80 200 GHz, and τ_f=+18 ppm/°C.

Full text of DOI:10.1111/j.1551-2916.2011.04450.x

J. Am. Ceram. Soc., 94 [9] 2933–2938 (2011)
DOI: 10.1111/j.1551-2916.2011.04450.x
r 2011 The American Ceramic Society
ournal
J
Microwave Dielectric Properties of Ba2Ca1ꢀxSrxWO6
Double Perovskites
Yuanyuan Zhou,z Siqin Meng,z Hongchao Wu,y and Zhenxing Yuew,z
zState Key Laboratory of New Ceramics and Fine Processing, Department of Materials Science and Engineering,
Tsinghua University, Beijing 100084, China
ySchool of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100084, China
Ba2Ca1ꢀxSrxWO6 (x 5 0–1) microwave dielectric ceramics
have been prepared using the two-step solid-state reaction
method. The substitution of Sr21 for Sr21 can effectively lower
the densification temperature of the ceramics from 15001 to
12001C. Single-phase ceramics with double perovskite struc-
tures were obtained, and structural transitions occurred in
Ba2Ca1ꢀxSrxWO6 via the phase sequence: cubic-rho-
mbohedral-monoclinic with an increase of x. The microwave
dielectric properties of the Ba2Ca1ꢀxSrxWO6 ceramics can be
effectively tuned by tailoring x. The dielectric constant (er)
remains almost unvaried, the quality factor (Q ꢁ f) decreases
monotonically, and the temperature coefficient of resonant
frequency (sf) changes in sign with the increase of x. A good
combination of the microwave dielectric properties was
obtained for Ba2Ca0.975Sr0.025WO6 sintered at 12501C:
er 5 23.9, Q ꢁ f 5 80 200 GHz, and sf 5 118 ppm/1C.
complete 1:1 ordering between the B-site ions. The B-site order-
ing is much easier to achieve for those double perovskites.
Considerable effort has been made toward understanding the
relationship between microwave dielectric properties and the
structure of the complex perovskite materials to gain better
insight into the basic factors that influence the dielectric
properties.19–23 In general, tolerance factor (t) is used as a mea-
sure of the stability of the perovskite phases, which influences
the structure and then the dielectric properties.
Double perovskite Ba2Ca1ꢀxSrxWO6 undergoes a phase tran-
sition with an increase of x.24 To the best of our knowledge, no
investigations on the microwave dielectric properties of
Ba2CaWO6 or Ba2SrWO6 have been carried out. This spurs
us to examine how the structure symmetry in the double perovs-
kites influences the microwave dielectric properties. Then, the
relationship between dielectric properties and t can be estab-
lished, which will be helpful for the development of structure–
property correlations. In addition, the systematic study of
Ba2Ca1ꢀxSrxWO6 may reveal potentially useful materials for
microwave applications. In the present work, the sintering
behavior, microstructure, and microwave dielectric properties
of the Ba2Ca1ꢀxSrxWO6 ceramics were investigated. The influ-
ence of crystal structure on the microwave dielectric properties
of Ba2Ca1ꢀxSrxWO6 was discussed.
