Phase transitions in Sr_(0.61)Ba_(0.39)Nb_2O_6:Ce~(3+): II. Linear birefringence studies of spontaneous and precursor polarization

摘要

The linear birefringence (LB) of Sr_(0.61 - x)Ba_(0.39)Nb_2O_6:Ce_x~(3+) (SBN61:Ce) has been measured as a function of temperature within the range of 78 ≤ T ≤ 850 K. 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 γ, ν and β 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 γ, ν and β 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 γ and ν of SBN61:Ce shift against those of the three-dimensional random-field Ising model.