In-situ domain observation during electric field cycling

The following links show the real time videos of the domain pattern evolution during electric field cycling.

Sample: Mn-doped BaTiO3 single crystal

Electric field: frequency 0.2 Hz (time 5s), <100> direction

Microscope: Optical polarizing microscope in transmission mode

(a) Aged sample: reversible domain switching ↔E

(b) Unaged sample: irreversible domain switching ↔E

(Please wait for some time, then click “►” button in the above window frame to replay the video; if the response is too slow, please click right mouse to download reversible and irreversible videos to play it with Windows Media Player.)

Explanation on the videos:

Ferroelectric crystals exhibit a spontaneous polarizations Ps due to a symmetry-lowering transition at a critical temperature (Curie temperature Tc). Ps can align along one of the several symmetry-allowed orientations, and a region with the same Ps is called a domain. One domain state can be switched to another (180° reversal or non-180° rotation) by an external electric field. Such domain switching, especially the non-180° one, can generate a huge nonlinear electrostrain due to the exchange of different crystallographic axes. This nonlinear strain may be in theory tens of times larger than the linear (conversed) piezoelectric strain. Unfortunately, the domain-switching process is inherently irreversible due to the energetic equivalence of different domain states. Therefore, the large electrostrain caused by domain switching is only a one-time effect, and thus has no practical applications. If domain switching can be somehow made reversible, a large recoverable electrostrain would be expected.

Very recently, we proposed a symmetry-conforming principle of point defects to realize reversible domain switching in an aged ferroelectric crystal. For a ferroelectric crystal containing point defects, after aging at ferroelectric state, defect symmetry conforms to crystal symmetry and thus can provide an intrinsic restoring force for reversible domain switching [see Video (a)]; consequently a giant recoverable electrostrain can be achieved in aged sample. On the other hand, without aging, defect symmetry inherits symmetry of paraelectric phase and can not provide restoring force, thus an irreversible domain switching was observed [see Video (b)] and a corresponding butterfly-typed electrostrain was achieved in unaged sample.

See L. X. Zhang and X. Ren, Physical Review B, 71: 174108, 2005 for details.