Lead-free KNbO3 ferroelectric nanorod based flexible nanogenerators and capacitors

• Published in: Nanotechnology Vol. 23; no. 37; p. 375401
• Main Authors: Jung, Jong Hoon, Chen, Chih-Yen, Yun, Byung Kil, Lee, Nuri, Zhou, Yusheng, Jo, William, Chou, Li-Jen, Wang, Zhong Lin
• Format: Journal Article
• Language: English
• Published: England IOP Publishing 21.09.2012
• ISSN: 0957-4484; 1361-6528
• DOI: 10.1088/0957-4484/23/37/375401

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 3.2 V and a closed-circuit current of 67.5 nA (current density 9.3 nA cm−2) at 0.38% strain and 15.2% s−1 strain rate, using randomly aligned lead-free KNbO3 ferroelectric nanorods (∼1 μm length) with piezoelectric coefficient (d33 ∼ 55 pm V −1). A flexible piezoelectric nanogenerator is mainly composed of KNbO3-poly(dimethylsiloxane) (PDMS) composite sandwiched by Au/Cr-coated polymer substrates. We deposit a thin poly(methyl methacrylate) (PMMA) layer between the KNbO3-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 KNbO3-PDMS composite device shows a nearly frequency-independent dielectric constant (∼3.2) and low dielectric loss (<0.006) for the frequency range of 102-105 Hz. 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.