Proton-transfer Ferroelectricity of Trans-Unitcell Ion-Displacement and Multiferroic Soliton in Sodium and Potassium Hydroxides

We show first-principles evidence of robust proton-transfer ferroelectricity with considerable polarization in sodium and potassium hydroxides, which are ready for commercial scale production. Moreover, even a small amount of proton vacancies can completely change the mode of proton-transfer from intra-unitcell to trans-unitcell, giving rise to a hitherto unreported type of multiferroic soliton with “mobile” magnetism and a tremendous polarization that can be two orders of magnitude higher compared with most perovskite ferroelectrics. Their vertical polarizations of thin-film are robust against depolarizing field, rendering various designs of 2D ferroelectric field-transistors with non-destructive readout and ultra-high on/off ratio via sensing the switchable metallic/insulating state.