biostudies-literatureChen XNational Science Foundation (NSF)DOEColorado Office of Economic Development and International TradeColorado Office of Economic Development and International Trade (OEDIT)National Science Foundatione2217150120https://www.ebi.ac.uk/biostudies/studies/S-EPMC9974471biostudies-literatureUnknown120(8)We have structurally characterized the liquid crystal (LC) phase that can appear as an intermediate state when a dielectric nematic, having polar disorder of its molecular dipoles, transitions to the almost perfectly polar-ordered ferroelectric nematic. This intermediate phase, which fills a 100-y-old void in the taxonomy of smectic LCs and which we term the "smectic Z_A," is antiferroelectric, with the nematic director and polarization oriented parallel to smectic layer planes, and the polarization alternating in sign from layer to layer with a 180 Å period. A Landau free energy, originally derived from the Ising model of ferromagnetic ordering of spins in the presence of dipole-dipole interactions, and applied to model incommensurate antiferroelectricity in crystals, describes the key features of the nematic-SmZ_A-ferroelectric nematic phase sequence.Proceedings of the National Academy of Sciences of the United States of AmericaThe smectic Z_A phase: Antiferroelectric smectic order as a prelude to the ferroelectric nematic.PMC99744711710711DE-SC001270420051701420736APP-35428Korblova EZhernenkov MWang CGlaser MAWalba DMMaclennan JEChen XFreychet GRadzihovsky LMartinez VZhu CClark NAfalseThe smectic Z_A phase: Antiferroelectric smectic order as a prelude to the ferroelectric nematic.We have structurally characterized the liquid crystal (LC) phase that can appear as an intermediate state when a dielectric nematic, having polar disorder of its molecular dipoles, transitions to the almost perfectly polar-ordered ferroelectric nematic. This intermediate phase, which fills a 100-y-old void in the taxonomy of smectic LCs and which we term the "smectic Z_A," is antiferroelectric, with the nematic director and polarization oriented parallel to smectic layer planes, and the polarization alternating in sign from layer to layer with a 180 Å period. A Landau free energy, originally derived from the Ising model of ferromagnetic ordering of spins in the presence of dipole-dipole interactions, and applied to model incommensurate antiferroelectricity in crystals, describes the key features of the nematic-SmZ_A-ferroelectric nematic phase sequence.2023-01-01T00:00:00Z2023 Feb2025-04-04T20:04:42.687Z2025-04-04T20:04:42.687ZS-EPMC99744713679110110.1073/pnas.2217150120