Origin and Mechanism of Piezoelectric and Photovoltaic Effects in (111) Polar Orientated NiO Films

Based on the current piezoelectric theory, NiO with the centrosymmetric structure is not piezoelectric. However, herein, this study shows the first observation of piezoelectric generation, rectifyingand bulk photovoltaic behaviors in NiO films with [111] orientation and the change in NiO crystal structure in piezoelectric process. The piezoelectric generation, rectifying, and bulk photovoltaic performances are enhanced by increasing (111) orientation, and attenuated and eliminated by applying a persistent stress on the NiO film. The NiO [111] is polar direction, and thus a spontaneous electric field (ES) is in the NiO film with [111] orientation. The existence of Es in (111) oriented NiO film is found to be the physical basis of the piezoelectric generators and photovoltaic and rectifying effects. Thus, NiO piezoelectric, rectifying, and bulk photovoltaic mechanism are presented at the atomic level. The mechanism may rewrite the current piezoelectric theory, and establish a unified theory of polar structure with wide implications. The polar-orientated films can be used to fabricate piezoelectric generators and other optoelectronic devices with high performances. Based on the existing piezoelectric theory, NiO with the centrosymmetric structure is not piezoelectric. However, herein, this study shows the observation of piezoelectric, rectifying and photovoltaic effects in (111)-oriented NiO films. These effects are attested to originate from the electric field produced by spontaneous polarization in the (111)-oriented NiO film. The polar structure piezoelectric and photovoltaic mechanism is thus presented.image

Automated summary

This study observes the piezoelectric, rectifying, and photovoltaic effects in (111)-oriented NiO films, which are found to originate from the electric field produced by spontaneous polarization. This finding may have significant implications for the current piezoelectric theory and establish a unified theory of polar structures. Additionally, this study provides possibilities for fabricating high-performance piezoelectric generators and optoelectronic devices.