Journal of Solid State Chemistry 177 (2004) 3995–4000 Microwave dielectric properties of BaO2CeO 2 nTiO 2 ceramics H. Sreemoolanadhan a,1 , M.T. Sebastian a,Ã , R. Ratheesh b,2 , R. Blachnik b , M. Woehlecke c , B. Schneider c , M. Neumann c , P. Mohanan d a Regional Research Laboratory, Ceramic Technology Division, Industrial Estate P.O., Papanamcode, Trivandrum, Kerala 695019, India b Anorganische Chemie, Universitat Osnabrueck, D-49069 Osnabrueck, Germany c Fachbereich Physik, Universitat Osnabrueck, D-49069 Osnabrueck, Germany d Department of Electronics, Cochin University of Science & Technology, Kochi 682022, India Received 7 May 2004; received in revised form 28 July 2004; accepted 3 August 2004 Available online 6 October 2004 Abstract The BaO–2CeO 2 –nTiO 2 ceramics with n ¼ 3; 4and5havebeenpreparedwithCeO 2 as starting material. The ceramics have been characterized using scanning electron microscopy, X-ray diffraction, Raman and X-ray photoelectron spectroscopy techniques. The microwave dielectric properties have been measured using standard dielectric resonator techniques. BaO–2CeO 2 –3TiO 2 (123), BaO–2CeO 2 –4TiO 2 (124) and BaO–2CeO 2 –5TiO 2 (125) ceramics showed dielectric constants of 38, 27 and 32, respectively. All the ceramicsshowedfairlygoodunloaded Q-factors.124and125compoundsexhibitedlow t f values,while123showedahigh t f value. r 2004 Elsevier Inc. All rights reserved. Keywords: Dielectric resonators; Microwave ceramics; Barium cerium titanates; Low-loss materials 1. Introduction The rapid expansion of telecommunication systems demands dielectric resonators (DRs) as basic compo- nents for designing filters and oscillators. Reducing the size is very important for high-quality and low-cost devices. One of the most suitable ways of miniaturizing thefiltersandreducingtheircostistousehighdielectric constant and low-loss ceramic DRs. The important characteristics required for a DR are high  r for miniaturization, high Q-factor for selectivity and small temperature variation of the frequency (t f ) for stability. DRs provide significant advantages in terms of com- pactness, light weight, temperature stability and rela- tively low cost in the production of a variety of microwave devices such as band-selection filters and solid-state oscillators [1,2]. Ceramics in the BaO–Ln 2 O 3 –TiO 2 system [Ln=lanthanides such as La, Sm, etc.] have been identified as promising materials for application at frequencies below 2GHz [3–8]. Many studies [4–8] have proved that these ceramics contained secondary phases like BaTi 4 O 9 , TiO 2 , Ln 2 Ti 2 O 7 , etc. in addition to the major phase, which could be either BaLn 2 Ti 5 O 14 or BaLn 2 Ti 4 O 12 compounds [Ln=lanthanides]. It may be noted that in the solid-state mixed oxide preparation method, rare-earth trioxides (Ln 2 O 3 ) were used in the raw material stage. Although many reports have discussed the phase formation, structure, microstructure and dielectric properties of typical BaO–Ln 2 O 3 –TiO 2 [Ln=rare earth] ceramics, very little attention was paid on Ce-based compounds [3,9–12].Mudrodubovaetal. [3] usedCe 2 O 3 as one of the starting materials. Hoffmann and Waser [9] used chemical method for the preparation of compounds but they decomposed during hot forging. ARTICLE IN PRESS www.elsevier.com/locate/jssc 0022-4596/$-see front matter r 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jssc.2004.08.005 Ã Corresponding author. Fax: +91-471-249-1712. E-mail address: mailadils@yahoo.com (M.T. Sebastian). 1 Present address: Advanced Materials and Ceramics Division, Vikram Sarabhai Space Centre, Trivandrum 695022, India. 2 Present address: Centre for Materials for Electronics Technology (C-MET), Athani (P.O), Thrissur 680 771, India.