Synthesis of ferroelectric BaTiO3 tube-like arrays by hydrothermal conversion of a vertically aligned TiO2 nanotube carpet

In this study, the conversion of TiO 2 nanotubes (NTs) into barium titanate (BaTiO 3 ) exploiting a two-step low-temperature synthesis method is reported. Vertically oriented TiO 2 NT arrays were grown by ultra-fast anodic oxidation of titanium foils in ammonium fluoride-based electrolytic solution and then converted into BaTiO 3 exploiting a shape-preserving hydrothermal treatment. A parametric study was carried out taking into account the effect of alkalinity, temperature and reaction time on the converted materials. The crystalline phase and morphology of the nanostructured material were investigated by means of X-ray diffraction, scanning and transmission electron microscopy, evidencing the formation of ordered polycrystalline BaTiO 3 arrays. The tetragonal phase of the obtained material was revealed by Raman spectroscopy and its ferroelectric behavior was confirmed by domain switching observation during electrical characterization. The tube-like nanostructured arrays of BaTiO 3 could open the way for new applications of energy harvesting materials where easy and low temperature processing, controlled morphology and functional properties are required. The systematic study on the hydrothermal conversion of TiO 2 nanotubes obtained by anodic oxidation allowed the fabrication of ferroelectric BaTiO 3 tube-like arrays.