Medium-density amorphous ice obtained by decay of water-helium gel

The article presents experimental studies of structural changes that occur during heating of nanosized powders of amorphous ice obtained by decay of a water-helium gel. Thermal annealing of the obtained samples was carried out by short exposures (about 15 minutes) at different temperatures in the range of 110–230 K. The behavior of the amorphous phase during annealing was analyzed within the framework of its description by a mixture of amorphous ices of low and medium density ($LDA$ and $MDA$, respectively). It was found that at the such description, the virgin sample was predominantly in the $MDA$ state, while the proportion of the $LDA$ phase was about 7 times less ($MDA/LDA\approx$ 7:1). It has been established that during annealing, a multistage process of structural transformations of the initial $LDA$ + $MDA$ sample takes place: from initial changes in the amorphous state at 110 K through crystallization of the cubic ice phase $I_c$ with its intensive growth at a temperature of 130 K to the transformation of cubic ice into the hexagonal phase $I_h$ in the temperature range $T$ = 135–230 K.