Mechanism of Quality Factor Compensation by Nb 2 O 5 Addition for Dielectric Properties of Low-T Sintered ZST Microwave
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Mechanism of Quality Factor Compensation by Nb2O5 Addition for Dielectric Properties of Low-T Sintered ZST Microwave Ceramics Yong H. Park *, Moo Y. Shin, Hyung H. Kim, Kyung H. Ko Dept of MS&E, Ajou Univ., Suwon 442-749, Korea, *[email protected] ABSTRACT It has been known that some additives such as Nb2O5 are efficient quality factor compensators to potential additives for low-T sintering of (Zr0.8Sn0.2)TiO4 such as ZnO. The compensation mechanism of Nb2O5 was analyzed in the light of its effects on the Zn incorporation in grains. ZST ceramics were prepared by conventional mixed oxide method and their microwave dielectric properties including quality factor, permittivity and temperature coefficient frequency (TCF) were measured at X-band. After sintering at 1350 and 1400oC, samples were post-annealed at 900~1100oC. It was found that as Nb2O5 was added, the quality factor of 6 mol % ZnO-ZST specimens increased from 24000 to 44000 without any sacrificing of other dielectric properties such as permittivity and TCF. According to TEM and XRD, Nb addition tends to enhance Zn diffusion toward grain boundaries while Nb moved in the opposite direction. Due to the fact that no second phases were formed, it was assumed that the redistribution of Zn and Nb could play a major role in the enhancement mechanism of quality factor. Post-annealing can also be a secondary booster for the quality factor of ZST. After annealing at 900~1100oC, the quality factor of a specimen with additives, increased again up to 48000 due to further decrease of oxygen vacancies resulting from further out-diffusion of Zn toward grain boundaries and incorporation of Nb into the grain. INTRODUCTION Zirconium tin titanate ((Zr0.8Sn0.2)TiO4; ZST) ceramics are among the most popular commercial dielectric materials for microwave devices [1-6]. However, a major disadvantage of pure ZST ceramics is their poor sinterability at
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