Calorimetric measurements of the glass transition are presented for metallic glasses, ${\mathrm{B}}_2$${\mathrm{O}}_3$, and organic polymers with cooling and heating rates ranging over more than three orders of magnitude. Fits of the onset temperatures of the glass transition to a Vogel-Fulcher-type equation give divergence temperatures significantly above the values obtained for Vogel-Fulcher fits to the viscosity. The width of the glass transition extrapolates to a sharp step transition at a finite heating and cooling rate, which is close to the range where the data were taken. The results suggest that the glass transition becomes independent of the experimental time scale in a regime that may be accessible to measurements.

• Received 19 June 1992

DOI:https://doi.org/10.1103/PhysRevB.46.11318