Sintering BaTi 4 O 9 /Ba 2 Ti 9 O 20 -based ceramics by glass addition Chien-Min Cheng a, *, Cheng-Fu Yang b, *, Shi-Hong Lo b , Tseung-Yuen Tseng a Department of Electronic Engineering, National Chiao Tung University, Hsinchu, Taiwan, ROC b Department of Electronic Engineering, Chinese Air Force Academy PO Box 90277-4, Kangshan, Kaohsiung, Taiwan 82012, ROC Received 22 April 1999; received in revised form 30 August 1999; accepted 12 September 1999 Abstract After calcining BaCO 3 +4TiO 2 mixed powder at 1150  C for 2 h, BaTi 4 O 9 is the major phase, Ba 4 Ti 13 O 30 and BaTi 5 O 11 are minor phases. After calcining 2BaCO 3 +9TiO 2 mixed powder at 1200  C for 10 h, Ba 2 Ti 9 O 20 is the major phase, BaTi 4 O 9 and BaTi 5 O 11 are the minor phases. The calcining powders are used as the BaTi 4 O 9 and Ba 2 Ti 9 O 20 precursors. MgO±CaO±SiO 2 ±Al 2 O 3 (MCAS) composite glass powder, fabricated by sol±gel method, is used as the low melting addition to lower the sintering temperatures of BaTi 4 O 9 and Ba 2 Ti 9 O 20 dielectric. The addition of MCAS glass does not inhibit the residual satellite phases to transform into BaTi 4 O 9 and Ba 2 Ti 9 O 20 . For MCAS-doped BaTi 4 O 9 and Ba 2 Ti 9 O 20 ceramics the major phases are BaTi 4 O 9 and Ba 2 Ti 9 O 20 , cor- dierite is observed as minor phase. The temperatures needed to densify the BaTi 4 O 9 and Ba 2 Ti 9 O 20 ceramics are lowered down with the increase amount of MCAS glass addition. For BaTi 4 O 9 and Ba 2 Ti 9 O 20 ceramics, both the densities and the dielectric constants (at 1 MHz) increase with the sintering temperature and decrease with the amount of MCAS glass addition. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: BaTi 4 O 9 ; Ba 2 Ti 9 O 20 ; Calcination; Glass sintering aid; Sintering 1. Introduction BaTi 4 O 9 and Ba 2 Ti 9 O 20 were the two most common high-Q dielectric materials used in the microwave range. BaTi 4 O 9 was ®rst reported by Roy, 1 and Ba 2 Ti 9 O 20 by Jonker, 2 and they were investigated as microwave materials by O'Bryan and Plourde et al. 3±6 The BaTi 4 O 9 and Ba 2 Ti 9 O 20 ceramic had superior dielectric proper- ties for microwave resonator applications. 4,5 For the preparation of monophasic samples of BaTi 4 O 9 and Ba 2 Ti 9 O 20 from BaCO 3 and TiO 2 by conventional solid- state reaction, the stoichiometry must be precisely con- trolled, since there are various thermodynamically stable compounds in the vicinity of the desired compo- sition of TiO 2 -rich BaO±TiO 2 system: BaTi 3 O 7 , BaTi 4 O 9 , BaTi 5 O 11 , and Ba 4 Ti 13 O 30 . 3,4,7±9 In the study reported by Ritter et al., the pattern of BaO:TiO 2 =1:4 was not completely formed BaTi 4 O 9 until 1300  C. 8 Lu et al. also reported that the BaO:TiO 2 =2:9 powder, obtained by sol±gel method, must be calcined at 1200  C for 110 h to produce Ba 2 Ti 9 O 20 sole phase. 7 In this research, the solid-state reaction processes of BaCO 3 and TiO 2 to form BaTi 4 O 9 and Ba 2 Ti 9 O 20 phase at dierent temperatures and times are developed, and our ®nding on the BaTi 4 O 9 and Ba 2 Ti 9 O 20 compounds have shown some degree of dierence from those in the literature. 4±9 In addition, a very high sintering temperature of 1400  C was required to achieve densi®cation of the ceramics. For that, it is imperative to lower the sintering temperatures of the BaTi 4 O 9 and Ba 2 Ti 9 O 20 ceramics in order to avoid the compositional ¯uctuation. 3±6 Low melting glass additions, chemical processing, and smal- ler particle sizes of starting materials are three of the methods used to reduce the sintering temperature of dielectric. 10 however, there are few references in the lit- erature reporting the in¯uence of glass addition on microwave properties of BaTi 4 O 9 and Ba 2 Ti 9 O 20 dielec- tric. 10 Because of these reasons, it drew our attention to, and provided motivation to study, the eects of glass ¯ux on the sintering behavior and properties of BaTi 4 O 9 and Ba 2 Ti 9 O 20 dielectric. MgO±CaO±SiO 2 ±Al 2 O 3 (MCAS) composite glass, 11 which is fabricated by sol±gel method, is used as the low melting glass addi- tion to lower the sintering temperature of BaTi 4 O 9 and Ba 2 Ti 9 O 20 dielectric. The BaO:TiO 2 =1:4 and 0955-2219/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0955-2219(99)00247-2 Journal of the European Ceramic Society 20 (2000) 1061±1067 * Corresponding author.