Effect of SiO 2 addition on the microstructure and microwave dielectric properties of ultra-low fire TiTe 3 O 8 ceramics Sea-Fue Wang * , Shea-Jue Wang, Yuh-Ruey Wang, Yung-Fu Hsu, Liang-Yo Chen, Jung-Shiung Tsai Department of Materials and Mineral Resources Engineering, National Taipei University of Technology, Taipei, Taiwan, ROC Received 20 August 2008; received in revised form 6 September 2008; accepted 4 October 2008 Available online 30 October 2008 Abstract In this study, calcined TiTe 3 O 8 powder mixed with different amounts of SiO 2 was sintered at various temperatures. The effect of SiO 2 addition on the densification, microstructural evolution and dielectric properties of TiTe 3 O 8 was investigated. Results indicate that SiO 2 addition inhibited the grain growth of TiTe 3 O 8 and reduced the evaporation of TeO 2 . TiTe 3 O 8 ceramics with 1 wt% SiO 2 addition and sintered at 750 8C possesses the best dielectric properties: e r value of 47.6, Q  f value of 48,800, and t f value of +152 ppm/8C. Excess SiO 2 addition results in the poor densification and the existence of secondary phase (SiO 2 ) dissolved in a small amount of TeO 2 . They degrade the dielectric properties and trade off the benefit from the SiO 2 addition. # 2008 Published by Elsevier Ltd and Techna Group S.r.l. Keywords: Microwave properties; Densification; Microstructural evolution; TiTe 3 O 8 1. Introduction The recent rapid expansion of telecommunication systems has a great demand for dielectric resonators (DRs) as basic components in designing filters and oscillators. Now, dielectric ceramics for use in resonators at microwave frequency have been paid increasing attention due to the fast growth of mobile communication systems such as cellular phone, global positioning systems and personal communication system. For the applications in microwave devices, a high dielectric constant (e > 20), a high dielectric loss quality (Q > 2000), and a near zero temperature coefficient of resonant frequency (0– 10 ppm/8C) are required. High dielectric constant makes possible to reduce the size of the material by a factor of 1=e 1=2 r so that the size of circuit can be reduced considerably. The high Q value enables low insertion loss and low bandwidth of the resonance frequency, which are required for achieving high frequency selectivity and stability in the microwave transmitter components. Recently, dielectric materials are often required to be co- fired with high conductivity electrodes such as Ag and Cu in order to minimize the microwave absorption loss or to form a multilayer structure to increase the volume efficiency, and the process is called as low temperature co-firable ceramic (LTCC) technology. However, the sintering temperatures of common dielectric ceramics are in the range between 1200 and 1500 8C, which is much higher than the melting temperature of Ag (961 8C) or Cu (1064 8C). For instance, the sintering temperatures of BaO–Nd 2 O 3 –TiO 2 –Nb 2 O 5 , Ba 6x Ln 8+2x/3 Ti 18 O 54 and (Zr, Sn)TiO 4 systems are around 1325, 1350 and 1400 8C, respectively [1–3]. There is considerable interest in the development of new materials with low sintering temperatures. One way involved is the investigation of the glass-forming additives on the properties of established microwave materials. For instance, the BaO– La 2 O 3 –4.7TiO 2 ceramic with the addition of 20 wt% PbO– B 2 O 3 –SiO 2 aid can reduce the sintering temperature down to 900 8C, but the microwave properties were degraded [4]. Another way is the use of new material systems with lower sintering temperatures, including Bi 2 O 3 and TeO 2 -based compounds [5]. The sintering temperature of Bi 12 MO 20d www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 35 (2009) 1813–1817 * Corresponding author. Present address: National Taipei University of Technology, Department of Materials and Mineral Resources Engineering, 1, Sec. 3, Chung-Hsiao E. Rd., Taipei 106, Taiwan, ROC. Tel.: +886 2 2771 2171x2735. E-mail address: seafuewang@yahoo.com (S.-F. Wang). 0272-8842/$34.00 # 2008 Published by Elsevier Ltd and Techna Group S.r.l. doi:10.1016/j.ceramint.2008.10.012