Observation of a time-dependent structural phase transition in potassium sodium bismuth titanate

Abstract

High-energy synchrotron diffraction has been employed to demonstrate a time-dependent structural phase transition in 0.2K1/2Bi1/2TiO3–0.8Na1/2Bi1/2TiO3. It is demonstrated that the rapid increase in electric field (≥0.25 kV mm−1 s−1) induces a transformation from rhombohedral to mixed phase rhombohedral and tetragonal symmetry. When the electric field is applied slowly (<0.25 kV mm−1 s−1), no transformation occurs, and rhombohedral symmetry is maintained. The extent of transformation increases with the rate of increase in electric field. High-speed capture of diffraction images (7 frames per second) has been used to show the evolution of the phase transformation as a function of time.

Strain Mechanisms in Lead-Free Ferroelectrics for Actuators

“…The origin of the large electromechanical response of incipient piezoelectrics is generally attributed to an electric field induced phase transition. [140][141][142][143][144][145][146][147] Figure 2.14 at point displays an ergodic relaxor state, as previously discussed. For BNT-based lead-free incipient piezoelectrics, it was demonstrated that the electric field induced phase transition coincides with the inflection point of the strain output 148 and the transformation is followed by switching of the newly created domains.…”

“…Discrepancies are inherent to the change in probing frequencies of the different characterization techniques employed. 143,144 It is noted that the removal of the electric field leads to a decay of 65 % in the polarization of BNT-0.25ST, indicating that although in BNT-0.25ST is higher than in BNT-0.28ST, it still has considerably lower values than its . Domain switching is a time-dependent kinetic process 73,[441][442][443] , while a first order phase transition is an infinitely fast discontinuous process occurring in the terahertz range.…”

“…Coherent switching following the electric field induced phase was previously demonstrated in BNT-based materials. 143,144 The non-zero, but considerably lower and values observed after 20 s of the removal of the electric field, can be attributed to certain irreversibility in the transformation of the core and presumably also in the shells adjacent to cores. Since negligible changes in are observed for the applied electric fields higher than 2 kV/mm, the values displayed in the inset of Figure 5.46 (a) seem to be related to a gradual increase of the electric field induced ferroelectric state at expense of the non-ergodic relaxor states near cores and/or to polarization induced due to enhanced intrinsic and extrinsic switching contributions.…”

“…For BNT-based lead-free incipient piezoelectrics, it was demonstrated that the electric field induced phase transition coincides with the inflection point of the strain output 148 and the transformation is followed by switching of the newly created domains. 143,144 Note that the inflection point of the strain curve also coincides with increased polarization. 148 Both processes lead to maximized 33 values (i.e., 33 ) and a maximized 33 3 = − .…”

“…This is justified considering that the small and large signal measurements indicate time-dependent switching processes that follow the phase transition rather than the phase transition that seems to be probed during the pulse experiments. 143,144 This entails the cycle-and electric field-dependent , , , and values observed in Section 5.2.4.3. Note that pulse experiments lead to a much lower switching as indicated by a decay of values that are 10 % of , in contrast to the studies performed on the Hz range that indicated a decay of values that are 35 % of .…”