Domain Structure Evolution and Polarization Degradation of [101]‐Oriented 0.74 Pb ( Mg 1/3 Nb 2/3 ) O 3 ‐0.26 PbTiO 3 Single Crystal underCyclic Electric Loadings

The polarization degradation of ferroelectrics, reflected in the hysteresis loop as a decrease of remnant polarization, is a serious concern in applications. In situ observation of the polarization and domain structure evolution are carried out for [101]‐Oriented 0.74 Pb ( Mg 1/3 Nb 2/3 ) O 3 ‐0.26 PbTiO 3 ( PMN ‐26 PT ) single crystal under cyclic electric field. Measurements of the polarization hysteresis loops are conducted under a polarized light microscope ( PLM ), which is effective in detecting the domain structure of the single crystal. Prior to the polarization measurements, the crystal was poled. Upon cyclic electric field, reversal of monoclinic ( M B ) takes place, and the phase transition from M B to orthorhombic ( O ) phase occurs under positive field, but not under negative field of an electric cycle at a field magnitude up to 840 V/mm. The polarization loop is asymmetrical with the positive coercive field (+ E c ) much less than the negative one (− E c ). As the field cycles, micro‐cracking occurs preferably in [101] direction, and a sudden drop appears in the curves of polarization versus number of cycles. Upon electric cycling at a field magnitude of 840 V/mm, the negative polarization increases slightly with the cycle number, indicating the rotation of a M B phase toward the applied field direction.