# Cubic ice Ic free from stacking defects synthesized from ice XVII

## TL;DR

This paper reports a new method to synthesize highly pure cubic ice Ic, free from stacking defects, using ice XVII, and confirms its structural purity through neutron diffraction analysis.

## Contribution

The authors developed a novel synthesis technique to produce large quantities of pure cubic ice Ic, overcoming previous limitations of stacking disorder.

## Key findings

- Successful synthesis of pure cubic ice Ic from ice XVII.
- Neutron diffraction confirms the structural purity of the synthesized ice.
- The method enables further studies of ice's fundamental properties.

## Abstract

Among the over eighteen different forms of water ice, only the common hexagonal phase and a cubic phase are present in nature on Earth. The existence of these two polytypes, almost degenerate in energy, represents one of the most important and unresolved topics in the physics of ice. It is now widely recognised that all the samples of "cubic ice" obtained so far are instead a stacking-disordered form of ice I (i.e. ice Isd), in which both hexagonal and cubic stacking sequences of hydrogen-bonded water molecules are present. Here we describe a new method to obtain cubic ice Ic in large quantities, and demonstrate its unprecedented structural purity from two independent neutron diffraction experiments performed on two of the leading neutron diffraction instruments in Europe.