Potassium titanate nanowires: Structure, growth, and optical properties

A simple one step hydrothermal reaction among ${\mathrm{TiO}}_2$ nanoparticles and KOH solution was found to result in potassium titanate nanowires. The diameters of these nanowires are about 10 nm and the lengths range from 500 nm to $2\mu \mathrm{m}.$ The nanowires were analyzed by a range of methods including powder x-ray diffraction (XRD), high resolution electron microscopy (HREM), selected area electron diffraction, electron energy loss spectroscopy, XRD and HREM image simulations. The structure of the nanowires is determined to be of the type of ${\mathrm{K}}_2{\mathrm{Ti}}_6{\mathrm{O}}_{13}.$ Based on HREM observations of the growth process of the nanowires, we propose that the growth of the namowire was initiated by the formation of the ${\mathrm{K}}_2{\mathrm{Ti}}_6{\mathrm{O}}_{13}$ nuclei inside the anatase matrix following the crystallographic relation ${\mathrm{}\left(200\right)\mathrm{}}_{\mathrm{nanowire}}{//\left(101\right)\mathrm{}}_{\mathrm{anatase}}.$ These nuclei subsequently grew to form one-dimensional nanowires via preferential growth along the [010] direction. Absorption experiments show that the potassium titanate nanowires are wide-band semiconductors with a band width $E_g\sim 3.45\mathrm{eV}.$