Defect annealing in Mn/Fe-implanted TiO2(rutile)

A study of the annealing processes and charge state of dilute Fe in rutile TiO2 single crystals was performed in the temperature range 143-662 K, utilizing online 57Fe emission Mossbauer spectroscopy following low concentrations (< 10(-3) at\%) implantation of 57Mn (T-1/2 = 1.5 min). Both Fe3+ and Fe2+ were detected throughout the temperature range. Three annealing stages were distinguished: (i) a broad annealing stage below room temperature leading to an increased Fe3+ fraction; (ii) a sharp annealing stage at similar to 330K characterized by conversion of Fe3+ to Fe2+ and changes in the hyperfine parameters of Fe2+, attributed to the annealing of Ti vacancies in the vicinity of the probe atoms; and (iii) an annealing stage in the temperature range from 550 to 600 K, where all Fe ions are transformed to Fe3+, attributed to the annealing of the nearby O vacancies. The dissociation energy of MnTi-VO pairs was estimated to be 1.60(15) eV. Fe2+ is found in an environment where it can probe the lattice structure through the nuclear quadrupole interaction evidencing the extreme radiation hardness of rutile TiO2. Fe3+ is found in a paramagnetic state with slow spin-lattice relaxation which follows a similar to T-n temperature dependence with 4.1 < n < 6.3 atT > 350 K.