Coexistence of domain relaxation with ferroelectric phase transitions in BaTiO3

Abstract

Low-frequency dielectric relaxation in BaTiO3 (BTO) ceramics has been studied under the applied and dc-field cooled conditions in the frequency domain spanning from 5 mHz to 20 kHz in the temperature range of 85 K to 430 K. We observe the coexistence of broad as well as sharp maxima in the dielectric loss (tanδ) across each of the three phase transitions. The broad tanδ maxima were found to shift to higher temperatures at higher frequencies following Arrhenius behaviour with activation energies ranging from 0.18 eV to 0.23 eV. Each of the tan δ maxima slowly merged and finally vanished above the corresponding phase transitions. Both the permittivity and the tanδ loss were found to suppress and shift towards lower frequencies as a function of applied dc-field and dc-field cooled conditions. This has been attributed to the relaxation of the mesoscopic ferroelectric sub-domains/domain boundaries forming and rearranging differently across each phase transition in BTO. We also observe low-frequency relaxation above the Curie temperature. Arrhenius analysis owes its origin to the space-charge relaxation across the barrier layer formed between the electrode and the sample. The broad relaxation maxima in the tetragonal regime appear to be due to sub-domain polar-regions, which might appear due to the atomic-level mismatch of the accommodation strain appearing during tet-cubic martensitic phase transition. These regions further reform across the successive tet-ortho and ortho-rhombo phase transitions giving rise to corresponding relaxation maxima.