Ferroelectric Ordering in Ice Nanotubes Confined in Carbon Nanotubes

The ice nanotubes with odd number of side faces formed inside carbon nanotubes (CNTs) are found to exhibit spontaneous electric polarizations along their tube axes by means of molecular dynamics simulations. The physical mechanism underlying the quasi-one-dimensional (Q1D) ferroelectricity is an interplay between the Q1D geometrical confinement of CNTs and the distinct orientational ordering of the hydrogen bonds dictated by the “ice rule”. This mechanism is fundamentally different from the conventional one seen in three-dimensional ferroelectric (FE) materials or in two-dimensional FE ice films. In addition, it is found that vacancies in the ice nanotubes can induce a net polarization normal to the tube axis.