Low-temperature sintering and microwave dielectric properties of Ba 5Nb4O15-BaWO4 composite ceramics for LTCC applications

Article abstract of DOI:10.1111/j.1551-2916.2008.02670.x

Low-temperature-sintered composite ceramics in Ba₅Nb ₄O₁₅-BaWO₄ system were prepared by cofiring mixtures of Ba₅Nb₄O₁₅ and BaWO₄ powders. Thermo-mechanical analysis indicated that a small amount of B ₂O₃ addition significantly promoted the densification process and lowered the sintering temperature to ～900°C. X-ray diffraction analysis revealed that Ba₅Nb₄O₁₅ and BaWO₄ coexisted in the sintered ceramics. With increasing B ₂O₃ content, a secondary phase, BaNb₂O ₆, appeared which affects the microwave dielectric properties. Microwave dielectric properties of the aforementioned compositions were as follows: dielectric constant of 16.8-19.2, Q × f values of 33 900-50 300 GHz, and a temperature coefficient of the resonant frequency of -3.4 to -8.6 ppm/°C. The chemical compatibility of BNW6502 ceramics with silver during the cofiring process has also been investigated, and no evidence of chemical reaction between Ag and ceramics was observed, indicating that the as-prepared composite ceramics are suitable for low-temperature cofired ceramics applications.

Full text of DOI:10.1111/j.1551-2916.2008.02670.x

J. Am. Ceram. Soc., 91 [10] 3275–3279 (2008)
DOI: 10.1111/j.1551-2916.2008.02670.x
r 2008 The American Ceramic Society
ournal
J
Low-Temperature Sintering and Microwave Dielectric Properties of
Ba Nb O –BaWO Composite Ceramics for LTCC Applications
5
4
15
4
w
Hao Zhuang, Zhenxing Yue, Fei Zhao, and Longtu Li
State Key Laboratory of New Ceramics and Fine Processing, Department of Materials Science and Engineering,
Tsinghua University, Beijing 100084, China
Low-temperature-sintered composite ceramics in Ba Nb O –
5
on the microwave dielectric properties due to introducing glassy
phase or the formation of secondary phase.
4
15
BaWO4 system were prepared by cofiring mixtures of
Ba Nb O and BaWO powders. Thermo-mechanical analysis
indicated that a small amount of B O addition significantly
5
4
15
4
5 4
Ba Nb O15, a hexagonal perovskite compound, is one of the
most promising materials due to its good dielectric properties of
2
3
1
0,11
promoted the densification process and lowered the sintering
temperature to B9001C. X-ray diffraction analysis revealed
that Ba Nb O and BaWO coexisted in the sintered ceramics.
e 5 39–40, Q ꢀ f 5 26000 GHz, and t 5 78 ppm/1C.
How-
ever, the high sintering temperature (14001–14501C) and the
large t value limit its application for LTCC microwave devices.
Therefore, the further improvement on dielectric properties and
r
f
5
4
15
4
f
With increasing B O content, a secondary phase, BaNb O ,
2
3
2
6
1
2,13
appeared which affects the microwave dielectric properties. Mi-
crowave dielectric properties of the aforementioned composi-
tions were as follows: dielectric constant of 16.8–19.2, Q ꢀ f
values of 33900–50300 GHz, and a temperature coefficient of
the resonant frequency of ꢁ3.4 to ꢁ8.6 ppm/1C. The chemical
compatibility of BNW6502 ceramics with silver during the co-
firing process has also been investigated, and no evidence of
chemical reaction between Ag and ceramics was observed, indi-
cating that the as-prepared composite ceramics are suitable for
low-temperature cofired ceramics applications.
sintering behavior is required. Kim et al.
2 3
used B O to lower
the sintering temperature of Ba Nb 15, and decreased the t
5
4
O
f
value through the formation of composite ceramics from
Ba Nb O and BaNb O .
