J. Am. Ceram. Soc., 95 [1] 232–237 (2012)
DOI: 10.1111/j.1551-2916.2011.04760.x
© 2011 The American Ceramic Society
ournal
J
Microwave and Infrared Dielectric Response of Temperature
Stable (1ꢀx)BaMoO4–xTiO2 Composite Ceramics
Jing Guo,‡,§ Di Zhou,‡,§ Hong Wang,‡,§,† Yuehua Chen,‡,§ Yi Zeng,‡,§
Feng Xiang,‡,§ Ying Wu,‡,§ and Xi Yao‡,§
‡Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education,
Xi’an Jiaotong University, Xi’an, 710049, China
§International Center for Dielectric Research, Xi’an Jiaotong University, Xi’an, 710049, China
The (1ꢀx)BaMoO4–xTiO2 (x = 0.0, 0.2, 0.3, 0.338, 0.4, 0.5,
0.66) ceramics were synthesized by the conventional mixed-
oxide process. The sintering behaviors, phase composition,
chemical compatibility with silver, and microwave dielectric
properties of pure (1ꢀx)BaMoO4–xTiO2 ceramics and
0.662BaMoO4–0.338TiO2 ceramic with H3BO3–CuO addition
were studied. Infrared reflectivity spectra of (1ꢀx)BaMoO4–x
TiO2 (0.2 ꢁ x ꢁ 0.4) composites were measured in the range
of 50–4500 cmꢀ1 at room temperature. X-ray diffraction anal-
ysis reveals that scheelite BaMoO4 and rutile TiO2 phase
coexist with each other at 1275°C and both of them do not
react with silver (Ag) at 850°C. When the mole fraction of
TiO2 (x value) is 0.4, a temperature stable microwave dielec-
tric material is obtained, with er = 13.8, Q 3 f = 40 500 GHz
(f = 8.02 G), and τf = ꢀ6.13 ppm/°C. Complex dielectric
spectra gained from the infrared spectra were extrapolated
down to microwave range, and they were in good agreement
with the measured microwave permittivity and dielectric losses.
With 5 wt% H3BO3 and 1 wt% CuO addition, the 0.662
BaMoO4–0.338TiO2 ceramics can be sintered well below 900°C,
and possess good microwave dielectric properties with er = 14,
Q 3 f = 48 360 GHz, and τf = +13.9 ppm/°C.
to compensate the τf value of BaMoO4 using ceramics with
large positive τf values. Many successful examples have been
achieved by mixing two or more materials with opposite τf
values, such as Zn2Te3O8–TiO2, (Mg0.95Zn0.05)TiO3–SrTiO3,
MgTiO3–ZnAl2O4–TiO2, Mg4Nb2O9–ZnAl2O4–TiO2, ZnNb2O6–
TiO2, Mg2TiO4–Co2TiO4–CaTiO3, CaWO4–TiO2, and Bi2MoO6–
TiO2.9–15 Our previous study on ZnMoO4–TiO2 system also
demonstrated that the rutile TiO2 (er = 105, Q 9 f =
46 000 GHz, τf = +465 ppm/°C) is an effective material to
compensate the negative τf value of ZnMoO4, which is also a
MoO3-rich compound similar to BaMoO4 but with a wol-
framite structure.16 For this reason, rutile TiO2 is chosen to
mix with BaMoO4 as a compensator.
Dielectric losses include intrinsic part and extrinsic part.
Intrinsic losses are determined by polar optical phonons and
extrinsic losses are caused by impurity, pores, size and shapes
of grains, etc. Wakino et al.17 and Tamura et al.18 have
reported the relation between intrinsic loss and infrared (IR)
spectra. A large amount of research on IR reflective spectra
of rutile TiO2 was done.19–21 But the investigation on IR
spectra of BaMoO4 was few and the complex dielectric
response was not discussed.22–24 Therefore, it is important to
study the intrinsic losses of (1ꢀx)BaMoO4–xTiO2 com-
pounds from the infrared spectra and it helps to understand
the dielectric loss at microwave region.
I. Introduction
ITH the development of high-frequency wireless com-
munication technology, low temperature cofired cera-
In this work, the sintering behaviors, phase composition,
chemical compatibility with silver, microwave dielectric prop-
erties, and complex dielectric response between 50 and
4500 cmꢀ1 of the (1ꢀx)BaMoO4–xTiO2 ceramics were stud-
ied. To lower the sintering temperature, H3BO3–CuO was
added to the composites and its influence on the compounds
was also investigated.
W
mic (LTCC) technology, which can integrate the passive
components to a function module, has attracted much scien-
tific and commercial attention. For microwave (MW) appli-
cations, dielectric materials should have a low sintering
temperature, a high quality factor (Q 9 f) value, a near-zero
temperature coefficient of resonant frequency (τf), and chemi-
cal compatibility with metal electrodes.1–5 Recently, MW
dielectric properties of AMoO4 ceramics with scheelite
(A = Ca, Sr, Ba) and wolframite (A = Mg, Mn, Zn) struc-
ture have been reported.6–8 All of them exhibit good MW
dielectric properties (permittivity er = 7–11, Q 9 f = 37 000–
90 000 GHz, τf = ꢀ57 to ꢀ87 ppm/°C). The BaMoO4 has
the largest negative τf value (ꢀ79.24 ppm/°C) and the lowest
sintering temperature (900°C/2 h) in the series of AMoO4
ceramics with scheelite structure. Therefore, it is interesting
II. Experimental Procedure
The (1ꢀx)BaMoO4–xTiO2 composite ceramics were prepared
by the conventional solid-state synthesis. Reagent-grade pow-
ders BaCO3 (>99%, Sinopharm Chemical Reagent Co. Ltd,
Shanghai, China), MoO3 (>99%, Fuchen Chemical Reagents,
Tianjin, China), rutile TiO2 (>99%, Linghua Co. Ltd.,
Zhaoqing, China), H3BO3 (>99.5%, Sinopharm Chemical
Reagent Co. Ltd), and CuO (>99%, Sinopharm Chemical
Reagent Co. Ltd) were used as starting materials. The
BaCO3 and MoO3 powders were milled with ethanol and
ZrO2 milling media (2 mm in diameter) for 4 h using a plan-
etary ball-mill. After being dried, the mixture was calcined in
air at 650°C for 4 h. Then, some BaMoO4 powder was mixed
with TiO2 according to the following formula (1ꢀx)
BaMoO4–xTiO2 (0 ꢁ x ꢁ 0.66). Furthermore, the other
powders were mixed with TiO2, 5 wt% H3BO3, and 1 wt%
CuO. The mixture was milled with zirconia balls in ethanol
for 4 h and then dried. After being mixed with PVA binder,
D. W. Johnson Jr—contributing editor
Manuscript No. 29623. Received April 20, 2011; approved June 21, 2011.
This work was supported by the National 973-project of China (2009CB623302),
NSFC projects of China (61025002, 109790365), and National Project of International
Science and Technology Collaboration (2009DFA51820).
†Author to whom correspondence should be addressed. e-mail: hwang@mail.xjtu.
edu.cn
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