Ice/Au Interfaces: Investigating Polarization under an External Bias Potential

Ordinary ice (hexagonal ice Ih) plays an important role in atmospheric processes and in the control of Earth's climate, as well as displaying a variety of properties that are significant for the existence of life. On the other hand, its proton-ordered counterpart phase, the Ice XI phase, is more stable at lower temperatures and is known to present ferroelectricity. Experimentally, it is difficult to observe the phase transition from ice Ih to ice XI, since hydrogen-ordering ice relies on highly cooperative reorientation dynamics of the water molecules. In this sense, the presence of ionic impurities seems to be a prerequisite to catalyze the order-disorder phase transition. However, recent experiments have indicated that the presence of a strain gradient applied to the surface can enhance symmetry breaking and promote the polarization of ordinary ice, as well as the growth of proton-ordered ice layers without the need for doping.

In this work, we analyzed the structure and electronic properties of ice Ih and XI at the interface of a gold (Au) electrode as a function of an external bias potential applied to the electrodes as well as uniaxial strain. This is accomplished using a combination of density functional theory (DFT) and non-equilibrium Green's function methods (NEGF). With this setup, we investigated the changes in ferroelectric polarization of ordinary ice induced by an external bias potential analyzing the changes in the molecular dipoles, as well as how an applied strain affects these properties.