Isotope and impurity effects on the glass transition and crystallization of pressure‐amorphized hexagonal and cubic ice Available to Purchase

Amorphous solid D₂O from hexagonal and cubic ices and H₂O from (HF, NH₃, and NH₄F) doped hexagonal ice have been prepared by Whalley’s method, and their thermal behavior has been investigated by differential scanning calorimetry from 103 to 250 K. For a heating rate of 30 K min⁻¹ , the temperature of the onset of the reversible glass■liquid transition, T_g, is raised by about 4 K when H₂O is substituted by D₂O. Doping with NH₃ and NH₄F causes little change in T_g but with HF T_g becomes undetectable. The increase in heat capacity at T_g is reduced by about a factor of 3 on deuteration but marginal changes occur on doping with NH₃ or NH₄F. The increase in T_g on deuteration is ≊4 times of that observed for the amorphous forms made from the vapor and the liquid, and more than twice of that expected from isoviscous or isorelaxational states, assuming that the functional form of the molecular reorientation rates with temperature is unaffected by isotopic substitution. NH₃ and NH₄F as dopants, which generally increase the reorientation rate of water molecules in hexagonal and cubic ices, have no detectable effect on the calorimetric relaxation rate of the pressure‐amorphized forms, thus indicating that the increase in the concentration of Bjerrum defects for these two dopants does not alter T_g. All these observations suggest that the structure of pressure‐amorphized solids is topologically different from that of the amorphous forms made from the vapor and the liquid.