Coordination changes in magnesium silicate glassesM. C. Wilding1, C. J. Benmore2, J. A. Tangeman3 and S. Sampath2, 4
1 University of California at Davis, Department of Geology Davis, CA 95616, USA
2 Argonne National Laboratory, Intense Pulsed Neutron Source Argonne, IL 60439, USA
3 Containerless Research Inc. - 906 University Place, Evanston, IL 60201, USA
4 University of Wyoming, Department of Chemistry - Laramie, WY 82071, USA
(Received 12 November 2003; accepted in final form 12 May 2004)
Glasses made from the magnesium silicate minerals enstatite ( ) and forsterite ( ) and three intermediate compositions can be considered as analogues of quenched melts from the Earth and Lunar mantle. Combined neutron and X-ray diffraction data show an abrupt change in glass structure in the narrow compositional range 38% to 33% ( ). These structural changes reflect a change from a glass characterized by corner-shared tetrahedra and an approximately equal mixture of and polyhedra, to one in which the average coordination of magnesium by oxygen is increased from to . Both these local environments are very different from that of their crystalline counterparts. The change in structure is associated with a discontinuous change in the rheological properties of these glass-forming liquids close to the forsterite composition.
61.10.Nz - X-ray diffraction.
61.12.Ld - Neutron diffraction.
61.43.Fs - Glasses.
© EDP Sciences 2004