Lead-free KNbO 3 ferroelectric nanorod based flexible nanogenerators and capacitors

Abstract

In spite of high piezoelectricity, only a few one-dimensional ferroelectric nano-materials with perovskite structure have been used for piezoelectric nanogenerator applications. In this paper, we report high output electrical signals, i.e.an open-circuit voltage of 3.2V and a closed-circuit current of 67.5nA (current density 9.3nAcm 2) at 0.38% strain and 15.2%s 1 strain rate, using randomly aligned lead-free KNbO 3 ferroelectric nanorods (∼1μm length) with piezoelectric coefficient (d 33∼55pmV 1). A flexible piezoelectric nanogenerator is mainly composed of KNbO 3-poly(dimethylsiloxane) (PDMS) composite sandwiched by Au/Cr-coated polymer substrates. We deposit a thin poly(methyl methacrylate) (PMMA) layer between the KNbO 3-PDMS composite and the Au/Cr electrode to completely prevent dielectric breakdown during electrical poling and to significantly reduce leakage current during excessive straining. The flexible KNbO 3-PDMS composite device shows a nearly frequency-independent dielectric constant (∼3.2) and low dielectric loss (<0.006) for the frequency range of 10 2-10 5Hz. These results imply that short and randomly aligned ferroelectric nanorods can be used for a flexible high output nanogenerator as well as high-k capacitor applications by performing electrical poling and further optimizing the device structure. © 2012 IOP Publishing Ltd.