Journal of Alloys and Compounds 478 (2009) 781–784
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
New dielectric material system of Nd(Mg Ti )O –CaTiO with ZnO
1
/2 1/2
3
3
addition at microwave frequencies
∗
Yuan-Bin Chen
Department of Engineering and Management, Chang Jung Christian University, 396 Chang Jung Rd., Sec.1, Kway Jen, Tainan 71101, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 November 2008
Received in revised form
The microwave dielectric properties and the microstructures of (1 − x)CaTiO –xNd(Mg1/2Ti1/2)O3 ceram-
3
ics prepared by the conventional solid-state route have been studied. Doping with 0.5 wt% ZnO
can effectively promote the densification and the microwave dielectric properties of (1 − x)CaTiO3–
27 November 2008
xNd(Mg1/2Ti1/2)O3. The dielectric constant decreases from 145 to 30.5 as x varies from 0.1 to 1.0. In the
Accepted 10 December 2008
Available online 24 December 2008
(
1 − x)CaTiO3–xNd(Mg1/2Ti1/2)O3 system, the microwave dielectric properties can be effectively controlled
◦
by varying the x value. The dielectric constant of 44, a Q × f value of 43,800 GHz and a ꢀf value of 1.2 ppm/ C
◦
were obtained for 0.1CaTiO3–0.9Nd(Mg1/2Ti1/2)O3 ceramics sintered at 1325 C for 4 h. A band-pass filter
Keywords:
is designed and simulated using the proposed dielectric to study its performance.
Dielectric properties
Microwave dielectric properties
X-ray
©
2009 Elsevier B.V. All rights reserved.
1
. Introduction
tric materials [3–6]. However, this requires a flexible procedure
that increases the cost and time for fabrication of dielectric res-
onators. Liquid phase sintering by adding glass has been found to
lower the firing temperature of ceramics. In this work, ZnO was
selected as a sintering aid to lower the sintering temperature of
The development of microwave communication systems
requires materials which can be used as resonators in filters or
oscillators at microwave frequencies in radar detectors, cellular
telephones, and global positioning satellite (GPS) devices. To sat-
isfy this demand, a material should have a reasonably high dielectric
constant (εr > 20) to allow size reduction of the component, a low
dielectric loss (Q > 5000, where Q = 1/tan ı) in the microwave fre-
quency range, and temperature stability (ꢀ = 0) [1]. The use of at
least two compounds with negative and positive temperature coef-
ficients, employed to form a solid solution or in mixed phases, is
(1 − x)CaTiO –xNd(Mg1/2Ti1/2)O3 ceramics.
3
2. Experimental procedure
Samples of CaTiO3 and Nd(Mg1/2Ti1/2)O3 were individually synthesized by con-
ventional solid-state methods from high-purity oxide (>99.9%) powders: CaCO3,
TiO2, Nd2O3, and MgO. A small amount of ZnO (0.5 wt%) was added as a sin-
tering aid. The starting materials were mixed according to the stoichiometry of
Nd(Mg1/2Ti1/2)O3 and CaTiO3, and then ground in distilled water for 10 h in a balling
f
the most promising method for obtaining a zero ꢀ . Although most
dielectric ceramics with high dielectric constants have positive ꢀf
values, materials with a high dielectric constant, high Q and neg-
f
◦
mill with agate balls. Both mixtures were dried and calcined at 1300 C for 4 h.
The crystalline phases of the calcined powder were identified by X-ray powder
◦
◦
diffraction (XRD) analysis using Cu K␣ radiation from 20 to 60 in 2Â. The calcined
ative ꢀ are desired to achieve this goal. Kim and colleagues have
powder was mixed to the desired composition (1 − x)CaTiO –xNd(Mg1/2Ti1/2)O3 and
f
3
2+
4+
reported many complex perovskites A(B1/2 B1/2 )O3 with neg-
ative ꢀf [2]. Among them, Nd(Mg1/2Ti1/2)O3 has a high dielectric
constant (ε ∼ 27), a high quality factor (Q × f value ∼46,000 GHz)
re-milled for 5 h with PVA solution as a binder. Pellets of 11 mm diameter and 5 mm
thickness were uniaxially pressed. After debinding, the pellets were sintered at tem-
◦
◦
peratures of 1325 C for 4 h. The heating and cooling rates were both set at 10 C/min.
The crystalline phases of calcined powder was identified by X-ray diffraction
patterns. Microstructure observations of the sintered surface were made by scan-
ning electron microscopy (SEM, Philips XL-40FEG). The bulk densities of the sintered
pellets were measured using Archimedes method. The microwave dielectric prop-
erties were calculated from the sizes of the samples and the resonant frequency,
using the Hakki and Coleman’s dielectric resonant TE011 and TE01␦ methods [7]. A
HP8757D network analyzer and a HP8350 sweep oscillator were employed to make
the measurements. The same technique was used to measure the temperature coef-
ficient of resonant frequency (ꢀf). The test set was placed over a thermostat in the
◦
and a negative ꢀ value (−49 ppm/ C). CaTiO (εr > 200, Q × f < 1000,
f
3
◦
> 1100 ppm/ C) with a positive ꢀ value was introduced into the
f
ꢀ
f
mixture to form a solid solution (1 − x)CaTiO –xNd(Mg1/2Ti1/2)O3
3
to compensate for the ꢀ value.
f
Chemical processing and the use of small particles of starting
◦
temperature range of 25–80 C. The temperature coefficient of resonant frequency
(
ꢀf) was also measured by the same method associated using Eq. (1)
∗ Fax: +886 6 335981.
f2 − f1
ꢀ
f =
(1)
f1(T2 − T1)
0925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2008.12.019