Dielectric relaxation of the amorphous ices

The dielectric properties of the low and high density amorphous ices are discussed in terms of those for supercooled water and crystalline ices, and also used to evaluate the transition behaviour upon pressure cycling at 130 K. The dielectric relaxation of the high density amorphous ice is described well by the symmetrical Cole-Cole function with an almost pressure independent relaxation time tau similar to 2 s at 133 K and a relaxation time distribution factor of 0.7. At the high to low density amorphous ice transition, the dielectric relaxation time increases by about two orders of magnitude despite a similar to 30% decrease in density, and tau of the low density amorphous ice is in the range 10(2)-10(3) s at 130 K. The relaxation time behaviour of the high density amorphous ice is similar to that of supercooled liquid water, whereas tau of the low density amorphous ice appears to be prolonged by the ice rules, in correspondence to that of the crystalline ices.