Local structure around oxygen atoms in CaMgSi2O6 glass by O K-edge EXELFS

An electron energy-loss spectroscopic (EELS) study was performed using a transmission electron microscope (TEM) equipped with a parallel-type EELS detector. Extended energy-loss fine structure (EXELFS) of oxygen K-edge was analyzed to investigate the local coordination environment around Mg atoms. The diameter of the selected area of a glass fragment was 200 nm and the maximum scattering angle collected in a spectrometer aperture was 16 mrad. The curve-fitting method was applied to O-(Si + Mg) shell on the radial distribution function calculated for the glass, when O-Si distance was fixed to 0.163 nm. and then O-Mg = 0.194(1) nm was obtained. The value is significantly shorter than that observed in the CaMgSi2O6 crystal (O-VIMg = 0.209 nm) and rather close to that in a synthetic spinel MgAl2O4(O-IVMg = 0.192 nm) used as a reference material, where Mg atoms are surrounded regularly by four nearest-neighbor oxygen atoms. The result is concordant with the suggestions of the X-ray-diffraction and the MD simulation studies.