Local structures around Mn, Co and Ni atoms in glasses of the systems CaMgSi2O6-CaMnSi2O6, CaMgSi2O6-CaCoSi2O6 and CaMgSi2O6-CaNiSi2O6 determined by the XAFS spectroscopy.

Abstract

Local structures around transition-metal atoms in silicate glasses of the systems CaMgSi2O6 (Di)-CaMnSi2O6(CaMnPx), Di-CaCoSi2O6 (CaCoPx) and Di-CaNiSi2O6 (CaNiPx) were investigated with the XAFS (X-ray Absorption Fine Structure) spectroscopy, by making use of SR (Synchrotron Radiation). The obtained distances suggest that the preference to the octahedral coordinations is in the decreasing order Ni2+, Co2+ and Mn2+. This order can be explained in view of the difference between the crystal-field stabilization energies for octahedral and tetrahedral coordinations in the high-spin states. ELNES (Energy-Loss Near Edge Structure) spectra were also measured around the Mn L2,3 edges to determine the oxidation states of Mn ions in glasses of the system Di-CaMnPx. Chemical shifts of the L2,3 edge threshold-energy and the ratios of L3/L2 threshold peaks in all the examined glasses were similar to those in MnO but unlike those in MnO2. The observed tendency of chemical shifts in the XANES spectra of Mn K-edges was identical with that in ELNES. The shifts of Co K- and Ni K-edges in the XANES spectra of all the examined glasses were similar to those of Co-olivine and NiO, respectively. These facts suggest that Mn, Co and Ni ions in the glasses are in divalent states.