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(0.6)Sr(0.4)TiO₃ (BST-0.6), and BaZr(0.25)Ti(0.75)O₃ (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.