Synthesis of Rutile-Phase Sn_xTi_1–xO₂ Solid-Solution and (SnO₂)_x/(TiO₂)_1–x Core/Shell Nanoparticles with Tunable Lattice Constants and Controlled Morphologies

We report the solvothermal synthesis of Sn x Ti 1– x O 2 solid-solution and (SnO 2 ) x /(TiO 2 ) 1– x core/shell nanoparticles with tunable lattice parameters and morphologies over the range of 0 ≤ x ≤ 1. The products are characterized by transmission electron microscopy, powder X-ray diffraction, and solid-state nuclear magnetic resonance spectroscopy. Rutile-phase particles with solid-solution or core/shell architectures are synthesized by combining titanium isopropoxide [Ti(O- i -Pr) 4 ] with Sn-containing precursors (SnCl 4 or SnO 2 nanoparticles, respectively) to favor rutile crystal growth over the typically observed anatase-phase TiO 2 . The transition from the anatase to the rutile TiO 2 phase is associated with increasing concentration of the Sn precursor. In the first case, we propose that the mixing of molecular Ti(O- i -Pr) 4 and SnCl 4 precursors leads to the formation of a Sn x Ti 1– x O 2 solid solution which preferentially crystallizes in the rutile phase due to thermodynamics. In the second case, we propose that the rutile SnO 2 nanoparticles act as nucleation sites for the heteroepitaxial growth of rutile TiO 2, lowering the energy barrier for particle growth and generating (SnO 2 ) x /(TiO 2 ) 1– x core/shell particles. The particle morphology and polydispersity are also altered systematically by varying the Ti/Sn ratio of the reactants, with particle elongation normal to the [110] direction observed for higher Sn concentrations. In the absence of Ti precursor, SnO 2 nanowires with diameters <5 nm are formed from SnCl 4 under the reaction conditions.