I. Introduction
ANY works have been focusing on developing dielectric
M
materials with high dielectric constant (er), high quality
factor (Q ꢁ f), and near zero temperature coefficient of resonant
frequency (tf) to be used for dielectric resonators, oscillators,
and filters at microwave frequencies.1–2 A3B0B002O9 complex
perovskites (where A5 Ba, Sr; B0 5 Mg, Zn, Ni, Co; B00 5 Nb,
Ta) are one of the most investigated materials because of the
outstanding and tunable dielectric properties present in a num-
ber of compositions.3–14 The highest reported Q values have been
observed in these systems that exhibit the so-called 1:2 type of
cation order on the B-sites. It is revealed that the good dielectric
properties of these materials are related closely to the B-site
cation ordering. However, to obtain a high degree of ordering,
prolonging high-temperature sintering and soaking time or in-
troducing small amounts of dopants is often necessary, which is
not suitable for practical applications. Moreover, microwave
dielectric properties of some 1:1 ordered perovskites with a gen-
eral formula A2(B0B00)O6 (A5 Ba, Sr, Ca; B0 5 lanthanides and
Y, B00 5 Nb, Ta) were also investigated.15–17 It is concluded that
ionic ordering driving force is favored by larger differences in
charges and ionic radii between the two B-site ions. Recently,
the dielectric properties of tungstate-based double perovskites
with the general formula A2(B0W)O6 (A5 Ba, Sr, Ca; B0 5 Mg,
Co, Zn, Ni) have been reported.18–20 Most of the compounds are
characterized by a cubic perovskite structure, with an almost
II. Experimental Procedure
Samples of Ba2Ca1ꢀxSrxWO6 (x 5 0–1) were prepared using a
precursor route. High-purity BaCO3 (499%), CaCO3 (499%),
SrCO3 (499%), and WO3 (499.99%) chemicals were used as
raw materials. First, CaWO4 and SrWO4 were prepared as
precursors by calcining mixtures of CaCO3, SrCO3, and WO3
chemicals at 8001C for 4 h, respectively. Secondly, nominal
amounts of BaCO3, CaWO4, and SrWO4 were weighed, ground,
and calcined at 10001C for 4 h. The calcined powder was re-
milled and dried. The resultant powder was added with a poly-
vinyl alcohol (5 wt%) solution as a binder and palletized into
cylindrical pellets of 10 mm diameter and 6 mm thickness under
a uniaxial pressure of 200 MPa. These pellets were debindered at
6001C for 4 h, and then sintered in the temperature range of
11501–15001C in air for 4 h.
The bulk densities of the sintered ceramics were measured
using the Archimedes method. The crystal structures were
determined by X-ray diffraction (XRD), using CuKa radiation
(D/Max-2500, Rigaku, Tokyo, Japan). Selected area electron
diffraction (SAED) patterns were recorded in a transmission
electron microscope (Tecnai G2 20, FEI, Hillsboro, OR), oper-
ating at 200 kV. The microstructure was observed by scanning
electron microscopy (JSM-6301F, JEOL, Tokyo, Japan), and
the chemical component elements were characterized by an en-
ergy-dispersive spectrometer (EDS) attached to the SEM. Ra-
man spectra were excited with an argon laser and recorded using
a Raman spectrometer (HR800, Horiba Jobin Yvon, Villeneuve
D’ascq, France). Microwave dielectric properties of the polished
X. M. Chen—contributing editor
Manuscript No. 27967. Received May 4, 2010; approved January 20, 2011.
This work was financially supported by the Natural Science Foundation of China
(Grant Nos. 50972074, 50921061, and 50672043), the Ministry of Science and Technology of
China (through 973-Project under 2009CB623306), and China Postdoctoral Science Foun-
dation (Grant No. 20090450352).
wAuthor to whom correspondence should be addressed. e-mail:yuezhx@mail.tsinghua.
edu.cn
2933

2934
Journal of the American Ceramic Society—Zhou et al.
Vol. 94, No. 9
samples were determined using a network analyzer (HP8720ES,
Hewlett-Packard, Santa Rosa, CA). The dielectric constants
were measured using the Hakki–Coleman postresonator method
by exciting the TE011 resonant mode of the dielectric resonators
using the electric probe of an antenna as suggested by Court-
ney.25,26 The unloaded quality factors were measured using the
TE01d mode in the cavity method.27 The temperature coefficients
of tf were measured by noting the variation of resonant fre-
quency of the TE011 mode in the reflection configuration over a
temperature range of 251–801C.
ordered arrangement of (Sr, Ca)O6 and WO6 octahedra. More-
over, the diffraction peaks shift to lower angles with an increase
21
of x owing to the different ionic radii of Ca21 (1.00 A) and Sr
˚
28
(1.18 A). According to Fu et al.,24 the structural transition
˚
occurs in Ba2Ca1ꢀxSrxWO6 via a phase sequence: cubic–rho-
mbohedral–monoclinic with an increase of x, which was derived
from the splitting of the basic (222) and (400) reflections. It is
said that neither the (222) reflection nor the (400) reflection splits
for the cubic structure. The (222) reflection splits into a doublet
with an intensity ratio of about 3:1 and the (400) reflection
shows no splitting for the rhombohedral structure. The (222)
reflection splits into a triplet and the (400) reflection into a dou-
blet for the monoclinic structure. The enlarged region contain-
ing the basic (222) and (400) reflections shown in Fig. 1(b)
indicates the phase transition compositions at x 5 0.1 and 0.9,
respectively.