5
4
15
4
2
6
BaWO
was reported to have low sintering temperature
(B11001C) and excellent microwave dielectric properties of
1
4
e 5 8, Q ꢀ f 5 57 500 GHz, and t 5 ꢁ78 ppm/1C. Because
r
f
of its large negative t ( 5 ꢁ78 ppm/1C), we could expect that a
f
dielectric material with near-zero t
might be obtained by combining Ba
our previous studies, the Ba Nb O –BaWO composite ceram-
f
value and high Q ꢀ f value
5
Nb 15 with BaWO . In
4
O
4
5
4
15
4
ics with excellent microwave dielectric properties of
5 21.0B16.9, Q ꢀ f 5 49 500B56 700 GHz, and t 5 8.9B
ꢁ4.3 ppm/1C were prepared at low sintering temperature of
e
r
f
I. Introduction
15
1
1001C. In order to further reduce the sintering temperature of
the composite ceramics, a small of amount of B was added in
the present work. In this paper, we investigated the low-
temperature sintering behaviors of Ba Nb 15–BaWO with
B O addition and discussed the relationship between the
N the past decades, microwave dielectric ceramics have re-
2 3
O
I
ceived much attention because of the rapid growth of wireless
communication industry. A large number of ceramic dielectric
materials have been developed. A high dielectric constant (e ), a
high quality factor (Q value), and a low-temperature coefficient
of resonant frequency (t ) are three key properties required for
5
4
O
4
r
2
3
amount of B O
2 3
addition and microwave dielectric properties.
f
1
microwave resonator materials.
Recently, the development of low-temperature cofired ceram-
ics (LTCC) have been stimulated by the benefits offered for the
fabrication of miniature multilayer devices involving the cofiring
of dielectric and highly conductive metal, such as silver and
II. Experimental Procedure
The low-temperature-sintered composite ceramics in
Ba
Ba
5
ders of BaCO
5
Nb
Nb
4
4
O
O
15–BaWO
15 and BaWO
, Nb , WO
materials. The stoichiometric Ba
4
system were prepared by cofiring mixtures
powders. High-purity (499.9%) pow-
, and B were used as starting
Nb 15 and BaWO powders
2
,3
4
copper and various LTCC materials have been explored.
4
However, most of commercial microwave dielectric materials
available exhibiting high quality factor, high dielectric constant,
and near-zero temperature coefficient of resonant frequency re-
quire high sintering temperature. In order to reduce the sintering
temperature of dielectric ceramics, there are several methods
3
2
O
5
3
O
2 3
5
4
O
4
were synthesized firstly by calcining the oxides mixtures at
10001C for 4 h and 7501C for 5 h, respectively. Then the com-
posite powders were prepared by mixing the pure Ba Nb O ,
5
4 15
4
,5
commonly explored : (1) adding the low melting point com-
pounds such as B , V ; (2) decreasing the particle size of
4
2 3
BaWO , and B O with weight ratios as listed in Table I. The
O
2 3
O
2 5
mixtures were ball milled for 5 h using zirconia balls in an al-
cohol medium. The slurries were dried, mixed with an appro-
priate amount of PVA (5 wt%) as a binder, and then screened
with a 60 mesh. The screened powders were pressed into cylin-
drical disks with a diameter of 10 mm and a height of about
6
–8
starting materials by chemical methods. The first method is
widely used to reduce the sintering temperature of commercially
developed dielectric ceramics. The low melting point compounds
may improve the densification process of ceramics, and then
9
2
improve the microwave dielectric properties. However, these
low melting point compounds may also have a detrimental effect
5 mm at a pressure of about 2000 kg/cm . These pellets were
preheated at 6001C for 4 h to expel the binder and then sintered
at temperatures from 8501 to 10001C for 4 h in air.
The bulk densities of the samples were measured by the
Archimedes method. The relative densities were obtained from
the bulk densities and the theoretical densities. The theoretical
densities were calculated from the following equation:
P. K. Davies—contributing editor
Manuscript No. 24659. Received May 12, 2008; approved July 23, 2008.
This work was supported by the Natural Science Foundation of China (Grant Nos.
50672043, 50621201, and 50632030), and the Ministry of Science and Technology of China
through 973-Project under 2002CB613307.
W1 þ W2
wAuthor to whom correspondence should be addressed. e-mail: yuezhx@tsinghua.
r ¼
(1)
W1=r þ W2=r
edu.cn
1
2
3
275

3
276
Journal of the American Ceramic Society—Zhuang et al.
