Temperature-resolved synchrotron X-ray diffraction of nanocrystalline titania in solvent: the effect of Cr-Sb and V-Sb doping

Nanocrystalline titania pigments were produced by high temperature-forced hydrolysis in a coordinating high-boiling solvent (and water for reference). The effect of synthesis conditions and codoping with Cr-Sb and V-Sb on particle size and anatase-to-rutile transformation (A -> R) was studied by temperature-resolved synchrotron X-ray diffraction. The experiments were performed directly on low concentration (3.5 vol.%) as-synthesized suspensions of titania nanoparticles (up to 230°C) and on the corresponding dried powders (up to 950°C). Crystallite size of as-synthesized nano-anatase is around 20 nm (glycol) or 70 nm (water); it exhibits a slow growth rate up to the onset temperature of the A -> R. Phase composition and crystallite size are drastically influenced by both synthesis conditions and doping. Synthesis in water resulted in the simultaneous occurrence of anatase and brookite; transformation into rutile begins early but with a slower rate with respect to glycol-based samples. Doping affected the A -> R, whose onset temperature in undoped titania (700°C) was lowered to 650°C (V-Sb) or prevented up to 950°C (Cr-Sb). Both (V-Sb) and (Cr-Sb) dopings reduced the volume thermal expansion rate of anatase