Origin and Mechanism of Anisotropic Piezoelectric Generation on the ZnO(1010) Crystal Plane

The experimental observation of pressure-induced structural changes is crucial for establishing the correct piezoelectric mechanism. Here, we show the in-plane anisotropic piezoelectric generation behavior on a ZnO non-polar (101̅0) crystal plane. The piezoelectric and rectification effects are found in the [0001] polar direction on the (101̅0) crystal facet. Neither effect was observed in the [12̅10] non-polar direction perpendicular to the [0001] direction. The piezoelectric generation and rectification properties can be reduced and vanished under pressure in the [0001] direction. The spontaneous polarization in the [0001] direction is evidenced to be the origin of piezoelectric effect. Pressure-induced structural change of ZnO is observed for the first time. In the piezoelectric effect, the applied stress causes the polar structure of ZnO to change into a non-polar structure, and the piezoelectric current is generated. This novel piezoelectric model will overturn the existing piezoelectric theory and piezoelectric generation mechanism and contribute to comprehending the crystal orientation-dependent piezoelectric properties and the development of new high-performance piezoelectric materials and devices.