The appearance of annealing pre-peaks in inorganic glasses: new experimental results and theoretical interpretation

The occurrence of annealing pre-peaks, or sub-Tg peaks, has been investigated by differential scanning calorimetry in silver iodomolybdate glasses and in mixed silver iodotungstatomolybdate glasses. It is demonstrated that these pre-peaks can be made to occur in any of these systems, provided that the appropriate experimental conditions, namely, a rapid quench followed by annealing at a temperature that is low but not too far below Tg, are used. Further, these peaks are simply precursors of the annealing ‘overshoot’, which is distinct from the ‘upper’ peak observed in ‘intrinsic cycles’ in glasses characterised by a narrow distribution of structural relaxation times. Contrary to some other authors' suggestions, a broad distribution of such relaxation times (i.e., a small value of the non-exponentially parameter, β) is neither a pre-requisite nor particularly conductive to the appearance of the pre-peaks.