High pressure x-ray diffraction measurements on Mg2SiO4 glass

The structure factors of Mg2SiO4 glass have been measured using high energy x-ray diffraction up to pressures of 30.2 GPa, and the equation of state measured up to 12.8 GPa. The average Mg–O coordination numbers were extracted from the experimental pair distribution functions assuming two cases (i) there is no change in Si–O coordination number with pressure and (ii) the average Si–O coordination number increases the same as for pure SiO2 glass. Both analyses give similar results and show a gradual increase in the average Mg–O coordination number from 5.0 at ambient pressure to ~ 6.6(6) at 30.2 GPa. There is good qualitative agreement between the experimental structure and equation of state data for the glass compared to several recent molecular dynamics simulations carried out on liquid Mg2SiO4.