57Fe emission Mossbauer spectroscopy following dilute implantation of 57Mn into In2O3

Emission Mossbauer spectroscopy has been utilised to characterize dilute Fe-57 impurities in In2O3 following implantation of Mn-57 (T-1/2 = 1.5 min.) at the ISOLDE facility at CERN. From stoichiometry considerations, one would expect Fe to adopt the valence state 3+, substituting In3+, however the spectra are dominated by spectral lines due to paramagnetic Fe2+. Using first principle calculations in the framework of density functional theory (DFT), the density of states of dilute Fe and the hyperfine parameters have been determined. The hybridization between the 3d-band of Fe and the 2p band of oxygen induces a spin-polarized hole on the O site close to the Fe site, which is found to be the cause of the Fe2+ state in In2O3. Comparison of experimental data to calculated hyperfine parameters suggests that Fe predominantly enters the 8b site rather than the 24d site of the cation site in the Bixbyite structure of In2O3. A gradual transition from an amorphous to a crystalline state is observed with increasing implantation/annealing temperature.