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J. Am. Ceram. Soc., 94 [9] 2800–2803 (2011)
DOI: 10.1111/j.1551-2916.2011.04727.x
© 2011 The American Ceramic Society
ournal
J
New Microwave Dielectric Ceramics BaLn2(MoO4)4
(Ln = Nd and Sm) with Low Loss
Di Zhou,†,‡,¶ Li-Xia Pang,§ Jing Guo,‡,¶ Ying Wu,‡,¶ Gao-Qun Zhang,‡,¶ Wei Dai,‡,¶
Hong Wang,‡,¶ and Xi Yao‡,¶
‡Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education,
Xi’an Jiaotong University, Xi’an, 710049, China
§Laboratory of Thin Film Techniques and Optical Test, Xi’an Technological University, Xi’an, 710032, China
¶International Center for Dielectric Research, Xi’an Jiaotong University, Xi’an, 710049, China,
In the present work, a pure monoclinic phase of BaNd2(MoO4)4
and BaSm2(MoO4)4 was formed at 850°C and 600°C, respec-
tively, via a solid-state reaction method. The ceramic samples
were found to be well densified at 960°C. Dense and homo-
geneous microstructures were revealed from the scanning
electron microscopy. The microwave dielectric behaviors were
studied as a function of sintering temperature and characterized
in the temperature range 25°C–120°C. The best properties were
obtained in ceramics sintered at 960°C with a permittivity
~11.7, a Q 3 f value of 45 000 GHz and a temperature coeffi-
cient of frequency about ꢀ41 ppm/°C for BaNd2(MoO4)4 cera-
mic at 9.9 GHz, and a permittivity ~11.8, a Q 3 f value of
20 000 GHz, and a temperature coefficient of frequency about
ꢀ34 ppm/°C for BaSm2(MoO4)4 ceramic at 9.7 GHz, respec-
tively.
dates and lanthanon molybdates. However, there is only
few report on the microwave dielectric properties of alkali
metal, lanthanon and molybdenum ternary system. Recently,
James and Ratheesh reported the preparation and microwave
dielectric properties of BaCe2(MoO4)4 ceramics with a er ~
12.3, Q 9 f ~ 16 000–24 000 GHz, and τf ~ ꢀ37 ppm/°C.11
In 2011, the BaNd2(MoO4)4 crystal was grown by Han et al.
and a potential value as a solid-state laser material has been
shown.12 These results attracted our attention to study the
microwave dielectric properties of other BaLn2(MoO4)4
ceramics. Considering the slightly smaller but close ionic radii
of Nd and Sm ions than Ce ion,13 the BaLn2(MoO4)4
(Ln = Nd and Sm) ceramics were chosen in the present work.
The phase evolution, microstructure, and microwave dielectric
properties (in temperature range 25°C–120°C) were studied.
I. Introduction
II. Experimental Procedure
ICROWAVE dielectric ceramics have been studied for
more than 40 years since they were applied in the
Proportionate amounts of reagent-grade starting materials
of BaCO3 (>99%, Shu-Du Powders Co. Ltd., Chengdu,
China), Nd2O3, Sm2O3 (>99%, Guo-Yao Co, Ltd, Shanghai,
China), and MoO3 (>99%, Fuchen Chemical Reagents,
Tianjin, China) were prepared according to the stoichiome-
tric formulation BaLn2(MoO4)4 (Ln = Nd and Sm) (Nd2O3
and Sm2O3 were pre-fired at 850°C for 4 h before use). Pow-
ders were mixed and milled for 4 h using a planetary mill
(Nanjing Machine Factory, Nanjing, China) by setting the
running speed at 150 rpm with the Yttria Stabilized Zirconia
(2 mm in diameter) milling media. Some of the mixed oxides
were then calcined at 600°C, 700°C, 850°C and 950°C for
4 h for phase evolution analysis. Most mixed oxides were
calcined at 700°C for 4 h for the further processing (re-mill-
ing, molding, sintering, etc.). After being crushed and
re-milled for 5 h using the ZrO2 milling media and deionized
water, powders were pressed into cylinders (10 mm in diame-
ter and 5 mm in height) in a steel die with 5 wt% PVA
binder addition under a uniaxial pressure of 200 MPa.
Samples were sintered in the temperature range from 920°C
to 1000°C for 2 h in the air atmosphere.
The crystalline structures of samples were investigated
using X-ray diffraction with CuKa radiation (Rigaku D/
MAX-2400 X-ray diffractometer, Tokyo, Japan). Micro-
structures of sintered ceramic were observed on the as-fired
surface with scanning electron microscopy (SEM) (JSM-
6460, JEOL, Tokyo, Japan). Dielectric behaviors at micro-
wave frequency were measured with the TE01d shielded
cavity method with a network analyzer (8720ES, Agilent,
Palo Alto, CA) and a temperature chamber (Delta 9023,
Delta Design, Poway, CA). The temperature coefficient of
M
microwave devices application, such as dielectric resonator,
dielectric filter, dielectric antenna, etc. The search for new
microwave dielectric ceramic has never been stopped due to
the fast development of wireless communication technology
and devices, such as portable phones, car-telephones, Blue-
tooth technology, global position system (GPS), wireless
fidelity (WIFI), etc. Microwave dielectric ceramics with a ser-
ies of dielectric permittivities er, high Q 9 f value, small tem-
perature coefficient of resonant frequency τf, nontoxic
constituents are needed.1–5
Many MoO3-rich systems have been found to show high
performance of microwave dielectric properties and advantage
in the low temperature co-fired ceramic technology (LTCC),
such as AMoO4 (er = 7–11, Q 9 f = 37 000–90 000 GHz,
τf = ꢀ57 to ꢀ87 ppm/°C),6,7 Bi2O3–MoO3 (er = 17–38,
Q 9 f = 9300–21 800 GHz, τf = ꢀ215 to +31 ppm/°C),8,9
Ln2O3–MoO3 (Ln = La and Nd) (er = 8.2–10.1, Q 9 f =
60 000–80 000 GHz, τf = ꢀ60 to ꢀ80 ppm/°C).10 It seems
that most MoO3-rich binary systems show high microwave
dielectric properties, especially for the alkali metals molyb-
J.-B. Lim—contributing editor
Manuscript No. 29643. Received April 26, 2011; approved June 05, 2011.
This work was supported by the National 973-project of China (2009CB623302).
†Author to whom correspondence should be addressed. e-mail: zhoudi1220@gmail.
com
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