Effects of Nd 2 O 3 on the microwave dielectric properties of BiNbO 4 ceramics
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Effects of Nd2 O3 on the microwave dielectric properties of BiNbO4 ceramics Whan Choi and Kyung-Yong Kim Ceramics Processing Center, Korea Institute of Science and Technology, Seoul, Korea
Myung-Rip Moon and Kyoo-Sik Bae Department of Electronic Materials Engineering, The University of Suwon, Suwon, Kyunggi-do 445-743, Korea (Received 3 November 1997; accepted 22 January 1998)
Effects of Nd substitution with Bi on the microwave dielectric properties of BiNbO4 were studied. Bi12x Ndx NbO4 ceramics sintered at 920–980 ±C consisted of orthorhombic and triclinic phases. The amount of triclinic phase increased with the increase in the Nd content, x, and sintering temperature. The apparent density and the dielectric constant decreased with the Nd content, but increased with sintering temperature, reached the peak values at 960 ±C and then rapidly decreased. The Q 3 f0 value was between 11,000 and 13,000 GHz over all sintering temperatures for x , 0.05, but for x > 0.05 it reached the peak value at 950 ±C and then rapidly decreased. The temperature coefficient of resonance frequency increased in the positive direction with the Nd content and showed the minimum value of 21.82 ppmy±C for x 0.025 sintered at 940 ±C. However, it rapidly increased in the negative direction for sintering temperature over 960 ±C.
I. INTRODUCTION
For the miniaturization of microwave components for portable phones and others, the multilayer technology commonly employed for the fabrication of advanced capacitors or printed wire boards is needed. To apply this technology, microwave dielectric ceramics must be cofired with inner circuit conductors below the melting temperature of the metals. Furthermore, since the device performance is greatly influenced by the loss due to the resistance of conductors, especially in the microwave frequency range of over a few hundreds MHz,1 it is desirable to use conductor metals of low resistivity such as Ag or Cu. However, the sintering temperature of conventional dielectric ceramics used for resonators, filters, and duplexers of portable phones ranges between 1200 and 1500 ±C, much higher than the melting temperature of Ag (961 ±C) or Cu (1064 ±C). Thus, research to enable cofiring either by using additives or developing new materials has been widely conducted. Among new microwave dielectrics under consideration, the Bi2 O3 –Nb2 O5 system is attractive for its relatively low sintering temperature (1100 ±C). The bismuth-based ceramics have been investigated for the application as multilayer capacitors2 or piezoelectric materials.3 However, the microwave properties of the Bi2 O3 –Nb2 O5 system were first studied by Kagata et al.4 They showed that BiNbO4 ceramics containing CuO and V2 O5 had a Q value of 4260 (at 4.3 GHz), er 43, and TCF 138 ppmy±C. This Q value is high enough, but the temperature coefficient of resonance frequency (TCF) of 138 ppmy±C is too high for the application J. Mater. Res., Vol. 13, No. 10, Oct 1998
as temperature-stable and temperature-
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