January 2000 Ž . Materials Letters 42 2000 207–211 www.elsevier.comrlocatermatlet ž / Microwave synthesis and sintering of Ba Mg Ta O 1r3 2r3 3 B. Vaidhyanathan, D.K. Agrawal ) , T.R. Shrout, Yi Fang Materials Research Laboratory, PennsylÕania State UniÕersity, UniÕersity Park, PA 16802, USA Received 5 July 1999; accepted 30 July 1999 Abstract Ž . Ba Mg Ta O , BMT, was synthesized and sintered by microwave processing at 2.45 GHz. Appropriate amounts of 1r3 2r3 3 BaCO , MgO, and non-stoichiometric Ta O were used as starting materials for the synthesis. BMT was obtained by 3 2 5yx heating the precursors in a multimode microwave cavity of 2 kW between 9008C and 13008C for just 20 min. The synthesis was carried out in N atmosphere to prevent the oxidation of Ta O . The perovskite BMT starts forming at 9008C and 2 2 5yx becomes single phase material at 13008C. The sintering of BMT was carried out in a single mode microwave cavity for 5 to 30 min at 14008C to 16008C without using any sintering aid. A relative density of 97% was obtained in 30 min of microwave sintering at 16008C. In contrast, it was found that to achieve the same densification, it requires 6 h of soaking at the same temperature in conventional sintering process. q 2000 Elsevier Science B.V. All rights reserved. Ž . Keywords: Microwave; Synthesis; Sintering; Ba Mg Ta O ; Perovskite oxides 1r3 2r3 3 1. Introduction Ž . Ž . Ba Mg Ta O BMT belongs to the com- 1r3 2r3 3 Ž . plex perovskite oxides, A B1 B2 O , and has a 1r3 2r3 3 dielectric constant of about 25 and possesses the Ž . highest Q value varied between 5000 and 50,000 w x in the oxide family 1,2 . It is a promising candidate material for the high frequency communication sys- tems and a suitable substrate for high-T supercon- c ducting thin films for microwave device applications wx 1 . BMT is also perhaps the most refractory dielec- Ž . wx tric oxide material known m.p. ) 30008C 3 . How- ever, the conventional synthesis of BMT requires temperatures as high as 15008C and a long process- ing duration of about 10 h. The self-sinterability of ) Corresponding author. Tel.: q1-814-863-8034; fax: q1-814- 863-3617. Ž . E-mail address: dxa4@psu.edu D.K. Agrawal BMT is very poor due to its refractory nature. Though sintering additives such as Mn 2 and Sn 3 have been used to obtain well sintered products, they have a detrimental effect on the dielectric properties of the BMT ceramic. Also, the conventional sintering method of BMT requires temperatures as high as w x 16508C for several hours 1,4 . This makes the syn- thesis and sintering of BMT very difficult and ineffi- cient. Therefore, development of new and highly efficient processing techniques for the synthesis and sintering of BMT is of great interest. Microwave processing of ceramic materials has w x been studied for over a decade 5–8 . The unique sintering mechanism makes microwave processing valuable in regard to the time and energy savings as well as improving product properties for the material systems which are dielectrically lossy at microwave frequency. Moreover, the dependence of microwave absorption of materials on the dielectric properties makes it possible to synthesize and sinter those fairly 00167-577Xr00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0167-577X 99 00185-8