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Conference: Bucharest University Faculty of Physics 2004 Meeting

Section: Solid State Physics and Materials Science

Title:

(Ba,Sr)TiO3 solid solutions for microwave applications

Authors:

C.Berbecaru(1), H.V.Alexandru(1), M.Negoita(1), A.Balabaneanu(1), F.Stanculescu(1), A.Ioachim(2), M.G.Banciu(2), L.Nedelcu(2), D.Ghetu(2)

Affiliation:

(1)Faculty of Physics, University of Bucharest

(2)National Institute of Materials Physics, Bucharest-Magurele, ROMANIA

E-mail

Keywords:

microwave,tunable filters, solid solutions

Abstract:

Commercial wireless technology, satellite telecommunication and global positioning systems, cellular phones and direct broadcasting satellite, made rapid progress due to improved performances of dielectric materials at microwave frequencies. Particularly, the solid solution system Ba1-XSrXTiO3 (BST) presents a major interest for electrically controlled devices, such as tunable filters, steerable antennas, phase shifters, varactors, etc. Solid solutions with X = 25, 50, 75, 90 % were prepared by standard powder technology-solid state reaction and sintered at 1230 oC and 1260 oC [1]. The temperature dependence of permitivity and of losses at low frequency (1 kHz) has shown interesting results [2]. The unit cell volume depends linearly on the Sr content W(Å3) = 61.1 + 3.6?X (from ref. [3]). We have estimated X-ray density as: r(g/cm3) » 5.99 ? 0.99×X. The measured densities of our samples r(g/cm3) » 5.50 ? 1.00×X, represents about 92 % of the X-ray density. Microwave measurements at 1÷3 GHz show substantial decrease of the permittivity from about 1600 to 200 and also of the losses from 12% to less than 2% with the Sr concentration increase from X = 25 to 90 %. It is concluded that sintering temperature has to be increased for samples of high Sr concentration. Moreover, the addition of MgO and MnO2 1 wt% each, improve sintering conditions and lower the microwave losses. References: [1] A.Ioachim et al, J.Optoelectr.Adv.Mater.5(2003)1389, [2] H.V.Alexandru et al, J.Mater.Sci.Eng.B ?in press, [3] Lon Wu et al, Jpn.J.Appl.Phys. 38 (1999) 5612.