Isotope and impurity effects on the glass transition and crystallization of pressurehyphen;amorphized hexagonal and cubic ice

摘要

Amorphous solid D2O from hexagonal and cubic ices and H2O from (HF, NH3, and NH4F) doped hexagonal ice have been prepared by Whalleyrsquo;s method, and their thermal behavior has been investigated by differential scanning calorimetry from 103 to 250 K. For a heating rate of 30 Kthinsp;minminus;1, the temperature of the onset of the reversible glasssquflg;liquid transition,Tg, is raised by about 4 K when H2O is substituted by D2O. Doping with NH3and NH4F causes little change inTgbut with HFTgbecomes undetectable. The increase in heat capacity atTgis reduced by about a factor of 3 on deuteration but marginal changes occur on doping with NH3or NH4F. The increase inTgon deuteration is ape;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. NH3and 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 pressurehyphen;amorphized forms, thus indicating that the increase in the concentration of Bjerrum defects for these two dopants does not alterTg. All these observations suggest that the structure of pressurehyphen;amorphized solids is topologically different from that of the amorphous forms made from the vapor and the liquid.