Flexoelectricity and surface ferroelectricity in natural ice

Abstract The phase diagram of ice is complex and contains many phases, but the most common (frozen water at ambient pressure, also known as 1h ice) is a non-polar material despite individual water molecules being polar themselves1,2. Consequently, ice is not piezoelectric and does not generate electricity under pressure3. On the other hand, flexoelectricity (coupling between polarization and strain gradient) is allowed by symmetry in all materials4,5, and therefore ice may polarize under bending. Here we report the measurement of the flexoelectricity of ice and calculate its repercussions for ice-electrification processes occurring in nature. In addition, the sensitivity of flexoelectricity to surface boundary conditions has revealed the existence of a ferroelectric phase transition around 163 K in the surface “skin layer” of bulk natural ice.