III. Results and Discussion
Ba2Ca1ꢀxSrxWO6 ceramics were well sintered at 15001C for
x 5 0, 12501C for x 5 0.025, 12251C for x 5 0.05, and 12001C
for x 5 0.1–1, respectively. Figure 1 shows the XRD patterns of
the well-sintered Ba2Ca1ꢀxSrxWO6 ceramics. It can be seen eas-
ily that every sample adopts a single perovskite structure, with-
out any second phase detected within the detectable level of
XRD. All superlattice lines indexed as (111), (311), (331), (511),
and (531), respectively, exist in a double cubic cell, indicating the
As the deviation of rhombohedral and monoclinic perovskite
structures from the cubic structure is very slight, an equivalent
cubic cell about the three perovskite structures can be used in the
research of some physical problems. The equivalent lattice
parameter (a) and unit cell volume (Vm) of well-sintered
Ba2Ca1ꢀxSrxWO6 were calculated, as shown in Fig. 2. It is
obvious that the lattice parameter increases with increasing x,
and the unit cell volume also increases accordingly because of
the larger ionic radius of Sr21 than Ca21
.
Figure 3 shows the SAED patterns of the well-sintered
Ba2Ca1ꢀxSrxWO6 ceramics, with x 5 0.025, 0.05, and 0.9,
respectively. All the maxima can be indexed on the basis of a
double pseudocubic perovskite, in accordance with the XRD
results.
Figure 4 shows the normalized Raman spectra of the well-
sintered Ba2Ca1ꢀxSrxWO6 ceramics. Narrow and intense bands
are usually observed for well-ordered structures. The 1:1 ordered
perovskites with the Fm-3m symmetry allow the appearance of
four Raman-active modes (G(Fm-3m) 5 A1g1Eg12F2g).29 As
can be seen in Fig. 4(a), three main modes were observed for
all samples. These results were observed previously in similar 1:1
ordered perovskites.30,31 The lowest band at B103 cmꢀ1 corre-
sponds to one of the F2g modes, the weaker band at B410 cmꢀ1
corresponds to the other F2g mode, and the highest band
at B830 cmꢀ1 can be ascribed to the A1g mode for cubic
Ba2CaWO6, respectively. The Eg mode is too weak to be de-
tected here. Raman spectra are suitable to study dynamic
changes in the structure.29 The F2g modes should split into a
doublet (F2g-A1g1Eg) if the cubic Fm-3m symmetry is re-
duced.29 Nine Raman-active modes were expected for the te-
tragonal I4/m symmetry and 24 for the monoclinic P21/n
structure, based on a new group-theory analysis.31 Thus, more
than four Raman-active modes are expected for the rho-
mbohedral and monoclinic structures with a lower symmetry
Fig. 1. XRD patterns (a) of well-sintered Ba2Ca1ꢀxSrxWO6 ceramics
( supper lattice reflections), and enlarged (222) and (400) reflection pat-
terns (b) of some representative samples.
Ã
Fig. 2. Lattice parameter (a) and unit cell volume (Vm) of well-sintered
Ba2Ca1ꢀxSrxWO6 ceramics vs. x.

September 2011
Microwave Dielectric Properties of Ba2Ca1ꢀxSrxWO6 Double Perovskites
2935
Fig. 3. SAED patterns of some well-sintered Ba2Ca1ꢀxSrxWO6 ceram-
ics: (a) x 5 0.025, (b) and (c) x 5 0.05, and (d) x 5 0.9. All maxima are
indexed in a pseudocubic structure.
than the cubic structure. In Fig. 4(b), an enlarged region con-
taining both of the F2g modes is shown. The splitting and broad-
ening behavior of the F2g modes further confirms the structure
transitions in the Ba2Ca1ꢀxSrxWO6 matrix. For x 5 0.025, no
splitting of the modes was detected. The lower F2g mode seems
to split into a doublet for x 5 0.05 and into a multiplet for
x 5 0.9. As the octahedral tilting is too small to be detected by
XRD and appears to be sufficient to be detected by Raman
spectroscopy,31 the structure transition compositions of Ba2-
Ca1ꢀxSrxWO6 can be fixed at x 5 0.05 and 0.9, respectively,
based on the Raman results.
