Analysis of polarization behavior in relaxation of BaTiO3-based ferroelectrics using wideband dielectric spectroscopy

Wideband dielectric spectra from the kilohertz to terahertz range are discussed for BaTiO₃-based ferroelectrics. Ceramics of BaTiO₃ (BT), Ba_0.6Sr_0.4TiO₃ (BST-0.6), and BaZr_0.25Ti_0.75O₃ (BZT-0.25) were selected as normal ferroelectrics, ferroelectrics with diffuse phase transition (DPT ferroelectrics), and relaxor ferroelectrics, respectively. The variation of ionic polarization in both BT and BST-0.6 ceramics with temperature could be explained by the softening of the soft phonon mode. In BZT-0.25, a permittivity anomaly at the dielectric maximum temperature (T_m) at low frequencies is not attributed to the softening of the soft phonon mode, but originates from the permittivity derived from the dipole polarization (ε_dipole). Relaxor behavior in BZT-0.25 is derived from the increase in the depression of ε_dipole on cooling across the T_m with increasing frequency. In dipole polarization, BT, BST- 0.6, and BZT-0.25 all exhibited a similar tendency of ε_dipole above the Curie temperature (T_c) and T_m. However, behavior of ε_dipole below the T_c can be explained by the ferroelectric domains in BT, whereas the variation of ε_dipole below the Tm could be explained by growth process of polar nanoregions (PNRs) in BST-0.6 and BZT-0.25. Regarding this, BT can be distinguished from BST-0.6 and BZT-0.25. Relaxation in BT could be interpreted as successive change in polarization mechanism from normal ferroelectrics to relaxor ferroelectrics via DPT ferroelectrics.