Synthesis, characterization and ferroelectric properties of lead-free K0.5Na0.5NbO3 nanotube arrays

Lead-free K0.5Na0.5NbO3 (KNN) nanotube arrays were synthesized by a sol-gel method with anodic aluminum oxide templates. The obtained KNN nanotubes exhibited a polycrystalline and monoclinic perovskite structure with diameters of ∼200 nm and wall thickness of ∼30–40 nm, respectively. The polarization-electric loop curve of the nanotubes array were examined showing the values of 2Pr and 2Ec at about 3.4 μC/cm2 and 13 kV/cm, respectively, under a maximum electric field of 12.5 kV/cm. The piezoelectric characteristics of individual KNN nanotube array was also identified through piezoresponse force microscopy.