Phase transformations and crystallization kinetics in electrospun TiO2 nanofibers in air and argon atmospheres

The effects of atmospheric air and argon environments on thermal-induced phase transformations in electrospun TiO2 nanofibers have been investigated in situ using synchrotron radiation diffraction. Diffraction results showed that the as-synthesized TiO2 nanofibers were initially amorphous, but crystallized to form anatase and rutile after thermal annealing in air or argon at elevated temperatures. The crystallization temperature of anatase was delayed by 100 °C in argon relative to in air, and the transformation of anatase into rutile occurs faster in argon atmosphere than in air due to the formation of oxygen vacancies. Non-linear strains formed in both polymorphs and the substantial elevation of rutile thermal expansion pointed to strain anisotropy in the rutile phase and the concomitant fibre breakage.