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 BaTiO
₃
-based ferroelectrics. Ceramics of BaTiO
₃
(BT), Ba
_0.6
Sr
_0.4
TiO
₃
(BST-0.6), and BaZr
_0.25
Ti
_0.75
O
₃
(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.