On the entangled growth of NaTaO₃ cubes and Na ₂Ti₃O₇ wires in sodium hydroxide solution

The entangled growth of sodium titanate Na₂Ti₃O ₇ nanowires and sodium tantalate NaTaO₃ cubes was investigated with electron microscopy, X-ray diffraction, and UV diffuse reflectance spectroscopy. Depending on the composition of the Ta ₂O₅- and TiO₂-particle-based powder mixtures, which served as educts, we observed different types of hybridization effects. These include the titanium-induced contraction of the NaTaO₃ perovskite-type unit cell and the generation of electronic defect states in NaTaO₃ that give rise to optical subbandgap transitions and tantalum-induced limitations of the Na₂Ti₃O₇ nanowire growth. The transformation from Ta₂O₅ to NaTaO₃ occurs through a dissolution-recrystallization process. A systematic analysis of the impact of different titanium sources on NaTaO ₃ dispersion and, thus, on the properties of the entangled nanostructures revealed that a perfect intermixture of cubes and nanowires can only be achieved when titanate nanosheets emerge during transformation as reaction intermediates and shield nucleation and growth of isolated NaTaO ₃ cubes. The here demonstrated approach can be highly instrumental for understanding the nucleation and growth of composite and entangled nanostructures in solution and - at the same time - provides an interesting new class of photoactive composite materials.