Abstract
The piezoelectricity of potassium and sodium niobate 1-Dimensional nanostructurs was examined by scanning probe microscope (SPM). Metal oxides with different morphologies were obtained by refluxing micro-sized niobium oxide (Nb2O5) with alkali metal hydroxides, potassium hydroxide (KOH) or sodium hydroxide (NaOH), for several days. Firstly, ferroelectric potassium niobate (KNbO3 with 50~100 nm diameter and 0.2-3.0 µm length) and non-ferroelectric sodium niobate hydrate nanowires, sandia octahedral molecular sieves (SOMS), (Na2Nb2O6.H2O with 200~500 nm diameter and 5~10 µm length), were obtained. Then, orthorhombic sodium niobate nanowires were produced from wiry SOMS by annealing above 400 ºC. Piezoelectric characterization was performed by piezoresponse force microscopy (PFM), responding the local vibrations induced by an AC power or combine with DC power applied between the conductive SPM tip and the bottom electrode of the sample. Ferroelectric properties including domain distribution, local polarization and hysteresis phenomenon under nano-scale were studied in detail. The results show the spontaneous polarization of ferroelectricity KNbO3 nanowires, with maximum piezoelectric coefficient about 7.9 pmV; while NaNbO3 nanowires exhibited a local piezoelectric phenomenon, which was absent in its un-poled anti-ferroelectric bulk material. The domain distribution (dzz = 0.5~4.0 pmV) along the nanowire axis periodicity, as an electric field parallels to the axis direction was applied. According to transmission electron microscopy (TEM) and X-ray diffraction studies, wiry NaNbO3 was along the [100] axis. Additionally, wiry NaNbO3 obtained at lower anneal temperature possess more oxygen vacancy. The domain wall of wiry NaNbO3 changes under an applied voltage difficultly. To our knowledge, the present work is the first report of the preparation of NaNbO3 nanowires as well as the determination of piezoelectricity. Here we able to image domain in those nanowires with PFM, both lattice contribution and domain wall contribution to piezoelectric were observed. Lateral mode PFM revealed preferred polarization orientation and strong imprint in NaNbO3 nanowires.