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

Abstract

We present synchrotron x-ray measurements in a diamond anvil cell of the molecular structure factor of ${\text{H}}_{2}\text{O}$ and ${\text{D}}_{2}\text{O}$ 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 $P\text{\ensuremath{-}}T$ diagram of the nearest-neighbor oxygen coordination number, ${n}_{\text{OO}}$, is disclosed. Also, a counterintuitive isotopic shift of the variation of ${n}_{\text{OO}}$ with pressure is observed.