Anomalous Effects of Lattice Strain and Ti3+ Interstitials on Room-Temperature Magnetic Ordering in Defect-Engineered Nano-TiO2

Defect engineering in n-type undoped metal oxides is a great challenge compared to the often-studied surface oxygen vacancies. The present investigation unravels new insights toward defect chemistry and defect engineering in anatase TiO2 nanoparticles. It is demonstrated that using the rapid cooling process, high concentration of Ti3+ interstitials, and lattice oxygen vacancies can be easily introduced in undoped metal oxides. The structural disorders in anatase TiO2 nanoparticles synthesized under two different argon-annealing processes have been comprehensively investigated using spectroscopy and electron microscopic analysis. Though excess of interstitial Ti3+ ions with one unpaired 3d electron in quenched TiO2 introduces local magnetic moments, they could be antiferromagnetically coupled via lattice Ti4+ ions, which limit the overall magnetic moment of the quenched materials. Lattice contraction was also found to enhance the ferromagnetic coupling between the defect complexes (Ti3+–F+ center) which he...