  While BiFeO3-based solid solutions show great promise for applications in
energy conversion and storage, realizing this promise necessitates
understanding the structure-property relationship in particular pertaining to
the relaxor-like characteristics often exhibited by solid solutions with
polar-to-non-polar morphotropic phase boundaries. To this end, we investigated
the role of the compositionally-driven relaxor state in (100-x)BiFeO3-xSrTiO3
[BFO-xSTO], via in situ synchrotron X-ray diffraction under bipolar
electric-field cycling. The electric-field induced changes to the crystal
structure, phase fraction and domain textures were monitored via the {111}pc,
{200}pc, and 1/2{311}pc Bragg peaks. The dynamics of the intensities and
positions of the (111) and (11-1) reflections reveal an initial non-ergodic
regime followed by long-range ferroelectric ordering after extended poling
cycles. The increased degree of random multi-site occupation in BFO-42STO
compared to BFO-35STO is correlated with an increase of the critical electric
field needed to induce the non-ergodic-to-ferroelectric transition, and a
decrease in the degree of domain reorientation. Although both compositions show
an irreversible transition to a long-range ferroelectric state, our results
suggest that the weaker ferroelectric response in BFO-42STO is related to an
increase in ergodicity. This, in turn, serves to guide the development of
BFO-based systems into promising platform for further property engineering
towards specific capacitor applications.
