Mössbauer spectroscopy of 57Fe in ?-Al2O3 following implantation of 57Mn*

The valence state and annealing reactions of Mn/Fe in single crystalline ?-Al2O3 have been determined following low fluence (<1012 cm - 2) 60 keV implantations of 57Mn + (T1/2 = 1.5 min) and emission Mössbauer spectroscopy on the 57m Fe daughter nuclei in the temperature range from 110-700 K. At 110 K, most probe atoms are found in the Fe2 + state in amorphous surroundings due to the implantation damage. A fraction of the Fe is found in cubic environment, possibly nano-precipitates of ?-Al2O3. This site is found to disappear from the spectra above 500 K. Annealing of the damage sites at increasing temperatures leads first to increased incorporation of the probe atoms as Fe3 + on Al sites, and, above room temperature, also as Fe4 + . The Fe3 + sub-spectrum is masked by slow paramagnetic relaxations following a T2 dependence, as expected for a two-phonon Raman process. Our data is consistent with data from 57Co and 57Fe implantations, suggesting a general increase in the average Fe valence state with lower implantation dose and negligible annealing reactions at room temperature.