Phase diagrams and isotopic effects of normal and deuterated water studied via x-ray diffraction up to 4.5 GPa and 500 K

We present synchrotron x-ray measurements in a diamond anvil cell of the molecular structure factor of H2O and D2O fluids up to 4.5 GPa and 500 K. We observe large changes in the structure factor and a dramatic increase in the oxygen coordination number over a 2 GPa pressure range. A P-T diagram of the nearest-neighbor oxygen coordination number, n(OO), is disclosed. Also, a counterintuitive isotopic shift of the variation of n(OO) with pressure is observed.