Lanthanide ion dopant effect on the phase transformation in ultrasonic assistant sol-gel derived titania nanostructures

In this work, TiO₂ nanoparticles doped with holmium (III) ion have been prepared by an ultrasonic assistant sol-gel method. We present the results of the investigation of holmium (III) ion doping on the structural properties of TiO₂ and its effect on the anatase to rutile phase transformation. It is found that the transformation temperature, measured from the XRD experiments, is found to increase with doping. The anatase lattice is shown to deform predominantly along the c-axis to accommodate substitutionally-incorporated holmium (III) ion. In order to understand the location of the dopant in TiO₂ lattice, photoacoustic (PA) absorptions of f-f transitions of the samples are studied. The results show that the holmium (III) ions incorporate interstitially as well as substitutionally. This retards the anatase-to-rutile transformation temperature.