Phase transitions in Sr _0.61 Ba _0.39 Nb ₂ O ₆ :Ce ³⁺: II. Linear birefringence studies of spontaneous and precursor polarization

Abstract:

The linear birefringence (LB) of Sr _0.61-x Ba _0.39 Nb ₂ O ₆ :Ce ³⁺ x (SBN61:Ce) has been measured as a function of temperature within the range of. Large tails have been observed above the ferroelectric phase transition temperatures T _c = 350, 328, 320 and 291 K for the concentrations x = 0, 0.0066, 0.0113 and 0.0207, respectively. Within an Ornstein-Zernike analysis the critical exponents and are determined. It suggests that pure SBN61 belongs to the 3D Ising universality class. Doping with Ce ³⁺ ions, which seem to act as random fields, enhances the relaxor properties. The critical exponents and of SBN61:Ce shift against those of the three-dimensional random-field Ising model.