Neutron Diffraction Study of Ice Polymorphs. I. Ice IX

The neutron diffraction spectrum of polycrystalline D₂O ice IX has been obtained and it is in agreement with a proton‐ordered structure for this ice. Values of the tetragonal, pseudocubic lattice parameters were found to be $a_0{\mathrm{\simeq c}}_0\text{\hspace{0.17em}=\hspace{0.17em}6.745\hspace{0.17em}±\hspace{0.17em}0.004 Å}$ at 80°K. A computer‐generated least‐squares fitting of the intensities of the 38 observed reflections gave the scale factor, thermal parameter, and the oxygen and deuteron position parameters. The O–O–O bond angles are appreciably distorted from the tetrahedral angle in this high‐pressure polymorph.