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Conference: Bucharest University Faculty of Physics 2007 Meeting

Section: Solid State Physics and Materials Science

Title:

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

Authors:

C. Berbecaru, H.V. Alexandru, C.Porosnicu, A. Velea, A. Ioachim*, L. Nedelcu*, M.Toacsen*

Affiliation:

Faculty of Physics, Bucharest University,

* National Institute of Materials Physics, Bucharest-Magurele,

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Keywords:

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) 1045–1048, [2] H.V.Alexandru et al, Appl Surf Sci 253 (2006) 354-357, [3] A.Ioachim et al Mater. Sci. EnG. C, 26 (2006) 1156-1161.