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Ceramic materials Ba (1-x) SrxTiO3 for electronics – synthesis and characterization

Ciceron A. Berbecaru 1Horia V. Alexandru 1Constantin Porosnicu 1Alin Velea 1Andrei Ioachim 2Liviu Nedelcu 2Mariana Toacsen 2

1. University of Bucharest, Faculty of Physics, Bucharest-Magurele p.o.box mg-11, Bucharest 76900, Romania
2. National Institute for Materials Physics, Bucharest- Magurele 010555, Romania

Abstract

Oxide based ceramics Ba (1-x) SrxTiO3 -BST are important for applications in electronics. Samples prepared by solid-state reaction from BaO, SrO and TiO2 were sintered 1200-1260 oC for 2 hours. The following compositions were tested x = 0.25, 0.40, 0.35, 0.50, 0.60, 0.75, 0.90 and small amounts of 1 wt. % MgO and 1 wt. % MnO2 were added to improve the grains crystallisation. Archimedes’s method for ceramic density measurements gives for x content the following values r(x) = 5.50–1.00 x, (g/cm3). XRD, EDAX, SEM methods were used for sample characterization. Perovskite structure, [1,2] was dominant and other minor phases were detected. Grains of ~5 mm size, well faceted, could be “seen” by SEM analysis for x = 0.75 samples. Pores and their dimensions grow for Sr content and sintering temperature increase. Dielectric permittivity and loss were investigated (1 kHz) and -150 to +150 oC temperature range at a pace of ~2 oC /min. Sharp transitions were noticed with the sintering temperature increase with some well defined peaks of permittivity of higher values (2000-4000). A shift of the Curie points to higher values was noticed with Sr content according to the eqn: Tc = 130 - 323·x, [3]. At room temperatures the permittivity measured at 1GHz show increasing values (1300 to 2500) with sintering temperature and decreased values of losses (2 % to less than 0.5 %). The x = 0.35 composition being in the ferroelectric phase could not be measured in microwave at room temperature. Our results points to important application of these BST compositions for microwave devices.

References: [1] Jae-Ho Jeon, J. Europ. Ceram. Soc., 24 (2004) p.1045–1048, [2] H.V.Alexandru et al, Appl. Surf. Sci., 253 (2006) p.354-357, [3] A.Ioachim et al Mater. Sci. EnG. C, 26 (2006) p.1156-1161.
 

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Presentation: Oral at E-MRS Fall Meeting 2007, Symposium H, by Ciceron A. Berbecaru
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-21 17:17
Revised:   2009-06-07 00:44