Orientation-dependent piezoresponse and high-performance energy harvesting of lead-free (K,Na)NbO3 nanorod arrays

Abstract

Rapid development of modern electronics promotes the research of high-efficiency self-powered devices and systems. Lead-free perovskite potassium sodium niobate (KNN) with high piezoelectric constant and biocompatibility are regarded as one of the most promising materials for building high-performance nanogenerators. In this work, well-aligned KNN nanorod arrays with [110]-orientation were directly grown on SrTiO₃ substrates by a one-step hydrothermal method. The growth of the KNN nanorods could be attributed to the orientation of an initial KNN layer and the release of the compressive stress induced by the SrTiO₃ substrate. The piezoelectric constant d₃₃ along the [110] orientation of nanorods is ∼140 pm V⁻¹, which is 2.5 times higher than the d₃₃ measured along the [001]-orientation. Those results agree with the first-principles calculation results, where the spontaneous polarization of the orthorhombic KNN lattice is confirmed to be [110]-oriented. Furthermore, the KNN nanorod arrays exhibit an outstanding energy harvesting performance with the impulsive output voltage of 10 V. A laterally-integrated nanogenerator could also be fabricated by making the KNN nanorods laterally aligned in a PDMS layer. This device shows comparative energy harvesting performance to the nanorod arrays, and exhibits much higher flexibility which allows them to be applied in diversified conditions.