Fig. 4. Raman spectra (a) of well-sintered Ba2Ca1ꢀxSrxWO6 ceramics
and enlarged F2g mode patterns (b) of some representative samples.
Figure 5 shows the SEM images and EDS spectra of some
well-sintered Ba2Ca1ꢀxSrxWO6 ceramics. Small grains and sev-
eral pores were observed for Ba2CaWO6 sintered at 15001C
(Fig. 5(a)). In contrast, pores are less for all the other samples,
even with a small substitution (x 5 0.025) of Sr21 for Ca21
(Fig. 5(b)). The grain size of the Ba2Ca1ꢀxSrxWO6 (x40) ce-
ramics was influenced by both the sintering temperature and the
Sr content. High sintering temperatures accelerate the grain
growth (see Figs. 5(b)–(d)), while at the same sintering temper-
ature, the grain size increases more markedly with the increase
of x. Moreover, degradation in grain uniformity becomes more
significant with a high Sr content (see Figs. 5(d)–(f)), which
would damage its dielectric properties. The EDS spectrum for
x 5 0.05 shows Ba, Ca, Sr, and W signals, and that for x 5 1
shows Ba, Sr, and W signals. This is consistent with the
compositions.
Figure 6 and Table 1 show the relative density and microwave
dielectric properties of the Ba2Ca1ꢀxSrxWO6 ceramics. It was
confirmed that it was really hard to sinter Ba2CaWO6 into dense
bodies. However, the substitution of Sr21 for Ca21 can effi-
ciently reduce the sintering temperature of Ba2CaWO6, and all
the Ba2Ca1ꢀxSrxWO6 ceramics with x40 were well sintered in
the temperature range of 12001–12501C. As shown in Fig. 6, the
relative densities of most Ba2Ca1ꢀxSrxWO6 ceramics are 497%.
As Sr21 is larger in size than Ca21, the instability of the crystal
structure is induced by the Sr21 substitution for Ca21, and
lattice activation increases, which promotes the sintering of
Ba2Ca1ꢀxSrxWO6. This may be the reason for the lower sinte-
ring temperature of Ba2Ca1ꢀxSrxWO6 (x40) ceramics. The
dielectric properties of Ba2CaWO6 sintered at 15001C were mea-
sured as er 5 22.8, Q ꢁ f 5 22 800 GHz, and tf 5 146 ppm/1C,
and those of Ba2SrWO6 sintered at 12001C were measured as
er 5 23.5, Q ꢁ f 5 39 700 GHz, and tf 5 ꢀ34 ppm/1C. By tailor-
ing x, the dielectric properties of Ba2Ca1ꢀxSrxWO6 can be effec-
tively tuned. The best combination of the microwave dielectric
properties was obtained for x 5 0.025: er 5 23.9, Q ꢁ f 5 80 200
GHz, and tf 5 118 ppm/1C.
The dielectric constants of the Ba2Ca1ꢀxSrxWO6 ceramics
with x40 are between 23 and 24. In general, the dielectric con-
stant is highly dependent on the relative density and ionic
polarizability at microwave frequencies, and increases with an
increase of B-site ionic polarizability.13,20 It can be seen that the
relative density of well-sintered Ba2Ca1ꢀxSrxWO6 (x40) is
497%; hence, its influence on the dielectric constant can be ig-
nored. The relationship between dielectric constant and micro-
scopic polarizability for cubic perovskites can be expressed
through the Clausius–Mossotti formula,32
er ꢀ 1 4p am
¼
(1)
er þ 2
3 Vm
where er is the relative dielectric constant, am is the macroscopic
polarizability, and Vm is the molar volume. The theoretical di-
electric constant etheo calculated from Eq. (1) is also shown in
Table 1. The deviation between e and etheo is slight with a small
value of x, and seems to increase with a large value of x due to a
greater distortion from the cubic structure. Any deviation from
cubic symmetry results in extra polarization; the larger the de-
viation from cubic symmetry, the larger the dielectric constant.16
Thus, compared with the calculated dielectric constant etheo, the

2936
Journal of the American Ceramic Society—Zhou et al.
