Database mining and first-principles assessment of organic proton-transfer ferroelectrics

In organic proton-transfer ferroelectrics (OPTFe), molecules are linked to form hydrogen-bonded networks, and proton transfer (PT) between molecules is the dominant mechanism of ferroelectric switching. The fast-switching frequencies of OPTFes make them attractive alternatives to conventional ceramic ferroelectrics, which contain rare and/or toxic elements and require high processing temperatures. In this study, we mined the Cambridge Structural Database (CSD) for potential OPTFes, uncovering most of the previously reported ones, both tautomeric compounds and acid-base salts, in addition to 12 new compounds, nine of which were tautomeric salts. The identification of PT tautomeric salts highlights a potential new avenue for engineering novel OPTFes. The CSD mining was based on identifying polar crystal structures with pseudoinversion symmetry and viable PT paths. The spontaneous polarization ${\mathbit{P}}_{\mathrm{s}}$ and the PT barriers ${U}_{\mathrm{PT}}$ were calculated for a selection of the compounds using density-functional theory.