Structural phase stability and electric field induced relaxor–ferroelectric phase transition in (1 − x)(Bi0.5Na0.5)TiO3–xBaTiO3 ceramics

• The well-known MPB compositions of [(1 − x)(Bi0.5Na0.5)TiO3–xBaTiO3] (x = 0.06, 0.07 and 0.075) show a transition sequence of rhombohedral + tetragonal − tetragonal − cubic phases as a function of temperature. Functionally important two-phase coexists from room temperature to 200 °C.
• The frequency-dispersion anomaly at lower temperatures indicates a progressive transition from ferroelectric to relaxor state upon heating. Therefore, phase coexistence plays a vital role in relaxor ferroelectric behavior among BNT–BT compositions.
• The non-ergodic relaxor phase can be transformed into ferroelectric phase by dc poling field.

Structure, phase transition, and dielectric relaxor behavior have been investigated in morphotropic phase boundary compositions of (1 − x)(Bi0.5Na0.5)TiO3-xBaTiO3 ceramics for x = 0.06, 0.07, and 0.075. In-situ structural thermal stability has been analyzed by using high-resolution synchrotron X-ray diffraction as a function of temperature. A transition sequence of rhombohedral + tetragonal − tetragonal − cubic phases is observed upon heating. The “rhombohedral + tetragonal” indicates a coexistence of rhombohedral R3c and tetragonal P4bm phases. The two-phase coexistence extends from room temperature to 200 °C. Zero-field dielectric permittivity reveals a frequency dispersion at low temperature region (T < Tm) and polar nanoregions below Burns temperature (TB). The two-phase coexistence plays a vital role for frequency dispersion below Tm. Dielectric spectra of pre-poled samples reveal a field-induced ferroelectric−relaxor phase transition at depolarization temperature Td.