Relaxation and Glass Transition in an Isostatically Compressed Diopside Glass

Relaxation of isostatically compressed CaMgSi 2 O 6 (diopside) glass is explored by ex situ differential scanning calorimetric (DSC) experiments. A diopside melt was compressed above its glass transition temperature under isostatic conditions at a pressure of 500 MPa. DSC analysis was performed at ambient pressure after slowly cooling the compressed melt under pressure (i.e., after freezing‐in the densified state). Compression‐induced enhancement of the overshoot in heat capacity was observed in the glass transition region. This indicates that a densified, quenched glass possesses a lower apparent fictive temperature, T fA , than a glass that was cooled under ambient pressure at the same cooling rate. However, a thermodynamic analysis indicates that the fictive temperature produced under pressure, T f0 , is actually much higher than that determined from DSC experiments at ambient pressure ( T f0 > T fA ).