Y-doped ZnO nanosheets: Gigantic piezoelectric response for an ultra-sensitive flexible piezoelectric nanogenerator

Abstract

Zinc oxide nanoparticles (NPs) with two different morphologies namely one-dimensional (1D) pure ‘pencil-like’ ZnO nanorods (NRs) and two-dimensional (2D) yttrium(Y)-doped ZnO nanosheets (NSs) were synthesized by wet chemical co-precipitation method. The morphological features and crystalline phase of as grown pure and Y-doped ZnO NPs were studied by scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) techniques. A possible growth mechanism was proposed to understand the drastic change observed in the morphology of ZnO NPs from 1D NRs to 2D NSs as a result of Y3+ doping. The charge compensation of dopant YO2- anions at the Zn2+ terminated polar surface of ZnO played a crucial role in the formation of 2D NSs network. A gigantic piezoelectric coefficient (d33 ~ 420 pm/V) was achieved for Y-ZnO NSs, which is largely enhanced as compared to pure ZnO (d33 ~ 12.4 pm/V). The dependence of piezoelectric coefficient (d33) of ZnO on ionicchargecrystalradius ratio of dopant ion is reported. Finally, both pure and Y-doped ZnO nanocrystals have been used as the building blocks for fabricating flexible piezoelectric nanogenerators (NGs). The Y-doped ZnO based NG showed an ultra-sensitive characteristics by generating an output voltage around 20 V under gentle finger tapping (~0.01 kgf) and thus can be used in near future for powering various self-powered devices.