Abstract: In this paper, several kinds of synthesis techniques were adopted; not only conventional solidstate
reaction method but also solution synthesis techniques, including co-precipitation and hydrothermal
synthesis, in addition to the gel-casting for complex shape of ceramic components and tape-casting of
large scale thin plate for microwave IC. Different kinds of microwave ceramics were prepared, such as
materials with low permittivity and high quality factor, moderate permittivity and good quality factor,
and, high permittivity and reasonable quality factor, in addition to near zero of temperature coefficient of
resonance frequency. Series of microwave devices were developed, for examples, dielectric resonators,
dielectric filters, GPS antennas, communication connectors, and thin substrates for microwave IC.
Abstract: Bearing in mind the attractive dielectrics properties of Ba5Nb4O15, Zn3Nb2O8 and ZnTiO3, we
have investigated the lowering of the sintering temperature of these dielectrics using ZnO-B2O3 glass frit
addition. The control of the temperature coefficient of the permittivity has been also examined using two
different methods. The first method consists in mixing the two oxides ZnTiO3 + TiO2 which exhibit a
temperature coefficient with opposite sign. The second method is based on the stacking of two ceramic
layers having opposite sign of temperature coefficients. This has been successfully tested in the
Ba5Nb4O15 / Zn3Nb2O8 system.
Abstract: The effects of Nb2O5 content upon the microwave characteristics of ZnTa2−xNbxO6 ceramics
are investigated. The appropriate sintering temperatures of ZnTa2−xNbxO6 ceramics slightly decrease with
the increase of Nb2O5 content, and the densities and dielectric constants of ZnTa2−xNbxO6 ceramics
linearly decrease with the increase of Nb2O5 content. As the Nb2O5 content increases, the Q×f value of
ZnTa2−xNbxO6 ceramic first decreases, reaches a minimum value at x=1.0, then increases and reaches a
maximum value at x=2.0. The τf values of ZnTa2−xNbxO6 ceramics are positive for x≤0.3, and change to
negative ones as x≥0.6.
Abstract: In this work hexagonal perovskite powders of CaLa4Ti4O15 were prepared by citrate sol-gel
method. The calcined temperature was 1150oC, which is lower than that of the conventional solid method.
Dense CLT ceramics were produced at sintering temperature of 1600oC. The crystal structures and
microstructures were investigated by XRD, TEM and SEM, respectively. Compared with samples
produced by solid method, the sol-gel derived CLT ceramics exhibited a near zero temperature coefficient
of resonant frequency (τf ) of -6 ppm/oC, and other microwave properties , εr ~ 43, Q×f ~ 42000 GHz were
also obtained. Moreover, the sintering temperature of the CLT ceramics could be reduced to 1400 oC by
addition of B2O3-ZnO.
Abstract: A middle permittivity dielectrics with the tunable temperature coefficient of dielectric constant
(τε) in the BaO-TiO2-Nb2O5 system, Ba3Ti5Nb6O28, has been synthesized and characterized. The
dielectric properties of Ba3Ti5Nb6O28 measured at 1MHz are as follows: dielectric constant (εr) ~38,
dielectric loss (tanδ)<0.0002, temperature coefficient of dielectric constant (τε)~-22ppm/°C. The
Ba3Ti5Nb6O28 phase satisfies the requirements of NP0 (MLCC) dielectrics, but the sintering temperature
of the Ba3Ti5Nb6O28 phase (1250~1300°C) is too high to be co-fired with Ag or Cu electrodes. To lower
the sintering temperature, an appropriate amount of ZnO-B2O3 frit (5~7wt.%) was added to the
Ba3Ti5Nb6O28 phase and dense ceramics were obtained at the sintering temperature lower than 1000°C.
Furthermore, the CaNb2O6 phase with the positive τε of 65ppm/°C was incorporated into the
Ba3Ti5Nb6O28 phase to adjust the temperature coefficient of dielectric constant from negative to
positive(-22~30ppm/°C). Near zero τε ceramics with high εr (38) and low tanδ (0.0002) were obtained at
the composition of Ba3Ti5Nb6O28/ CaNb2O6/ ZB frit=76:17:7 wt.%.
Abstract: BaCu(B2O5) (BCB) powder was prepared using BaO,CuO and B2O3 as the main materials.
Microwave dielectric ceramics of tungsten–bronze-type BaSm2Ti4O12 (BST) were prepared by doping
BCB as the sintering aid. The amount of BCB was varied from 1.0 to 10.0wt.%. The microstructure and
dielectric properties of BST were investigated. The sintering temperature of BST ceramics with 6.0wt.%
BCB addition can be effectively reduced to 900 oC, about 450 oC lower than that of pure BST ceramics.
Good microwave dielectric properties of εr = 62.38, Q×f = 4573 GHz and τf = -27.65 ppm/ oC were
Abstract: Microwave dielectric ceramics 0.4(Ca0.61Nd0.26)TiO3-0.6(Li0.5Sm0.5)TiO3 (CNLST) were
prepared by doping CuO as the liquid-phase sintering aid. The effects of CuO on the microstructures
and dielectric properties were investigated. Due to the liquid-phase effect, the sintering temperature of
CNLST with 0.5wt.% CuO addition has be effectively reduced to 1100°C, while good microwave
dielectric properties of εr=83.4, Q•f=3880GHz, τf =2.1ppm/°C.
Abstract: The effects of CuO-MoO3 addition on the sintering behavior and microwave dielectric
properties of ZnO-TiO2 ceramics were investigated. ZnO-TiO2 ceramics were prepared with conventional
solid-state method and sintered at temperatures from 850 to 1050 °C. The sintering temperature of
ZnO-TiO2 ceramics with CuO-MoO3 addition could be effectively reduced to 950 °C due to the liquid
phase effects resulting from the additives. A proper amount of CuO-MoO3 addition could effectively
improve the densification and microwave dielectric properties of ZnO-TiO2 ceramics. ZnO-TiO2
ceramics with 3 wt% addition sintered at 950 °C for 4 h exhibited better microwave dielectric properties
as follows: εr of 26.8, a Q×f value of 16780 GHz at 5.42 GHz, and a τ
f value of +34.7 ppm/°C.
Abstract: Rectangular cavity perturbation method was used to measure microwave dielectric loss (MDL)
during the solid state reaction synthesis of SrFeCo0.5Oy. In the process of solid state reaction, the dielectric
loss is investigated under different temperatures. The phases of the samples synthesized at different
temperatures were characterized by XRD. The variation of MDL with temperature illustrates that the
phase transformation occurs. The reasons why the pure perovskite phase can be obtained by using
microwave processing were also discussed.
Abstract: The plagioclase feldspar (NaxCa1-xAl2-xSi2+xO8, 0<x<0.67), has been synthesized under sub-solidus conditions using the solid-reaction technique. X-ray diffraction (XRD) was used to study the temperature dependency of the phase and structure transformations. Scanning electron microscopy (SEM) was performed to demonstrate the micro-structure of the sintered samples. The dielectric properties in microwave (MW) frequency region, including the dielectric constant, Qxf and the temperature coefficient were measured by the microwave network analyzer. The results revealed the value of Qxf decreases when 0≤x≤0.2, while increases when 0.2≤x≤0.67. The lowest value of Qxf was at x = 0.2.