Phase Transition of Cubic Ice Ic

Abstract

A study of phase transition of ice Ic is made by Takagi’s method, where twenty five order parameters and a unit cell comprising eight molecules are used and energies of interaction between molecules are considered. The free energy is minimized with respect to these parameters by the simplex method. When the interaction-energy parameter is positive, the ordered phase is ferroelectric and a minimum unit cell has two molecules. When it is negative, the ordered phase is antiferroelectric and a minimum unit cell has four molecules. In this phase, the direction of dipoles on one sublattice of the diamond structure is normal to that of the dipoles on the other sublattice.