Vol. 91, No. 10
Table I. The Ba Nb O , BaWO , and B O Content of all
5
4
15
4
2
3
Samples
Sample
5 4
Ba Nb O15 (wt%)
BaWO
4
(wt%)
2 3
B O (wt%)
BNW6502
BNW6002
BNW6004
BNW6006
35
40
40
40
65
60
60
60
0.2
0.2
0.4
0.6
Where r
1
and r
2
are the theoretical density of Ba
5
Nb
15 phase and 6.38 g/cm for
BaWO4 phase. W1 and W2 are the weight fraction of
Ba Nb 15 and BaWO
The crystalline phases of the sintered samples were deter-
4
O15 and
3
3
4 5 4
BaWO , 6.32 g/cm for Ba Nb O
1
6
5
4
O
4
.
mined by X-ray diffraction (XRD), using CuKa radiation (Rig-
aku D/Max-2500, Tokyo, Japan). Shrinkage curve was
determined using thermo-mechanical analysis (TMA) (SETAR-
AM TGA TMA DSC) technique. The microstructures of sin-
tered ceramics were observed by scanning electron microscopy
Fig. 1. X-ray diffraction patterns of Ba
tered at 9001C for 4 h. Inset shows secondary phase reflections at around
yB291 and 301.
5 4 4
Nb O15–BaWO ceramics sin-
2
(
SEM). The composition analysis was performed using energy-
dispersive spectroscopy (EDS: model INCA, Oxford Instru-
ments, Oxford, U.K.). A network analyzer (HP8720ES, Hew-
lett-Packard, Santa Rosa, CA) was used to measure the
microwave dielectric properties. The dielectric constants were
account the main difference between the above samples was the
content, the formation of the Nb-rich barium metanio-
2 3
B O
1
7
measured using the Hakki and Coleman postresonator
method by exciting the TE011 resonant mode of the dielectric
resonators using the electric probe of an antenna as suggested by
bate, BaNb
2
O
6, may be attributed to the reaction of Ba Nb
5
4
O
15
1
2,13
and B . Kim et al.
O
2 3
also found that the addition of B
2
O
3
in
Ba Nb O could result in the formation of BaNb O . More-
5
4
15
2
6
1
8
Courtney. The measuring error is about 1%. The unloaded
quality factors were measured using the TE01d mode in the
2 6
over, the BaNb O has two polymorphic phases: hexagonal and
2
0
20
orthorhombic. Recent literature revealed that the hexagonal
BaNb O was a low-temperature phase, and could be trans-
1
9
cavity method. All measurements were made in the frequency
range of 8–11 GHz at room temperature. The temperature co-
2
6
formed to the orthorhombic phase over a broad temperature
range 411501C. So in the present system, when the B
amount is over 0.4 wt%, a very small amount of BaNb
isted as the hexagonal phase, as shown in Fig. 1 (inset).
efficients of the resonant frequencies (t
temperature range from 201 to 801C. The t
f
) were obtained in the
values were calcu-
2 3
O
f
2 6
O ex-
lated by the following relationship:
In order to evaluate the sintering behavior of the composite
ceramics, the TMA technique was used to characterize the sinte-
ring shrinkage. Figure 2 shows the shrinkage and shrinking rate
as a function of temperature for the pressed samples. It
f2 ꢁ f1
tf ¼
(2)
f1ðT2 ꢁ T1Þ
1 2 1 2
where f and f are the resonant frequencies at T and T , re-
spectively.
For cofiring experiments, the ceramic slurries combined ceramic
powders with organic additions were tape-casted to form a green
film. Silver electrode was screen-printed onto the green film using a
screen printer. The samples were cofired at 9001C for 4 h in the air.
SEM and EDS were used to characterize the diffusion of silver.
III. Results and Discussion
Figure 1 shows the XRD patterns of the B
Ba Nb 15–BaWO ceramics sintered at 9001C for 4 h. It is
clearly seen that all of the peaks could be indexed in terms of the
Ba Nb 15 (J) and BaWO (.). For the samples BNW6002
and BNW6502 with 0.2 wt% B , the crystalline phases were
Ba Nb O and BaWO , and there was no evidence of any sec-
2 3
O -doped
5
4
O
4
5
4
O
4
2 3
O
5
4
15
4
ondary phase present, which is also observed in the undoped
1
5
samples in our previous work. This suggests that two phases,
Ba Nb 15 and BaWO , coexisted in the present LTCC mate-
rials. The coexistence of Ba Nb O and BaWO in the sintered
5
4
O
4
5
4
15
4
bodies might be attributed to the different crystallized structures
of two phases and the different coordination numbers (CN) of
Nb and W in their crystal structures. Ba
onal perovskite structure in which the CN of Nb is 6, while
BaWO has a scheelite structure with four coordination of W .
