Enhancement of thermal stability of TiO2 nanowires embedded in anodic aluminum oxide template

Titania (TiO2) nanowires with diameters of 20, 50, and 80 nm were successfully synthesized via the template-assistant method. The TiO2 nanowires embedded in anodic aluminum oxide template have extremely high crystallization and anatase-to-rutile phase transition temperatures than that of the free-state TiO2 powders, and the thermal stability of embedded TiO2 nanowires depends on the diameter of the templates. The growth and nucleation activation energy of rutile in 20 nm nanowires are determined to be E-g = 2.8 +/- 0.2 eV and E-n = 2.7 +/- 0.2 eV, respectively, much higher than that of the free-state TiO2 powders with E-g = 1.6 +/- 0.2 eV and E-n = 1.9 +/- 0.2 eV. The pressure induced by the difference of thermal expansion coefficient between the TiO2 and aluminum oxide acts as an effective barrier that prevents phase transition, resulting in the enhancement of the TiO2 structural stability.