Speaker
Haraldur Gunnlaugsson
(Aarhus University)
Description
TiO2 has a wide range of applications. It is used as pigments in paints, sunscreen and food products, and as a photocatalyst, where doping by ion-implantation has been found useful to tailor the photocatalytic properties. TiO2 is used as a host for the upconversion process and in recent years there have been reports on dilute magnetism in this system, where the charge state of Fe is of importance.
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 on-line 57Fe emission Mössbauer spectroscopy following low concentrations (<10-3 at.%) implantation of 57Mn (T½ = 1.5 min.). Both Fe3+ and Fe2+ were detected in the entire 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 ~330 K 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.
iii) An annealing stage in the temperature range 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 and Fe3+ found in a paramagnetic state with slow spin-lattice relaxation which does not follow the expected T2 dependence expected for a Raman process.
Primary author
Haraldur Gunnlaugsson
(Aarhus University)