4
5 4
Nb O15 has a hexag-
51
61
The differences in the crystal structure and the CN of Nb and W
limit the formation of solid solution between Ba Nb O and
BaWO , thus Ba Nb O and BaWO can coexist in the as-sin-
5
4
15
4
5
4
15
4
Fig. 2. Dilatometric curves (solid line, dL/l
0
) and their derivatives (dot-
Nb
tered ceramics. With increasing B
BNW6004 with 0.4 wt% B and BNW6006 with 0.6 wt%
B O , peaks for BaNb O indicated by appeared. Taking into
2 3
O content, for samples
ted line, dL/dT) of Ba Nb 15–BaWO ceramics (a) 35%Ba
4
5
4
O
5
4 15
O –
O
2 3
65%BaWO without B O addition, (b) BNW6502, (c) BNW6002, and
2 3
4
Ã
2
3
2
6
(d) BNW6006.

October 2008
Sintering and Dielectric Properties of Ba Nb O –BaWO for LTCC Applications
5
3277
4
15
4
demonstrates that the onset of shrinkage takes place at B9201C
and a maximum densification rate occurs at B11301C for sam-
ple without B O (as shown in Fig. 2(a)). With the addition of
grain growth of the Ba
Fig. 3(a), small pores are observed in the sample BNW6002;
these pores may be attributed to the poor sinterability with low
5
Nb
4
O
15–BaWO
4
mixture. From
2
3
2 3
small amount of B O , as shown in Figs. 2(b) and (c), the dens-
2 3 2 3
B O content (0.2 wt%). With increasing B O content, dense
ification rate is a little faster than that of the undoped sample.
The highest densification rate occurs at B9251C, which is much
lower than that of the undoped sample. These experiments sug-
ceramics can be observed. Furthermore, the grain size increases
with increasing B O content. This suggests that the sinterability
2
3
of the Ba Nb O –BaWO ceramics can be improved by B O
3
5
4
15
4
2
gest that a small amount of B
2
O
3
addition is effective to lower
addition. It is noted from Fig. 3(d) that the grain size of
BNW6502 is much larger than that of BNW6002 (Fig. 3(a)).
The main difference between the two samples is the Ba Nb O
the sintering temperature and promote the densification process
of Ba Nb O –BaWO composite ceramics. Thus, the low-tem-
5
4
15
4
5
4
15
15
perature sintering could be achieved at about 9001C for the
present composite ceramics, which could meet the requirement
for LTCC applications. From Figs. 2(b) and (c), it can also be
observed that the densification range of BNW6002 is large than
that of BNW6502, which may be due to the different sintering
content. The sample BNW6002 contains more Ba
which has much higher sintering temperature (14001C) com-
pared with BaWO (11001C). The existence of Ba Nb 15 may
suppress the grain growth of the Ba Nb O –BaWO ceramics.
5 4
Nb O
,
4
5
4
O
5
4
15
4
It can be also observed that there exist two types of grains in all
the above samples: one is the large grains (B3 mm) and the other
is the small grains (o1 mm). To confirm the composition of the
two types of grains of the sample BNW6502, EDS was used. The
results are shown in Fig. 4. The results show that the larger
5 4 4
temperature of Ba Nb O15 (14001C) and BaWO (11001C).
Compared with sample BNW6502, BNW6002 contains more
Ba Nb O , which has a negative effect on the sintering tem-
5
4
15
perature and results in the larger densification range of
BNW6002. The addition of large amount of B (Fig. 2(d))
O
2 3
4
grains are composed of pure BaWO and the smaller ones are
produces two minima on the densification rate curve, which in-
dicates two stages of the sintering process. Noticeable densifi-
cation starts at about 6251C, which is much lower than the
undoped sample (B9201C). The first peak, at 7701C, may be
related to the liquid-phase sintering with a high densification
rate, while the second peak, at 9251C, signifies the final densifi-
composed of pure Ba Nb O , which may be due to much lower
5
4
15
sintering temperature of BaWO (11001C) compared with that
4
5 4 4
of Ba Nb O15 (14001C). At low sintering temperature, BaWO
grains grow superiorly.