Vol. 94, No. 9
Fig. 5. SEM images of well-sintered Ba2Ca1ꢀxSrxWO6 ceramics: (a) x 5 0, (b) x 5 0.025, (c) x 5 0.05, (d) x 5 0.1, (e) x 5 0.5, and (f) x 5 1. EDS spectra
where crosses mark are also shown.
real dielectric constant should be less changed with x. This is
why the measured er is almost unvaried.
related to microstructure, second phase, porosity, etc.33,34 Be-
cause the relative density is 497%, and no second phase was
detected, the effects of the density and second phase on Q ꢁ f for
Ba2Ca1ꢀxSrxWO6 may be neglected. The decreased Q ꢁ f value
may be related to the increase of lattice anharmonicity caused
dielectric loss.9,34,35 Moreover, the degradation in grain unifor-
mity could result in dielectric loss, which also causes the Q ꢁ f
value to decrease.
However, the dielectric loss of Ba2Ca1ꢀxSrxWO6 is much
more sensitive to x than the dielectric constant. Basically, the
Q ꢁ f value of the well-sintered Ba2Ca1ꢀxSrxWO6 ceramics de-
creases monotonically with the increase of x. The dielectric loss
measured represents the overall loss, including intrinsic loss re-
lated to the lattice anharmonicity and extrinsic contributions

September 2011
Microwave Dielectric Properties of Ba2Ca1ꢀxSrxWO6 Double Perovskites
2937
Fig. 7. Relationship of the te value vs. t for Ba2Ca1ꢀxSrxWO6 ceramics.
where aL is the coefficient of linear thermal expansion. The aL
values are usually almost independent of composition for most
ceramics; hence, a common value of 8 ppm/1C was used here. t
was calculated using the Shannon ionic radii.28 As a function of
decreasing t, the phase transition sequence is considered to be
cubic-rhombohedral-monoclinic. In the cubic phase region,
te increases steeply as t decreases and changes in sign near the
edge of the cubic stability range. After the onset of the cubic-
rhombohedral phase transition, te varies slightly and is once
again slightly close to zero. That is to say, the decrease of t does
not result in a huge change in the value of te in the rho-
mbohedral region. te increases abruptly again as t decreases
with the onset of the rhombohedral–monoclinic phase transi-
tion, and then increases slightly in the monoclinic region. The
trend of te variation vs. t is similar in nature to that observed in
Ba- and Sr-based complex perovskites.22 Therefore, it can
be concluded that the onset of phase transitions is the major
factor that influences the behavior of te as well as tf for
Ba2Ca1ꢀxSrxWO6.
Fig. 6. Variations of relative density, dielectric constant, and Q ꢁ f
value vs. x for Ba2Ca1ꢀxSrxWO6 ceramics.
The tf value of Ba2Ca1ꢀxSrxWO6 was not affected by the
sintering temperature, but actually the composition. The com-
position induces a change in structure and then a change in the
sign of tf, as shown in Table 1. In a perovskite structure, tf is
closely related to oxygen octahedra tilting, which could be eval-
uated by the tolerance factor (t). For the Ba2Ca1ꢀxSrxWO6 sys-
tem, t is defined as
RðBaÞ þ RðOÞ
h
i
t ¼
(2)
pffiffiffi
IV. Conclusions
2
ð1ꢀxÞRðCaÞþxRðSrÞþRðWÞ þ RðOÞ
2
Ba2Ca1ꢀxSrxWO6 (x 5 0–1) double perovskites were prepared
using a precursor route and their dielectric properties were stud-
ied in the microwave frequency range. Ba2CaWO6 has poor sin-
terability, and its sintering temperature is 415001C, which leads
to a low dielectric constant and Q ꢁ f value. The substitution of
Sr21 for Ca21 can lower the sintering temperature and improve
the sinterability; therefore, all the Ba2Ca1ꢀxSrxWO6 (x40) ce-
ramics can be sintered into dense bodies in the temperature
range of 12001–12501C. Furthermore, a structural transition in
the Ba2Ca1ꢀxSrxWO6 system via the phase sequence: cubic-
rhombohedral-monoclinic with an increase of x was confirmed
by the XRD and Raman results.
