In-situ high-pressure neutron scattering study of ice phases Ih, II, III and VI

Water ice has very rich P-T phase diagram with known 20 crystalline phases and at least three amorphous states, and their properties are often exhibiting anomalous behavior. To better understand the nature of hydrogen bonds, study of water-water interactions in these phases under equilibrium conditions is very important. Recently, using a piston-cylinder pressure cell (~20 mm3) and a new bellows assembly designed by DAC Tools, LLC, we can load and change the pressure up to 11 kbar at low temperatures. With this high-pressure setup, we measured diffraction and inelastic neutron scattering (INS) in-situ under high pressure for hydrogen-disordered phases ice Ih, III and VI, and for hydrogen-ordered phase ice II. Lattice and molecular dynamics simulations were also performed for these ice phases and compared to the INS spectra. We observed large broadening of the intra-molecular H-O-H bending mode for the hydrogen-ordered and -disordered ice phases, which is explained by the Fermi resonance coupling between the overtone of the librational band and the bending mode of water.