The dielectric properties at microwave frequency were mea-
sured on the sintered ceramic samples and the results are listed
in Table II. In order to indicate clearly the effects of sintering
temperature on the microwave dielectric properties, the varia-
tions of dielectric constants and Q ꢀ f values of Ba Nb O –
9
cation process. A reduced densification rate exists in the tem-
perature region of 7701–9251C, which implies that the
densification is hindered by the formation of pores which may
be due to the pore coalescence upon sintering with an excessive
5
4
15
4
BaWO ceramics with sintering temperature are shown in Fig. 5.
9
. This result suggests that no more than 1 wt% of B
of B O
2 3
O
2 3
From Fig. 5(a), it can be observed that the dielectric constant
increases with increasing temperature initially, and then satu-
rated (for sample BNW6502 and BNW6006) or slightly dropped
(for sample BNW6002 and BNW6004). As the relative densities
of the samples are all above 95%, the effect of porosity on the
microwave dielectric properties can be neglected. Thus, for
samples BNW6002, BNW6004, and BNW6006, the dielectric
is necessary for sintering to occur at temperatures o9251C with
minimal porosity.
Figure 3 shows the SEM micrographs for sintered surface of
the composite ceramics sintered at 9001C. The evolution of the
microstructures relative to the B O content was observed from
2
3
2 3
Figs. 3(a)–(c). The addition of B O significantly improved the
5 4 4
Fig. 3. Scanning electron microscopy photographs of the as-fired surface of Ba Nb O15–BaWO ceramics sintered at 9001C. (a) BNW6002,
(b) BNW6004, (c) BNW6006, and (d) BNW6502.

3
278
Journal of the American Ceramic Society—Zhuang et al.
Vol. 91, No. 10
5 4 4
Fig. 5. Microwave dielectric properties of Ba Nb O15–BaWO ceram-
vi c as l us ien. tered at different temperatures, (a) dielectric constant and (b) Q ꢀ f
BNW6006. Noticeably, the dielectric constant of BNW6502 is
much lower than that of BNW6002, although they have the
same amount of B O . The difference between the dielectric
2
3
constants may be due to the different amount of BaWO
4
, which
5 8,
is reported to have microwave dielectric properties of e
r
1
4
Q ꢀ f 5 57500 GHz, and t
f
5 ꢁ78 ppm/1C. BNW6502 con-
tains more BaWO than BNW6002 which induces the lower di-
4
electric constant of BNW6502.
Figure 5(b) shows the Q ꢀ f values of Ba
5 4 4
Nb O15–BaWO
Fig. 4. Scanning electron microscopy photograph of the sample
BNW6502 sintered at 9001C and its EDS spectrum. (a) BNW6502 sin-
tered at 9001C, (b) EDS spectrum of A, and (c) EDS spectrum of B.
ceramics with different sintering temperature. It is observed that
the maximum Q ꢀ f values can be obtained around 9001–9501C.
The Q ꢀ f values increase with increasing temperature initially,
then reached the maximum value, finally, dropped or remain
nearly unchanged at 10001C. This phenomenon agrees well with
the dilatometric curves (See Fig. 2). The samples are over-heated
when sintered at 10001C. It can also be observed that the op-
timized sintering temperature of BNW6002 is 9501C, while that
of BNW6004 and 6003 is 9001C. This agrees well with the den-
sity curves, which is not provided here. For samples BNW6002,
BNW6004, and BNW6006 sintered at optimized temperature,
the Q ꢀ f values decrease from 39 800 to 33 900 GHz with in-
creasing B O content. As the samples’ relative densities are all
constants are mainly affected by the secondary phase—hexag-
onal BaNb
According to XRD data shown in Fig. 1, diffraction peaks as-
sociated with hexagonal BaNb appeared during low-temper-
ature firing of Ba Nb O –BaWO when the addition of B O is
2 6 2 3
O and the glassy phase caused by B O addition.
