Microstructure and dielectric properties of Ba(Cd 1/3 Ta 2/3 )O 3 microwave ceramics synthesized with a boron oxide sint
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Jian Sun Center for Solid State Science, Arizona State University, Tempe, Arizona 85287; and School of Materials Science and Engineering, Shanghai Jiao-tong University, Shanghai 20003, People’s Republic of China
Richard Taylor School of Information and Electrical Engineering, University of Queensland, St. Lucia, QLD 4064, Australia
David J. Smith Center for Solid State Science, and Department of Physics and Astronomy, Arizona State University, Tempe, Arizona 85287
N. Newmana) Science and Engineering of Materials Program, and Department of Chemical and Materials Engineering, Arizona State University, Tempe, Arizona 85287 (Received 20 February 2004; accepted 16 August 2004)
The use of boron as a sintering aid reduces the sintering temperature, enhances the sintering density, and improves the microwave properties of Ba(Cd1/3Ta2/3)O3 ceramic dielectrics. Observations by transmission electron microscopy indicate that the liquid sintering mechanism contributes to the improvement in sintering density for boron concentrations exceeding 0.5 wt%. The introduction of as small as 0.01% boron also results in the production of high-density samples (∼95%), presumably indicating that a point defect mechanism may also play an important role in the sintering process. X-ray diffraction data combined with high-resolution transmission electron microscopy images show that boron-doped Ba(Cd1/3Ta2/3)O3 ceramic material has a well-ordered hexagonal structure. Annealing treatment is found to improve the microwave properties. The best sample has a dielectric constant of 32, a temperature coefficient of resonant frequency of 80 ± 15 ppm/°C, and a quality factor of >25,000 at 2 GHz.
I. INTRODUCTION
The development of low-loss temperature-compensated microwave materials with high-dielectric constants will facilitate the miniaturization of satellite, ground-based, and portable communication systems.1,2 Since the 1970s, there have been substantial advances in dielectric ceramics for microwave applications, including Ba2Ti9O20, BaTi 4 O 9 , Zr 1 − x Sn x TiO 4 , Ba(Zn 1 / 3 Ta 2 / 3 )O 3 , and Ba6−3xRE8+2xTi18O54.3 A significant improvement in the performance of dielectric filters has been made recently as a result of improved device designs and these material developments.4
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0456 3526
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 12, Dec 2004 Downloaded: 13 Mar 2015
Ba(Zn 1/3 Ta 2/3 )O 3 , Ba(Mg 1/3 Ta 2/3 )O 3 , and related perovskite compounds show tremendous potential for widespread use in microwave systems due to their excellent high frequency properties.5,6 Ba(Zn1/3Ta2/3)O3, in particular, has a large dielectric constant (⑀ ∼ 30) and ultralow loss tangent (tan ␦ < 2 × 10−5 at 2 GHz). Furthermore, when doped with Ni, its temperature coefficient of resonant frequency tf can be tuned to near zero.7 Our recent theoretical investigation of Ba(Zn x Cd1/3−xTa2/3)O3 suggests that the relative contribution of d-electron bonding can p
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