Piezoelectricity of lead-free (K, Na)NbO3 nanoscale single crystals

(K, Na)NbO3 (KNN) is a promising lead-free compound that is more suitable for piezoelectric applications requiring environmental or even biological compatibility than the traditional lead-based Pb(Zr, Ti)O-3 systems. In this work, we synthesized single crystalline KNN nanorods (NRs) with various K/Na ratios, which were used as ideal specimens for investigating the compositional dependence of piezoelectricity. Piezoresponse force microscopy (PFM) was utilized to characterize the three-dimensional (3-D) morphology and piezoelectric properties of single crystalline KNN NRs. A phase boundary was confirmed around a K/Na ratio of similar to 45/55 based on local switching behavior, whereby enhanced piezoresponse in KNN single crystals was obtained with specific domain structures. The methodology demonstrated in this work can also be applied for further fundamental studies on KNN as well as other lead-free piezoelectric materials.