2 6
O
5
4
15
4
2
3
over 0.4 wt%. Hexagonal BaNb
2
O
6
is reported to have micro-
5 42, and
5 ꢁ800 ppm/1C. The relative high dielectric constant (B42)
of BaNb O will cause the increase of dielectric constant of
wave dielectric properties of Q ꢀ f 5 4000 GHz, e
r
2
0
t
f
2
6
2
3
composites with increasing B
2
O
3
content. However, the increase
of B will increase the glassy phase, which will cause the de-
above 95%, the effect of the density on the Q ꢀ f values of
O
2 3
Ba Nb 15–BaWO ceramics should be neglected. The decrease
4
5
4
O
crease of dielectric constant. Considering the both effects of
BaNb O (positive) and glassy phase (negative) on the dielectric
of Q ꢀ f values may be resulted in the formation of the
BaNb O , whose Q ꢀ f value is only B4000 GHz. Moreover,
2
6
2
6
constant of the samples, the slight increase in dielectric constant
with increasing B is observed for BNW6002, BNW6004, and
2 3
the addition of B O may cause the formation of glassy phase
O
2 3
which may also contribute to the slight decrease of the Q ꢀ f
values. The Q ꢀ f value of BNW6502 (50 300 GHz) is different
from the other samples again. This may be due to the more
Table II. Relative Density and Microwave Dielectric
Properties of Ba Nb O –BaWO Ceramics Sintered at 9001C
4
content of the low dielectric loss phase, BaWO . Further more,
the larger grain size of BNW6502 observed in Fig. 3(e) may also
contribute to the higher Q ꢀ f value. For samples BNW6002,
5
4
15
4
Sample
Relative Density (%)
e
r
Q ꢀ f (GHz)
t
f
(ppm/1C)
f
BNW6004, and BNW6006, it can be seen that the t values de-
crease from ꢁ3.4 to ꢁ8.6 ppm/1C. This may be due to large
BNW6502
BNW6002
BNW6004
BNW6006
96.3
95.4
96.7
96.5
16.8
18.9
19.1
19.2
50 300
36 500
36 000
33 900
ꢁ6.4
ꢁ3.4
ꢁ6.3
ꢁ8.6
negative t value of BaNb O (ꢁ800 ppm/1C). However, as the
f
2
6
BaNb O amount is small, the decreases of t values are small.
2
6
f
For compatibility tests, the silver electrode was screen-printed
onto BNW6502 green bodies using a screen printer. Figure 6

October 2008
Sintering and Dielectric Properties of Ba Nb O –BaWO for LTCC Applications
5
3279
4
15
4
IV. Conclusions
B O can significantly lower the sintering temperature of
2
3
Ba Nb O –BaWO ceramics from B11001 to B9001C. It is
5
4
15
4
found that large addition of B
hexagonal BaNb , which affects the microwave dielectric
properties of Ba Nb O –BaWO ceramics. The amount of
2 3
O will cause the formation of
2 6
O
5
4
15
4
BaWO
dielectric properties of the ceramics. The low-temperature fired
Ba Nb 15–BaWO possesses excellent microwave dielectric
properties: er of 16.8B19.2, Q ꢀ f values of 33 900B50 300
GHz, and a t
4
also influences the sintering behavior and microwave
5
4
O
4
f
between ꢁ3.4 and Bꢁ8.6 ppm/1C. Also, this
material is compatible with Ag electrodes, therefore, is suitable
for LTCC applications.
References
1
W. Wersing, ‘‘Microwave Ceramics for Resonators and Filters,’’ Curr. Opin.
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2
2 6 2 5
ZnNb O Microwave Dielectric Ceramics Doped with ZnO–V O Additions,’’
Fig. 6. Scanning electron microscopy photograph and the EDS analy-
sis of BNW6502 cofired with Ag in the air at 9001C for 4 h. Inset shows
the EDS analysis at the interface between Ag and BNW6502.
J. Mater. Sci., 40, 6581–3 (2005).
3
K. Wakino, T. Nishikawa, Y. Ishikawa, and H. Tamura, ‘‘Dielectric Resonator
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M. T. Sebastian and H. Jantunen, ‘‘Low Loss Dielectric Materials for LTCC
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5
shows the SEM image and the EDS analysis of the sample. It
can be seen that the silver electrodes has good chemical com-
patibility and coheres closely with BNW6502 ceramics. The in-
terface between BNW6502 and silver electrode is clear and
further analysis is performed on the Ag and BNW6502 inter-
face. The result is shown in the inset of Fig. 6. It can be seen that
the Ag penetration depth is B1.5 mm. Figure 7 shows the XRD
patterns of BNW6502 ceramic and mixture of BNW6502 and
Ag ceramic. No secondary phases are observed in Fig. 7, im-
electric Properties of Low-Temperature Sintered Mg
Ceram. Soc., 25, 2865–70 (2005).
