Neutron-Diffraction Study of Ice Polymorphs. III. Ice Ic

Neutron‐diffraction spectra have been recorded at 80°K for polycrystalline D₂O cubic ice (Ic) obtained by the transformation of the high‐pressure ices II, V, and IX. Spectral differences were found among these ice Ic preparations, principally in the degree of asymmetry of the (111) cubic reflection and in the extent of line broadening. The cubic (111) peak of greatest symmetry was obtained by the transformation of ice II. The line broadening appears to be associated with the small particle sizes of the ice Ic produced by the transformation of the high‐pressure ices under controlled‐temperature conditions. Peak centroids for scattering angles between 15° and 62° give a weighted cubic lattice parameter, $a_0\text{\hspace{0.17em}=\hspace{0.17em}6.353\hspace{0.17em}±\hspace{0.17em}0.001 Å}$ . As revealed by an analysis of neutron‐diffraction line intensities, attempts to induce the formation of ice Ic by the quenching of aqueous ferrous chloride or potassium chloride solutions in liquid nitrogen were unsuccessful.