Two different methods, the conventional direct oxide synthesized method and the two-step indirect synthesized (IS) method, were employed to synthesize the 0.75Pb(Fe2/3W1/3)O3-0.25PbTiO3 ceramics. The low-field dielectric responses were investigated using the empirical law and the Curie-Weiss law. The temperature-dependent local ordering parameters were derived from the experimental results using the spin-glass model and the modified-Landau theory separately. According to the experimental data and the fitting results, it is concluded that the temperature-dependent local order parameters are changed from a short-range-ordered relaxor to a long-range-ordered ferroelectric state using the IS method. On the basis of the physical concepts of the spin-glass model, the modified-Landau theory and the ordering models, it is suggested that local polarizations are affected not only by degree of ordering but also by space charge polarization. In contrast, the glassy behavior of local polarization is affected only by degree of ordering but has nothing to do with space charge polarization. It is because local fields induced by space charge polarization have the same effect on local polarizations and are neutralized when calculating the correlation between neighboring polar microregions. On the other hand, the freezing process of local polarizations is affected by both degree of ordering and space charge polarization because local polarization affected by local fields cannot be neutralized when calculating the individual behavior of local polarization.
Relation:
Journal of Applied Physics, Vol.109 no.3, pp.034106 J. Appl. Phys.
