Lattice dynamics and dielectric spectroscopy of BZT and NBT lead-free perovskite relaxors – comparison with lead-based relaxors

Abstract

Appearance of the polar nanoregions (PNR) and their manifestation in the dielectric spectra is discussed for lead-free Ba(Zr_xTi_1−x)O₃ (BZT-x) and (Na_1/2Bi_1/2)TiO₃ (NBT) ceramics. Phonon softening is not as pronounced as in the lead-based relaxors, but the relaxation contribution is dominating in all cases, caused by the dynamics of the off-centred ions (Ti⁴⁺, Bi³⁺, Pb²⁺). In the lead-based relaxors, where there is no relation between the quenched chemical clusters at the B-sites and PNR, which concern the A-site Pb-ion correlations, the relaxation dynamics follows the Vogel–Fulcher behaviour with a clear freezing. However, in BZT and NBT, the PNR are smaller, since they are localised within the small quenched chemical clusters of BaTiO₃ and BiTiO₃, respectively. Their dynamics is Arrhenius-like, which indicates hopping of the off-centred Ti⁴⁺ and Bi³⁺ ions, respectively, without their complete freezing. BZT can be classified as a dipolar glass and NBT as a nanoscopic ferroelectric with peculiar Bi-ion dynamics.

Keywords:

• relaxor ferroelectrics
• polar phonons
• polar nanoregions
• dielectric spectroscopy
• off-centred ions

Additional information

Funding

This work was supported by the Czech Science Foundation [grant number 13-15110S].