Aged sample: reversible domain switching

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Explanation on the domain switching behavior:

The left figure shows a series of domain micrographs and its correspondence to the measured P-E hysteresis loop for aged Mn-BaTiO3 samples. Beside each micrograph, the corresponding defect symmetry (small rectangle) state, Ps (thick arrow) and PD states (thin arrow) are also illustrated.

For an aged multi-domain sample, defect symmetry follows the tetragonal crystal symmetry, and averaged defect polarization PD aligns along the direction of PS within each domain according to defect symmetry principle. Before electric field is applied, the averaged polarization equals to zero, corresponding to point A in the P-E hysteresis loop curve. When electric field is applied, PS is switched to the direction of electric field and domain switching occurs. This contributes to an increase of polarization. When the field reaches maximum, an nearly single domain configuration is observed. Consequently, polarization increases to maximum (point B in P-E curve). However, defect symmetry and PD cannot be rotated in such a diffusionless domain-switching process. This unswitched defect symmetry and associated PD consequently provide a restoring force favoring a reversible domain switching. Thus after removing the electric field, single domain configuration reverses to the original multi-domain pattern so that defect symmetry follows crystal symmetry in every domain. As the result of restoration of original multi-domain state, the averaged macroscopic polarization becomes zero (point C in P-E curve). The same is true for reverse electric field (see C-D-E cycle). Thus, we observed an interesting reversible domain switching process during electric field cycling in aged sample. It corresponds well to the peculiar double hysteresis loop.