Dielectric properties of 0.4Na0.5Bi0.5TiO3-(0.6-x)SrTiO3-xPbTiO3 solid solutions

In this paper we present our measurements of the linear and nonlinear dielectric permittivity of 0.4Na0.5Bi0.5TiO3-(0.6-x)SrTiO3-xPbTiO3 solid solutions (x = 0, 0.05, 0.1, 0.15). The dielectric anomaly increases in the system with respect to the concentration of lead, showing that interactions between dipolar entities are modified. The system exhibits dipolar-glass-like behaviour at low values of x (0⩽x<0.1). Relaxor behaviour emerges in the sample where x=0.1. Furthermore, a spontaneous first-order phase transition from relaxor to normal ferroelectric is observed at x⩾0.15. A few peculiar dispersion regions are observed in the ferroelectric phase, which we attribute to the coexistence of ferroelectric and dipolar glass phases. On the other hand, the nonlinear dielectric response indicates the existence of compressible polar nanoregions as common elementary dipolar entities in both relaxor and glass-like states. Dielectric spectra were approximated with empirical Cole-Cole or Havriliak-Negami equations. It is shown that the temperature dependencies of mean relaxation times, which were obtained from dielectric spectra, follow the Vogel-Fulcher equation in all samples. Moreover, distributions of relaxation times are obtained and a phase diagram is presented.