where R(Ba), R(Ca), R(Sr), R(W), and R(O) correspond to the
ionic radii of Ba21, Ca21, Sr21, W61, and O2ꢀ, respectively. The
relationship between the temperature coefficient of dielectric
constant (te) and the tolerance factor in Ba- and Sr-based com-
plex perovskites was found by Reaney et al.,22 whereas the data
of Ba2Ca1ꢀxSrxWO6 were not included. To make a comparison,
a graph of te vs. t for Ba2Ca1ꢀxSrxWO6 is shown in Fig. 7. Note
that te was calculated by the equation
te ¼ ꢀ2ðtf þ aLÞ
(3)
Table I. Sintering Temperature, Relative Density, and Microwave Dielectric Properties of Ba2Ca1ꢀxSrxWO6 Ceramics
Composition x
Sintering temperature (1C)
Relative density (%)
f0 (GHz)
er
etheo
Q ꢁ f (GHz)
tf (ppm/1C)
0
1500
1250
1225
1200
1200
1200
1200
1200
1200
95.1
98.9
99.1
98.7
98.5
98.3
98.6
97.6
97.9
9.773
9.669
9.536
9.751
9.851
10.060
10.302
10.143
10.218
22.8
23.9
24.0
23.5
23.4
23.3
23.7
23.3
23.5
24.01
24.05
23.95
23.89
22.60
22.55
21.66
20.1
22800
80200
77800
60100
54100
45 200
40600
36 100
39 700
146
118
ꢀ20
ꢀ16
ꢀ15
ꢀ14
ꢀ14
ꢀ31
ꢀ34
0.025
0.05
0.1
0.25
0.5
0.75
0.9
1
19.36

2938
Journal of the American Ceramic Society—Zhou et al.
Vol. 94, No. 9
16L. Abdul Khalam, H. Sreemoolanathan, R. Ratheesh, P. Mohanan, and M. T.
Sebastian, ‘‘Preparation, Characterization and Microwave Dielectric Properties of
Ba(B01/2Nb1/2)O3 [B0 5 La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Yb and In] Ce-
ramics,’’ Mater. Sci. Eng. B, 107, 264–70 (2004).
The change in structure does not produce significant altera-
tions in the dielectric constant, but does have a significance effect
on Q ꢁ f and tf values. The Q ꢁ f value of the well-sintered
Ba2Ca1ꢀxSrxWO6 ceramics decreases monotonically with the
increase of x, which may be related to the increase of lattice-
anharmonicity-caused dielectric loss. The tf value changes in sign
with the increase of x. The onset of phase transitions is the major
factor that influences the behavior of tf for Ba2Ca1ꢀxSrxWO6.
Ba2Ca0.975Sr0.025WO6 ceramics sintered at 12501C for 4 h
show excellent microwave dielectric properties: er 5 23.9,
Q ꢁ f 5 80 200 GHz, and tf 5 118 ppm/1C. The low dielectric
loss and the small tf value make the ceramics very promising in
practical microwave applications.
17L. Abdul Khalam and M. T. Sebastian, ‘‘Low Loss Dielectrics in the Ca(B01/2
Nb1/2)O3 [B0 5 Lanthanides, Y] System,’’ J. Am. Ceram. Soc., 90, 1467–74 (2007).
18J. J. Bian, K. Yan, and Y. F. Dong, ‘‘Microwave Dielectric Properties of
A1ꢀ3x/2Lax(Mg1/2W1/2)O3 (A5 Ba, Sr, Ca; 0.0rxr0.05) Double Perovskites,’’
Mater. Sci. Eng. B, 147, 27–34 (2008).
19D. D. Khalyavin, J. Han, A. M. R. Senos, and P. Q. Mantas, ‘‘Synthesis and
Dielectric Properties of Tungsten-Based Complex Perovskites,’’ J. Mater. Res., 18,
2600–7 (2003).
20F. Zhao, Z. X. Yue, Z. L. Gui, and L. T. Li, ‘‘Preparation, Characterization
and Microwave Dielectric Properties of A2BWO6 (A5 Sr, Ba; B 5 Co, Ni, Zn)
Double Perovskite Ceramics,’’ Jpn. J. Appl. Phys., 44, 8066–71 (2005).
21E. L. Colla, I. M. Reaney, and N. Setter, ‘‘Effect of Structural Changes in
Complex Perovskites on the Temperature Coefficient of the Relative Permittivity,’’
J. Appl. Phys., 74, 3414–25 (1993).
22I. M. Reaney, E. L. Colla, and N. Setter, ‘‘Dielectric and Structural Charac-
teristics of Ba- and Sr-Based Complex Perovskites as a Function of Tolerance
Factor,’’ Jpn. J. Appl. Phys., 33, 3984–90 (1994).
