THE NATURE OF THE GLASS-TRANSITION IN A SILICA-RICH OXIDE MELT

The atomic-scale dynamics of the glass-to-liquid transition are, in ge neral, poorly understood in inorganic materials. Here, two-dimensional magic angle spinning nuclear magnetic resonance spectra collected jus t above the glass transition of K2Si4O9 at temperatures as high as 583 degrees C are presented. Rates of exchange for silicon among silicate species, which involves Si-O bond breaking, have been measured and ar e shown to be closely related in time scale to those defined by viscos ity. Thus, even at viscosities as high as 10(10) pascal seconds, local bond breaking (in contrast to the cooperative motion of large cluster s) is of major importance in the control of macroscopic flow and diffu sion.