BST solid solutions, temperature evolution of the ferroelectric transitions

• Published in: Applied surface science 2006-10, Vol.253 (1), p.354-357
• Main Authors: Alexandru, H.V., Berbecaru, C., Ioachim, A., Nedelcu, L., Dutu, A.
• Format: Article
• Language: English
• Subjects: Barium strontium titanate solid solutions; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Dielectric, piezoelectric, ferroelectric and antiferroelectric materials; Dielectrics, piezoelectrics, and ferroelectrics and their properties; Exact sciences and technology; Ferroelectric transitions; Niobates, titanates, tantalates, pzt ceramics, etc; Physics
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2006.06.011

Solid solutions Ba 1 − x Sr x TiO 3 (BST) are of high technological importance, particularly in microwave domain. Barium titanate has “naturally” three transitions, between four stable ferroelectric phases: (C) cubic, (T) tetragonal, (O) orthorhombic, (R) rhombohedral. Jaffe et al . [B. Jaffe, W.R. Cook, H. Jaffe, Piezoelectric Ceramics, Academic Press, 1971] has given the dependence of the transition temperatures up to 30% of Sr content. We have extrapolated these temperatures and we have found that some phases might disappear at higher Sr concentrations. A family of solid solutions with x = 25, 50, 75, 90% was prepared by standard solid-state reaction and sintered at 1230 and 1260 °C, respectively. The permitivities and the dielectric losses were measured with a self-acting bridge (1 kHz), on a large temperature range (±200 °C). The composition x = 25% shows three peak values of permittivity as expected, while the composition x = 50%, only two peak values, corresponding to phase transitions cubic–tetragonal–rhombohedral, phase orthorhombic being excluded. Compositions with x ≥ 63%, Sr shows only one peak value corresponding to a genuine transition cubic–rhombohedral. The cubic transition to several lower phases shows almost a linear decrease of the Curie point with the increase of Sr fraction. For Sr concentration x ≥ 80%, the Curie point appears to fall more rapidly than linear. To our best knowledge, there is for the first time, this effect is reported.