かんらん石のＭｏｅｓｓｂａｕｅｒ法による研究 変数の温度依存性とスペクトルの帰属

Abstract

Mössbauer spectra of synthetic Mg, Fe, Mn, Ca-olivines have been measured at various temperatures and examined on the following. Variations of the spectral shape, the resolution due to the substitution of Ca, Mn for Mg, and of Mössbauer parameters versus the absorber temperature were analyzed by the Lorentzian curve fitting method. The results show that the superimposed spectra of quadrupole splitting doublets due to 57Fe in octahedrally coordinated M1 and M2 sites are composed of the outer 0-0 and inner I-I pairs and these are gradually seperated as the absorber temperature and the substitution of Mn for Mg increase (refer to Figs. 1-3 and Table 2). The site identification that the 0-0 and I-I doublets correspond to Fe2+ in the M2 and M1 sites respectively, was established on the bases of the temperature dependences of Δ and δ (Fig. 4). On the analogy of CaMgSiO4 (Onken, 1965), it was confirmed that a larger Mn2+ relative to Fe2+ shows relative enrichment in the larger M2 site. The fact supports the above-mentioned site identification. Both computer calculated areas under the component absorption peaks of fayalite with uniform distribution of Fe2+ in M1 and M2 are nearly the same and independent of the absorber temperature. This shows that the recoil-free fractions of Fe2+ in both sites may be nearly identical (Fig. 5). The relations of site distortion, bond length and Δ in main Ca, Mg, Fe-minerals are compared (Table 3). A smaller and more distorted M1 site than the M2 site in olivine has a peculiar nature in comparison with the other minerals.