BaTiO3 nanotube arrays by hydrothermal conversion of TiO2 nanotube carpets grown by anodic oxidation

The demand for well controlled synthesis routes for nanosized piezoelectric materials, as 1D nanostructures of ferroelectric perovskites, has significantly increased during the last decade. Several synthesis methods, as hydrothermal synthesis, sol-gel deposition in templating structures and electrospinning have been explored. A quite promising and interesting approach is the conversion of 1D nanostructured precursors. The present work proposes a thermal promoted conversion method of TiO2 nanotubes (NTs) to synthesize BaTiO3 NTs. Vertically oriented TiO2 NT arrays were prepared by anodic oxidation of a titanium foil into ammonium fluoride based electrolytic solution. Crystalline phase and morphology of the film were investigated, evidencing the formation of a highly ordered 1D NTs carpet with length ranging from few hundred nanometers up to several tens on micrometers. The conversion of TiO2 NTs is pursued by a new, simple approach based on the thermal promoted Barium infiltration of TiO2 nanotubes, exploring several solutions of different Ba salts. The heat treatment was set in order to promote Barium incorporation into the TiO2 structure, obtaining the conversion into BaTiO3. The morphology and crystal structures of the resulting BaTiO3 NTs were characterized by FESEM, XRD and Raman spectroscopy. The properties of the NTs obtained by this new approach is then compared to that of nanotubes prepared by a low temperature hydrothermal conversion approach, according to the method proposed by Yang and coworkers.