The smectic Z<sub>A</sub> phase: Antiferroelectric smectic order as a prelude to the ferroelectric nematic.
basic_science · Level V
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- Record sourced from PubMed, PMID 36791101.
- Also identified by DOI 10.1073/pnas.2217150120 and PMC identifier 9974471.
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Abstract
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<sub>A</sub>," 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<sub>A</sub>-ferroelectric nematic phase sequence.