Mössbauer spectroscopy under high pressures and temperatures

Sammanfattning: Iron plays a very important role in Earth materials. 57Fe- Mössbauer spectroscopy provides valuable information on the oxidation state and the near surrounding of iron atoms in crystal structures. This dissertation combines Mössbauer spectroscopy with heated diamond anvil cell techniques which allows in situ high pressure and temperature studies of iron-containing materials under rock-forming conditions.Experiments on metallic iron (Fe) and olivine ((Mg, Fe)2SiO4) of different compositions have been performed with the aim to improve experimental techniques and to optimise measuring conditions. All samples were of synthetic origin and enriched in 57Fe to various degrees in order to enhance the signal to noise ratios. Experiments on iron were carried out at 573 K and pressures up to 12 GPa. The α - ε transition was observed at P > 10 GPa.Mg-Fe olivines of the composition 40, 50, 65 and 100 mole-% fayalite have been investigated at temperatures up to 673 K and pressures to 12 GPa and the change of the 57Fe hyperfine parameters with P and T were recorded for the different experimental conditions. The olivine - γ-phase transition was observed in pure fayalite at T ≈ 573 K and P = 10.3 GPa. The examination of the pressure dependence of the cation distribution between the M1 and M2 sites was marred by a strong overlap of the M1 and M2 resonance quadrupole doublets and could only be established for Fa65.Results indicate that pressure has almost no influence on the ordering of iron at M1 or M2 sites and the samples retained a highly disordered character.