The effects of MnO2 doping on the microstructure and phase transition of ferroelectric CaBi4Ti4O15 (CBT) ceramics with x mol % of MnO2 (CBT-xM; x = 0;1;3) have been studied. The single-phase crystal structure and the plate-like grain morphology are clearly observed for all compositions, while extended grains are observed with x = 3. The dielectric permittivity and dielectric loss show that the Mn 2+ and Mn3+ ions are preferentially incorporated into the A- and B-sites, respectively, up to a limiting extent of approximately x = 2. The ac conductivity decreases and the activation energy increases with increasing Mn content owing to the decrease in the number of conducting carriers and increase in covalence, respectively. The Curie temperature TC is independent of MnO2 doping within the experimental accuracy, and the dielectric constant satisfies the Curie-Weiss law above TC. The temperature dependence of the soft mode with x = 0 and 1 shows a significant softening towards T1 ∼ TC + 113°C (at T 1, the square of the soft mode frequency ω2 s → 0). ω22 is approximately proportional to T - T1. These findings indicate that the displacive nature of the phase transition is not affected by MnO2 doping, at least below x = 3.
ASJC Scopus subject areas
- Physics and Astronomy(all)