Coordination of Mg 2+ in oxide glasses determined by x-Ray emission spectroscopy

Abstract

Chemical shifts of K α 1.2 of Mg 2+ having octahedral or tetrahedral coordination in several oxide crystals were systematically measured using a high resolution spectrometer of the 2-crystal type. The shift between the emissions from 6- and 4-coordinated Mg 2+ was small (≈0.25eV), but large enough to be measured, with the peak energy for 6-coordinated Mg 2+ being higher. The fact is in accordance with the well established relation for Al 3+. A nearly linear relation was obtained between the shift and Lewis basicity of the oxides. The relation was applied to the determination of the coordination number of Mg 2+ in borate and silicate glasses. Magnesium in xK 2O· yMgO·(100− x− y)B 2O 3 glasses ( x + y⩽40 mol%) was found to be in 6-coordination, while in the glass 25K 2O·25MgO·50SiO 2 it was found to be in 4-coordination. These results agreed well with expectations from the chemical shift-basicity relationship.