Raman spectra and structure of silicon-oxygen groups in crystalline, liquid, and glassy Mg2SiO4

We have measured the Raman spectra of magnesium orthosilicate at temperatures from 300 to 2170 K and have shown that liquid magnesium orthosilicate can be supercooled to 1600 K and can be prepared in the form of glass at quenching rates above 400 K/s. Analysis of Raman results indicates that, in contrast to crystalline Mg2SiO4, liquid and glassy magnesium orthosilicate contains not only isolated [SiO4]4− groups but also polymerized anions made up of corner-shared [SiO4] tetrahedra. This accounts for the observed deep (down to 600 K) supercooling and vitrification of liquid magnesium orthosilicate. During cooling, large [SiO4] groups have a tendency to depolymerize, and the concentration of isolated [SiO4]4− tetrahedra in the super-cooled magnesium orthosilicate melt increases, leading to spontaneous crystallization below 1550 K.