Mg coordination in a MgSiO₃ glass using neutron diffraction coupled with isotopic substitution

Abstract : Neutron diffraction with isotopic substitution (Mg25/^natMg) is used to investigate the Mg environment in MgSiO₃ glass. The neutron-diffraction data are coupled with x-ray diffraction and a reverse Monte Carlo modeling. The Mg environment can be fully resolved from other contributions. We show that two Mg-O contributions are present at ∼1.99 ± 0.01 Å and 2.21 ± 0.01 Å, with an average coordination number of 4.5 ± 0.1 O neighbors around Mg. These distorted Mg sites participate in an inhomogeneous distribution of Mg atoms. This organization results from the liquid state and has implications in understanding the immiscibility gap and glass forming ability.