Paramagnetic behavior of Co doped TiO2 nanocrystals controlled by self-purification mechanism.

Doping in nanocrystals is a challenging process because of the self- purification mechanism which tends to segregate out the dopants resulting in a greater dopant concentration near the surface than at the interior of nanocrystals. In the present work nanocrystals of TiO 2 doped with different atom % of Co were synthesized by peroxide gel method. XRD analysis confirmed the tetragonal anatase structure and HRTEM images showed the rod-like morphology of the samples. Raman modes of anatase phase of TiO 2 along with weak intensity peaks of Co 3 O 4 for higher Co dopant concentrations were observed for the samples. EPR measurements revealed the presence of cobalt in +2 oxidation state in the TiO 2 matrix. SQUID measurements indicated paramagnetic behavior of the Co doped TiO 2 nanocrystals. The paramagnetic behavior is attributed to an increased concentration of Co 2+ ions and an increased presence of Co 3 O 4 phase near the surface of the TiO 2 nanocrystals due to self-purification mechanism. [ABSTRACT FROM AUTHOR]