The ultrahigh piezoelectricity of lead magnesium niobate-lead titanate (PMN-PT) single crystals is utilized for medical imaging and ultrasonic devices. It has been revealed that the domain structure is miniaturized down to the nanometer scale, indicating that the domain structure and its response to electric fields could play more roles. In this Letter, we report real-time direct observations of polarization reversals in PMN-PT with the use of in situ electrical biasing transmission electron microscopy. We find that a dominant behavior is a reversible response composed of the reorientation of nanoscale non-180° domain walls (DWs) and movement and/or elimination of microscale DWs. These results basically agree with some predictions made by adaptive phase theory (Jin et al.) which gives explanations of extrinsic contributions to the high piezoelectricity of this material.
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