Analysis on dipole polarization of BaTiO3-based ferroelectric ceramics by Raman spectroscopy

Abstract

Analysis of asymmetric Raman line shape disclosed the variation of phonon correlation length in A1(3TO) mode, LA1(3TO), with temperature in the ceramics of BaTiO3 (BT), Ba0.6Sr0.4TiO3 (BST-0.6) and BaZr0.25Ti0.75O3 (BZT-0.25), namely normal ferroelectrics, ferroelectrics with diffuse phase transition (DPT ferroelectrics) and relaxor ferroelectrics, respectively. In BT, LA1(3TO) exhibited steep increase at the Curie temperature (Tc) on cooling. This is attributed to the formation of the ferroelectric domains at the Tc. Both BST-0.6 and BZT-0.25 showed gradual increase in LA1(3TO) on cooling across the dielectric maximum temperature (Tm), indicating the continuous increase in the average size of the polar nanoregions (PNRs). Normal ferroelectrics can be distinguished from DPT and relaxor ferroelectrics in this point. LA1(3TO) of BZT-0.25 was longer than that of BST-0.6 near the Tm. This suggests the size of PNRs in BZT-0.25 is larger than that in BST-0.6. Huge dipole polarization of BZT-0.25, giving rise to the strong relaxor behavior, could be originated from the contribution of the large PNRs near the Tm. DPT ferroelectrics can be also differentiated from relaxor ferroelectrics in terms of the average size of PNRs.