3 4 2
(VO ) Ceramic,’’ J. Eur.
6
K. P. Surendran, P. C. R. Varma, and M. R. Varma, ‘‘Solid State and Solution
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831–44 (2007).
3
1
7
A. B. Gaikwad, S. C. Navale, V. Samuel, A. V. Murugan, and V. Ravi, ‘‘A Co-
4 3 2 9
Precipitation Technique to Prepare BiNbO , MgTiO and MgTa O Powders,’’
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8
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the Sol-Gel Derived Ba
4
)9.33Ti18O
plying that the reaction of low-fired Ba Nb
5
4
O
15–BaWO
4
with
9
H. T. Kim, S. H. Kim, S. Nahm, and J. D. Byun, ‘‘Low-Temperature Sintering
and Microwave Dielectric Properties of Zinc Metatitanate–Rutile Mixtures Using
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Ag electrodes did not occur. This result is in accordance with
the SEM and EDS results as shown in Fig. 6. Therefore,
Ba Nb O15–BaWO could be selected as suitable candidates
5 4 4
for LTCC materials, because of low sintering temperature,
good microwave dielectric properties, and compatibility with
electrodes.
10
R. Ratheesh, M. T. Sebastian, P. Mohanan, M. E. Tobar, J. Hartnett,
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Method,’’ Mater. Lett., 45, 279–85 (2000).
2
5
O
5
4
O
11
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12
D. W. Kim, K. S. Hong, C. S. Yoon, and C. K. Kim, ‘‘Low-Temperature
Sintering and Microwave Dielectric Properties of Ba 15–BaNb Mixtures
for LTCC Applications,’’ J. Eur. Ceram. Soc., 23, 2597–601 (2003).
5
M
4
O
2 6
O
13
D. W. Kim, J. R. Kim, S. H. Yoon, K. S. Hong, and C. K. Kim, ‘‘Microwave
Dielectric Properties of Low-Fired Ba Nb 15,’’ J. Am. Ceram. Soc., 85, 2759–62
2002).
5
4
O
(
14
S. H. Yoon, D. W. Kim, S. Y. Cho, and K. S. Hong, ‘‘Investigation of the
Relations Between Structure and Microwave Dielectric Properties of Divalent
Metal Tungstate Compounds,’’ J. Eur. Ceram. Soc., 26, 2051–4 (2006).
15
H. Zhuang, Z. X. Yue, F. Zhao, and L. T. Li, ‘‘Microstructure and Microwave
Dielectric Properties of Ba Nb 15–BaWO Composite Ceramics,’’ J. Alloy. Co-
mpd. doi: 10.1016/j.jallcom.2008.04.073.
5
4
O
4
16
Z. Q. Tian, H. X. Liu, H. T. Yu, and S. X. Ouyang, ‘‘Effect of BaWO
4
on
,’’ Mater.
Microstructure Microwave Dielectric Properties of Ba(Mg1/3Nb2/3)O
3
Chem. Phys., 86, 228–32 (2004).
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17
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MMT-8, 402–10 (1960).
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18
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Microwave Theory Tech., MMT-18, 476 (1970).
J. Krupka, K. Derzakowski, B. Riddle, and J. B. Jarbis, ‘‘A Dielectric Res-
19
onator for Measurements of Complex Permittivity of Low Loss Dielectric Mate-
rials as a Function of Temperature,’’ Meas. Sci. Technol., 9, 1751–6 (1998).
D. W. Kim, H. B. Hong, K. S. Hong, C. K. Kim, and D. J. Kim, ‘‘The Re-
20
Fig. 7. X-ray diffraction patterns of BNW6502 ceramic and mixture of
BNW6502 and Ag sintered at 9001C for 4 h in the air.
versible Phase Transition and Dielectric Properties of BaNb
J. Appl. Phys., 41, 6045–8 (2002).
O
Polymorphs,’’ Jpn.
&
2
6