Glass-to-glass and liquid-to-liquid phase transitions are observed in bulk and confined water, with or without applied pressure. They result from the competition of two liquid phases separated by an enthalpy difference depending on temperature. The classical nucleation equation of these phases is completed by this quantity existing at all temperatures, a pressure contribution, and an enthalpy excess. This equation leads to two homogeneous nucleation temperatures in each liquid phase; the first one (T nbelow T m ) being the formation temperature of an "ordered" liquid phase and the second one corresponding to the overheating temperature (T n+ above T m ). Thermodynamic properties, double glass transition temperatures, sharp enthalpy and volume changes are predicted in agreement with experimental results. The first-order transition line at T LL =0.833×T m between fragile and strong liquids joins two critical points. Glass phase above T g becomes "ordered" liquid phase disappearing at T LL at low pressure and at T n+ =1.302×T m at high pressure.
1-Introduction:Multiple liquid-to-liquid phase transitions (LLPTs) that are observed in several metallic glassforming melts, have already been predicted using a classical nucleation equation completed by an enthalpy difference of two liquid phases depending on the square of the reduced temperature =(T-T m )/T m , where T m is the melting temperature [1]. The objectives of this paper are to extend the application of this renewed equation to the thermodynamic properties of water, to explain the occurrence of glass-to-glass phase transitions in amorphous water, and to show that the low-density phases obtained under decompression are glass phases analogous to those produced by vapour deposition at temperatures close to T g [2-5].First-order transformations under pressure, induce high density amorphous phase [6][7][8][9][10][11][12][13][14], because the pressure increases the enthalpy and facilitates the glass transformation towards an equilibrium phase of higher density. These enthalpy and entropy changes cannot exceed in principle the value of the frozen enthalpy and entropy [15]. Any glass freezes enthalpy and entropy below T g , which are available for exothermic relaxation or first-order transitions.The water glass state is obtained by vapor deposition, liquid hyperquenching, confined water cooling, and application of high pressure to ice followed by various relaxation annealing [16]. A warming