Antiferroelectric phase transition in (Sr_1-xCa_x)TiO₃ (0.12<x≤0.40): I. Dielectric studies

Abstract

Results of a detailed dielectric study of phase transition in Sr_1-xCa_xTiO₃ in the composition range 0.18≤x≤0.40 are reported. It is shown that the temperatures T'_m and T"_m corresponding to the peaks in the real (ε'(T)) and imaginary (ε"(T)) parts of the dielectric constant, respectively, are not only coincident but also frequency independent, suggesting that these anomalies are due to a thermodynamic phase transition and not a dipole glass/relaxor ferroelectric transition. The Curie-Weiss temperature, as determined from the ε'(T) data above the transition temperature, is found to be negative. Using Landau theory considerations, the negative Curie-Weiss temperature is interpreted in terms of an antiferroelectric phase transition. It is proposed that the smearing of the ε'(T) data in the composition range 0.016≤x≤0.12 reported by Bednorz and Muller is due to the frustration introduced by the antiferroelectric interactions caused by Ca²⁺ substitution and the ferroelectric interactions of the SrTiO₃ matrix.