Nature of electric field driven ferroelectric phase transition in lead-free Na_1/2Bi_1/2TiO₃: In-situ temperature dependent ferroelectric hysteresis and Raman scattering studies

Abstract

Electric field driven in-situ high-temperature polarization (P) vs. electric field (E) and switching current (I) vs. E measurements performed on Na_0.5Bi_0.5TiO₃ (NBT) ceramics gave a direct evidence for the exact nature of polar ordering and witnessed a new ferroelectric phase transition sequence viz. R.T→FE180°C→FE+FE2200°C→ ≥200°C FE+AFE. In-situ high-temperature Raman scattering studies performed on poled NBT revealed the local structural origins of the aforementioned electric field driven Ferroelectric (FE) phase transition sequence. The origin of observed two ferroelectric phase co-existence in a narrow temperature range between 180°C–200°C is due to the local structural distortion in the Ti-O bond coupled through TiO₆ octahedral tilt transition. The observed antiferroelectric (AFE) phase coexistence above 200°C is strongly driven by the A-O phonon vibrations as a consequence of a change in A-site symmetry i.e. antiparallel A-site cation displacements.