References
1W. Wersing, ‘‘Microwave Ceramics for Resonators and Filters,’’ Curr. Opin.
Solid State Mater. Sci., 1, 715–31 (1996).
23I. M. Reaney and R. Ubic, ‘‘Dielectric and Structural Characteristics of Per-
ovskites and Related Materials as a Function of Tolerance Factor,’’ Ferroelectrics,
228, 23–38 (1999).
2R. J. Cava, ‘‘Dielectric Materials for Applications in Microwave Communica-
tions,’’ J. Mater. Chem., 11, 54–65 (2001).
3S. Kawashima, M. Nishida, I. Ueda, and H. Ouchi, ‘‘Ba(Zn1/3Ta2/3)O3 Ce-
ramics with Low Dielectric Loss at Microwave Frequencies,’’ J. Am. Ceram. Soc.,
66, 421–3 (1983).
24W. T. Fu, S. Akerboom, and D. J. W. IJdo, ‘‘Crystal Structures of the Double
Perovskites Ba2Sr1ꢀxCaxWO6,’’ J. Solid State Chem., 180, 1547–52 (2007).
25B. W. Hakki and P. D. Coleman, ‘‘A Dielectric Resonator Method of Mea-
suring Inductive Capacitance in the Millimeter Range,’’ IEEE Trans. Microwave
Theory Technol., 8, 402–10 (1960).
4S. B. Desu and H. M. Obryan, ‘‘Microwave Loss Quality of BaZn1/3Ta2/3O3
Ceramics,’’ J. Am. Ceram. Soc., 68, 546–51 (1985).
5K. Endo, K. Fujimoto, and K. Murakawa, ‘‘Dielectric Properties of Ceramics
in Ba(Co1/3 Nb2/3)O3–Ba(Zn1/3Nb2/3)O3 Solid Solution,’’ J. Am. Ceram. Soc., 70,
C215–8 (1987).
26W. E. Courtney, ‘‘Analysis and Evaluation of a Method of Measuring the
Complex Permittivity and Permeability of Microwave Insulators,’’ IEEE Trans.
Microwave Theory Technol., 18, 476–85 (1970).
6K. H. Yoon, D. P. Kim, and E. S. Kim, ‘‘Effect of BaWO4 on the Microwave
Dielectric Properties of Ba(Mg1/3Ta2/3)O3 Ceramics,’’ J. Am. Ceram. Soc., 77,
1062–6 (1994).
27J. Krupka, K. Derzakowski, B. Riddle, and J. B. Jarvis, ‘‘A Dielectric Res-
onator for Measurements of Complex Permittivity of Low Loss Dielectric Mate-
rials as Function of Temperature,’’ Meas. Sci. Technol., 9, 1751–6 (1998).
28R. D. Shannon, ‘‘Revised Effective Ionic Radii and Systematic Study of Inter
Atomic Distances in Halides and Chalcogenides,’’ Acta Crystallogr., A32, 751–7
(1976).
7I. T. Kim, Y. H. Kim, and S. J. Chung, ‘‘Ordering and Microwave Dielectric
Properties of Ba(Ni1/3Nb2/3)O3 Ceramics,’’ J. Mater. Res., 12, 518–25 (1997).
8M. A. Akbas and P. K. Davies, ‘‘Ordering-Induced Microstructures and Mi-
crowave Dielectric Properties of the Ba(Mg1/3Nb2/3)O3–BaZrO3 System,’’ J. Am.
Ceram. Soc., 81, 670–6 (1998).
29I. G. Siny, R. Tao, R. S. Katiyar, R. Y. Guo, and A. S. Bhalla, ‘‘Raman
Spectroscopy of Mg–Ta Order–Disorder in BaMg1/3Ta2/3O3,’’ J. Phys. Chem.
Solid, 59, 181–95 (1998).
9J. Venkatesh and V. R. K. Murthy, ‘‘Microwave Dielectric Properties of (Ba,
Sr)(Zn1/3Ta2/3)O3 Dielectric Resonators,’’ Mater. Chem. Phys., 58, 276–9 (1999).
