Origin and Mechanism of Anisotropic Piezoelectric Generation on the ZnO(10(1)over-bar0) 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 (10 (1) over bar0) crystal plane. The piezoelectric and rectification effects are found in the [0001] polar direction on the (10 (1) over bar0) crystal facet. Neither effect was observed in the [1 (2) over bar 10] 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.

Automated summary

The experimental observation of pressure-induced structural changes in ZnO non-polar (10 (1) over bar0) crystal plane reveals the in-plane anisotropic piezoelectric behavior. Piezoelectric and rectification effects are observed in the [0001] polar direction, but not in the [1 (2) over bar 10] non-polar direction perpendicular to it. Pressure reduces or eliminates the piezoelectric and rectification properties in the [0001] direction. The origin of the piezoelectric effect is attributed to the spontaneous polarization in the [0001] direction. Additionally, pressure-induced structural changes in ZnO are observed for the first time.