Low temperature specific heats of permanently densified glassy GeO2

Specific heat was measured over the temperature range 0.4–25 K in GeO2 glasses, compacted at pressures of 2 and 6 GPa to achieve more than 20% densification. Above 1 K, specific heat C was reduced by up to a factor of 2.5 with increasing density; the variation being stronger than that observed below 1 K. The broad peak observed above 1 K in a C/T 3 vs. T plot shifted to higher temperatures with increasing density, exhibiting changes which cannot be explained by the modifications of the elastic continuum. In addition, the peak showed no changes in shape, clearly indicating that the overall distribution of the underlying vibrational modes was independent of density. The temperature dependence of C over the explored range was in qualitative agreement with the predictions of the Soft Potential Model.