10R. I. Scott, M. Thomas, and C. Hampson, ‘‘Development of Low Cost, High
Performance Ba(Zn1/3Nb2/3)O3 Based Materials for Microwave Resonator Appli-
cations,’’ J. Eur. Ceram. Soc., 23, 2467–71 (2003).
30I. Gregora, J. Petzelt, J. Pokorny, V. Vorlı
´
cek, Z. Zikmund, R. Zurmuhlen,
¨
and N. Setter, ‘‘Raman Spectroscopy of the Zone Center Improper Ferroelastic
Transition in Ordered Ba(Y1/2Ta1/2)O3 Complex Perovskite Ceramic,’’ Solid State
Commun., 94, 899–903 (1995).
11M. Bieringer, S. M. Moussa, L. D. Noailles, A. Burrows, C. J. Kiely, M. J.
Rosseinsky, and R. M. Ibberson, ‘‘Cation Ordering, Domain Growth, and Zinc
Loss in the Microwave Dielectric Oxide Ba3ZnTa2O9,’’ Chem. Mater., 15, 586–97
(2003).
31A. Dias, G. Subodh, M. T. Sebastian, M. M. Lage, and R. L. Moreira, ‘‘Vib-
rational Studies and Microwave Dielectric Properties of A-Site-Substituted Tellu-
rium-Based Double Perovskites,’’ Chem. Mater., 20, 4347–55 (2008).
32A. J. Bosman and E. E. Havinga, ‘‘Temperature Dependence of Dielectric
Constants of Cubic Ionic Compounds,’’ Phys. Rev., 129, 1593–60 (1963).
12C.-W. Ahn, H.-J. Jang, S. Nahm, H.-M. Park, and H.-J. Lee, ‘‘Effects of Mi-
crostructure on the Microwave Dielectric Properties of Ba(Co1/3Nb2/3)O3 and
(1ꢀx)Ba(Co1/3Nb2/3)O3–x Ba(Zn1/3Nb2/3)O3 Ceramics,’’ J. Eur. Ceram. Soc., 23,
2473–8 (2003).
33R. Zurmuhlen, J. Petzelt, S. Kamba, V. alentin, V. Voitsekhovskii, E. Colla,
¨
and N. Setter, ‘‘Dielectric Spectroscopy of Ba(B01/2B1/2)O3 Complex Perovskite
Ceramics: Correlations Between Ionic Parameters and Microwave Dielectric Prop-
erties. I. Infrared Reflectivity Study (1010–1014 Hz),’’ J. Appl. Phys., 77, 5341–50
(1995).
13M. W. Lufaso, ‘‘Crystal Structures, Modeling, and Dielectric Property Rela-
tionships of 2:1 Ordered Ba3M0M2O9 (M0 5 Mg, Ni, Zn; M00 5 Nb, Ta) Perovs-
kites,’’ Chem. Mater., 16, 2148–56 (2004).
34W. S. Kim, E. S. Kim, and K. H. Yoon, ‘‘Effects of Sm31 Substitution on
Dielectric Properties of Ca1ꢀxSm2x/3TiO3 Ceramics at Microwave Frequencies,’’
J. Am. Ceram. Soc., 82, 2111–5 (1999).
14M. S. Fu, X. Q. Liu, and X. M. Chen, ‘‘Effects of Mg Substitution on Mi-
crostructures and Microwave Dielectric Properties of Ba(Zn1/3Nb2/3)O3 Perovskite
Ceramics,’’ J. Am. Ceram. Soc., 93, 787–95 (2010).
35J. Petzelt, S. Pacesova, J. Fousek, S. Kamba, V. Zelezny, V. Koukal, J. Sch-
warzbach, B. P. Gorshunov, G. V. Kozolov, and A. A. Volkov, ‘‘Dielectric Spec-
tra of Some Ceramics for Microwave Applications in the Range of 1010–1014 Hz,’’
31 51
15M. Takata and K. Kageyama, ‘‘Microwave Characteristics of A(B
B )O3
1/2 1/2
Ceramics (A 5 Ba, Ca, Sr; B31 5 La, Nd, Sm, Yb; B51 5 Nb, Ta),’’ J. Am. Ceram.
Soc., 72, 1955–9 (1989).
Ferroelectrics, 93, 77–85 (1989).
&