Abstract :
Solid solutions Ba1 xSrxTiO3 (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 8C, respectively. The
permitivities and the dielectric losses were measured with a self-acting bridge (1 kHz), on a large temperature range ( 200 8C). 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.
